The mediastinum

Elizabeth Baines; Karine Gendron

doi:10.22233/9781910443941.10

The mediastinum

British Small Animal Veterinary Association , 276 (2024); https://doi.org/10.22233/9781910443941.10

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The mediastinum

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Authors: Elizabeth Baines and Karine Gendron
From: BSAVA Manual of Canine and Feline Thoracic Imaging
Item: Chapter 10, pp 276 - 325
DOI: 10.22233/9781910443941.10
Copyright: © 2024 British Small Animal Veterinary Association
Publication Date: January 2024

Abstract

The mediastinum is a connective tissue septum that lies between the left and right pleural cavities and forms a space for the passage of viscera, nerves and blood vessels. Imaging techniques facilitate assessment of mediastinal anatomy and pathology. This chapter delineates normal mediastinal anatomy in dogs and cats, including the boundaries and contents of mediastinal compartments. Pathologies affecting the mediastinum are explored, encompassing neoplasia, fluid accumulation, inflammation and pneumomediastinum. Diagnostic imaging features are detailed for various mediastinal structures and associated diseases, emphasizing key differentiating features. The utility of ultrasonography, computed tomography and scintigraphy for mediastinal assessment is also discussed.

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Figures

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10.1

Lateral aspect of the median plane. The mediastinum divides the thoracic cavity into left and right sides and is partitioned relative to the pericardium. 1 = cranial mediastinum; 2 = dorsal mediastinum; 3 = middle mediastinum; 4 = ventral mediastinum; 5 = caudal mediastinum. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2024 British Small Animal Veterinary Association

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10.1 Lateral aspect of the median plane. The mediastinum divides the thoracic cavity into left and right sides and is partitioned relative to the pericardium. 1 = cranial mediastinum; 2 = dorsal mediastinum; 3 = middle mediastinum; 4 = ventral mediastinum; 5 = caudal mediastinum. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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10.2

Transverse aspect of the cranial mediastinum at the level of the second thoracic vertebra. The cranial mediastinum is between the longus colli muscles (M) and sternum (S), between the left and right mediastinal pleurae, and is wider dorsally to accommodate the thoracic viscera. All thoracic viscera except the lungs are in the mediastinum. CA = right and left common carotid arteries; Cm = cranioventral mediastinal reflection; CrVC = cranial vena cava; DCV = right and left deep cranial vertebral veins; Ls = left subclavian artery; O = oesophagus; Rs = right subclavian artery; T = trachea; VV = right and left vertebral veins. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. (Redrawn after Suter (1984)) © 2024 British Small Animal Veterinary Association

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10.2 Transverse aspect of the cranial mediastinum at the level of the second thoracic vertebra. The cranial mediastinum is between the longus colli muscles (M) and sternum (S), between the left and right mediastinal pleurae, and is wider dorsally to accommodate the thoracic viscera. All thoracic viscera except the lungs are in the mediastinum. CA = right and left common carotid arteries; Cm = cranioventral mediastinal reflection; CrVC = cranial vena cava; DCV = right and left deep cranial vertebral veins; Ls = left subclavian artery; O = oesophagus; Rs = right subclavian artery; T = trachea; VV = right and left vertebral veins. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. (Redrawn after Suter (1984))

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10.3

Ventral aspect of the thorax. On DV and VD views, the dorsal, middle and ventral mediastina summate with each other and therefore the mediastinum is simply divided into thirds relative to the heart. The cranial mediastinum (CM) is cranial to the heart, caudal to the thoracic inlet, and between the left and right cranial lung lobes. The ventral portion of the right cranial lobe (Rcr) crosses to the left, outlining the right side of the cranioventral mediastinal reflection, which is the position of the vestigial thymus (Th). The middle mediastinum is at the level of the heart. The caudal mediastinum is caudal to the heart, cranial to the diaphragm, and the ventral portion is displaced to the left by the accessory lobe of the right lung (A) and called the caudoventral mediastinal reflection (CVM). The accessory lobe is in the mediastinal recess, which lies between the CVM and the plica venae cavae (not depicted). The plica venae cavae surrounds and is ventral to the caudal vena cava (CdVC). Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. (Redrawn after Suter (1984)) © 2024 British Small Animal Veterinary Association

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10.3 Ventral aspect of the thorax. On DV and VD views, the dorsal, middle and ventral mediastina summate with each other and therefore the mediastinum is simply divided into thirds relative to the heart. The cranial mediastinum (CM) is cranial to the heart, caudal to the thoracic inlet, and between the left and right cranial lung lobes. The ventral portion of the right cranial lobe (Rcr) crosses to the left, outlining the right side of the cranioventral mediastinal reflection, which is the position of the vestigial thymus (Th). The middle mediastinum is at the level of the heart. The caudal mediastinum is caudal to the heart, cranial to the diaphragm, and the ventral portion is displaced to the left by the accessory lobe of the right lung (A) and called the caudoventral mediastinal reflection (CVM). The accessory lobe is in the mediastinal recess, which lies between the CVM and the plica venae cavae (not depicted). The plica venae cavae surrounds and is ventral to the caudal vena cava (CdVC). Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. (Redrawn after Suter (1984))

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10.4

(a) Lateral and (b) VD thoracic radiographs of an adult dog showing the location of the mediastinum (green). All thoracic structures except the thoracic boundaries, lungs and pleural cavities are within the mediastinum and adhered by connective tissue. On lateral views, the mediastinum summates with all structures within the thoracic cavity. On DV and VD views, the mediastinum summates with the midline structures, the caudal vena cava, and portions of the lung. The mediastinum is widest where it surrounds the heart and dorsally to accommodate structures like the oesophagus, trachea and aorta. The amount of connective tissue in the ventral portion of the cranial and caudal mediastina is substantially reduced to two apposing serous membranes. However, mediastinal fat accumulation may occur in overweight and obese animals and some dog breeds (e.g. Bulldogs). The thinner ventral portions of the mediastinum and the plica venae cavae are occasionally seen on DV and VD radiographs (darker green lines). The ventral part of the cranial mediastinum contains lymph nodes and internal thoracic blood vessels, and the thymus in juvenile animals. (c) Transverse CT image (lung window) of an adult dog with bilateral pneumothorax. The image was obtained at the level of the second thoracic vertebra (T2). Both pleural cavities are enlarged and filled with gas (*). The gas contrasts with the normal cranial mediastinum (green), which makes the shape of the mediastinum more obvious. The ventral portion of the cranial mediastinum (arrowed) is narrow and is deflected towards the left. The dorsal portion is roughly in the median plane and wider to accommodate the oesophagus (O), trachea (T), left subclavian artery (L), brachiocephalic trunk (B) and cranial vena cava (CrVC). These mediastinal structures are bound together by loose connective tissue (adventitia), which also joins to the longus colli muscles (M). In the image, the connective tissue is the fat attenuating substance that connects the viscera, blood vessels and muscles. Unlike normal pleural cavities, which are potential spaces, the mediastinum is an actual space that is filled with tissues and organs that are mostly tubular. RCr = right cranial lung lobe. © 2024 British Small Animal Veterinary Association

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10.4 (a) Lateral and (b) VD thoracic radiographs of an adult dog showing the location of the mediastinum (green). All thoracic structures except the thoracic boundaries, lungs and pleural cavities are within the mediastinum and adhered by connective tissue. On lateral views, the mediastinum summates with all structures within the thoracic cavity. On DV and VD views, the mediastinum summates with the midline structures, the caudal vena cava, and portions of the lung. The mediastinum is widest where it surrounds the heart and dorsally to accommodate structures like the oesophagus, trachea and aorta. The amount of connective tissue in the ventral portion of the cranial and caudal mediastina is substantially reduced to two apposing serous membranes. However, mediastinal fat accumulation may occur in overweight and obese animals and some dog breeds (e.g. Bulldogs). The thinner ventral portions of the mediastinum and the plica venae cavae are occasionally seen on DV and VD radiographs (darker green lines). The ventral part of the cranial mediastinum contains lymph nodes and internal thoracic blood vessels, and the thymus in juvenile animals. (c) Transverse CT image (lung window) of an adult dog with bilateral pneumothorax. The image was obtained at the level of the second thoracic vertebra (T2). Both pleural cavities are enlarged and filled with gas (*). The gas contrasts with the normal cranial mediastinum (green), which makes the shape of the mediastinum more obvious. The ventral portion of the cranial mediastinum (arrowed) is narrow and is deflected towards the left. The dorsal portion is roughly in the median plane and wider to accommodate the oesophagus (O), trachea (T), left subclavian artery (L), brachiocephalic trunk (B) and cranial vena cava (CrVC). These mediastinal structures are bound together by loose connective tissue (adventitia), which also joins to the longus colli muscles (M). In the image, the connective tissue is the fat attenuating substance that connects the viscera, blood vessels and muscles. Unlike normal pleural cavities, which are potential spaces, the mediastinum is an actual space that is filled with tissues and organs that are mostly tubular. RCr = right cranial lung lobe.

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10.5

(a) DV and (b) lateral thoracic radiographs of a skeletally mature cat highlighting the structures normally visible in the mediastinum. On DV and VD views, the cranial mediastinum of cats is not wider than the summated vertebral column. a = trachea; b = end-on tracheal bifurcation approximating the location of the carina; c = cardiac silhouette; d = aorta; e = caudal vena cava; f = position of oesophagus; g = width of cranial mediastinum; h = cardiac silhouette apex; i = caudoventral mediastinal reflection. © 2024 British Small Animal Veterinary Association

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10.5 (a) DV and (b) lateral thoracic radiographs of a skeletally mature cat highlighting the structures normally visible in the mediastinum. On DV and VD views, the cranial mediastinum of cats is not wider than the summated vertebral column. a = trachea; b = end-on tracheal bifurcation approximating the location of the carina; c = cardiac silhouette; d = aorta; e = caudal vena cava; f = position of oesophagus; g = width of cranial mediastinum; h = cardiac silhouette apex; i = caudoventral mediastinal reflection.

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10.6

(a) DV thoracic radiograph of a mature dog showing the ventral part of the cranial mediastinum (arrowed). The dog is slightly rotated and has accumulated fat, which accentuates this structure. (b) Close-up of a right lateral thoracic radiograph of a 2-year-old dog showing a portion of the cranioventral mediastinum (arrowed) as a thin line of soft tissue opacity between the left (L) and right (R) cranial lung lobes. (c) Transverse CT image obtained at the level of the first rib (window width 2000 HU, window level –500 HU). The cranioventral mediastinum is clearly seen between the left and right cranial lung lobes (arrowed). © 2024 British Small Animal Veterinary Association

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10.6 (a) DV thoracic radiograph of a mature dog showing the ventral part of the cranial mediastinum (arrowed). The dog is slightly rotated and has accumulated fat, which accentuates this structure. (b) Close-up of a right lateral thoracic radiograph of a 2-year-old dog showing a portion of the cranioventral mediastinum (arrowed) as a thin line of soft tissue opacity between the left (L) and right (R) cranial lung lobes. (c) Transverse CT image obtained at the level of the first rib (window width 2000 HU, window level –500 HU). The cranioventral mediastinum is clearly seen between the left and right cranial lung lobes (arrowed).

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10.7

(a) Close-up of a VD radiograph of the caudal thorax of a skeletally mature normal dog. The caudoventral mediastinal reflection is seen as a narrow band of soft tissue opacity (arrowed) separating the accessory (A) and left caudal (L) lung lobes. (b) Transverse thoracic CT image obtained at the level of the accessory lobe (window width 2000 HU, window level –500 HU). The caudoventral mediastinal reflection is clearly delineated (arrowed). The extension of the accessory lobe (A) across the midline and dorsal to the caudal vena cava can be seen. © 2024 British Small Animal Veterinary Association

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10.7 (a) Close-up of a VD radiograph of the caudal thorax of a skeletally mature normal dog. The caudoventral mediastinal reflection is seen as a narrow band of soft tissue opacity (arrowed) separating the accessory (A) and left caudal (L) lung lobes. (b) Transverse thoracic CT image obtained at the level of the accessory lobe (window width 2000 HU, window level –500 HU). The caudoventral mediastinal reflection is clearly delineated (arrowed). The extension of the accessory lobe (A) across the midline and dorsal to the caudal vena cava can be seen.

