Basics of thoracic image interpretation

Peter Scrivani; Tobias Schwarz

doi:10.22233/9781910443941.7

British Small Animal Veterinary Association , 102 (2024); https://doi.org/10.22233/9781910443941.7

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Basics of thoracic image interpretation

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Authors: Peter Scrivani and Tobias Schwarz
From: BSAVA Manual of Canine and Feline Thoracic Imaging
Item: Chapter 7, pp 102 - 131
DOI: 10.22233/9781910443941.7
Copyright: © 2024 British Small Animal Veterinary Association
Publication Date: January 2024

Abstract

This chapter provides a comprehensive overview of thoracic imaging interpretation in veterinary medicine, emphasizing key considerations for accurate diagnosis. Directional terminology and anatomical planes of the thorax and the various body systems within are explained. Classical signs of congenital conditions causing volume or pressure overloading of the heart are outlined alongside other thoracic diseases detectable via imaging, such as neoplasia and inflammation. The relationship between diagnostic imaging, pathology and histopathology is explored. Finally, the chapter examines the role of imaging signs in screening tests, detailing the difference between general and special signs and stressing the potential for errors and biases to affect image interpretation.

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Figures

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7.1

Improved work efficiency and avoiding repetitive injury is possible with an ergonomic workstation. The optimal desk height varies with the size of the user and different tasks. Adjustable desks allow users to make small height modifications for different tasks and larger variations to shift between sitting and standing positions. When sitting, it is important to have a comfortable chair that supports the spine. For both sitting and standing, the display monitor should be tilted 10–20 degrees, positioned about an arm’s length away and a couple of inches below eye level. The keyboard should be flat or have a slight negative incline to avoid wrist extension and be wide enough for hands to be about shoulder-width apart. The mouse should be easy to move and comfortable to grip. Good ambient lighting is essential and can be achieved with a combination of natural light, overhead light and task lighting. When possible, extraneous stressors (e.g. background noise) should be eliminated and items that promote a calm pleasant workplace introduced. © 2024 British Small Animal Veterinary Association

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7.1 Improved work efficiency and avoiding repetitive injury is possible with an ergonomic workstation. The optimal desk height varies with the size of the user and different tasks. Adjustable desks allow users to make small height modifications for different tasks and larger variations to shift between sitting and standing positions. When sitting, it is important to have a comfortable chair that supports the spine. For both sitting and standing, the display monitor should be tilted 10–20 degrees, positioned about an arm’s length away and a couple of inches below eye level. The keyboard should be flat or have a slight negative incline to avoid wrist extension and be wide enough for hands to be about shoulder-width apart. The mouse should be easy to move and comfortable to grip. Good ambient lighting is essential and can be achieved with a combination of natural light, overhead light and task lighting. When possible, extraneous stressors (e.g. background noise) should be eliminated and items that promote a calm pleasant workplace introduced.

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7.2

Lateral thoracic radiograph of a 3-year-old Labrador Retriever cross with dyspnoea. There is partial effacement of the cardiac silhouette by pleural fluid and opacification of the accessory lung lobe, containing some gas bubbles (arrowed). Based on these signs, a very reasonable diagnosis is pyothorax and pneumonia secondary to a migrating foreign body. However, a diagnosis of accessory lung lobe torsion was made at surgery. Although the accessory lung lobe infrequently undergoes torsion, the combination of pleural effusion and lung consolidation with vesicular pattern is a classic radiographic pattern of lung lobe torsion. Failure to include relevant differentials can occur when subconscious pattern recognition bias influences the ‘best match’. © 2024 British Small Animal Veterinary Association

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7.2 Lateral thoracic radiograph of a 3-year-old Labrador Retriever cross with dyspnoea. There is partial effacement of the cardiac silhouette by pleural fluid and opacification of the accessory lung lobe, containing some gas bubbles (arrowed). Based on these signs, a very reasonable diagnosis is pyothorax and pneumonia secondary to a migrating foreign body. However, a diagnosis of accessory lung lobe torsion was made at surgery. Although the accessory lung lobe infrequently undergoes torsion, the combination of pleural effusion and lung consolidation with vesicular pattern is a classic radiographic pattern of lung lobe torsion. Failure to include relevant differentials can occur when subconscious pattern recognition bias influences the ‘best match’.

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7.3

Lateral thoracic radiograph of an 8-year-old Rottweiler. The linear mineralization summating with the cardiac silhouette craves the attention of the viewer (‘power of the obvious’). It is difficult to concentrate on other areas, such as the gas-distended oesophagus, until this obvious lesion has been dealt with. It is therefore best to describe the mineralization first. This is incidental aortic mineralization, commonly seen in older dogs. © 2024 British Small Animal Veterinary Association

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7.3 Lateral thoracic radiograph of an 8-year-old Rottweiler. The linear mineralization summating with the cardiac silhouette craves the attention of the viewer (‘power of the obvious’). It is difficult to concentrate on other areas, such as the gas-distended oesophagus, until this obvious lesion has been dealt with. It is therefore best to describe the mineralization first. This is incidental aortic mineralization, commonly seen in older dogs.

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7.4

Lateral thoracic radiograph of an 8-year-old Golden Retriever with dyspnoea and lethargy. Most observers are initially drawn to the multiple soft tissue opacities in the ventral thorax. However, the key to resolving this case is recognizing that the cardiac silhouette is not visible. It can be assumed that the heart is present in a living dog. Therefore, border effacement is the likely cause for this, which can only be caused by a soft tissue structure in direct contact with the heart, such as the pericardial sac, pleural fluid or masses, lungs that have the opacity of soft tissue, herniated abdominal content or mediastinal masses. Eliminating the least likely candidates first and using context from other views and other radiographic signs such as the dorsal deviation of the trachea, a cranial mediastinal mass is the most likely and is consistent with the confirmed diagnosis of thymoma. © 2024 British Small Animal Veterinary Association

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7.4 Lateral thoracic radiograph of an 8-year-old Golden Retriever with dyspnoea and lethargy. Most observers are initially drawn to the multiple soft tissue opacities in the ventral thorax. However, the key to resolving this case is recognizing that the cardiac silhouette is not visible. It can be assumed that the heart is present in a living dog. Therefore, border effacement is the likely cause for this, which can only be caused by a soft tissue structure in direct contact with the heart, such as the pericardial sac, pleural fluid or masses, lungs that have the opacity of soft tissue, herniated abdominal content or mediastinal masses. Eliminating the least likely candidates first and using context from other views and other radiographic signs such as the dorsal deviation of the trachea, a cranial mediastinal mass is the most likely and is consistent with the confirmed diagnosis of thymoma.

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7.5

Making use of the available spatial resolution by using the pan and magnification tools: the same dorsoventral thoracic radiograph of a 13-year-old Miniature Poodle displayed at (a) 25% resolution and (b) 100% resolution. If the entire digital radiograph cannot be displayed on the monitor at the original resolution, then the image should be evaluated at least twice. Firstly, the entire image should be displayed within the maximum available screen area. Secondly, each part of the image should be evaluated at the original resolution. The pulmonary nodule (arrowed) is more noticeable in (b). T9 = ninth thoracic vertebra. © 2024 British Small Animal Veterinary Association

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7.5 Making use of the available spatial resolution by using the pan and magnification tools: the same dorsoventral thoracic radiograph of a 13-year-old Miniature Poodle displayed at (a) 25% resolution and (b) 100% resolution. If the entire digital radiograph cannot be displayed on the monitor at the original resolution, then the image should be evaluated at least twice. Firstly, the entire image should be displayed within the maximum available screen area. Secondly, each part of the image should be evaluated at the original resolution. The pulmonary nodule (arrowed) is more noticeable in (b). T9 = ninth thoracic vertebra.

