The pleural space

Mairi Frame; Alison King

doi:10.22233/9781910443941.11

The pleural space

British Small Animal Veterinary Association , 326 (2024); https://doi.org/10.22233/9781910443941.11

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The pleural space

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Authors: Mairi Frame and Alison King
From: BSAVA Manual of Canine and Feline Thoracic Imaging
Item: Chapter 11, pp 326 - 355
DOI: 10.22233/9781910443941.11
Copyright: © 2024 British Small Animal Veterinary Association
Publication Date: January 2024

Abstract

This chapter provides a comprehensive overview of imaging techniques for evaluating diseases of the pleural space in veterinary patients. The text examines both normal imaging anatomy and common radiographic manifestations of pleural diseases. Both physiological and pathological presentations are covered, with an emphasis on radiography, computed tomography and ultrasonography. The characteristic imaging features of conditions such as pleural effusion, pneumothorax, thick pleura and neoplastic processes are described and showcased.

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Figures

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11.1

Pleural anatomy. Dorsal planes through the thorax (a) dorsally and (b) ventrally, and transverse planes through the thorax (c) cranially and (d) caudally. Red lines denote pleurae. The pulmonary and parietal pleurae are joined at the lung hilus. The parietal pleura is divided into continuous costal, mediastinal and diaphragmatic pleurae and folds back upon itself establishing the lines of pleural reflection and forming the pleural recesses. The parietal pleurae extend cranially through the thoracic inlet to form the pleural cupolas. In carnivores, the left and right pleural cavities may communicate with each other via fenestrations in the caudal mediastinum but the pleural cavities do not communicate with the 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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11.1 Pleural anatomy. Dorsal planes through the thorax (a) dorsally and (b) ventrally, and transverse planes through the thorax (c) cranially and (d) caudally. Red lines denote pleurae. The pulmonary and parietal pleurae are joined at the lung hilus. The parietal pleura is divided into continuous costal, mediastinal and diaphragmatic pleurae and folds back upon itself establishing the lines of pleural reflection and forming the pleural recesses. The parietal pleurae extend cranially through the thoracic inlet to form the pleural cupolas. In carnivores, the left and right pleural cavities may communicate with each other via fenestrations in the caudal mediastinum but the pleural cavities do not communicate with the mediastinum. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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11.2

VD thoracic radiograph of a normal dog demonstrating the caudal mediastinal reflection (arrowed), which is the thin ventral part of the caudal mediastinum. When taking thoracic radiographs, it is important to remember that the pleural space extends beyond the lungs and into the costodiaphragmatic recesses to avoid the caudal margins being missed, as has happened in this case (arrowheads). © 2024 British Small Animal Veterinary Association

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11.2 VD thoracic radiograph of a normal dog demonstrating the caudal mediastinal reflection (arrowed), which is the thin ventral part of the caudal mediastinum. When taking thoracic radiographs, it is important to remember that the pleural space extends beyond the lungs and into the costodiaphragmatic recesses to avoid the caudal margins being missed, as has happened in this case (arrowheads).

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11.3

Left lateral thoracic radiograph of a dog with pulmonary heterotopic osseous metaplasia. These incidental findings are commonly observed in older dogs, are of minor consequence and should not be mistaken for pulmonary nodules. A pleural line is also visible (arrowed). © 2024 British Small Animal Veterinary Association

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11.3 Left lateral thoracic radiograph of a dog with pulmonary heterotopic osseous metaplasia. These incidental findings are commonly observed in older dogs, are of minor consequence and should not be mistaken for pulmonary nodules. A pleural line is also visible (arrowed).

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11.4

(a) Transverse, post-contrast thoracic CT image of a dog, displayed in a lung window. The visceral and parietal pleurae cannot be distinguished from each other but are visible as a hyperdense line medial to the intercostal muscles (arrowed). The caudal mediastinal reflection can be seen as a faint hyperdense line running between the left caudal and accessory lung lobes (arrowhead). (b) Dorsal plane thoracic CT image of a dog with mild pneumothorax, displayed in a lung window. The cranial and caudal mediastinal reflections are the ventral portions of the cranial mediastinum and caudal mediastinum, respectively. They are visible as hyperdense lines (arrowed) between the left and right cranial lung lobes and accessory and left caudal lung lobes, respectively. The plica venae cavae appears similarly but is between the right caudal and accessory lobes (arrowhead). A small volume of pleural gas is visible (*). © 2024 British Small Animal Veterinary Association