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10.8

VD thoracic radiographs of an adult dog positioned (a) in the usual position with thoracic limbs extended cranially and (b) in a ‘humanoid’ position with the thoracic limbs lying lateral to the thoracic wall. The latter position reduces summation of the thoracic girdle with the cranial thorax. © 2024 British Small Animal Veterinary Association

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10.8 VD thoracic radiographs of an adult dog positioned (a) in the usual position with thoracic limbs extended cranially and (b) in a ‘humanoid’ position with the thoracic limbs lying lateral to the thoracic wall. The latter position reduces summation of the thoracic girdle with the cranial thorax.

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10.9

(a) DV thoracic radiograph of an 8-year-old Bulldog bitch. The width of the cranial mediastinum (arrowed) and location of the trachea are within normal limits for this breed. (b) DV thoracic radiograph of a 7-year-old male Chihuahua with tracheal collapse. The cranial mediastinum is wide, which could be due to a mass lesion. The presence of large subcutaneous fat deposits, however, supports a conclusion of physiological mediastinal fat deposition. © 2024 British Small Animal Veterinary Association

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10.9 (a) DV thoracic radiograph of an 8-year-old Bulldog bitch. The width of the cranial mediastinum (arrowed) and location of the trachea are within normal limits for this breed. (b) DV thoracic radiograph of a 7-year-old male Chihuahua with tracheal collapse. The cranial mediastinum is wide, which could be due to a mass lesion. The presence of large subcutaneous fat deposits, however, supports a conclusion of physiological mediastinal fat deposition.

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10.11

(a) Dorsal aspect of the canine thorax. The location of the tracheobronchial lymph nodes relative to the tracheal bifurcation is shown. (b) Lateral radiograph of an 8-year-old neutered Labrador Retriever bitch with chronic systemic coccidioidomycosis. Many small pulmonary, tracheobronchial and cranial mediastinal lymph nodes are faintly mineralized (some arrowed). Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2024 British Small Animal Veterinary Association

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10.11 (a) Dorsal aspect of the canine thorax. The location of the tracheobronchial lymph nodes relative to the tracheal bifurcation is shown. (b) Lateral radiograph of an 8-year-old neutered Labrador Retriever bitch with chronic systemic coccidioidomycosis. Many small pulmonary, tracheobronchial and cranial mediastinal lymph nodes are faintly mineralized (some arrowed). Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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10.13

(a) Lateral and dorsal aspects of the perihilar region depicting normal anatomy and different causes for increased opacity of the perihilar region based on differences in location and mass effects. (ai) Normal perihilar structures. Note that the angle between the principal bronchi can vary with breed and centring of the X-ray beam. (aii) Left and right tracheobronchial lymph node enlargement. Both nodes can accentuate the ventral deflection of the trachea at the carina. The right sits just ventral to, and the left just dorsal to, the trachea. (aiii) Middle tracheobronchial lymph node enlargement. Note that the lymph node lies between the principal bronchi and, when enlarged, displaces the principal bronchi laterally and ventrally. (aiv) Cranial mediastinal lymph node enlargement. If these nodes are large enough, they can displace the trachea dorsally, cranial to the carina. Note that heart base tumours are often located in this region and can produce a similar effect. (av) Pulmonary artery enlargement. Enlarged pulmonary arteries (and sometimes veins) can be mistaken for enlarged lymph nodes. This is a diagram of enlargement of the pulmonic trunk (main pulmonary artery) in dirofilariasis. (avi) Left atrial enlargement. On DV and VD radiographs, both left atrial enlargement and middle tracheobronchial lymphadenomegaly cause lateral displacement of the principal bronchi. However, with lymphadenomegaly, there are usually no other concurrent signs of cardiomegaly. On lateral radiographs, the lymphadenomegaly displaces the bronchi ventrally, whereas left atrial enlargement displaces the carina and principal bronchi (especially the left) dorsally. (b) Close-up of a lateral thoracic radiograph of a 3-year-old male neutered crossbreed dog with enlarged right, left and middle tracheobronchial lymph nodes due to systemic fungal disease. Note the ventral depression of the trachea and principal bronchi. (c) Transverse thoracic CT image (soft tissue window). The enlarged middle tracheobronchial lymph node (arrowed) is dorsal to the heart (H). The adjacent left cranial lung lobe (caudal part) is consolidated (*). (d) Dorsal thoracic CT reconstruction (lung window). The middle tracheobronchial lymph node (M) displaces the principal bronchi laterally. (e) Close-up of a lateral thoracic radiograph of a dog with multicentric lymphoma. The middle (light blue), right (red) and left (dark blue) tracheobronchial and cranial mediastinal (yellow) lymph nodes are moderately enlarged. (f) Close-up of a lateral thoracic radiograph of a 5-year-old Cocker Spaniel with multicentric lymphoma. The tracheobronchial lymph nodes are large, causing ventral displacement and separation of the cranial lobar bronchi (red) and caudal lobar bronchi (blue). Ventral displacement of the bronchi is an important feature that distinguishes increased opacity of the hilar region due to lymphadenomegaly from left atrial enlargement, which causes dorsal bronchial displacement. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. (a, Redrawn after Suter (1984)) © 2024 British Small Animal Veterinary Association

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10.13 (a) Lateral and dorsal aspects of the perihilar region depicting normal anatomy and different causes for increased opacity of the perihilar region based on differences in location and mass effects. (ai) Normal perihilar structures. Note that the angle between the principal bronchi can vary with breed and centring of the X-ray beam. (aii) Left and right tracheobronchial lymph node enlargement. Both nodes can accentuate the ventral deflection of the trachea at the carina. The right sits just ventral to, and the left just dorsal to, the trachea. (aiii) Middle tracheobronchial lymph node enlargement. Note that the lymph node lies between the principal bronchi and, when enlarged, displaces the principal bronchi laterally and ventrally. (aiv) Cranial mediastinal lymph node enlargement. If these nodes are large enough, they can displace the trachea dorsally, cranial to the carina. Note that heart base tumours are often located in this region and can produce a similar effect. (av) Pulmonary artery enlargement. Enlarged pulmonary arteries (and sometimes veins) can be mistaken for enlarged lymph nodes. This is a diagram of enlargement of the pulmonic trunk (main pulmonary artery) in dirofilariasis. (avi) Left atrial enlargement. On DV and VD radiographs, both left atrial enlargement and middle tracheobronchial lymphadenomegaly cause lateral displacement of the principal bronchi. However, with lymphadenomegaly, there are usually no other concurrent signs of cardiomegaly. On lateral radiographs, the lymphadenomegaly displaces the bronchi ventrally, whereas left atrial enlargement displaces the carina and principal bronchi (especially the left) dorsally. (b) Close-up of a lateral thoracic radiograph of a 3-year-old male neutered crossbreed dog with enlarged right, left and middle tracheobronchial lymph nodes due to systemic fungal disease. Note the ventral depression of the trachea and principal bronchi. (c) Transverse thoracic CT image (soft tissue window). The enlarged middle tracheobronchial lymph node (arrowed) is dorsal to the heart (H). The adjacent left cranial lung lobe (caudal part) is consolidated (*). (d) Dorsal thoracic CT reconstruction (lung window). The middle tracheobronchial lymph node (M) displaces the principal bronchi laterally. (e) Close-up of a lateral thoracic radiograph of a dog with multicentric lymphoma. The middle (light blue), right (red) and left (dark blue) tracheobronchial and cranial mediastinal (yellow) lymph nodes are moderately enlarged. (f) Close-up of a lateral thoracic radiograph of a 5-year-old Cocker Spaniel with multicentric lymphoma. The tracheobronchial lymph nodes are large, causing ventral displacement and separation of the cranial lobar bronchi (red) and caudal lobar bronchi (blue). Ventral displacement of the bronchi is an important feature that distinguishes increased opacity of the hilar region due to lymphadenomegaly from left atrial enlargement, which causes dorsal bronchial displacement. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. (a, Redrawn after Suter (1984))

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10.14

(a) Lateral and (b) VD thoracic radiographs of a 6-year-old Australian Cattle Dog with mild lymphadenomegaly of the cranial sternal lymph nodes (arrowed in (a), red lines in (b)) secondary to abdominal neoplasia. © 2024 British Small Animal Veterinary Association

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10.14 (a) Lateral and (b) VD thoracic radiographs of a 6-year-old Australian Cattle Dog with mild lymphadenomegaly of the cranial sternal lymph nodes (arrowed in (a), red lines in (b)) secondary to abdominal neoplasia.

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10.15

Close-up of a VD radiograph of the cranial thorax in an 8-year-old Border Collie with lymphadenomegaly of the mediastinal lymph nodes. The cranial mediastinum is wide and mildly convex (arrowed). © 2024 British Small Animal Veterinary Association

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10.15 Close-up of a VD radiograph of the cranial thorax in an 8-year-old Border Collie with lymphadenomegaly of the mediastinal lymph nodes. The cranial mediastinum is wide and mildly convex (arrowed).

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10.16

Lateral thoracic radiograph of a 5-month-old female Domestic Shorthaired cat. The thymus is seen as a faint triangular soft tissue opacity (arrowed) cranial to the heart. It was not visible on the DV view. © 2024 British Small Animal Veterinary Association

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10.16 Lateral thoracic radiograph of a 5-month-old female Domestic Shorthaired cat. The thymus is seen as a faint triangular soft tissue opacity (arrowed) cranial to the heart. It was not visible on the DV view.

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10.17

DV thoracic radiograph of a 1-year-old Boxer bitch, showing a small thymic sail sign (arrowed) just cranial to the heart and to the left of the midline. © 2024 British Small Animal Veterinary Association

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10.17 DV thoracic radiograph of a 1-year-old Boxer bitch, showing a small thymic sail sign (arrowed) just cranial to the heart and to the left of the midline.

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10.18

Sagittal T2-weighted MRI scan of the thorax of a 3-month-old Italian Spinone bitch. The thymus (T) is seen as a hyperintense solid soft tissue structure cranial to the heart. © 2024 British Small Animal Veterinary Association

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10.18 Sagittal T2-weighted MRI scan of the thorax of a 3-month-old Italian Spinone bitch. The thymus (T) is seen as a hyperintense solid soft tissue structure cranial to the heart.