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7.6

Making use of the available contrast resolution by adjusting the window centre and width: the same lateral thoracic radiograph of a 4-year-old Labrador Retriever cross is shown using different display windows. In (a), the window and level are optimized for evaluating the skeleton; in (b), the lungs. The cardiac silhouette is dorsally located due to dehydration. In (a), this finding could be erroneously attributed to pneumothorax. In (b), the pulmonary blood vessels are clearly seen extending to the periphery of the thoracic cavity. Images should be evaluated using different windows and levels to make use of all the available grayscale information. © 2024 British Small Animal Veterinary Association

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7.6 Making use of the available contrast resolution by adjusting the window centre and width: the same lateral thoracic radiograph of a 4-year-old Labrador Retriever cross is shown using different display windows. In (a), the window and level are optimized for evaluating the skeleton; in (b), the lungs. The cardiac silhouette is dorsally located due to dehydration. In (a), this finding could be erroneously attributed to pneumothorax. In (b), the pulmonary blood vessels are clearly seen extending to the periphery of the thoracic cavity. Images should be evaluated using different windows and levels to make use of all the available grayscale information.

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7.7

Lateral thoracic radiograph of a 9-year-old Beagle with myasthenia gravis associated with thymoma. The myasthenia gravis has caused megaoesophagus. Notice the oesophageal diameter is severely diffusely increased and the lumen contains a large volume of gas. The thymoma (arrowed) forms a small mass-like tumour, which is circumscribed, round, and has a homogeneous soft tissue opacity. Viscera are either solid or hollow. During radiography, it is impossible to determine whether the thymic mass is solid or hollow (cystic and fluid-filled) as both would produce a silhouette. For similar reasons, the heart, which is a hollow organ, is often described in terms of the cardiac silhouette. The trachea and oesophagus are hollow and gas-filled, and cross-sectional imaging is required to determine their internal architecture. © 2024 British Small Animal Veterinary Association

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7.7 Lateral thoracic radiograph of a 9-year-old Beagle with myasthenia gravis associated with thymoma. The myasthenia gravis has caused megaoesophagus. Notice the oesophageal diameter is severely diffusely increased and the lumen contains a large volume of gas. The thymoma (arrowed) forms a small mass-like tumour, which is circumscribed, round, and has a homogeneous soft tissue opacity. Viscera are either solid or hollow. During radiography, it is impossible to determine whether the thymic mass is solid or hollow (cystic and fluid-filled) as both would produce a silhouette. For similar reasons, the heart, which is a hollow organ, is often described in terms of the cardiac silhouette. The trachea and oesophagus are hollow and gas-filled, and cross-sectional imaging is required to determine their internal architecture.

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7.8

(a) Ventrodorsal thoracic radiograph and (b) transverse thoracic CT image of a 6-month-old mixed-breed dog with a right caudal lung lobe abscess and pneumonia due to a migrating plant awn. On the radiograph, no air–fluid interface is observed because a vertically oriented X-ray beam was used. CT was performed in dorsal recumbency and an air–fluid interface (arrowed) is detected due to gravity-dependent distribution of gas and fluid. Gravity-dependent distribution of gas and fluid in the lungs is also evident on the CT image: the lungs are more lucent and the pulmonary blood vessels are smaller ventrally. To the right of and dorsal to the abscess and in the ventral tip of the accessory lung lobe, there are patches of lung consolidation without volume loss attributed to the infiltration of fluid and inflammatory cells into the lung parenchyma (i.e. pneumonia). The right caudal lung lobe also has a diffuse ground-glass opacity and larger pulmonary blood vessels due to increased blood flow typical of inflammation. Increased blood flow to poorly ventilated lung can produce a ventilation:perfusion mismatch (physiological right-to-left shunting). The plant awn is not seen. A = aorta; CVC = caudal vena cava; T10 = tenth thoracic vertebra. © 2024 British Small Animal Veterinary Association

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7.8 (a) Ventrodorsal thoracic radiograph and (b) transverse thoracic CT image of a 6-month-old mixed-breed dog with a right caudal lung lobe abscess and pneumonia due to a migrating plant awn. On the radiograph, no air–fluid interface is observed because a vertically oriented X-ray beam was used. CT was performed in dorsal recumbency and an air–fluid interface (arrowed) is detected due to gravity-dependent distribution of gas and fluid. Gravity-dependent distribution of gas and fluid in the lungs is also evident on the CT image: the lungs are more lucent and the pulmonary blood vessels are smaller ventrally. To the right of and dorsal to the abscess and in the ventral tip of the accessory lung lobe, there are patches of lung consolidation without volume loss attributed to the infiltration of fluid and inflammatory cells into the lung parenchyma (i.e. pneumonia). The right caudal lung lobe also has a diffuse ground-glass opacity and larger pulmonary blood vessels due to increased blood flow typical of inflammation. Increased blood flow to poorly ventilated lung can produce a ventilation:perfusion mismatch (physiological right-to-left shunting). The plant awn is not seen. A = aorta; CVC = caudal vena cava; T10 = tenth thoracic vertebra.

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7.9

Connective tissues and their relationships to adjacent structures. (a) Serous membrane. (b) Body wall and organs. (c) Formation of connecting peritoneum (ligaments, mesenteries and omenta). (d) Serous cavity (e.g. pleural cavity). In the thorax, the parietal pleura attaches to the body wall via the endothoracic fascia, a third type of connective tissue. 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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7.9 Connective tissues and their relationships to adjacent structures. (a) Serous membrane. (b) Body wall and organs. (c) Formation of connecting peritoneum (ligaments, mesenteries and omenta). (d) Serous cavity (e.g. pleural cavity). In the thorax, the parietal pleura attaches to the body wall via the endothoracic fascia, a third type of connective tissue. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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7.10

Volume-rendered CT images of a 9-year-old mixed-breed dog showing the (a) cranioventral, (b) left, (c) ventral and (d) dorsal aspects of the thorax, back and thoracic limbs. The surface regions of the thorax and back are identified. The ventral surface of the thorax is called the pectoral region or chest. It is divided into: the presternal region (orange) that overlies the descending pectoral muscles between the median (1) and lateral (2) pectoral grooves, the sternal region (green) that overlies the sternum, the region of the thoracic mammary glands (not shaded), the scapular region (yellow) that overlies the scapulae, the costal region (blue) that overlies the osseous portion of the ribs, and the cardiac region (dotted line in (b)) that overlies the heart caudal to the moveable tricipital line. The solid line in (b) and (c) indicates the costal arch, which is formed by the cartilaginous portions of the asternal ribs connecting the most caudal rib to the sternum. Dorsally, the surface regions of the back (regions of the dorsum) are the lumbar region (unmarked) and the thoracic vertebral region (red); the portion between the dorsal borders of the scapulae is further characterized as the interscapular region (withers). © 2024 British Small Animal Veterinary Association

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7.10 Volume-rendered CT images of a 9-year-old mixed-breed dog showing the (a) cranioventral, (b) left, (c) ventral and (d) dorsal aspects of the thorax, back and thoracic limbs. The surface regions of the thorax and back are identified. The ventral surface of the thorax is called the pectoral region or chest. It is divided into: the presternal region (orange) that overlies the descending pectoral muscles between the median (1) and lateral (2) pectoral grooves, the sternal region (green) that overlies the sternum, the region of the thoracic mammary glands (not shaded), the scapular region (yellow) that overlies the scapulae, the costal region (blue) that overlies the osseous portion of the ribs, and the cardiac region (dotted line in (b)) that overlies the heart caudal to the moveable tricipital line. The solid line in (b) and (c) indicates the costal arch, which is formed by the cartilaginous portions of the asternal ribs connecting the most caudal rib to the sternum. Dorsally, the surface regions of the back (regions of the dorsum) are the lumbar region (unmarked) and the thoracic vertebral region (red); the portion between the dorsal borders of the scapulae is further characterized as the interscapular region (withers).