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11.4 (a) Transverse, post-contrast thoracic CT image of a dog, displayed in a lung window. The visceral and parietal pleurae cannot be distinguished from each other but are visible as a hyperdense line medial to the intercostal muscles (arrowed). The caudal mediastinal reflection can be seen as a faint hyperdense line running between the left caudal and accessory lung lobes (arrowhead). (b) Dorsal plane thoracic CT image of a dog with mild pneumothorax, displayed in a lung window. The cranial and caudal mediastinal reflections are the ventral portions of the cranial mediastinum and caudal mediastinum, respectively. They are visible as hyperdense lines (arrowed) between the left and right cranial lung lobes and accessory and left caudal lung lobes, respectively. The plica venae cavae appears similarly but is between the right caudal and accessory lobes (arrowhead). A small volume of pleural gas is visible (*).

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11.5

(a) Thoracic ultrasound image obtained using an intercostal window in a normal dog. The appearance of the curved pleurae (arrowed) between adjacent ribs (*) has been likened to the eyes of an alligator above the water (gator sign) or the outspread wings of a bat (bat sign). Horizontal reverberation artefacts can be seen (A-lines; see Chapter 2). In real-time imaging, the pleural line can be seen moving against the body wall producing the ‘glide’ sign – this motion cannot be inferred from the appearance of a static image. The appearance of pneumothorax on a static image is indistinguishable from the presence of normal air-filled lung. (b) B-mode ultrasonogram and resulting M-mode trace. These images were obtained in a normal patient during breathing by directing the sound beam (white line) down through the intercostal space between two ribs (*) and show the ‘seashore’ sign. In the far field, below the pleural line (arrowed), the normal air-filled lung moves, producing a granular pattern over time (the ‘sand’). In the near field, above the pleural line, the static body wall produces horizontal lines (the ‘sea’). © 2024 British Small Animal Veterinary Association

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11.5 (a) Thoracic ultrasound image obtained using an intercostal window in a normal dog. The appearance of the curved pleurae (arrowed) between adjacent ribs (*) has been likened to the eyes of an alligator above the water (gator sign) or the outspread wings of a bat (bat sign). Horizontal reverberation artefacts can be seen (A-lines; see Chapter 2). In real-time imaging, the pleural line can be seen moving against the body wall producing the ‘glide’ sign – this motion cannot be inferred from the appearance of a static image. The appearance of pneumothorax on a static image is indistinguishable from the presence of normal air-filled lung. (b) B-mode ultrasonogram and resulting M-mode trace. These images were obtained in a normal patient during breathing by directing the sound beam (white line) down through the intercostal space between two ribs (*) and show the ‘seashore’ sign. In the far field, below the pleural line (arrowed), the normal air-filled lung moves, producing a granular pattern over time (the ‘sand’). In the near field, above the pleural line, the static body wall produces horizontal lines (the ‘sea’).

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11.6

Right lateral thoracic radiograph of a cat with a large volume of pleural effusion due to lymphoma. In the cranioventral thorax, the pleural cavities are expanded and have a homogeneous fluid opacity that effaces most of the cranial mediastinal structures, cardiac silhouette and cranial border of the diaphragmatic cupula. The cranial lung lobes are severely reduced in size, retracted from the body walls and increased in opacity, and have rounded or scalloped margins. Abdominal effusion (peritoneal fluid) is also present and partially effaces the caudal border of the diaphragmatic cupula. © 2024 British Small Animal Veterinary Association

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11.6 Right lateral thoracic radiograph of a cat with a large volume of pleural effusion due to lymphoma. In the cranioventral thorax, the pleural cavities are expanded and have a homogeneous fluid opacity that effaces most of the cranial mediastinal structures, cardiac silhouette and cranial border of the diaphragmatic cupula. The cranial lung lobes are severely reduced in size, retracted from the body walls and increased in opacity, and have rounded or scalloped margins. Abdominal effusion (peritoneal fluid) is also present and partially effaces the caudal border of the diaphragmatic cupula.