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10.19

Transverse aspect of the caudal mediastinum at the level of the eighth thoracic vertebra. The caudal mediastinum is between the vertebral column and sternum, between the pericardium and diaphragm, and between the left and right pleural cavities. The caudal mediastinum is wider dorsally to accommodate the intrathoracic structures like the aorta (Ao), azygos vein (Az), and oesophagus (O). In addition, the dorsal part of the caudal mediastinum contains the mediastinal serous cavity (MSC). The ventral part of the mediastinum (caudoventral mediastinal reflection (CVM)) is thin and displaced to the left by the accessory lung lobe, which lies in the mediastinal recess (Mr). The right boundary of the mediastinal recess is the plica venae cavae (P), which surrounds and is ventral to the caudal vena cava (CdVC). The CVM should not be mistaken for the phrenicopericardial ligament (PPL). H = Outline of position of the heart. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. (Redrawn after Suter (1984)) © 2024 British Small Animal Veterinary Association

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10.19 Transverse aspect of the caudal mediastinum at the level of the eighth thoracic vertebra. The caudal mediastinum is between the vertebral column and sternum, between the pericardium and diaphragm, and between the left and right pleural cavities. The caudal mediastinum is wider dorsally to accommodate the intrathoracic structures like the aorta (Ao), azygos vein (Az), and oesophagus (O). In addition, the dorsal part of the caudal mediastinum contains the mediastinal serous cavity (MSC). The ventral part of the mediastinum (caudoventral mediastinal reflection (CVM)) is thin and displaced to the left by the accessory lung lobe, which lies in the mediastinal recess (Mr). The right boundary of the mediastinal recess is the plica venae cavae (P), which surrounds and is ventral to the caudal vena cava (CdVC). The CVM should not be mistaken for the phrenicopericardial ligament (PPL). H = Outline of position of the heart. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. (Redrawn after Suter (1984))

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10.20

The mediastinal serous cavity is in the dorsal part of the caudal mediastinum to the right of the oesophagus (o) between the heart base and diaphragm. (ai, bi, ci) Lateral and (aii, bii, cii) orthogonal thoracic radiographs in an adult cat with severe bilateral pleural fluid: (a) on presentation, (b) after placement of bilateral chest tubes. The left chest tube (red) pierces the left caudal lung lobe and loops upon itself in the mediastinal serous cavity. The mediastinal serous cavity is in the dorsal part of the caudal mediastinum to the right of the oesophagus (o) between the heart base and diaphragm. (ai, bi, ci) Lateral and (aii, bii, cii) orthogonal thoracic radiographs in an adult cat with severe bilateral pleural fluid: (c) after repositioning the left chest tube. The left chest tube is retracted and the mediastinal serous cavity (MSC) is gas distended. (di) transverse and (dii) dorsal thoracic CT images of the same cat showing the gas distended MSC. (e) Close-up transverse thoracic CT image showing the path of the chest tube (arrowed) through the left caudal lung lobe from the body wall to the MSC. The path goes through the bronchus (B), missing the adjacent pulmonary artery (A) and vein (V). © 2024 British Small Animal Veterinary Association

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10.20 The mediastinal serous cavity is in the dorsal part of the caudal mediastinum to the right of the oesophagus (o) between the heart base and diaphragm. (ai, bi, ci) Lateral and (aii, bii, cii) orthogonal thoracic radiographs in an adult cat with severe bilateral pleural fluid: (a) on presentation, (b) after placement of bilateral chest tubes. The left chest tube (red) pierces the left caudal lung lobe and loops upon itself in the mediastinal serous cavity. The mediastinal serous cavity is in the dorsal part of the caudal mediastinum to the right of the oesophagus (o) between the heart base and diaphragm. (ai, bi, ci) Lateral and (aii, bii, cii) orthogonal thoracic radiographs in an adult cat with severe bilateral pleural fluid: (c) after repositioning the left chest tube. The left chest tube is retracted and the mediastinal serous cavity (MSC) is gas distended. (di) transverse and (dii) dorsal thoracic CT images of the same cat showing the gas distended MSC. (e) Close-up transverse thoracic CT image showing the path of the chest tube (arrowed) through the left caudal lung lobe from the body wall to the MSC. The path goes through the bronchus (B), missing the adjacent pulmonary artery (A) and vein (V).

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10.21

(a) VD thoracic radiograph of a mature dog with moderate rotation of the thorax. Note that the cardiac silhouette has moved in the same direction as the sternum. A true mediastinal shift is likely absent. (b) VD thoracic radiograph of the same dog. The dog is well positioned and the spinous processes summate with the vertebral bodies and sternebrae. Note that the cardiac silhouette is in a normal position and there is no mediastinal shift. The previous displacement of the cardiac silhouette was simply due to rotation. (c) DV thoracic radiograph of an 8-year-old neutered male Oriental cat with a unilateral tension pneumothorax. The mediastinum is shifted to the right due to severe expansion of the left pleural cavity. Although the cat is poorly positioned with marked rotation, the cardiac apex is rotated in the opposite direction to the sternum, confirming the mediastinal shift. © 2024 British Small Animal Veterinary Association

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10.21 (a) VD thoracic radiograph of a mature dog with moderate rotation of the thorax. Note that the cardiac silhouette has moved in the same direction as the sternum. A true mediastinal shift is likely absent. (b) VD thoracic radiograph of the same dog. The dog is well positioned and the spinous processes summate with the vertebral bodies and sternebrae. Note that the cardiac silhouette is in a normal position and there is no mediastinal shift. The previous displacement of the cardiac silhouette was simply due to rotation. (c) DV thoracic radiograph of an 8-year-old neutered male Oriental cat with a unilateral tension pneumothorax. The mediastinum is shifted to the right due to severe expansion of the left pleural cavity. Although the cat is poorly positioned with marked rotation, the cardiac apex is rotated in the opposite direction to the sternum, confirming the mediastinal shift.

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(a) VD thoracic radiograph of an anaesthetized 6-year-old neutered male mixed-breed dog with a left mediastinal shift due to left lung atelectasis. The cardiac silhouette has moved towards the left due to diminished left lung volume (ipsilateral shift). (b) DV thoracic radiograph of a puppy with a right mediastinal shift due to congenital lobar emphysema. The trachea and cardiac silhouette are markedly shifted into the right side of the thorax due to the presence of the hyperinflated left lung lobe (contralateral shift). (c) DV thoracic radiograph of a dog with a right mediastinal shift due to a left cranial lobar pulmonary mass. The cardiac silhouette is displaced towards the right, away from the mass (contralateral shift). © 2024 British Small Animal Veterinary Association

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10.22 (a) VD thoracic radiograph of an anaesthetized 6-year-old neutered male mixed-breed dog with a left mediastinal shift due to left lung atelectasis. The cardiac silhouette has moved towards the left due to diminished left lung volume (ipsilateral shift). (b) DV thoracic radiograph of a puppy with a right mediastinal shift due to congenital lobar emphysema. The trachea and cardiac silhouette are markedly shifted into the right side of the thorax due to the presence of the hyperinflated left lung lobe (contralateral shift). (c) DV thoracic radiograph of a dog with a right mediastinal shift due to a left cranial lobar pulmonary mass. The cardiac silhouette is displaced towards the right, away from the mass (contralateral shift).

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(a) Lateral and (b) ventral aspects of the five main locations of mediastinal masses: V = cranioventral masses; W = craniodorsal masses; X = hilar and perihilar masses; Y = caudodorsal masses; Z = caudoventral masses. Several structures are labelled for reference: A = thoracic descending aorta; C = caudal vena cava; F = mediastinal fat; H = heart; M = shadow of intrathoracic part of longus colli muscle; O = oesophagus; T = trachea. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. (Redrawn after Suter (1984)) © 2024 British Small Animal Veterinary Association

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10.23 (a) Lateral and (b) ventral aspects of the five main locations of mediastinal masses: V = cranioventral masses; W = craniodorsal masses; X = hilar and perihilar masses; Y = caudodorsal masses; Z = caudoventral masses. Several structures are labelled for reference: A = thoracic descending aorta; C = caudal vena cava; F = mediastinal fat; H = heart; M = shadow of intrathoracic part of longus colli muscle; O = oesophagus; T = trachea. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. (Redrawn after Suter (1984))

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DV thoracic radiograph of a 10-year-old neutered male Domestic Shorthaired cat with pleural and mediastinal fluid due to congestive heart failure. Triangular ‘reverse fissures’ that might represent mediastinal fluid can be seen (arrowed). © 2024 British Small Animal Veterinary Association

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10.25 DV thoracic radiograph of a 10-year-old neutered male Domestic Shorthaired cat with pleural and mediastinal fluid due to congestive heart failure. Triangular ‘reverse fissures’ that might represent mediastinal fluid can be seen (arrowed).

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10.26

Transverse CT images obtained from a normal dog using a soft tissue algorithm at the level of the (a) second thoracic vertebra, (b) heart base and (c) ninth thoracic vertebra. All images were acquired after intravenous administration of non-ionic iodinated contrast medium and are displayed with a soft tissue window (window width 300 HU, window level 40 HU). (b) Contrast medium can be seen within the left and right ventricles. The unlabelled hyperattenuating structures within the lungs (seen as small round structures) are the pulmonary arteries and veins beginning to fill with contrast medium. (d) Sagittal thoracic MRI image of a 4-year-old Staffordshire Bull Terrier bitch. Although cardiac movement impedes full interpretation, enlarged cranial mediastinal and tracheobronchial lymph nodes (arrowed) are seen. A = aorta; C = vena cava (cranial in (a), caudal in (c)); L = left ventricle; O = oesophagus; R = right ventricle; T = trachea. © 2024 British Small Animal Veterinary Association

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10.26 Transverse CT images obtained from a normal dog using a soft tissue algorithm at the level of the (a) second thoracic vertebra, (b) heart base and (c) ninth thoracic vertebra. All images were acquired after intravenous administration of non-ionic iodinated contrast medium and are displayed with a soft tissue window (window width 300 HU, window level 40 HU). (b) Contrast medium can be seen within the left and right ventricles. The unlabelled hyperattenuating structures within the lungs (seen as small round structures) are the pulmonary arteries and veins beginning to fill with contrast medium. (d) Sagittal thoracic MRI image of a 4-year-old Staffordshire Bull Terrier bitch. Although cardiac movement impedes full interpretation, enlarged cranial mediastinal and tracheobronchial lymph nodes (arrowed) are seen. A = aorta; C = vena cava (cranial in (a), caudal in (c)); L = left ventricle; O = oesophagus; R = right ventricle; T = trachea.

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10.28

(a) Lateral thoracic radiograph of a 5-year-old mixed-breed dog with subtle pneumomediastinum secondary to a perforating oesophageal foreign body (a fishhook). The small amounts of gas contrasting with the outer surface of the trachea (arrowed) are an important radiographic finding. (b) Lateral thoracic radiograph of an 8-year-old neutered female Domestic Shorthaired cat with pneumomediastinum, pneumothorax, extensive subcutaneous emphysema, and pulmonary contusions after a road traffic accident. A ruptured trachea was identified on endoscopic examination. (c) Close-up of a lateral trunk radiograph of an emaciated 12-year-old Domestic Shorthaired cat with extension of pneumomediastinum to pneumoretroperitoneum. The thoracic and abdominal aorta and kidneys are contrasted by gas. Minimal trauma to the aortic hiatus allows gas tracking into the retroperitoneal space. This finding is typically of minor consequence but should be differentiated from gas originating from ruptured abdominal organs. © 2024 British Small Animal Veterinary Association

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10.28 (a) Lateral thoracic radiograph of a 5-year-old mixed-breed dog with subtle pneumomediastinum secondary to a perforating oesophageal foreign body (a fishhook). The small amounts of gas contrasting with the outer surface of the trachea (arrowed) are an important radiographic finding. (b) Lateral thoracic radiograph of an 8-year-old neutered female Domestic Shorthaired cat with pneumomediastinum, pneumothorax, extensive subcutaneous emphysema, and pulmonary contusions after a road traffic accident. A ruptured trachea was identified on endoscopic examination. (c) Close-up of a lateral trunk radiograph of an emaciated 12-year-old Domestic Shorthaired cat with extension of pneumomediastinum to pneumoretroperitoneum. The thoracic and abdominal aorta and kidneys are contrasted by gas. Minimal trauma to the aortic hiatus allows gas tracking into the retroperitoneal space. This finding is typically of minor consequence but should be differentiated from gas originating from ruptured abdominal organs.

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10.29

Left lateral neck radiograph of a 6-year-old neutered crossbreed bitch with a penetrating pharyngeal injury. Summating with the oropharynx and the retropharyngeal soft tissues are two fine parallel linear radiopacities (arrowed) that are consistent with a stick. In addition, there are multiple linear gas opacities tracking along the deep cervical fascia and cranial mediastinum, contrasting with the adventitial surface of the trachea and the brachiocephalic trunk and consistent with deep fascial emphysema and pneumomediastinum. © 2024 British Small Animal Veterinary Association

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10.29 Left lateral neck radiograph of a 6-year-old neutered crossbreed bitch with a penetrating pharyngeal injury. Summating with the oropharynx and the retropharyngeal soft tissues are two fine parallel linear radiopacities (arrowed) that are consistent with a stick. In addition, there are multiple linear gas opacities tracking along the deep cervical fascia and cranial mediastinum, contrasting with the adventitial surface of the trachea and the brachiocephalic trunk and consistent with deep fascial emphysema and pneumomediastinum.