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7.11

Object planes. Contrast-enhanced thoracic CT images (soft tissue window) of a 9-year-old mixed-breed dog. All three images are oriented at 90 degrees to each other. (a, b) Long-axis and (c) short-axis images of the heart. The terms long-axis (longitudinal axis) and short-axis (transverse axis) describe planes through a specific organ or tissue. The long and short axes of a structure might not correspond to the three conventional planes that divide the thorax. For example, (a) may also be called a sagittal oblique image of the thorax, (b) a transverse oblique image and (c) a dorsal oblique image. Both terms for each image are correct, but the former indicates that the emphasis is on the heart versus the thorax. LA = left atrium; LV = left ventricle; RV = right ventricle. © 2024 British Small Animal Veterinary Association

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7.11 Object planes. Contrast-enhanced thoracic CT images (soft tissue window) of a 9-year-old mixed-breed dog. All three images are oriented at 90 degrees to each other. (a, b) Long-axis and (c) short-axis images of the heart. The terms long-axis (longitudinal axis) and short-axis (transverse axis) describe planes through a specific organ or tissue. The long and short axes of a structure might not correspond to the three conventional planes that divide the thorax. For example, (a) may also be called a sagittal oblique image of the thorax, (b) a transverse oblique image and (c) a dorsal oblique image. Both terms for each image are correct, but the former indicates that the emphasis is on the heart versus the thorax. LA = left atrium; LV = left ventricle; RV = right ventricle.

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7.12

Body planes. Thoracic CT images (lung window) of a 9-year-old mixed-breed dog depicting (a) the median plane, (b) a sagittal plane, (c) a transverse plane and (d) a dorsal plane. These terms of orientation are used primarily when describing planes through the entire thorax versus individual thoracic structures. Images representing oblique planes are also possible. © 2024 British Small Animal Veterinary Association

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7.12 Body planes. Thoracic CT images (lung window) of a 9-year-old mixed-breed dog depicting (a) the median plane, (b) a sagittal plane, (c) a transverse plane and (d) a dorsal plane. These terms of orientation are used primarily when describing planes through the entire thorax versus individual thoracic structures. Images representing oblique planes are also possible.

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7.13

(a) Movement of extracellular fluid between the interstitium, capillary and lymphatic vessels. The systemic circulation (versus the pulmonary circulation) is depicted. The interstices collectively form the interstitium and are filled with extracellular fluid. There is a constant movement of fluid between the interstitium, capillary lumen and lymphatic vessel lumen. The movement of extracellular fluid between the blood vessel and interstitium is governed by a balance of hydrostatic (red arrows) and oncotic (colloid osmotic; blue arrows) pressure gradients, described as Starling forces. The brown arrow denotes drainage of the interstitial fluid as lymph by the lymphatic system. (b) The interstitium between a bronchus and a pulmonary artery is thick where connective tissue joins two adventitia and creates fluid-filled spaces called interstices. (c) The alveolar interstitium is a much thinner shared membrane between the alveolus and capillary that allows for gaseous exchange. 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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7.13 (a) Movement of extracellular fluid between the interstitium, capillary and lymphatic vessels. The systemic circulation (versus the pulmonary circulation) is depicted. The interstices collectively form the interstitium and are filled with extracellular fluid. There is a constant movement of fluid between the interstitium, capillary lumen and lymphatic vessel lumen. The movement of extracellular fluid between the blood vessel and interstitium is governed by a balance of hydrostatic (red arrows) and oncotic (colloid osmotic; blue arrows) pressure gradients, described as Starling forces. The brown arrow denotes drainage of the interstitial fluid as lymph by the lymphatic system. (b) The interstitium between a bronchus and a pulmonary artery is thick where connective tissue joins two adventitia and creates fluid-filled spaces called interstices. (c) The alveolar interstitium is a much thinner shared membrane between the alveolus and capillary that allows for gaseous exchange. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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7.14

The pericardium comprises a fibrous pericardium and serous pericardium. The serous pericardium can be further divided into the visceral pericardium, pericardial cavity and parietal pericardium. 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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7.14 The pericardium comprises a fibrous pericardium and serous pericardium. The serous pericardium can be further divided into the visceral pericardium, pericardial cavity and parietal pericardium. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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7.15

The five major anatomical compartments in the thorax (from left to right): thoracic boundaries, pleural cavities, cardiac silhouette, mediastinum and lungs. During image interpretation, once an abnormality is identified, it is helpful to first localize the abnormality to one or more of these major anatomical compartments. Subsequent evaluation may further define the anatomical location within the anatomical compartment or reveal additional findings that help prioritize the differential diagnosis. © 2024 British Small Animal Veterinary Association

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7.15 The five major anatomical compartments in the thorax (from left to right): thoracic boundaries, pleural cavities, cardiac silhouette, mediastinum and lungs. During image interpretation, once an abnormality is identified, it is helpful to first localize the abnormality to one or more of these major anatomical compartments. Subsequent evaluation may further define the anatomical location within the anatomical compartment or reveal additional findings that help prioritize the differential diagnosis.

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7.16

Transverse thoracic CT images of a 7-year-old Golden Retriever with pneumothorax. (a) The left pleural cavity contains a large volume of gas and the left caudal lung lobe is partially collapsed. The opacity of this lung lobe is only minimally increased because there is a comparable reduction in blood flow to that lung lobe due to hypoxic vasoconstriction (note the reduction in size and number of the pulmonary blood vessels). The left pulmonary ligament (arrowed) can be seen attaching the left lung to the mediastinum. (b) Following thoracocentesis, the volume of pleural gas is reduced and the left caudal lung lobe is expanded and aerated with an opacity that is similar to that of the right caudal lung lobe. In normal animals, the opacity of the lung parenchyma (airspace) reflects a balance between the amount of air and blood in the lung. During disease, pulmonary opacification is due to the infiltration of fluid, fibre or cells into the lung and/or reduced aeration. Pulmonary hyperlucency is generally due to increased spacing of the soft tissue structures of the lung (e.g. emphysema) or reduced blood flow (e.g. hypovolaemia). © 2024 British Small Animal Veterinary Association

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7.16 Transverse thoracic CT images of a 7-year-old Golden Retriever with pneumothorax. (a) The left pleural cavity contains a large volume of gas and the left caudal lung lobe is partially collapsed. The opacity of this lung lobe is only minimally increased because there is a comparable reduction in blood flow to that lung lobe due to hypoxic vasoconstriction (note the reduction in size and number of the pulmonary blood vessels). The left pulmonary ligament (arrowed) can be seen attaching the left lung to the mediastinum. (b) Following thoracocentesis, the volume of pleural gas is reduced and the left caudal lung lobe is expanded and aerated with an opacity that is similar to that of the right caudal lung lobe. In normal animals, the opacity of the lung parenchyma (airspace) reflects a balance between the amount of air and blood in the lung. During disease, pulmonary opacification is due to the infiltration of fluid, fibre or cells into the lung and/or reduced aeration. Pulmonary hyperlucency is generally due to increased spacing of the soft tissue structures of the lung (e.g. emphysema) or reduced blood flow (e.g. hypovolaemia).