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11.7

Transverse thoracic CT image of a dog with a large volume of pleural effusion. The image was obtained with the dog in ventral recumbency and is displayed in a soft tissue window. Both pleural cavities are expanded and filled with fluid-attenuating material that collects ventrally (*). Both lungs are partially collapsed and float on the pleural fluid. The ventral portions of the lungs (arrowheads) are void of air and have a soft tissue opacity. In this image, it is possible to differentiate fluid from soft tissue because of the contrast resolution provided by the soft tissue window display. However, the air-filled portions of the lungs (arrowed) resemble pneumothorax because pulmonary blood vessels and bronchi are not seen extending to the body wall. A lung window would reveal that the pulmonary structures are present and extend to the body wall. © 2024 British Small Animal Veterinary Association

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11.7 Transverse thoracic CT image of a dog with a large volume of pleural effusion. The image was obtained with the dog in ventral recumbency and is displayed in a soft tissue window. Both pleural cavities are expanded and filled with fluid-attenuating material that collects ventrally (*). Both lungs are partially collapsed and float on the pleural fluid. The ventral portions of the lungs (arrowheads) are void of air and have a soft tissue opacity. In this image, it is possible to differentiate fluid from soft tissue because of the contrast resolution provided by the soft tissue window display. However, the air-filled portions of the lungs (arrowed) resemble pneumothorax because pulmonary blood vessels and bronchi are not seen extending to the body wall. A lung window would reveal that the pulmonary structures are present and extend to the body wall.

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11.8

Thoracic ultrasound image obtained using an acoustic window on the gravity-dependent thoracic wall in a cat with bicavitary effusions (pleural and peritoneal). Small volumes of anechoic fluid are seen in the dependent pleural cavity (arrowed) and in the heart chambers (blood). Pleural fluid is differentiated from pericardial fluid by its angular shape. Pleural fluid is differentiated from mediastinal fluid by its location between the heart and the body wall. Free fluid moves with gravity so small volumes can be more easily identified by scanning from the gravity-dependent surface. Pericardial, mediastinal and peritoneal fluids are not seen in this image. © 2024 British Small Animal Veterinary Association

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11.8 Thoracic ultrasound image obtained using an acoustic window on the gravity-dependent thoracic wall in a cat with bicavitary effusions (pleural and peritoneal). Small volumes of anechoic fluid are seen in the dependent pleural cavity (arrowed) and in the heart chambers (blood). Pleural fluid is differentiated from pericardial fluid by its angular shape. Pleural fluid is differentiated from mediastinal fluid by its location between the heart and the body wall. Free fluid moves with gravity so small volumes can be more easily identified by scanning from the gravity-dependent surface. Pericardial, mediastinal and peritoneal fluids are not seen in this image.

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11.9

Close-up of a DV thoracic radiograph of a dog with pneumothorax following lung lobectomy. The right lung is reduced in size and retracted from the body wall (arrowed). The space between the body wall and right lung (the right pleural cavity) is expanded and has a gas opacity that is devoid of vascular markings (arrowhead). © 2024 British Small Animal Veterinary Association

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11.9 Close-up of a DV thoracic radiograph of a dog with pneumothorax following lung lobectomy. The right lung is reduced in size and retracted from the body wall (arrowed). The space between the body wall and right lung (the right pleural cavity) is expanded and has a gas opacity that is devoid of vascular markings (arrowhead).

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11.10

Dorsal thoracic CT image of a dog in ventral recumbency with bilateral pneumothorax, displayed in a lung window. Both lungs have reduced size and are retracted from the diaphragm. The right lung is also partially retracted from the body wall and mediastinum. Both pleural cavities are non-attenuating and lack internal architecture, indicating the presence of gas. © 2024 British Small Animal Veterinary Association

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11.10 Dorsal thoracic CT image of a dog in ventral recumbency with bilateral pneumothorax, displayed in a lung window. Both lungs have reduced size and are retracted from the diaphragm. The right lung is also partially retracted from the body wall and mediastinum. Both pleural cavities are non-attenuating and lack internal architecture, indicating the presence of gas.

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11.11

B-mode ultrasonogram and resulting M-mode trace of a dog with pneumothorax following lung lobectomy and obtained during breathing. On the M-mode trace, the ‘barcode/stratosphere’ sign results from pleural gas obscuring the lung. The lung is in the far field deep to the pleural line (arrowed). This produces a series of static horizontal lines in the far field deep to the pleural line and replaces the normal granular pattern (sand) produced by lung slide. The appearance of these parallel lines is similar to those produced in the near field by the static body wall. On static B-mode images, it is impossible to distinguish between normal air-filled lung and pneumothorax. © 2024 British Small Animal Veterinary Association

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11.11 B-mode ultrasonogram and resulting M-mode trace of a dog with pneumothorax following lung lobectomy and obtained during breathing. On the M-mode trace, the ‘barcode/stratosphere’ sign results from pleural gas obscuring the lung. The lung is in the far field deep to the pleural line (arrowed). This produces a series of static horizontal lines in the far field deep to the pleural line and replaces the normal granular pattern (sand) produced by lung slide. The appearance of these parallel lines is similar to those produced in the near field by the static body wall. On static B-mode images, it is impossible to distinguish between normal air-filled lung and pneumothorax.