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10.30

Transverse CT image (lung window) of a 5-year-old Siberian Husky with severe pneumomediastinum, severe subcutaneous emphysema and mild bilateral pneumothorax. The image was obtained at the level of the eighth thoracic vertebra. The dorsal part of the caudal mediastinum is wide and contains a large volume of gas (pneumomediastinum) that dissects through the connective tissue and contrasts with the adventitia surrounding the aorta (A) and oesophagus (O). The body wall contains a large volume of gas (subcutaneous emphysema) that dissects through the connective tissue (fascia). In the ventral part of the thoracic cavity, the normal plica venae cavae (1), caudoventral mediastinal reflection (2) and phrenicopericardial ligament (3) are seen as thin, soft tissue opacities. The former two are between lung lobes and define the boundaries of the mediastinal recess. The latter is contrasted by gas in both pleural cavities (bilateral pneumothorax). Note how the gas in the mediastinum and body wall is interrupted by numerous internal soft tissue septa, which provide a barrier to flow. The gas-filled spaces in the mediastinum and body wall are pathologically created by the disruption of the connective tissue. The pleural cavities are pre-existing potential spaces that do not have internal septa. C = caudal vena cava. © 2024 British Small Animal Veterinary Association

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10.30 Transverse CT image (lung window) of a 5-year-old Siberian Husky with severe pneumomediastinum, severe subcutaneous emphysema and mild bilateral pneumothorax. The image was obtained at the level of the eighth thoracic vertebra. The dorsal part of the caudal mediastinum is wide and contains a large volume of gas (pneumomediastinum) that dissects through the connective tissue and contrasts with the adventitia surrounding the aorta (A) and oesophagus (O). The body wall contains a large volume of gas (subcutaneous emphysema) that dissects through the connective tissue (fascia). In the ventral part of the thoracic cavity, the normal plica venae cavae (1), caudoventral mediastinal reflection (2) and phrenicopericardial ligament (3) are seen as thin, soft tissue opacities. The former two are between lung lobes and define the boundaries of the mediastinal recess. The latter is contrasted by gas in both pleural cavities (bilateral pneumothorax). Note how the gas in the mediastinum and body wall is interrupted by numerous internal soft tissue septa, which provide a barrier to flow. The gas-filled spaces in the mediastinum and body wall are pathologically created by the disruption of the connective tissue. The pleural cavities are pre-existing potential spaces that do not have internal septa. C = caudal vena cava.

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Transverse CT image at the level of the first cervical vertebra of a 3-year-old male Labrador Retriever with pneumomediastinum due to a penetrating injury (window width 300 HU, window level 50 HU). Left and ventral to the larynx, there is a hyperattenuating structure surrounded by soft tissue swelling. During exploratory surgery, this structure was found to be a stick. © 2024 British Small Animal Veterinary Association

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10.31 Transverse CT image at the level of the first cervical vertebra of a 3-year-old male Labrador Retriever with pneumomediastinum due to a penetrating injury (window width 300 HU, window level 50 HU). Left and ventral to the larynx, there is a hyperattenuating structure surrounded by soft tissue swelling. During exploratory surgery, this structure was found to be a stick.

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10.32 Sites, causes and main radiographic signs of mediastinal masses. CdVC = caudal vena cava; PPDH = peritoneopericardial diaphragmatic hernia.

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(ai) Lateral and (aii) DV thoracic radiographs of a 3-year-old Siamese cat with a large cranial thoracic mass due to thymic lymphoma. The mass has a homogeneous soft tissue opacity with indistinct margins. On the lateral view, the tumour displaces the carina to the seventh intercostal space, suggesting that the mass is cranial to the heart. On the DV view, the origin of the mass is clearly mediastinal as the tumour is in the midline and displaces both cranial lung lobes caudolaterally. The tracheobronchial lymph nodes are also enlarged and a small volume of pleural fluid is present. (b) Lateral thoracic radiograph of a Himalayan cat with nodular fat necrosis in the caudoventral aspect of the mediastinum. Nodular fat necrosis is usually an incidental finding of minor consequence and more commonly seen in the abdomen. The eggshell-like mineralization is a typical feature. (c) Lateral thoracic radiograph of a 13-year-old neutered male Domestic Shorthaired cat with a caudal mediastinal abscess. The abscess forms a relatively well defined rounded soft tissue mass between the cardiac silhouette and the diaphragm, summated with the caudal vena cava. An oesophagostomy feeding tube is in place. (d) Lateral thoracic radiograph of a dog with a mediastinal haematoma and pneumothorax following a road traffic accident. The haematoma forms a large mass in the cranial and ventral mediastina with dorsal tracheal displacement, an irregular margin and slightly heterogeneous soft tissue opacity. © 2024 British Small Animal Veterinary Association

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10.33 (ai) Lateral and (aii) DV thoracic radiographs of a 3-year-old Siamese cat with a large cranial thoracic mass due to thymic lymphoma. The mass has a homogeneous soft tissue opacity with indistinct margins. On the lateral view, the tumour displaces the carina to the seventh intercostal space, suggesting that the mass is cranial to the heart. On the DV view, the origin of the mass is clearly mediastinal as the tumour is in the midline and displaces both cranial lung lobes caudolaterally. The tracheobronchial lymph nodes are also enlarged and a small volume of pleural fluid is present. (b) Lateral thoracic radiograph of a Himalayan cat with nodular fat necrosis in the caudoventral aspect of the mediastinum. Nodular fat necrosis is usually an incidental finding of minor consequence and more commonly seen in the abdomen. The eggshell-like mineralization is a typical feature. (c) Lateral thoracic radiograph of a 13-year-old neutered male Domestic Shorthaired cat with a caudal mediastinal abscess. The abscess forms a relatively well defined rounded soft tissue mass between the cardiac silhouette and the diaphragm, summated with the caudal vena cava. An oesophagostomy feeding tube is in place. (d) Lateral thoracic radiograph of a dog with a mediastinal haematoma and pneumothorax following a road traffic accident. The haematoma forms a large mass in the cranial and ventral mediastina with dorsal tracheal displacement, an irregular margin and slightly heterogeneous soft tissue opacity.

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The appearance of mediastinal fat on ultrasonography. (a) Dorsal plane image of the cranial mediastinum of an obese 6-year-old Cocker Spaniel. Cranial to the heart and internal to the thick hyperechoic thoracic wall, the mediastinal fat appears as a large amount of homogeneous tissue with a coarse echotexture. (b) Dorsal plane image of the cranial thorax of a 9-year-old neutered male Maltese. A triangular region of hyperechoic tissue (F) is seen cranial to the heart: a very small amount of pleural fluid surrounds the tip (arrowed). The tissue was presumed to be mediastinal fat and confirmed by FNA. (Courtesy of G. Seiler) © 2024 British Small Animal Veterinary Association

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10.34 The appearance of mediastinal fat on ultrasonography. (a) Dorsal plane image of the cranial mediastinum of an obese 6-year-old Cocker Spaniel. Cranial to the heart and internal to the thick hyperechoic thoracic wall, the mediastinal fat appears as a large amount of homogeneous tissue with a coarse echotexture. (b) Dorsal plane image of the cranial thorax of a 9-year-old neutered male Maltese. A triangular region of hyperechoic tissue (F) is seen cranial to the heart: a very small amount of pleural fluid surrounds the tip (arrowed). The tissue was presumed to be mediastinal fat and confirmed by FNA. (Courtesy of G. Seiler)

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(a) Dorsal plane image of the cranial thorax of a 10-year-old neutered female Domestic Shorthaired cat with biopsy-confirmed carcinoma and haemorrhage. In the cranial mediastinum, the tumour is seen as a large heterogenous mass (arrowed) that is cranial to the heart and surrounded by fluid in both pleural cavities (*). (b) The cranial mediastinum of a 5-year-old neutered Flat-Coated Retriever bitch with a lobulated mass (*) attributed to a round cell sarcoma. Enlarged mediastinal lymph nodes are also present. (a, Courtesy of G. Seiler) © 2024 British Small Animal Veterinary Association

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10.35 (a) Dorsal plane image of the cranial thorax of a 10-year-old neutered female Domestic Shorthaired cat with biopsy-confirmed carcinoma and haemorrhage. In the cranial mediastinum, the tumour is seen as a large heterogenous mass (arrowed) that is cranial to the heart and surrounded by fluid in both pleural cavities (*). (b) The cranial mediastinum of a 5-year-old neutered Flat-Coated Retriever bitch with a lobulated mass (*) attributed to a round cell sarcoma. Enlarged mediastinal lymph nodes are also present. (a, Courtesy of G. Seiler)

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Dorsal plane image of the cranial thorax of a 10-year-old neutered crossbreed bitch with metastatic melanoma. There are large, relatively homogeneous masses with anechoic crescentic caudal borders in the cranial mediastinum. Definitive histopathological diagnosis was not made. © 2024 British Small Animal Veterinary Association

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10.36 Dorsal plane image of the cranial thorax of a 10-year-old neutered crossbreed bitch with metastatic melanoma. There are large, relatively homogeneous masses with anechoic crescentic caudal borders in the cranial mediastinum. Definitive histopathological diagnosis was not made.

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Dorsal plane image of the cranial thorax of a 3-year-old neutered male British Shorthaired cat. Adjacent to the cranial vena cava, there are three well defined, relatively hypoechoic, rounded structures (consistent with enlarged lymph nodes) and a scant amount of pleural fluid. © 2024 British Small Animal Veterinary Association

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10.37 Dorsal plane image of the cranial thorax of a 3-year-old neutered male British Shorthaired cat. Adjacent to the cranial vena cava, there are three well defined, relatively hypoechoic, rounded structures (consistent with enlarged lymph nodes) and a scant amount of pleural fluid.

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10.38

(a) Transverse plane left intercostal image of a biopsy-confirmed thymoma; dorsal is to the right. In the cranial mediastinum, the tumour is seen as a large, hypoechoic, lobulated mass (M) that partially surrounds mediastinal blood vessels. The blood vessels are seen as round hypoechoic structures dorsal to the mass. (b) Dorsal plane image of a thymoma. The cranial mediastinum is filled by a hypoechoic lobulated mass. (Courtesy of G. Seiler) © 2024 British Small Animal Veterinary Association

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10.38 (a) Transverse plane left intercostal image of a biopsy-confirmed thymoma; dorsal is to the right. In the cranial mediastinum, the tumour is seen as a large, hypoechoic, lobulated mass (M) that partially surrounds mediastinal blood vessels. The blood vessels are seen as round hypoechoic structures dorsal to the mass. (b) Dorsal plane image of a thymoma. The cranial mediastinum is filled by a hypoechoic lobulated mass. (Courtesy of G. Seiler)

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(a) Dorsal plane image of the caudal thorax of a 13-year-old neutered male Domestic Shorthaired cat with a caudal mediastinal abscess. Between the heart (*) and the diaphragm, the abscess forms a large space-occupying lesion that is round, relatively well defined and homogeneous. (b) Transverse plane image of the caudal thorax of a 2-year-old neutered crossbreed bitch. There is a large, complex, loculated mass with a slightly irregular but relatively well defined wall. © 2024 British Small Animal Veterinary Association

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10.39 (a) Dorsal plane image of the caudal thorax of a 13-year-old neutered male Domestic Shorthaired cat with a caudal mediastinal abscess. Between the heart (*) and the diaphragm, the abscess forms a large space-occupying lesion that is round, relatively well defined and homogeneous. (b) Transverse plane image of the caudal thorax of a 2-year-old neutered crossbreed bitch. There is a large, complex, loculated mass with a slightly irregular but relatively well defined wall.