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7.17

Right lateral thoracic radiographs of (a) a 10-month-old German Shepherd Dog with a patent ductus arteriosus and (b) an 8-year-old Golden Retriever with subaortic stenosis. Both dogs had echocardiographically confirmed left heart enlargement. (a) Left heart enlargement is easily seen as the cardiac silhouette is tall and wide with prominent bulges of the left atrium and left ventricle. This is due to volume overload causing eccentric hypertrophy of the left heart. Although the dog has a left-to-right shunt (aorta to pulmonic trunk), it is the left side of the heart that experiences the volume overload because of the pulmonary drainage: the affected cardiac chambers enlarge. (b) The left heart enlargement is not detected. This is due to pressure overload causing concentric hypertrophy of the left ventricle: the affected cardiac chamber decreases in size due to increased muscular thickness. In (a), there is loss of the cranial cardiac waist due to focal enlargement of the aortic arch and pulmonic trunk, and the pulmonary blood vessels are enlarged and numerous due to pulmonary overcirculation. In (b), there is loss of the cranial cardiac waist due to post-stenotic dilatation of the aortic arch, and a mediastinal fat pad mildly displaces the cardiac silhouette dorsally. © 2024 British Small Animal Veterinary Association

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7.17 Right lateral thoracic radiographs of (a) a 10-month-old German Shepherd Dog with a patent ductus arteriosus and (b) an 8-year-old Golden Retriever with subaortic stenosis. Both dogs had echocardiographically confirmed left heart enlargement. (a) Left heart enlargement is easily seen as the cardiac silhouette is tall and wide with prominent bulges of the left atrium and left ventricle. This is due to volume overload causing eccentric hypertrophy of the left heart. Although the dog has a left-to-right shunt (aorta to pulmonic trunk), it is the left side of the heart that experiences the volume overload because of the pulmonary drainage: the affected cardiac chambers enlarge. (b) The left heart enlargement is not detected. This is due to pressure overload causing concentric hypertrophy of the left ventricle: the affected cardiac chamber decreases in size due to increased muscular thickness. In (a), there is loss of the cranial cardiac waist due to focal enlargement of the aortic arch and pulmonic trunk, and the pulmonary blood vessels are enlarged and numerous due to pulmonary overcirculation. In (b), there is loss of the cranial cardiac waist due to post-stenotic dilatation of the aortic arch, and a mediastinal fat pad mildly displaces the cardiac silhouette dorsally.

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7.18

(a) Lateral and (b) dorsoventral thoracic radiographs of a 15-year-old mixed-breed dog with cardiogenic pulmonary oedema and postcapillary pulmonary hypertension due to a ruptured chorda tendina (confirmed via echocardiography). The cardiac silhouette is tall, long and wide with bulges of the left atrium, left ventricle and right atrium. The caudodorsal lung field has a severe ground-glass opacity due to elevated left atrial pressure and reduced pulmonary venous drainage causing left-sided congestive heart failure. Elevated left atrial pressure also increases systolic right ventricular pressure by increasing the load on the right ventricle. © 2024 British Small Animal Veterinary Association

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7.18 (a) Lateral and (b) dorsoventral thoracic radiographs of a 15-year-old mixed-breed dog with cardiogenic pulmonary oedema and postcapillary pulmonary hypertension due to a ruptured chorda tendina (confirmed via echocardiography). The cardiac silhouette is tall, long and wide with bulges of the left atrium, left ventricle and right atrium. The caudodorsal lung field has a severe ground-glass opacity due to elevated left atrial pressure and reduced pulmonary venous drainage causing left-sided congestive heart failure. Elevated left atrial pressure also increases systolic right ventricular pressure by increasing the load on the right ventricle.

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7.19

Lateral thoracic radiographs of (a) a 5-year-old Labrador Retriever with a chronic intermittent cough due to a bronchial foreign body and (b) an adult cat that was found dead. Assessing lung volume is one of the most important steps in the imaging interpretation of lung disease. (a) The dog has chronic obstructive atelectasis of the right middle lung lobe. The affected lung lobe is small and has patchy areas of consolidation. The foreign body is undetectable. The insert shows a plant awn that was endoscopically removed from the bronchus and an American penny as a size reference. (b) The cat has acute obstructive air trapping, diffusely affecting both lungs. Post-mortem lungs are frequently collapsed. In this cat, the lungs are severely expanded and the diaphragm is flat due to a valve-like tracheal foreign body seen cranial and dorsal to the cardiac silhouette, consistent with kibble. ((b) Courtesy of Lance Rozear) © 2024 British Small Animal Veterinary Association

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7.19 Lateral thoracic radiographs of (a) a 5-year-old Labrador Retriever with a chronic intermittent cough due to a bronchial foreign body and (b) an adult cat that was found dead. Assessing lung volume is one of the most important steps in the imaging interpretation of lung disease. (a) The dog has chronic obstructive atelectasis of the right middle lung lobe. The affected lung lobe is small and has patchy areas of consolidation. The foreign body is undetectable. The insert shows a plant awn that was endoscopically removed from the bronchus and an American penny as a size reference. (b) The cat has acute obstructive air trapping, diffusely affecting both lungs. Post-mortem lungs are frequently collapsed. In this cat, the lungs are severely expanded and the diaphragm is flat due to a valve-like tracheal foreign body seen cranial and dorsal to the cardiac silhouette, consistent with kibble. ((b) Courtesy of Lance Rozear)

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(a) Lateral and (b) dorsoventral thoracic radiographs of a 2-year-old dog with heartworm infection. This dog had pulmonary hypertension due to increased pulmonary arterial resistance. The pulmonary arteries are moderately enlarged and tortuous (best seen on the dorsoventral view), and the pulmonic trunk and the right heart are moderately enlarged. The dog also has caval syndrome as the presence of worms is interfering with tricuspid valve closure, obstructing blood flow through the right heart and increasing systemic venous pressure: there is enlargement of the caudal vena cava and abdominal distention with absent serosal contrast due to ascites (peritoneal fluid). Starling forces can lead to fluid moving out of the capillaries when blood hydrostatic pressure is high. © 2024 British Small Animal Veterinary Association

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7.20 (a) Lateral and (b) dorsoventral thoracic radiographs of a 2-year-old dog with heartworm infection. This dog had pulmonary hypertension due to increased pulmonary arterial resistance. The pulmonary arteries are moderately enlarged and tortuous (best seen on the dorsoventral view), and the pulmonic trunk and the right heart are moderately enlarged. The dog also has caval syndrome as the presence of worms is interfering with tricuspid valve closure, obstructing blood flow through the right heart and increasing systemic venous pressure: there is enlargement of the caudal vena cava and abdominal distention with absent serosal contrast due to ascites (peritoneal fluid). Starling forces can lead to fluid moving out of the capillaries when blood hydrostatic pressure is high.