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11.12

Location of interlobar fissures. (a) Fissures of the lateral aspect of the left lung. (b) Fissures of the lateral aspect of the right lung. (c) Fissures of the dorsal aspect of the lungs. (d) Fissures of the ventral aspect of the lungs. A = accessory lobe; LCd = left caudal lung lobe; LCdCr = caudal part of the left cranial lung lobe; LCrCr = cranial part of the left cranial lung lobe; RCd = right caudal lung lobe; RCr = right cranial lung lobe; RM = right middle lung lobe. 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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11.12 Location of interlobar fissures. (a) Fissures of the lateral aspect of the left lung. (b) Fissures of the lateral aspect of the right lung. (c) Fissures of the dorsal aspect of the lungs. (d) Fissures of the ventral aspect of the lungs. A = accessory lobe; LCd = left caudal lung lobe; LCdCr = caudal part of the left cranial lung lobe; LCrCr = cranial part of the left cranial lung lobe; RCd = right caudal lung lobe; RCr = right cranial lung lobe; RM = right middle lung lobe. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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11.13

(a) Close-up of a DV thoracic radiograph of a dog with a moderate volume of pleural effusion demonstrating a thin interlobar fissure (arrowed). (b) Close-up of a DV thoracic radiograph of a dog with a moderate volume of pleural effusion demonstrating a wedge-shaped interlobar fissure (arrowed). (c) Left lateral thoracic radiograph of a dog with a moderate volume of pleural effusion demonstrating multiple interlobar fissures (arrowed). (d) Transverse post-contrast thoracic CT image of a dog with a small volume of pleural effusion, displayed in a lung window. Pleural fluid accumulates in the ventral aspect of the right pleural space (*) and between lung lobes forming interlobar fissures with variably increased thickness (arrowed). The ventral tip of the right lung is deviated in a medial direction due to it ‘floating’ in the fluid. This displacement demonstrates how mobile lung tissue is in the presence of fluid and therefore how lung lobe torsion can occur in the presence of pleural effusion. © 2024 British Small Animal Veterinary Association

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11.13 (a) Close-up of a DV thoracic radiograph of a dog with a moderate volume of pleural effusion demonstrating a thin interlobar fissure (arrowed). (b) Close-up of a DV thoracic radiograph of a dog with a moderate volume of pleural effusion demonstrating a wedge-shaped interlobar fissure (arrowed). (c) Left lateral thoracic radiograph of a dog with a moderate volume of pleural effusion demonstrating multiple interlobar fissures (arrowed). (d) Transverse post-contrast thoracic CT image of a dog with a small volume of pleural effusion, displayed in a lung window. Pleural fluid accumulates in the ventral aspect of the right pleural space (*) and between lung lobes forming interlobar fissures with variably increased thickness (arrowed). The ventral tip of the right lung is deviated in a medial direction due to it ‘floating’ in the fluid. This displacement demonstrates how mobile lung tissue is in the presence of fluid and therefore how lung lobe torsion can occur in the presence of pleural effusion.

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11.14

Transverse post-contrast thoracic CT images of a dog with hydropneumothorax displayed in (a) soft tissue and (b) lung windows. Contrast material was administered intravenously. Both lungs have reduced size and are retracted from the body wall. The expanded pleural cavities contain both fluid (X) and gas (*). In the right lung, the parenchyma of the ventral tip is void of air and is contrast enhancing (arrowed). The pleural fluid does not contrast enhance. The soft tissue window shows greater contrast between the lung tip and adjacent pleural fluid, making it easier to differentiate them. The lung window, however, provides better contrast between lung and gas in the pleural cavity. This demonstrates the importance of maximizing the available contrast resolution by using multiple windows to examine CT images. © 2024 British Small Animal Veterinary Association

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11.14 Transverse post-contrast thoracic CT images of a dog with hydropneumothorax displayed in (a) soft tissue and (b) lung windows. Contrast material was administered intravenously. Both lungs have reduced size and are retracted from the body wall. The expanded pleural cavities contain both fluid (X) and gas (*). In the right lung, the parenchyma of the ventral tip is void of air and is contrast enhancing (arrowed). The pleural fluid does not contrast enhance. The soft tissue window shows greater contrast between the lung tip and adjacent pleural fluid, making it easier to differentiate them. The lung window, however, provides better contrast between lung and gas in the pleural cavity. This demonstrates the importance of maximizing the available contrast resolution by using multiple windows to examine CT images.