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(a) Transverse CT image at the level of the fifth intercostal space of a 7-year-old neutered Labrador Retriever bitch with a thymoma (T) (window width 300 HU, window level 50 HU). (b) Post-contrast transverse CT image at the level of the fifth intercostal space of a 5-year-old neutered male crossbreed dog with a thymoma (T) (window width 300 HU, window level 50 HU). Pleural effusion (P) is also present. © 2024 British Small Animal Veterinary Association

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10.40 (a) Transverse CT image at the level of the fifth intercostal space of a 7-year-old neutered Labrador Retriever bitch with a thymoma (T) (window width 300 HU, window level 50 HU). (b) Post-contrast transverse CT image at the level of the fifth intercostal space of a 5-year-old neutered male crossbreed dog with a thymoma (T) (window width 300 HU, window level 50 HU). Pleural effusion (P) is also present.

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(a) DV thoracic radiograph of a 4-year-old Staffordshire Bull Terrier bitch with subtle increased mediastinal width. (b) Reformatted dorsal oblique contrast CT image at the level of the heart base allowing observation of enlarged cranial mediastinal and middle tracheobronchial lymph nodes (arrowed) (window width 400 HU, window level 40 HU). © 2024 British Small Animal Veterinary Association

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10.41 (a) DV thoracic radiograph of a 4-year-old Staffordshire Bull Terrier bitch with subtle increased mediastinal width. (b) Reformatted dorsal oblique contrast CT image at the level of the heart base allowing observation of enlarged cranial mediastinal and middle tracheobronchial lymph nodes (arrowed) (window width 400 HU, window level 40 HU).

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10.42

Transverse CT image at the level of the seventh intercostal space of a 2-year-old neutered Dogue de Bordeaux bitch with lymphoma undergoing CT-guided biopsy (window width 2000 HU, window level –500 HU). The lymphoma is seen as a large, soft tissue attenuating tumour in the dorsal mediastinum between the vertebrae, heart and both lungs. The needle (N) is shown within the skin and from this position is advanced further into the mass (see Chapter 3). © 2024 British Small Animal Veterinary Association

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10.42 Transverse CT image at the level of the seventh intercostal space of a 2-year-old neutered Dogue de Bordeaux bitch with lymphoma undergoing CT-guided biopsy (window width 2000 HU, window level –500 HU). The lymphoma is seen as a large, soft tissue attenuating tumour in the dorsal mediastinum between the vertebrae, heart and both lungs. The needle (N) is shown within the skin and from this position is advanced further into the mass (see Chapter 3).

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10.43

Transverse CT image at the level of the seventh rib of a 10-year-old neutered crossbreed bitch with metastatic melanoma (window width 1500 HU, window level 300 HU). CT was performed to determine the extent of disease. Just dorsal to the right seventh costochondral junction, there is an irregularly marginated osteolytic lesion with a spiculated periosteal reaction and an associated soft tissue mass. Assessment of the acquired CT images using all appropriate windows will maximize the available information (see also Chapter 3). © 2024 British Small Animal Veterinary Association

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10.43 Transverse CT image at the level of the seventh rib of a 10-year-old neutered crossbreed bitch with metastatic melanoma (window width 1500 HU, window level 300 HU). CT was performed to determine the extent of disease. Just dorsal to the right seventh costochondral junction, there is an irregularly marginated osteolytic lesion with a spiculated periosteal reaction and an associated soft tissue mass. Assessment of the acquired CT images using all appropriate windows will maximize the available information (see also Chapter 3).

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10.44

Right lateral and ventral scintigrams of the head, neck and cranial thorax of a 12-year-old hyperthyroid Domestic Shorthaired cat, obtained 20 minutes after intravenous injection of sodium 99mTc-pertechnetate. Thoracic radiographs obtained prior to the study revealed a poorly defined cranial mediastinal mass. There is a focus of uptake associated with the right thyroid lobe, much higher in intensity than the salivary glands. The left thyroid lobe is not visible. A second intense focus of uptake is seen in the thorax, corresponding to the lesion seen on radiographs. Final diagnosis was hyperthyroidism with ectopic hyperfunctioning thyroidal tissue in the cranial mediastinum. (Courtesy of F. Morandi) © 2024 British Small Animal Veterinary Association

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10.44 Right lateral and ventral scintigrams of the head, neck and cranial thorax of a 12-year-old hyperthyroid Domestic Shorthaired cat, obtained 20 minutes after intravenous injection of sodium 99mTc-pertechnetate. Thoracic radiographs obtained prior to the study revealed a poorly defined cranial mediastinal mass. There is a focus of uptake associated with the right thyroid lobe, much higher in intensity than the salivary glands. The left thyroid lobe is not visible. A second intense focus of uptake is seen in the thorax, corresponding to the lesion seen on radiographs. Final diagnosis was hyperthyroidism with ectopic hyperfunctioning thyroidal tissue in the cranial mediastinum. (Courtesy of F. Morandi)

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10.45

(a) Left lateral thoracic radiograph of a 12-year-old Siamese cat with two small cranial mediastinal cysts (arrowed). (b) Dorsal plane image of the cranial thorax of a 12-year-old spayed female Domestic Shorthaired cat with an ultrasonographically confirmed mediastinal cyst. On radiographs (not shown), the cyst appeared as a round soft tissue opacity cranial to the heart. Ultrasonographically, the cyst appears as an anechoic fluid-filled structure separated into two cavities by a thin septum. (c) Transverse CT image of the caudal mediastinum of an 11-year-old St. Bernard with confirmed cystic adenocarcinoma arising from the accessory lung lobe. The neoplasm produces two large fluid-filled cystic structures (C) in the dorsal part of the caudal mediastinum, adjacent to the left and right caudal lung lobes, caudal vena cava (CV), oesophagus (*) and aorta (A). The appearance of the larger cyst is similar to that of empyema of the mediastinal serous cavity. GB = gallbladder. (b, Courtesy of G. Seiler) © 2024 British Small Animal Veterinary Association

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10.45 (a) Left lateral thoracic radiograph of a 12-year-old Siamese cat with two small cranial mediastinal cysts (arrowed). (b) Dorsal plane image of the cranial thorax of a 12-year-old spayed female Domestic Shorthaired cat with an ultrasonographically confirmed mediastinal cyst. On radiographs (not shown), the cyst appeared as a round soft tissue opacity cranial to the heart. Ultrasonographically, the cyst appears as an anechoic fluid-filled structure separated into two cavities by a thin septum. (c) Transverse CT image of the caudal mediastinum of an 11-year-old St. Bernard with confirmed cystic adenocarcinoma arising from the accessory lung lobe. The neoplasm produces two large fluid-filled cystic structures (C) in the dorsal part of the caudal mediastinum, adjacent to the left and right caudal lung lobes, caudal vena cava (CV), oesophagus (*) and aorta (A). The appearance of the larger cyst is similar to that of empyema of the mediastinal serous cavity. GB = gallbladder. (b, Courtesy of G. Seiler)

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10.46

(a) DV and (b) left lateral thoracic radiographs of a 2-year-old Cocker Spaniel bitch following a road traffic accident. The cranial mediastinum is wide with caudal retraction of the lungs from the thoracic inlet and has a homogeneous soft tissue opacity that effaces the borders of the cardiac silhouette. In addition, the lungs are slightly retracted from the body wall and surrounded by gas, consistent with pneumothorax. © 2024 British Small Animal Veterinary Association

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10.46 (a) DV and (b) left lateral thoracic radiographs of a 2-year-old Cocker Spaniel bitch following a road traffic accident. The cranial mediastinum is wide with caudal retraction of the lungs from the thoracic inlet and has a homogeneous soft tissue opacity that effaces the borders of the cardiac silhouette. In addition, the lungs are slightly retracted from the body wall and surrounded by gas, consistent with pneumothorax.

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10.47

Dorsal plane image of the ventral aspect of the cranial mediastinum of a 3-year-old cat with a moderate bilateral pleural effusion. The entire width of the cat is included in the image. Note the left and right ribs (R). The cranial mediastinum is seen as a narrow echogenic band (between arrows) between the left and right pleural spaces, which are expanded and filled with anechoic fluid. Note the small blood vessels identified within the mediastinum with colour Doppler. © 2024 British Small Animal Veterinary Association

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10.47 Dorsal plane image of the ventral aspect of the cranial mediastinum of a 3-year-old cat with a moderate bilateral pleural effusion. The entire width of the cat is included in the image. Note the left and right ribs (R). The cranial mediastinum is seen as a narrow echogenic band (between arrows) between the left and right pleural spaces, which are expanded and filled with anechoic fluid. Note the small blood vessels identified within the mediastinum with colour Doppler.

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10.48

Lateral thoracic radiograph of an adult dog with pythiosis (infection by Pythium insidiosum, a fungus-like organism). The dorsal part of the mediastinum has a generalized increased opacity that is worst near the lung hilus and extends caudodorsally towards the diaphragm. No loss of definition of the cardiac silhouette is detected. © 2024 British Small Animal Veterinary Association

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10.48 Lateral thoracic radiograph of an adult dog with pythiosis (infection by Pythium insidiosum, a fungus-like organism). The dorsal part of the mediastinum has a generalized increased opacity that is worst near the lung hilus and extends caudodorsally towards the diaphragm. No loss of definition of the cardiac silhouette is detected.

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10.49

(a) Reformatted dorsal oblique contrast CT image of the ventral thorax of a 4-year-old neutered German Shorthaired Pointer bitch with Actinomyces infection showing irregular, peripherally enhancing masses in the caudal thorax (*) and enlargement of the cranial sternal lymph nodes (arrowed). (b) Transverse contrast CT image (soft tissue window) obtained at the level of the tenth thoracic vertebra of an 8-year-old Boxer with spread of suppurative inflammation throughout the thoracic cavity. The dog has bilateral pneumothorax. The dog was positioned in dorsal recumbency; note the gravity-dependent distribution of the pleural fluid and gas. The fluid was consistent with pyothorax (pleural empyema). The gas contrasts with the plica venae cavae (1) and caudoventral mediastinal reflection (2). Both are severely thickened and irregularly margined due to the infiltration of inflammatory cells and fluid, consistent with mediastinitis. A = aorta; C = caudal vena cava. © 2024 British Small Animal Veterinary Association

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10.49 (a) Reformatted dorsal oblique contrast CT image of the ventral thorax of a 4-year-old neutered German Shorthaired Pointer bitch with Actinomyces infection showing irregular, peripherally enhancing masses in the caudal thorax (*) and enlargement of the cranial sternal lymph nodes (arrowed). (b) Transverse contrast CT image (soft tissue window) obtained at the level of the tenth thoracic vertebra of an 8-year-old Boxer with spread of suppurative inflammation throughout the thoracic cavity. The dog has bilateral pneumothorax. The dog was positioned in dorsal recumbency; note the gravity-dependent distribution of the pleural fluid and gas. The fluid was consistent with pyothorax (pleural empyema). The gas contrasts with the plica venae cavae (1) and caudoventral mediastinal reflection (2). Both are severely thickened and irregularly margined due to the infiltration of inflammatory cells and fluid, consistent with mediastinitis. A = aorta; C = caudal vena cava.

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10.50

Right lateral thoracic radiograph of a normal oesophagus of an 8-year-old cat under general anaesthesia. The oesophageal lumen contains a small amount of gas dorsal to the heart (blue on inset) and a small amount of fluid cranial to the diaphragm (red on inset) that redistributed on other views. © 2024 British Small Animal Veterinary Association

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10.50 Right lateral thoracic radiograph of a normal oesophagus of an 8-year-old cat under general anaesthesia. The oesophageal lumen contains a small amount of gas dorsal to the heart (blue on inset) and a small amount of fluid cranial to the diaphragm (red on inset) that redistributed on other views.