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(a) Transverse and (b) sagittal thoracic CT angiograms of a 2-month-old Staffordshire Bull Terrier with a vascular ring anomaly. There is good opacification of the left heart, aorta and pulmonic trunk following a systemic venous injection of contrast material. (a) The vascular ring can be seen surrounding the trachea and oesophagus. The vascular ring anomaly comprises a persistent right fourth aortic arch and a patent ductus arteriosus. In normal dogs, the aortic arch is to the left of the trachea (not to the right as in this dog) and the ductus arteriosus does not contrast enhance because it forms a ligamentum arteriosum. Note that the ductus arteriosus is derived from the left sixth aortic arch and connects the aorta to the pulmonic trunk. (b) This image was acquired to the right of the midline (the ductus arteriosus is not included) and image acquisition was timed so that contrast material was in the levophase. Contrast material is present in the left atrium but not in the right ventricle. The cranial vena cava has an intravascular catheter (arrowed). AA = aortic arch; DA = ductus arteriosus; LA = left atrium; O = oesophagus; PT = pulmonic trunk; RV = right ventricle; T = trachea. © 2024 British Small Animal Veterinary Association

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7.21 (a) Transverse and (b) sagittal thoracic CT angiograms of a 2-month-old Staffordshire Bull Terrier with a vascular ring anomaly. There is good opacification of the left heart, aorta and pulmonic trunk following a systemic venous injection of contrast material. (a) The vascular ring can be seen surrounding the trachea and oesophagus. The vascular ring anomaly comprises a persistent right fourth aortic arch and a patent ductus arteriosus. In normal dogs, the aortic arch is to the left of the trachea (not to the right as in this dog) and the ductus arteriosus does not contrast enhance because it forms a ligamentum arteriosum. Note that the ductus arteriosus is derived from the left sixth aortic arch and connects the aorta to the pulmonic trunk. (b) This image was acquired to the right of the midline (the ductus arteriosus is not included) and image acquisition was timed so that contrast material was in the levophase. Contrast material is present in the left atrium but not in the right ventricle. The cranial vena cava has an intravascular catheter (arrowed). AA = aortic arch; DA = ductus arteriosus; LA = left atrium; O = oesophagus; PT = pulmonic trunk; RV = right ventricle; T = trachea.

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Lateral thoracic radiograph of a 12-year-old Maine Coon cat with nasal lymphoma. During staging, the cat was also diagnosed with a peritoneopericardial diaphragmatic hernia, which is a congenital developmental anomaly of variable clinical importance. The cardiac silhouette is enlarged with distorted shape and heterogeneous opacity. The ventral aspect of the diaphragm is effaced and the caudal sternebrae are fused. CT revealed herniation of liver lobes, choleliths, the gallbladder and the fatty falciform ligament through a defect in the ventral midline of the diaphragm into the pericardial cavity. © 2024 British Small Animal Veterinary Association

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7.22 Lateral thoracic radiograph of a 12-year-old Maine Coon cat with nasal lymphoma. During staging, the cat was also diagnosed with a peritoneopericardial diaphragmatic hernia, which is a congenital developmental anomaly of variable clinical importance. The cardiac silhouette is enlarged with distorted shape and heterogeneous opacity. The ventral aspect of the diaphragm is effaced and the caudal sternebrae are fused. CT revealed herniation of liver lobes, choleliths, the gallbladder and the fatty falciform ligament through a defect in the ventral midline of the diaphragm into the pericardial cavity.

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Lateral thoracic radiograph of a 7-year-old Labrador Retriever with a histologically confirmed pulmonary chondrosarcoma. The neoplasm forms a large solitary tumour in the left caudal lung lobe. The tumour is rounded, circumscribed and has a homogeneous soft tissue opacity. In addition, the tumour forms a positive summation shadow with the ribs, vertebral bodies and pulmonary blood vessels. © 2024 British Small Animal Veterinary Association

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7.23 Lateral thoracic radiograph of a 7-year-old Labrador Retriever with a histologically confirmed pulmonary chondrosarcoma. The neoplasm forms a large solitary tumour in the left caudal lung lobe. The tumour is rounded, circumscribed and has a homogeneous soft tissue opacity. In addition, the tumour forms a positive summation shadow with the ribs, vertebral bodies and pulmonary blood vessels.

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Lateral thoracic radiograph of a 5-year-old Bearded Collie with pneumonia. The results of the tracheal wash showed septic suppurative inflammation due to polymicrobial infection (Gram-positive cocci, Gram-positive rods and Gram-negative rods). In this case, the infiltration of fluid and inflammatory cells into the airspace displaced the air and caused a large portion of the cranioventral lung field to be consolidated. Border effacement of the pulmonary blood vessels and air bronchograms can be seen. © 2024 British Small Animal Veterinary Association

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7.24 Lateral thoracic radiograph of a 5-year-old Bearded Collie with pneumonia. The results of the tracheal wash showed septic suppurative inflammation due to polymicrobial infection (Gram-positive cocci, Gram-positive rods and Gram-negative rods). In this case, the infiltration of fluid and inflammatory cells into the airspace displaced the air and caused a large portion of the cranioventral lung field to be consolidated. Border effacement of the pulmonary blood vessels and air bronchograms can be seen.

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Lateral thoracic radiograph of a 12-year-old Tibetan Terrier with bilateral degenerative atrioventricular valve disease. The cardiac silhouette is tall with a large bulge of the left atrium. The results of this evaluation are negative for cardiogenic pulmonary oedema. © 2024 British Small Animal Veterinary Association

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7.25 Lateral thoracic radiograph of a 12-year-old Tibetan Terrier with bilateral degenerative atrioventricular valve disease. The cardiac silhouette is tall with a large bulge of the left atrium. The results of this evaluation are negative for cardiogenic pulmonary oedema.

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Transverse thoracic CT images taken following intravenous contrast medium administration in (a) a 7-year-old Labrador Retriever, (b) an 8-year-old Scottish Terrier and (c) a 9-year-old Rat Terrier. Each dog has a single round circumscribed mass that was localized to the dorsal part of the caudal mediastinum. In (a), inflammatory disease (specifically, mediastinal serous cavity empyema) was prioritized because the mass comprised homogeneous non-contrast-enhancing fluid. In (b) and (c), a neoplasm was prioritized because the mass contained contrast-enhancing tissue in addition to irregular non-contrast-enhancing cavities. Epithelial (mesothelioma, carcinoma) and mesenchymal (sarcoma) neoplasms were possible, and the tumours underwent histology and immunohistology in both dogs. In (b), the tumour is a mesothelioma of the mediastinal serous cavity. In (c), the tumour is a pulmonary adenocarcinoma. It can be difficult to differentiate whether a lesion is in the mediastinum or lung. Imaging patterns may help prioritize the broad category of disease (i.e. developmental, inflammatory, neoplastic or degenerative) or may provide a specific diagnosis. However, the same imaging patterns can commonly be produced by many different diseases. During radiography, simply observing a soft tissue mass in the caudal mediastinum would not have been sufficient to prioritize inflammatory versus neoplastic disease without additional clinical information. © 2024 British Small Animal Veterinary Association

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7.26 Transverse thoracic CT images taken following intravenous contrast medium administration in (a) a 7-year-old Labrador Retriever, (b) an 8-year-old Scottish Terrier and (c) a 9-year-old Rat Terrier. Each dog has a single round circumscribed mass that was localized to the dorsal part of the caudal mediastinum. In (a), inflammatory disease (specifically, mediastinal serous cavity empyema) was prioritized because the mass comprised homogeneous non-contrast-enhancing fluid. In (b) and (c), a neoplasm was prioritized because the mass contained contrast-enhancing tissue in addition to irregular non-contrast-enhancing cavities. Epithelial (mesothelioma, carcinoma) and mesenchymal (sarcoma) neoplasms were possible, and the tumours underwent histology and immunohistology in both dogs. In (b), the tumour is a mesothelioma of the mediastinal serous cavity. In (c), the tumour is a pulmonary adenocarcinoma. It can be difficult to differentiate whether a lesion is in the mediastinum or lung. Imaging patterns may help prioritize the broad category of disease (i.e. developmental, inflammatory, neoplastic or degenerative) or may provide a specific diagnosis. However, the same imaging patterns can commonly be produced by many different diseases. During radiography, simply observing a soft tissue mass in the caudal mediastinum would not have been sufficient to prioritize inflammatory versus neoplastic disease without additional clinical information.