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11.15

Thoracic ultrasound image obtained using a left intercostal window in a dog with pleural effusion. The left pleural cavity contains a medium volume of anechoic fluid and the left lung is partially collapsed (reduced size). The ventral portion of the lung is echogenic and triangular with fluid-filled bronchi (arrowed). The dorsal portion of the lung is aerated, and the boundary between the aerated and consolidated portions is clearly seen (arrowhead). © 2024 British Small Animal Veterinary Association

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11.15 Thoracic ultrasound image obtained using a left intercostal window in a dog with pleural effusion. The left pleural cavity contains a medium volume of anechoic fluid and the left lung is partially collapsed (reduced size). The ventral portion of the lung is echogenic and triangular with fluid-filled bronchi (arrowed). The dorsal portion of the lung is aerated, and the boundary between the aerated and consolidated portions is clearly seen (arrowhead).

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11.16

(a) VD thoracic radiograph of a Chihuahua with recent onset of right-sided chylous effusion. The right lung has reduced size but normal shape, forming sharp (acute) angles at the tips. The lung is retracted from the body wall and the moderately expanded pleural space has a fluid opacity. (b) VD thoracic radiograph of an Afghan hound with chronic bilateral chylothorax, which was drained prior to radiography. Both lungs have reduced size with rounded margins and thick interlobar fissures indicating chronicity and scarring of the visceral pleura. The lungs are retracted from the body wall and the mildly expanded pleural spaces have a fluid opacity. The cardiac silhouette is irregularly margined due to prior pericardiectomy. (c) Ventral aspect post-mortem photograph of the opened thorax of the same dog as in (b). Both lungs are collapsed around the heart and covered in multiple layers of fibrinous adhesions. The parietal pleurae also have marked fibrinous changes. These findings are consistent with chronic fibrinous pleuritis. © 2024 British Small Animal Veterinary Association

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11.16 (a) VD thoracic radiograph of a Chihuahua with recent onset of right-sided chylous effusion. The right lung has reduced size but normal shape, forming sharp (acute) angles at the tips. The lung is retracted from the body wall and the moderately expanded pleural space has a fluid opacity. (b) VD thoracic radiograph of an Afghan hound with chronic bilateral chylothorax, which was drained prior to radiography. Both lungs have reduced size with rounded margins and thick interlobar fissures indicating chronicity and scarring of the visceral pleura. The lungs are retracted from the body wall and the mildly expanded pleural spaces have a fluid opacity. The cardiac silhouette is irregularly margined due to prior pericardiectomy. (c) Ventral aspect post-mortem photograph of the opened thorax of the same dog as in (b). Both lungs are collapsed around the heart and covered in multiple layers of fibrinous adhesions. The parietal pleurae also have marked fibrinous changes. These findings are consistent with chronic fibrinous pleuritis.

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11.17

Altered cardiac position in lateral thoracic radiographs with pneumothorax. The dorsal displacement (‘elevation’) of the cardiac silhouette seen on lateral radiographs can be explained by loss of the air-filled lung supporting the heart in its normal anatomical position. Note that, in lateral recumbency, the lung closer to the detector collapses more than the uppermost lung due to gravity. Also, less gas is present in the gravity-dependent pleural cavity. These factors cause the heart to shift laterally and the cardiac apex to rotate away from the sternum. (Note the heart sinks laterally and is not elevated dorsally.) The space created between the cardiac apex and the sternum is highlighted by the X-ray beam. The increased distance between the heart and sternum that would be seen on the radiograph is indicated by X. 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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11.17 Altered cardiac position in lateral thoracic radiographs with pneumothorax. The dorsal displacement (‘elevation’) of the cardiac silhouette seen on lateral radiographs can be explained by loss of the air-filled lung supporting the heart in its normal anatomical position. Note that, in lateral recumbency, the lung closer to the detector collapses more than the uppermost lung due to gravity. Also, less gas is present in the gravity-dependent pleural cavity. These factors cause the heart to shift laterally and the cardiac apex to rotate away from the sternum. (Note the heart sinks laterally and is not elevated dorsally.) The space created between the cardiac apex and the sternum is highlighted by the X-ray beam. The increased distance between the heart and sternum that would be seen on the radiograph is indicated by X. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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11.18