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10.51

Close-up of a lateral thoracic radiograph of a dog with a diffusely enlarged, gas-filled oesophagus and cranioventral lung consolidation (aspiration pneumonia). The soft tissue stripe (arrowed) is a silhouette of the tracheal and oesophageal walls, contrasted dorsally and ventrally by gas. © 2024 British Small Animal Veterinary Association

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10.51 Close-up of a lateral thoracic radiograph of a dog with a diffusely enlarged, gas-filled oesophagus and cranioventral lung consolidation (aspiration pneumonia). The soft tissue stripe (arrowed) is a silhouette of the tracheal and oesophageal walls, contrasted dorsally and ventrally by gas.

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10.52

Fluoroscopic oesophagram with orally administered liquid barium suspension in a 1.5-year-old French Bulldog with severe laryngeal collapse and possible regurgitation. At the level of the second rib pair, the oesophagus has a sinuous course, which completely resolved with neck position and oesophageal peristalsis, consistent with a redundant oesophagus. © 2024 British Small Animal Veterinary Association

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10.52 Fluoroscopic oesophagram with orally administered liquid barium suspension in a 1.5-year-old French Bulldog with severe laryngeal collapse and possible regurgitation. At the level of the second rib pair, the oesophagus has a sinuous course, which completely resolved with neck position and oesophageal peristalsis, consistent with a redundant oesophagus.

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10.54

Right lateral thoracic radiograph of a 2-month-old Siberian Husky with regurgitation due to congenital megaoesophagus. The oesophagus is severely enlarged and distended, primarily with gas. Thin lines of soft tissue opacity represent the stretched oesophageal walls (arrowed), and the trachea and cardiac silhouette are mildly ventrally depressed. Note a tracheal stripe sign is less apparent in right lateral recumbency due to the redistribution of gas and fluid within the oesophageal lumen. Ventral to the fifth thoracic vertebra, the dorsal oesophageal wall is focally indented by the bronchoesophageal artery. Summating with the heart, the ventral tip of the left cranial lung lobe (caudal part) has mildly increased pulmonary opacity, consistent with aspiration pneumonia. © 2024 British Small Animal Veterinary Association

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10.54 Right lateral thoracic radiograph of a 2-month-old Siberian Husky with regurgitation due to congenital megaoesophagus. The oesophagus is severely enlarged and distended, primarily with gas. Thin lines of soft tissue opacity represent the stretched oesophageal walls (arrowed), and the trachea and cardiac silhouette are mildly ventrally depressed. Note a tracheal stripe sign is less apparent in right lateral recumbency due to the redistribution of gas and fluid within the oesophageal lumen. Ventral to the fifth thoracic vertebra, the dorsal oesophageal wall is focally indented by the bronchoesophageal artery. Summating with the heart, the ventral tip of the left cranial lung lobe (caudal part) has mildly increased pulmonary opacity, consistent with aspiration pneumonia.

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10.55

VD thoracic radiograph of a 5-year-old hound with acquired megaoesophagus due to myasthenia gravis. Note the gas-filled oesophagus, indented on the left by the aorta and on the right by the azygos vein (arrowed). The soft tissue stripes, representing the oesophageal wall, converge caudally at the oesophageal hiatus of the diaphragm. The dog also has aspiration pneumonia, seen here causing border effacement of portions of the left and right sides of the cardiac silhouette. © 2024 British Small Animal Veterinary Association

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10.55 VD thoracic radiograph of a 5-year-old hound with acquired megaoesophagus due to myasthenia gravis. Note the gas-filled oesophagus, indented on the left by the aorta and on the right by the azygos vein (arrowed). The soft tissue stripes, representing the oesophageal wall, converge caudally at the oesophageal hiatus of the diaphragm. The dog also has aspiration pneumonia, seen here causing border effacement of portions of the left and right sides of the cardiac silhouette.

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10.56

Lateral fluoroscopic oesophagram of a 2-year-old mixed-breed dog a week after a dog fight. A low-osmolar, non-ionic contrast medium was orally administered to examine for suspected oesophageal perforation. The oesophageal lumen is opacified by the contrast medium and has normal linear striations (arrowed). In the mid to caudal neck, contrast medium has leaked out of the oesophagus and into a large gas-filled pocket (arrowheads) between the oesophagus and vertebral column. In the caudoventral neck, deep wounds and a Penrose drain are visible. © 2024 British Small Animal Veterinary Association

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10.56 Lateral fluoroscopic oesophagram of a 2-year-old mixed-breed dog a week after a dog fight. A low-osmolar, non-ionic contrast medium was orally administered to examine for suspected oesophageal perforation. The oesophageal lumen is opacified by the contrast medium and has normal linear striations (arrowed). In the mid to caudal neck, contrast medium has leaked out of the oesophagus and into a large gas-filled pocket (arrowheads) between the oesophagus and vertebral column. In the caudoventral neck, deep wounds and a Penrose drain are visible.

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10.57

Lateral fluoroscopic oesophagram (inverted grayscale) with orally administered liquid barium suspension in a 2-year-old Labrador Retriever, 2 weeks after surgical repair of an oesophageal rupture that occurred during balloon dilation of strictures secondary to general anaesthesia. The oesophageal luminal surface is highly irregular due to scar tissue formation and inflammation (oesophagitis). At the cranial edge of the image, haemoclips partially summate with a trace of barium coating the lumen. © 2024 British Small Animal Veterinary Association

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10.57 Lateral fluoroscopic oesophagram (inverted grayscale) with orally administered liquid barium suspension in a 2-year-old Labrador Retriever, 2 weeks after surgical repair of an oesophageal rupture that occurred during balloon dilation of strictures secondary to general anaesthesia. The oesophageal luminal surface is highly irregular due to scar tissue formation and inflammation (oesophagitis). At the cranial edge of the image, haemoclips partially summate with a trace of barium coating the lumen.

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10.58

Transverse CT angiogram (arterial phase, soft tissue window) of the cranial neck of an adult mixed-breed dog with extensive regional and distant metastasis of a thyroid carcinoma, including large tumour thrombi in the jugular vein (JV). Associated with the neoplasm, there is a collection of anomalous blood vessels with arteriovenous shunting ventral to the oesophagus (*) and surrounding the trachea (note the tracheal tube). Arising from this, a vessel enters the cranial oesophageal wall, which is moderately irregularly thick and abnormally enhancing. © 2024 British Small Animal Veterinary Association

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10.58 Transverse CT angiogram (arterial phase, soft tissue window) of the cranial neck of an adult mixed-breed dog with extensive regional and distant metastasis of a thyroid carcinoma, including large tumour thrombi in the jugular vein (JV). Associated with the neoplasm, there is a collection of anomalous blood vessels with arteriovenous shunting ventral to the oesophagus (*) and surrounding the trachea (note the tracheal tube). Arising from this, a vessel enters the cranial oesophageal wall, which is moderately irregularly thick and abnormally enhancing.

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10.59

Transverse T2-weighted MRI image at the thoracic inlet of a 6-month-old Boxer with mediastinitis and brachial plexitis secondary to a perforating oesophageal foreign body (stick). The stick (FB) is located within the oesophageal lumen and has caused a focal wall rupture (arrowed). Surrounding the oesophagus and trachea (T), the mediastinum is severely swollen and hyperintense. The first thoracic vertebra (T1), manubrium (M) and first rib pair can be seen. © 2024 British Small Animal Veterinary Association

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10.59 Transverse T2-weighted MRI image at the thoracic inlet of a 6-month-old Boxer with mediastinitis and brachial plexitis secondary to a perforating oesophageal foreign body (stick). The stick (FB) is located within the oesophageal lumen and has caused a focal wall rupture (arrowed). Surrounding the oesophagus and trachea (T), the mediastinum is severely swollen and hyperintense. The first thoracic vertebra (T1), manubrium (M) and first rib pair can be seen.

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10.60

Right lateral thoracic radiograph of a 12-year-old terrier with a rawhide toy lodged in the caudal oesophagus (arrowed). The thoracic oesophagus is enlarged, and the lumen contains gas and a focal soft tissue opacity with linear gas striations attributed to the rawhide toy. An oesophageal foreign body with soft tissue opacity may resemble a focal mass, but the parallel gas lines facilitated the diagnosis in this case. © 2024 British Small Animal Veterinary Association

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10.60 Right lateral thoracic radiograph of a 12-year-old terrier with a rawhide toy lodged in the caudal oesophagus (arrowed). The thoracic oesophagus is enlarged, and the lumen contains gas and a focal soft tissue opacity with linear gas striations attributed to the rawhide toy. An oesophageal foreign body with soft tissue opacity may resemble a focal mass, but the parallel gas lines facilitated the diagnosis in this case.

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10.61

Two different puppies with a vascular ring anomaly comprising PRAA and segmental oesophageal dilatation cranial to the heart base. In both puppies, the cranial thoracic oesophagus is moderately distended. (a) Lateral thoracic radiograph. The oesophageal lumen is gas filled to the level of the third rib (outlined blue in inset) and contains a few mineral particles ventrally (gravel sign). (b) Lateral oesophagram. The oesophageal lumen is filled with barium and has a filling defect that is highly suggestive of indentation by the right aortic arch. © 2024 British Small Animal Veterinary Association

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10.61 Two different puppies with a vascular ring anomaly comprising PRAA and segmental oesophageal dilatation cranial to the heart base. In both puppies, the cranial thoracic oesophagus is moderately distended. (a) Lateral thoracic radiograph. The oesophageal lumen is gas filled to the level of the third rib (outlined blue in inset) and contains a few mineral particles ventrally (gravel sign). (b) Lateral oesophagram. The oesophageal lumen is filled with barium and has a filling defect that is highly suggestive of indentation by the right aortic arch.

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VD thoracic radiograph of a 12-week-old mixed-breed dog with PRAA that contributes to a vascular ring anomaly. At the level of the fourth thoracic vertebra, the abnormal right aortic arch causes severe leftward deviation of the trachea (arrowed). Also note that the cranial mediastinum is wide due to the segmental enlargement of the oesophagus. © 2024 British Small Animal Veterinary Association

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10.62 VD thoracic radiograph of a 12-week-old mixed-breed dog with PRAA that contributes to a vascular ring anomaly. At the level of the fourth thoracic vertebra, the abnormal right aortic arch causes severe leftward deviation of the trachea (arrowed). Also note that the cranial mediastinum is wide due to the segmental enlargement of the oesophagus.

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10.63

Transverse CT angiograms at the cranial aspect of the heart in three different dogs. Diagnosis of a vascular ring anomaly hinges on identifying the spatial arrangement of the blood vessels, trachea and oesophagus. However, the ligamentum arteriosum is not usually identifiable except in cases with PDA. Diagnosis also depends on identifying the result of a vascular ring (e.g. segmental oesophageal enlargement). (a) Normal arrangement. The oesophagus (*) and aortic arch (Ao) are to the left of the trachea (T). (b) Type 1 PRAA. The aortic arch circles to the right of the trachea and oesophagus. The oesophagus is compressed between the aorta, the pulmonic trunk on the left and the ligamentum arteriosum dorsally. (c) Type 3 PRAA with an aberrant left subclavian artery (LSc). Cranial to its origin on the descending aorta, the left subclavian artery runs dorsally and laterally to the oesophagus and contributes to the compression. Not shown on this slice, the right subclavian artery (RSc) has a separate origin from the trunk (C) that gives rise to both common carotid arteries. © 2024 British Small Animal Veterinary Association

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10.63 Transverse CT angiograms at the cranial aspect of the heart in three different dogs. Diagnosis of a vascular ring anomaly hinges on identifying the spatial arrangement of the blood vessels, trachea and oesophagus. However, the ligamentum arteriosum is not usually identifiable except in cases with PDA. Diagnosis also depends on identifying the result of a vascular ring (e.g. segmental oesophageal enlargement). (a) Normal arrangement. The oesophagus (*) and aortic arch (Ao) are to the left of the trachea (T). (b) Type 1 PRAA. The aortic arch circles to the right of the trachea and oesophagus. The oesophagus is compressed between the aorta, the pulmonic trunk on the left and the ligamentum arteriosum dorsally. (c) Type 3 PRAA with an aberrant left subclavian artery (LSc). Cranial to its origin on the descending aorta, the left subclavian artery runs dorsally and laterally to the oesophagus and contributes to the compression. Not shown on this slice, the right subclavian artery (RSc) has a separate origin from the trunk (C) that gives rise to both common carotid arteries.