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(a) Lateral thoracic radiograph, (b) transverse thoracic CT image and (c) sagittal CT image of an 8-year-old mixed-breed dog with cytologically confirmed suppurative inflammation. CT was performed with the dog in dorsal recumbency. In the sternal region, left caudoventral to the xiphoid process, the inflammation forms a large solitary mass with a thick irregular wall, large fluid-filled cavity and a small bone fragment. Adjacent to the mass, there is fat stranding in the body wall fasciae and body wall muscles. The superficial fascia is also mildly swollen with increased attenuation and indistinct margins. Both pleural cavities contain a small volume of gravity-dependent fluid. The adjacent cutaneous tissues also are thick and have a soft tissue attenuation. The imaging diagnosis is a presumed body wall abscess with locally extensive fasciitis, myositis and oedema; although direct extension into the serous cavities is not detected, pleuritis and pyothorax (pleural empyema) are possible given the presence of pleural fluid. The results of this evaluation are negative for osteomyelitis and peritonitis. The bone fragment is a segment of the costal cartilage and may be a sequestrum or nidus for infection. © 2024 British Small Animal Veterinary Association

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7.27 (a) Lateral thoracic radiograph, (b) transverse thoracic CT image and (c) sagittal CT image of an 8-year-old mixed-breed dog with cytologically confirmed suppurative inflammation. CT was performed with the dog in dorsal recumbency. In the sternal region, left caudoventral to the xiphoid process, the inflammation forms a large solitary mass with a thick irregular wall, large fluid-filled cavity and a small bone fragment. Adjacent to the mass, there is fat stranding in the body wall fasciae and body wall muscles. The superficial fascia is also mildly swollen with increased attenuation and indistinct margins. Both pleural cavities contain a small volume of gravity-dependent fluid. The adjacent cutaneous tissues also are thick and have a soft tissue attenuation. The imaging diagnosis is a presumed body wall abscess with locally extensive fasciitis, myositis and oedema; although direct extension into the serous cavities is not detected, pleuritis and pyothorax (pleural empyema) are possible given the presence of pleural fluid. The results of this evaluation are negative for osteomyelitis and peritonitis. The bone fragment is a segment of the costal cartilage and may be a sequestrum or nidus for infection.

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Transverse trunk CT images (bone window) at the level of the (a) third, (b) ninth and (c) twelfth thoracic vertebrae, and (d) the seventh lumbar vertebra of a 4-month-old mixed-breed dog with osteochondromatosis diagnosed on post-mortem examination. Based on the CT signs, the dog has a generalized random, non-aggressive polyosteopathy consistent with an imaging diagnosis of presumed osteochondromatosis (alternatively, presumed multiple cartilaginous exostosis). This idiopathic acquired developmental condition produces multiple benign masses containing cartilage and bone. These masses are typically clinically inconsequential except when causing intraluminal airway obstruction or compression of significant structures. (b) A large rib mass severely compresses the left lung. (d) A pedunculated vertebral mass extends into the vertebral canal compressing nerves of the cauda equina. Many more small masses were present throughout the skeleton. © 2024 British Small Animal Veterinary Association

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7.28 Transverse trunk CT images (bone window) at the level of the (a) third, (b) ninth and (c) twelfth thoracic vertebrae, and (d) the seventh lumbar vertebra of a 4-month-old mixed-breed dog with osteochondromatosis diagnosed on post-mortem examination. Based on the CT signs, the dog has a generalized random, non-aggressive polyosteopathy consistent with an imaging diagnosis of presumed osteochondromatosis (alternatively, presumed multiple cartilaginous exostosis). This idiopathic acquired developmental condition produces multiple benign masses containing cartilage and bone. These masses are typically clinically inconsequential except when causing intraluminal airway obstruction or compression of significant structures. (b) A large rib mass severely compresses the left lung. (d) A pedunculated vertebral mass extends into the vertebral canal compressing nerves of the cauda equina. Many more small masses were present throughout the skeleton.

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(a) Lateral and (b) ventrodorsal thoracic radiographs of an 11-year-old mixed-breed dog with an oesophageal foreign body. When the reason for the imaging study is to confirm an oesophageal foreign body and note the location and any other outcome, then it is appropriate to simply describe that the oesophageal foreign body is in the caudal oesophagus, immediately cranial to the diaphragm. Gas is not detected in the mediastinum and the rest of the thorax is normal, so the results of the evaluation are negative for oesophageal perforation and aspiration pneumonia. When the reason for performing the examination is to determine the cause of the clinical signs, then the abnormality should first be described in terms of imaging signs before a definitive or differential diagnosis is provided, or it is concluded that the clinical question is not answered by the study. When it is difficult to describe the findings of an imaging study because the results are not straightforward, then a failproof method is to first describe the abnormal anatomical structure, or the location of the abnormality, and then describe the general imaging signs (e.g. changes in size, shape, margination, opacity). For example: the thoracic oesophagus is diffusely enlarged and has a large, irregularly shaped, circumscribed mineral opacity that is just cranial to the diaphragm; cranially, the oesophageal lumen is gas-filled. © 2024 British Small Animal Veterinary Association

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7.29 (a) Lateral and (b) ventrodorsal thoracic radiographs of an 11-year-old mixed-breed dog with an oesophageal foreign body. When the reason for the imaging study is to confirm an oesophageal foreign body and note the location and any other outcome, then it is appropriate to simply describe that the oesophageal foreign body is in the caudal oesophagus, immediately cranial to the diaphragm. Gas is not detected in the mediastinum and the rest of the thorax is normal, so the results of the evaluation are negative for oesophageal perforation and aspiration pneumonia. When the reason for performing the examination is to determine the cause of the clinical signs, then the abnormality should first be described in terms of imaging signs before a definitive or differential diagnosis is provided, or it is concluded that the clinical question is not answered by the study. When it is difficult to describe the findings of an imaging study because the results are not straightforward, then a failproof method is to first describe the abnormal anatomical structure, or the location of the abnormality, and then describe the general imaging signs (e.g. changes in size, shape, margination, opacity). For example: the thoracic oesophagus is diffusely enlarged and has a large, irregularly shaped, circumscribed mineral opacity that is just cranial to the diaphragm; cranially, the oesophageal lumen is gas-filled.