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10.64

Close-up DV thoracic radiograph of the caudal oesophagus in a mature dog. In cases of suspected S. lupi infection, it is essential to follow the left outline of the aorta (arrowed). A second bulge in this area (arrowheads) is consistent with an oesophageal S. lupi granuloma, aortic aneurysm secondary to S. lupi infection or both. © 2024 British Small Animal Veterinary Association

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10.64 Close-up DV thoracic radiograph of the caudal oesophagus in a mature dog. In cases of suspected S. lupi infection, it is essential to follow the left outline of the aorta (arrowed). A second bulge in this area (arrowheads) is consistent with an oesophageal S. lupi granuloma, aortic aneurysm secondary to S. lupi infection or both.

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Close-up lateral oesophagram showing a small dorsal oesophageal wall filling defect consistent with S. lupi granuloma. Thoracic spondylitis (arrowed) is considered to be pathognomonic for S. lupi infection, especially in endemic areas. Spondylosis deformans is also present caudally and is an incidental finding of minor consequence unrelated to the infection. © 2024 British Small Animal Veterinary Association

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10.65 Close-up lateral oesophagram showing a small dorsal oesophageal wall filling defect consistent with S. lupi granuloma. Thoracic spondylitis (arrowed) is considered to be pathognomonic for S. lupi infection, especially in endemic areas. Spondylosis deformans is also present caudally and is an incidental finding of minor consequence unrelated to the infection.

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10.66

Transverse CT image obtained immediately caudal to the carina of an 8-year-old neutered male Dalmatian (window level -215 HU, window width 1996 HU (lung window)). An S. lupi granuloma is visible in the oesophagus (arrowed). The mineralization within is indicative of malignant transformation (osteosarcoma or fibrosarcoma). Dorsal to the mass, the oesophageal lumen contains a small amount of gas and the wall of the aorta (A) is partially mineralized. H = heart. © 2024 British Small Animal Veterinary Association

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10.66 Transverse CT image obtained immediately caudal to the carina of an 8-year-old neutered male Dalmatian (window level -215 HU, window width 1996 HU (lung window)). An S. lupi granuloma is visible in the oesophagus (arrowed). The mineralization within is indicative of malignant transformation (osteosarcoma or fibrosarcoma). Dorsal to the mass, the oesophageal lumen contains a small amount of gas and the wall of the aorta (A) is partially mineralized. H = heart.

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10.67

A 2-year-old Boxer with a history of hyporexia and regurgitation due to oesophageal pythiosis. (a) Lateral thoracic radiograph. An ill-defined dorsal mediastinal mass is present. Moderate oesophageal gas is dorsally displaced and interrupted at the level of the heart base. (b) Transverse CT image. The oesophagus (arrowed) is severely circumferentially thick, and this infiltrative process extends into the mediastinum and along the pulmonary vasculature. © 2024 British Small Animal Veterinary Association

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10.67 A 2-year-old Boxer with a history of hyporexia and regurgitation due to oesophageal pythiosis. (a) Lateral thoracic radiograph. An ill-defined dorsal mediastinal mass is present. Moderate oesophageal gas is dorsally displaced and interrupted at the level of the heart base. (b) Transverse CT image. The oesophagus (arrowed) is severely circumferentially thick, and this infiltrative process extends into the mediastinum and along the pulmonary vasculature.

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10.68

(a, b) Orthogonal thoracic radiographs in a dog with gastro-oesophageal intussusception. The stomach (arrowed) is displaced cranially into the caudal oesophagus. The displaced stomach appears as a large, circumscribed mass with homogeneous soft tissue opacity. Note the characteristic cranially convex margin of the stomach that is contrasted by gas within the oesophageal lumen. The oesophagus is severely enlarged and displaces the cardiac silhouette and trachea ventrally. © 2024 British Small Animal Veterinary Association

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10.68 (a, b) Orthogonal thoracic radiographs in a dog with gastro-oesophageal intussusception. The stomach (arrowed) is displaced cranially into the caudal oesophagus. The displaced stomach appears as a large, circumscribed mass with homogeneous soft tissue opacity. Note the characteristic cranially convex margin of the stomach that is contrasted by gas within the oesophageal lumen. The oesophagus is severely enlarged and displaces the cardiac silhouette and trachea ventrally.

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10.69

Endoscopic appearance of the tracheal bifurcation. The left and right principal bronchi are clearly visible, with the carina in the middle. (Reproduced from the BSAVA Manual of Canine and Feline Endoscopy and Endosurgery; courtesy of T McCarthy) © 2024 British Small Animal Veterinary Association

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10.69 Endoscopic appearance of the tracheal bifurcation. The left and right principal bronchi are clearly visible, with the carina in the middle. (Reproduced from the BSAVA Manual of Canine and Feline Endoscopy and Endosurgery; courtesy of T McCarthy)

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10.70

Left lateral thoracic radiograph of a 9-year-old crossbreed dog. In animals with a deep thorax conformation, such as this dog, the trachea diverges from the vertebral column with a more pronounced angle. The tracheal bifurcation (arrowed) is located at the fifth intercostal space. © 2024 British Small Animal Veterinary Association

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10.70 Left lateral thoracic radiograph of a 9-year-old crossbreed dog. In animals with a deep thorax conformation, such as this dog, the trachea diverges from the vertebral column with a more pronounced angle. The tracheal bifurcation (arrowed) is located at the fifth intercostal space.

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10.71

Lateral thoracic radiograph of a dog with mild dorsal elevation of the ventral tracheal wall at the first intercostal space. This appearance is a normal variant usually observed in shallow-chested dogs, such as terriers, and results from the right subclavian artery coursing ventral to the trachea at this level. © 2024 British Small Animal Veterinary Association

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10.71 Lateral thoracic radiograph of a dog with mild dorsal elevation of the ventral tracheal wall at the first intercostal space. This appearance is a normal variant usually observed in shallow-chested dogs, such as terriers, and results from the right subclavian artery coursing ventral to the trachea at this level.

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10.73

Close-up lateral thoracic radiograph of a normal Dachshund depicting calculation of the TD:TI. The thoracic inlet distance (black arrow) is measured from the ventral aspect of the vertebral column at the midpoint of the most cranial rib to the dorsal surface of the manubrium at its point of minimal thickness. The tracheal diameter (white arrow) is measured between the internal surfaces of the tracheal wall oriented perpendicularly to the tracheal long axis at the point where the thoracic inlet line crosses the midpoint of the tracheal lumen. In this dog, the TD:TI is 0.2. © 2024 British Small Animal Veterinary Association

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10.73 Close-up lateral thoracic radiograph of a normal Dachshund depicting calculation of the TD:TI. The thoracic inlet distance (black arrow) is measured from the ventral aspect of the vertebral column at the midpoint of the most cranial rib to the dorsal surface of the manubrium at its point of minimal thickness. The tracheal diameter (white arrow) is measured between the internal surfaces of the tracheal wall oriented perpendicularly to the tracheal long axis at the point where the thoracic inlet line crosses the midpoint of the tracheal lumen. In this dog, the TD:TI is 0.2.

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10.74

Lateral thoracic radiograph of a 5-year-old Labrador Retriever bitch without respiratory signs depicting pseudocollapse of the trachea. Note the band of soft tissue opacity summating with the dorsal portion of the cervical tracheal lumen (arrowed). The dorsal tracheal wall is visible in a normal position. This normal finding should not be mistaken for tracheal collapse. © 2024 British Small Animal Veterinary Association

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10.74 Lateral thoracic radiograph of a 5-year-old Labrador Retriever bitch without respiratory signs depicting pseudocollapse of the trachea. Note the band of soft tissue opacity summating with the dorsal portion of the cervical tracheal lumen (arrowed). The dorsal tracheal wall is visible in a normal position. This normal finding should not be mistaken for tracheal collapse.

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10.76

Lateral thoracic radiograph of a 2-month-old Bulldog puppy with dyspnoea of 3 weeks’ duration. The tracheal diameter is diffusely very small and consistent with tracheal hypoplasia (a congenital developmental anomaly). However, although tracheal hypoplasia may have contributed to the severity of the clinical signs, the clinical signs fully resolved following treatment for severe concurrent laryngitis and suspected bronchitis. © 2024 British Small Animal Veterinary Association

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10.76 Lateral thoracic radiograph of a 2-month-old Bulldog puppy with dyspnoea of 3 weeks’ duration. The tracheal diameter is diffusely very small and consistent with tracheal hypoplasia (a congenital developmental anomaly). However, although tracheal hypoplasia may have contributed to the severity of the clinical signs, the clinical signs fully resolved following treatment for severe concurrent laryngitis and suspected bronchitis.

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10.77

Transverse CT image of the trachea at the level of the sixth cervical vertebra of a Beagle cross with mucopolysaccharidosis VII. The tracheal cartilages are thick for the breed and overlap, resulting in a reduced tracheal lumen. © 2024 British Small Animal Veterinary Association

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10.77 Transverse CT image of the trachea at the level of the sixth cervical vertebra of a Beagle cross with mucopolysaccharidosis VII. The tracheal cartilages are thick for the breed and overlap, resulting in a reduced tracheal lumen.

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10.78

Caudal cervical tracheal malformation in a small-breed dog. (a) Lateral thoracic radiograph. At the level of the thoracic inlet, the tracheal lumen is severely narrowed by a smooth, broad-based mass effacing the ventral tracheal wall. (b) Transverse CT image of the neck. The apparent mass is due to buckling and rigid inward bowing of the tracheal rings. Note the trachea has a ‘W’ shape typical of this condition (arrowed). © 2024 British Small Animal Veterinary Association

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10.78 Caudal cervical tracheal malformation in a small-breed dog. (a) Lateral thoracic radiograph. At the level of the thoracic inlet, the tracheal lumen is severely narrowed by a smooth, broad-based mass effacing the ventral tracheal wall. (b) Transverse CT image of the neck. The apparent mass is due to buckling and rigid inward bowing of the tracheal rings. Note the trachea has a ‘W’ shape typical of this condition (arrowed).

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10.80

The dependence of tracheal collapse on phase of respiration. During inspiration, there is a slightly negative pressure within the lumen of the cervical trachea when air moves towards the thorax. This pressure difference collapses the cervical trachea when the tracheal wall lacks sufficient stability. In the thoracic area, the pressure within the trachea is higher than the pressure within the thoracic cavity, which results in tracheal distention. During expiration, the cervical trachea is distended due to the luminal pressure exceeding the outside pressure when air flows towards the larynx. However, the thoracic pressure exceeds the intratracheal pressure, which collapses the thoracic trachea when the tracheal wall lacks sufficient stability. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. (Redrawn after Suter (1984)) © 2024 British Small Animal Veterinary Association

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10.80 The dependence of tracheal collapse on phase of respiration. During inspiration, there is a slightly negative pressure within the lumen of the cervical trachea when air moves towards the thorax. This pressure difference collapses the cervical trachea when the tracheal wall lacks sufficient stability. In the thoracic area, the pressure within the trachea is higher than the pressure within the thoracic cavity, which results in tracheal distention. During expiration, the cervical trachea is distended due to the luminal pressure exceeding the outside pressure when air flows towards the larynx. However, the thoracic pressure exceeds the intratracheal pressure, which collapses the thoracic trachea when the tracheal wall lacks sufficient stability. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. (Redrawn after Suter (1984))

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10.81

(a) Lateral radiograph centred on the thoracic inlet of a 15-year-old Miniature Poodle showing partial collapse of the extrathoracic (cervical) portion and a distended intrathoracic portion of the trachea during inspiration. Also notice the well expanded and aerated lungs and height of the principal bronchi. (b) Lateral radiograph demonstrating partial collapse of the intrathoracic portion and normal diameter of the cervical portion of the trachea during expiration. Notice the smaller lung volume, pulmonary opacification and collapsed principal bronchi. © 2024 British Small Animal Veterinary Association

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10.81 (a) Lateral radiograph centred on the thoracic inlet of a 15-year-old Miniature Poodle showing partial collapse of the extrathoracic (cervical) portion and a distended intrathoracic portion of the trachea during inspiration. Also notice the well expanded and aerated lungs and height of the principal bronchi. (b) Lateral radiograph demonstrating partial collapse of the intrathoracic portion and normal diameter of the cervical portion of the trachea during expiration. Notice the smaller lung volume, pulmonary opacification and collapsed principal bronchi.

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10.82

Lateral cervicothoracic radiograph of a 16-year-old Chihuahua with extensive cervical and thoracic tracheal collapse. Notice the curvilinear ventral and undulating dorsal aspect of the collapsing tracheal wall. © 2024 British Small Animal Veterinary Association

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10.82 Lateral cervicothoracic radiograph of a 16-year-old Chihuahua with extensive cervical and thoracic tracheal collapse. Notice the curvilinear ventral and undulating dorsal aspect of the collapsing tracheal wall.

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10.83

Lateral cervical radiograph of a 6-year-old Domestic Shorthaired cat with chronic inspiratory stridor. Notice the marked collapse of the caudal cervical trachea. A congenital deformation in the cranial end of the trachea with significant luminal obstruction was found on post-mortem examination. (Reproduced from Hendricks and O’Brien (1985) with permission © 2024 British Small Animal Veterinary Association

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10.83 Lateral cervical radiograph of a 6-year-old Domestic Shorthaired cat with chronic inspiratory stridor. Notice the marked collapse of the caudal cervical trachea. A congenital deformation in the cranial end of the trachea with significant luminal obstruction was found on post-mortem examination. (Reproduced from Hendricks and O’Brien (1985) with permission

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10.84

Lateral cervicothoracic radiograph of a 7-month-old Domestic Shorthaired cat suffering from a tracheal intubation injury sustained during a routine spay procedure. The laceration site is not directly visible but the secondary subcutaneous emphysema and pneumomediastinum are. The tracheal wall is contrasted by gas on both sides. © 2024 British Small Animal Veterinary Association

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10.84 Lateral cervicothoracic radiograph of a 7-month-old Domestic Shorthaired cat suffering from a tracheal intubation injury sustained during a routine spay procedure. The laceration site is not directly visible but the secondary subcutaneous emphysema and pneumomediastinum are. The tracheal wall is contrasted by gas on both sides.

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10.85

Lateral thoracic radiograph of a 4-year-old Domestic Shorthaired cat with complete tracheal rupture due to a road traffic accident. Notice the absence of tracheal rings within the ballooned radiolucent area extending from the second to fourth intercostal spaces. This gas bubble contained in local mediastinal tissues is sometimes referred to as a pseudotrachea. (Courtesy of E. Friend) © 2024 British Small Animal Veterinary Association

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10.85 Lateral thoracic radiograph of a 4-year-old Domestic Shorthaired cat with complete tracheal rupture due to a road traffic accident. Notice the absence of tracheal rings within the ballooned radiolucent area extending from the second to fourth intercostal spaces. This gas bubble contained in local mediastinal tissues is sometimes referred to as a pseudotrachea. (Courtesy of E. Friend)

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10.86

Lateral cervical radiograph of a 7-year-old Rottweiler with chronic upper respiratory distress. There is a mass of soft tissue and mineral opacity arising from the ventral aspect of the tracheal wall, inhibiting further passage of the endotracheal tube. An oesophageal tube can be seen dorsally. Final diagnosis was a tracheal chondrosarcoma. © 2024 British Small Animal Veterinary Association

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10.86 Lateral cervical radiograph of a 7-year-old Rottweiler with chronic upper respiratory distress. There is a mass of soft tissue and mineral opacity arising from the ventral aspect of the tracheal wall, inhibiting further passage of the endotracheal tube. An oesophageal tube can be seen dorsally. Final diagnosis was a tracheal chondrosarcoma.

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10.87

Transverse contrast-enhanced CT image at the level of the sixth cervical vertebra of a 10-year-old Domestic Shorthaired cat with chronic inspiratory dyspnoea. There is a contrast-enhancing soft tissue mass (arrowed) arising from the dorsal wall of the trachea (T) adjacent to the gas-distended oesophagus (O). Final diagnosis was a tracheal lymphoma. Tracheal resection and chemotherapy maintained this cat in remission for almost 2 years. © 2024 British Small Animal Veterinary Association

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10.87 Transverse contrast-enhanced CT image at the level of the sixth cervical vertebra of a 10-year-old Domestic Shorthaired cat with chronic inspiratory dyspnoea. There is a contrast-enhancing soft tissue mass (arrowed) arising from the dorsal wall of the trachea (T) adjacent to the gas-distended oesophagus (O). Final diagnosis was a tracheal lymphoma. Tracheal resection and chemotherapy maintained this cat in remission for almost 2 years.

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10.88

Lateral thoracic radiograph of a 5-year-old Domestic Shorthaired cat with a mineral opaque foreign body in the caudal trachea. (Courtesy of E. Friend) © 2024 British Small Animal Veterinary Association

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10.88 Lateral thoracic radiograph of a 5-year-old Domestic Shorthaired cat with a mineral opaque foreign body in the caudal trachea. (Courtesy of E. Friend)

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10.89

Lateral thoracic radiograph of a 5-year-old Lurcher with several nodules (arrowheads) in the caudal thoracic trachea representing Oslerus osleri granulomas. (Courtesy of A. Holloway) © 2024 British Small Animal Veterinary Association

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10.89 Lateral thoracic radiograph of a 5-year-old Lurcher with several nodules (arrowheads) in the caudal thoracic trachea representing Oslerus osleri granulomas. (Courtesy of A. Holloway)

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10.90

A 3-year-old Labrador Retriever with rodenticide toxicity (warfarin) causing submucosal tracheal and pulmonary haemorrhage. (a) Lateral thoracic radiograph. The cranial mediastinum shows increased soft tissue opacity with caudal displacement of the lungs from the first rib pair. At this level, the tracheal lumen is severely narrowed. In addition, there is patchy pulmonary opacification. (b) DV thoracic radiograph. The cranial mediastinum is severely widened, the cranial lung lobes are caudally displaced and there is increased opacity in the left caudal lung lobe. © 2024 British Small Animal Veterinary Association

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10.90 A 3-year-old Labrador Retriever with rodenticide toxicity (warfarin) causing submucosal tracheal and pulmonary haemorrhage. (a) Lateral thoracic radiograph. The cranial mediastinum shows increased soft tissue opacity with caudal displacement of the lungs from the first rib pair. At this level, the tracheal lumen is severely narrowed. In addition, there is patchy pulmonary opacification. (b) DV thoracic radiograph. The cranial mediastinum is severely widened, the cranial lung lobes are caudally displaced and there is increased opacity in the left caudal lung lobe.

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10.91

Lateral thoracic radiograph of an 8-year-old Golden Retriever with dilated cardiomyopathy. Note the general dorsal displacement of the trachea secondary to cardiac enlargement. © 2024 British Small Animal Veterinary Association

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10.91 Lateral thoracic radiograph of an 8-year-old Golden Retriever with dilated cardiomyopathy. Note the general dorsal displacement of the trachea secondary to cardiac enlargement.

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10.92

Lateral thoracic radiograph of an 8-year-old Boxer with recent lethargy. At the level of the heart base, the trachea is focally displaced dorsally by a soft tissue opacity. Moderate pleural effusion is also present. On echocardiography, a heart base mass was seen encircling and compressing vessels and the heart was otherwise structurally normal. The location of the mass is consistent with an aortic body tumour. © 2024 British Small Animal Veterinary Association

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10.92 Lateral thoracic radiograph of an 8-year-old Boxer with recent lethargy. At the level of the heart base, the trachea is focally displaced dorsally by a soft tissue opacity. Moderate pleural effusion is also present. On echocardiography, a heart base mass was seen encircling and compressing vessels and the heart was otherwise structurally normal. The location of the mass is consistent with an aortic body tumour.

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10.93

Lateral thoracic radiograph of a 6-month-old mixed-breed dog with moderate to severe pulmonic stenosis (‘hat sign’). The large post-stenotic dilatation of the pulmonic trunk (arrowed) summates with the trachea. © 2024 British Small Animal Veterinary Association

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10.93 Lateral thoracic radiograph of a 6-month-old mixed-breed dog with moderate to severe pulmonic stenosis (‘hat sign’). The large post-stenotic dilatation of the pulmonic trunk (arrowed) summates with the trachea.

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10.94

(a) Lateral thoracic radiograph of a 15-year-old Domestic Shorthaired cat with a mediastinal carcinoma 2 years after successful radiation treatment of a thymoma. Notice the dorsal tracheal deviation pivoting at the level of the fourth rib. There is also visible cranial lung lobe atelectasis (air bronchograms) and pleural effusion. (b) Lateral thoracic radiograph of a dog with tracheobronchial lymphadenopathy causing ventral deviation and compression of the caudal thoracic trachea. © 2024 British Small Animal Veterinary Association

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10.94 (a) Lateral thoracic radiograph of a 15-year-old Domestic Shorthaired cat with a mediastinal carcinoma 2 years after successful radiation treatment of a thymoma. Notice the dorsal tracheal deviation pivoting at the level of the fourth rib. There is also visible cranial lung lobe atelectasis (air bronchograms) and pleural effusion. (b) Lateral thoracic radiograph of a dog with tracheobronchial lymphadenopathy causing ventral deviation and compression of the caudal thoracic trachea.

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10.95

Lateral thoracic radiograph of an 11-year-old Domestic Shorthaired cat with a large thymoma causing dorsal tracheal deviation and caudal displacement of the carina (eighth intercostal space). The heart is located at the caudodorsal aspect of the mass. The caudal displacement of the carina is pathognomonic for a cranial mediastinal mass. © 2024 British Small Animal Veterinary Association

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10.95 Lateral thoracic radiograph of an 11-year-old Domestic Shorthaired cat with a large thymoma causing dorsal tracheal deviation and caudal displacement of the carina (eighth intercostal space). The heart is located at the caudodorsal aspect of the mass. The caudal displacement of the carina is pathognomonic for a cranial mediastinal mass.

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10.96

Lateral thoracic radiograph of a 2-year-old Irish Setter with a neuroendocrine tumour in the dorsal part of the cranial mediastinum causing ventral deviation of the cranial thoracic trachea. © 2024 British Small Animal Veterinary Association

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10.96 Lateral thoracic radiograph of a 2-year-old Irish Setter with a neuroendocrine tumour in the dorsal part of the cranial mediastinum causing ventral deviation of the cranial thoracic trachea.

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10.97

Close-up of a lateral thoracic radiograph of a dog with pleural effusion. The trachea is straight but parallel to the thoracic vertebral column, a common feature in pleural effusion. © 2024 British Small Animal Veterinary Association

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10.97 Close-up of a lateral thoracic radiograph of a dog with pleural effusion. The trachea is straight but parallel to the thoracic vertebral column, a common feature in pleural effusion.

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10.98

Lateral cervical radiograph of a 2-month-old Weimaraner with canine strangles. There is severe mandibular and retropharyngeal lymphadenopathy, the latter causing ventral deviation of the larynx and cranial trachea. © 2024 British Small Animal Veterinary Association

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10.98 Lateral cervical radiograph of a 2-month-old Weimaraner with canine strangles. There is severe mandibular and retropharyngeal lymphadenopathy, the latter causing ventral deviation of the larynx and cranial trachea.

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10.99

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10.99 Lateral cervical radiograph of a 10-year-old Dobermann with a mineralized thyroid tumour causing dorsal deviation of the cranial trachea.