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Transverse (a) T1-weighted and (b) T2-weighted brain MR images and (c) a lateral thoracic radiograph of a 15-year-old Domestic Longhaired cat with imaging diagnoses of a presumed territorial infarction of the left middle cerebral artery and an incidental pulmonary nodule of uncertain clinical importance. The pulmonary nodule was an incidental finding because it was unexpected and did not relate to the clinical signs nor the MRI diagnosis. The clinical importance of the pulmonary nodule was uncertain because the likely cause was not determined during imaging; the differential diagnosis included benign and malignant neoplasms and chronic inflammatory conditions (e.g. granuloma). Post-mortem examination confirmed cerebral infarction and diagnosed a pulmonary carcinoma that was unlikely to be related to the brain abnormality and clinical signs. © 2024 British Small Animal Veterinary Association

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7.30 Transverse (a) T1-weighted and (b) T2-weighted brain MR images and (c) a lateral thoracic radiograph of a 15-year-old Domestic Longhaired cat with imaging diagnoses of a presumed territorial infarction of the left middle cerebral artery and an incidental pulmonary nodule of uncertain clinical importance. The pulmonary nodule was an incidental finding because it was unexpected and did not relate to the clinical signs nor the MRI diagnosis. The clinical importance of the pulmonary nodule was uncertain because the likely cause was not determined during imaging; the differential diagnosis included benign and malignant neoplasms and chronic inflammatory conditions (e.g. granuloma). Post-mortem examination confirmed cerebral infarction and diagnosed a pulmonary carcinoma that was unlikely to be related to the brain abnormality and clinical signs.

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Orthogonal thoracic radiographs of (a, b) a 4-year-old Australian Shepherd Dog with lymphoma and (c, d) a 13-year-old Standard Poodle with multiple lung masses. One of the limitations of planar imaging is lack of depth perception within the displayed image. On the lateral views (a, c), both dogs have an abnormal soft tissue opacity that summates with the lung hilus: the opacity may be in the body wall, the mediastinum or either lung. One of the best ways to overcome the lack of depth perception is to obtain an orthogonal view. On the orthogonal views (b, d) the abnormality is localized to the mediastinum in the Australian Shepherd Dog and to the left lung in the Standard Poodle. © 2024 British Small Animal Veterinary Association

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7.31 Orthogonal thoracic radiographs of (a, b) a 4-year-old Australian Shepherd Dog with lymphoma and (c, d) a 13-year-old Standard Poodle with multiple lung masses. One of the limitations of planar imaging is lack of depth perception within the displayed image. On the lateral views (a, c), both dogs have an abnormal soft tissue opacity that summates with the lung hilus: the opacity may be in the body wall, the mediastinum or either lung. One of the best ways to overcome the lack of depth perception is to obtain an orthogonal view. On the orthogonal views (b, d) the abnormality is localized to the mediastinum in the Australian Shepherd Dog and to the left lung in the Standard Poodle.

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(a) Right lateral, (b) left lateral, (c) dorsoventral and (d) ventrodorsal thoracic radiographs of a 6-year-old Boxer with bilateral pleural fluid and a cranial thoracic mass. Each observable form in a radiograph is primarily the result of differential absorption of the X-ray beam. In (a), (b) and (c), the cardiac silhouette and mass are not seen. In (d), the cardiac silhouette and mass are visible because the pleural fluid shifted to the dorsal portion of the pleural cavities with the animal in dorsal recumbency. This allows for greater differential absorption of the X-ray beam across the image. To better understand this process, each image can be considered as a grid of tiny squares. Each square is the smallest picture element, or pixel. Each pixel has a shade of grey (opacity) that corresponds to the amount of absorption of the X-ray beam as it passed through the patient at that location. Whiter areas have greater absorption and blacker areas have less absorption. With radiography, there are five recognizable opacities, and adjacent pixels that have a similar opacity will result in identifiable forms (silhouettes) within the image. Ideally, these forms will signify a specific object within the patient. The ability to look at an image and differentiate structures due to differences in opacity is called contrast: the greater the contrast, the easier it is to differentiate structures. However, silhouettes do not always signify true objects within the patient. When objects that are adjacent in the image have a similar opacity, then there will be border effacement (silhouetting) between the objects creating a novel form (silhouette) that represents more than one object in the patient. Note, these objects may not be adjacent within the patient because planar images lack depth perception. All identifiable forms in the image are summation shadows that may be brighter (positive) or darker (negative). For example, the ribs form positive summation shadows and the lungs form negative summation shadows. Occasionally, summation shadows form that do not represent patient anatomy. © 2024 British Small Animal Veterinary Association

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7.32 (a) Right lateral, (b) left lateral, (c) dorsoventral and (d) ventrodorsal thoracic radiographs of a 6-year-old Boxer with bilateral pleural fluid and a cranial thoracic mass. Each observable form in a radiograph is primarily the result of differential absorption of the X-ray beam. In (a), (b) and (c), the cardiac silhouette and mass are not seen. In (d), the cardiac silhouette and mass are visible because the pleural fluid shifted to the dorsal portion of the pleural cavities with the animal in dorsal recumbency. This allows for greater differential absorption of the X-ray beam across the image. To better understand this process, each image can be considered as a grid of tiny squares. Each square is the smallest picture element, or pixel. Each pixel has a shade of grey (opacity) that corresponds to the amount of absorption of the X-ray beam as it passed through the patient at that location. Whiter areas have greater absorption and blacker areas have less absorption. With radiography, there are five recognizable opacities, and adjacent pixels that have a similar opacity will result in identifiable forms (silhouettes) within the image. Ideally, these forms will signify a specific object within the patient. The ability to look at an image and differentiate structures due to differences in opacity is called contrast: the greater the contrast, the easier it is to differentiate structures. However, silhouettes do not always signify true objects within the patient. When objects that are adjacent in the image have a similar opacity, then there will be border effacement (silhouetting) between the objects creating a novel form (silhouette) that represents more than one object in the patient. Note, these objects may not be adjacent within the patient because planar images lack depth perception. All identifiable forms in the image are summation shadows that may be brighter (positive) or darker (negative). For example, the ribs form positive summation shadows and the lungs form negative summation shadows. Occasionally, summation shadows form that do not represent patient anatomy.

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(a) Lateral and (b) dorsoventral thoracic radiographs, and (c) transverse and (d) dorsal thoracic CT images of a 9-year-old German Shorthaired Pointer with cytologically confirmed pulmonary carcinoma and neutrophilic inflammation. Imaging signs of disease are either detected or not detected. Evidence of the neoplasm is present on all four images. On the lateral thoracic radiograph, an indistinct perihilar opacity is detected. On the dorsoventral thoracic radiograph, narrowing of the bronchus to the right caudal lung lobe is detected (arrowed). On both CT images, a tumour (T) caudal to the carina and compression of the right caudal lobar bronchus are detected. In all images, pulmonary nodules are not detected, and the results of this evaluation are negative for pulmonary metastasis. © 2024 British Small Animal Veterinary Association

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7.33 (a) Lateral and (b) dorsoventral thoracic radiographs, and (c) transverse and (d) dorsal thoracic CT images of a 9-year-old German Shorthaired Pointer with cytologically confirmed pulmonary carcinoma and neutrophilic inflammation. Imaging signs of disease are either detected or not detected. Evidence of the neoplasm is present on all four images. On the lateral thoracic radiograph, an indistinct perihilar opacity is detected. On the dorsoventral thoracic radiograph, narrowing of the bronchus to the right caudal lung lobe is detected (arrowed). On both CT images, a tumour (T) caudal to the carina and compression of the right caudal lobar bronchus are detected. In all images, pulmonary nodules are not detected, and the results of this evaluation are negative for pulmonary metastasis.

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Intercostal thoracic ultrasound image of a 16-year-old Domestic Shorthaired cat. Imaging test results are either positive or negative for disease. Positive and negative test results are either true or false. In this cat, lung consolidation (an imaging sign) is detected in the ventral lung tip of one lobe. Lung consolidation occurs with many different conditions including pneumonia, haemorrhage, neoplasia and atelectasis. Therefore, the ultrasound test results are positive for each of these conditions: the results are not positive for lung consolidation, which is a sign and not a disease. Additional information (e.g. history, vital signs, blood analysis) is needed to prioritize whether the positive results are likely true or false because the test is not specific for one cause. Typically, only one result is true-positive, and the rest are false-positive. © 2024 British Small Animal Veterinary Association

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7.34 Intercostal thoracic ultrasound image of a 16-year-old Domestic Shorthaired cat. Imaging test results are either positive or negative for disease. Positive and negative test results are either true or false. In this cat, lung consolidation (an imaging sign) is detected in the ventral lung tip of one lobe. Lung consolidation occurs with many different conditions including pneumonia, haemorrhage, neoplasia and atelectasis. Therefore, the ultrasound test results are positive for each of these conditions: the results are not positive for lung consolidation, which is a sign and not a disease. Additional information (e.g. history, vital signs, blood analysis) is needed to prioritize whether the positive results are likely true or false because the test is not specific for one cause. Typically, only one result is true-positive, and the rest are false-positive.

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Dorsoventral thoracic radiographs of a 7-year-old Samoyed with a tension pneumothorax, obtained (a) before and (b) after thoracocentesis. In both radiographs, the pleural cavities contain gas and both lungs are collapsed. The pneumothorax is worst on the right side and there is a mediastinal shift to the left. Prior to thoracocentesis, the thoracic cavity was severely expanded causing a barrel-chested conformation: the ribs were spread farther apart and more perpendicular to the vertebral column. In addition, the diaphragm was displaced caudally and was flatter than normal. Pneumothorax is either open or closed. The results of this evaluation are negative for causes of open pneumothorax because no sign of body wall trauma (e.g. rib fracture, fascial gas) is detected and the prior probability is low as there was no history of trauma. The results of this evaluation also are negative for tracheal or oesophageal perforation as pneumomediastinum was not detected. The results of this evaluation are positive for causes of closed pneumothorax (e.g. lung neoplasia, pulmonary abscess rupture, grass awn migration, spontaneous). The results of this evaluation are indeterminate for a lung abnormality because any abnormality would be obscured by the lung collapse. However, spontaneous pneumothorax is most likely based on the imaging signs and high prior probability: spontaneous pneumothorax is common in northern dog breeds. This diagnosis was confirmed during CT, surgery and histology as there were ruptured lung bullae without underlying lung disease. © 2024 British Small Animal Veterinary Association

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7.35 Dorsoventral thoracic radiographs of a 7-year-old Samoyed with a tension pneumothorax, obtained (a) before and (b) after thoracocentesis. In both radiographs, the pleural cavities contain gas and both lungs are collapsed. The pneumothorax is worst on the right side and there is a mediastinal shift to the left. Prior to thoracocentesis, the thoracic cavity was severely expanded causing a barrel-chested conformation: the ribs were spread farther apart and more perpendicular to the vertebral column. In addition, the diaphragm was displaced caudally and was flatter than normal. Pneumothorax is either open or closed. The results of this evaluation are negative for causes of open pneumothorax because no sign of body wall trauma (e.g. rib fracture, fascial gas) is detected and the prior probability is low as there was no history of trauma. The results of this evaluation also are negative for tracheal or oesophageal perforation as pneumomediastinum was not detected. The results of this evaluation are positive for causes of closed pneumothorax (e.g. lung neoplasia, pulmonary abscess rupture, grass awn migration, spontaneous). The results of this evaluation are indeterminate for a lung abnormality because any abnormality would be obscured by the lung collapse. However, spontaneous pneumothorax is most likely based on the imaging signs and high prior probability: spontaneous pneumothorax is common in northern dog breeds. This diagnosis was confirmed during CT, surgery and histology as there were ruptured lung bullae without underlying lung disease.

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7.36

(a, b) Orthogonal thoracic radiographs of a 9-year-old Golden Retriever with a heart base tumour confirmed during echocardiography. There is a large soft tissue tumour at the cranial aspect of the heart base, left and ventral to the caudal fourth of the trachea. A sensitive test is one that produces few false-negative results. Radiographic signs are not sensitive for a chemodectoma arising from the aortic bodies because the tumour must be large before it is detectable. Echocardiographic and CT signs are more sensitive because smaller tumours are detectable. A specific test is one that produces few false-positive results. Imaging signs are moderately specific for a chemodectoma because there are very few other types of tumour that occur in this precise location. The accuracy of the imaging signs can be affected by how the imaging study was performed and evaluated (e.g. obtaining one view versus multiple views, using windowing and zoom). © 2024 British Small Animal Veterinary Association

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7.36 (a, b) Orthogonal thoracic radiographs of a 9-year-old Golden Retriever with a heart base tumour confirmed during echocardiography. There is a large soft tissue tumour at the cranial aspect of the heart base, left and ventral to the caudal fourth of the trachea. A sensitive test is one that produces few false-negative results. Radiographic signs are not sensitive for a chemodectoma arising from the aortic bodies because the tumour must be large before it is detectable. Echocardiographic and CT signs are more sensitive because smaller tumours are detectable. A specific test is one that produces few false-positive results. Imaging signs are moderately specific for a chemodectoma because there are very few other types of tumour that occur in this precise location. The accuracy of the imaging signs can be affected by how the imaging study was performed and evaluated (e.g. obtaining one view versus multiple views, using windowing and zoom).

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7.37

(a) Lateral and (b) dorsoventral thoracic radiographs of an 11-year-old mixed-breed dog with a surgically and histologically confirmed pulmonary adenocarcinoma. Image interpretation is an educated opinion, subject to error and differences of opinion. It can be difficult to differentiate whether an abnormality localizes to the mediastinum or lung. Consequently, a perfectly reasonable and acceptable interpretation of this imaging study would have been to prioritize a cranial mediastinal mass over a lung mass, based on the midline location in the thoracic cavity (between the thoracic inlet, trachea and heart), undetected air bronchograms and a possible ‘sail’ sign. Understanding that errors may occur and factoring that in when making patient care decisions is part of best practice. When possible, causes of error should be minimized, mistakes should be learned from to reduce future errors and errors should be reported as soon as possible to facilitate appropriate patient care. © 2024 British Small Animal Veterinary Association

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7.37 (a) Lateral and (b) dorsoventral thoracic radiographs of an 11-year-old mixed-breed dog with a surgically and histologically confirmed pulmonary adenocarcinoma. Image interpretation is an educated opinion, subject to error and differences of opinion. It can be difficult to differentiate whether an abnormality localizes to the mediastinum or lung. Consequently, a perfectly reasonable and acceptable interpretation of this imaging study would have been to prioritize a cranial mediastinal mass over a lung mass, based on the midline location in the thoracic cavity (between the thoracic inlet, trachea and heart), undetected air bronchograms and a possible ‘sail’ sign. Understanding that errors may occur and factoring that in when making patient care decisions is part of best practice. When possible, causes of error should be minimized, mistakes should be learned from to reduce future errors and errors should be reported as soon as possible to facilitate appropriate patient care.