(a) Close-up of a lateral thoracic radiograph of a Whippet with traumatic pneumothorax showing increased distance between the cardiac silhouette and sternum. The space between the cardiac apex and sternum has a gas opacity with absent lung markings (A). Patchy lung consolidation summating with the heart (B) is likely due to pulmonary contusion. (b) Left lateral thoracic radiograph of a dog with pneumothorax. There is increased distance between the cardiac silhouette and the sternum (arrowed). Both lungs are small but have maintained their triangular shape. They have increased opacity and have retracted from the body walls and diaphragm. The pleural spaces are expanded and have a gas opacity without lung markings. This is especially noticeable in the lumbodiaphragmatic recesses (arrowheads) and costomediastinal recess ventral to the heart (arrowed). © 2024 British Small Animal Veterinary Association

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11.18 (a) Close-up of a lateral thoracic radiograph of a Whippet with traumatic pneumothorax showing increased distance between the cardiac silhouette and sternum. The space between the cardiac apex and sternum has a gas opacity with absent lung markings (A). Patchy lung consolidation summating with the heart (B) is likely due to pulmonary contusion. (b) Left lateral thoracic radiograph of a dog with pneumothorax. There is increased distance between the cardiac silhouette and the sternum (arrowed). Both lungs are small but have maintained their triangular shape. They have increased opacity and have retracted from the body walls and diaphragm. The pleural spaces are expanded and have a gas opacity without lung markings. This is especially noticeable in the lumbodiaphragmatic recesses (arrowheads) and costomediastinal recess ventral to the heart (arrowed).

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11.19

(a) DV thoracic radiograph of a cat with increased thoracic volume and a unilateral (left) pleural effusion due to pyothorax. Due to thoracic expansion, the ribs are at right angles to the vertebral column and there is an increased distance between ribs. The left pleural space is severely expanded with a homogeneous fluid opacity that effaces the adjacent borders of the mediastinum, body wall and diaphragm. The expanded space severely compresses the left lung and displaces the trachea (arrowed), principal bronchi and heart to the right, compressing the right lung. (b) DV radiograph of a cat with increased thoracic volume due to unilateral (right) tension pneumothorax. As in (a), the ribs are at right angles to the vertebral column and there is an increased distance between them. The diaphragm is flat with ‘tenting’ of its costal attachments (arrowed). The severely enlarged right pleural cavity has a gas opacity without lung markings. In addition to increased thoracic volume, the pressure within the right pleural space has caused complete collapse and medial displacement of the right lung (arrowheads) and a left cardiac shift. © 2024 British Small Animal Veterinary Association

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11.19 (a) DV thoracic radiograph of a cat with increased thoracic volume and a unilateral (left) pleural effusion due to pyothorax. Due to thoracic expansion, the ribs are at right angles to the vertebral column and there is an increased distance between ribs. The left pleural space is severely expanded with a homogeneous fluid opacity that effaces the adjacent borders of the mediastinum, body wall and diaphragm. The expanded space severely compresses the left lung and displaces the trachea (arrowed), principal bronchi and heart to the right, compressing the right lung. (b) DV radiograph of a cat with increased thoracic volume due to unilateral (right) tension pneumothorax. As in (a), the ribs are at right angles to the vertebral column and there is an increased distance between them. The diaphragm is flat with ‘tenting’ of its costal attachments (arrowed). The severely enlarged right pleural cavity has a gas opacity without lung markings. In addition to increased thoracic volume, the pressure within the right pleural space has caused complete collapse and medial displacement of the right lung (arrowheads) and a left cardiac shift.

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11.20

(a) Pleural fluid distribution in left lateral recumbency. The lungs are small and retracted away from the body wall and mediastinum in the direction of the arrows. There is greater collapse of the left lung due to gravity and the heart shifts to the left side as a consequence. Fluid in the left and right pleural cavities will contribute to diffuse increased opacity of the thoracic cavity relating to the volume of fluid present and create wide interlobar fissures. Fluid in the costomediastinal recesses will efface the ventral border of the cardiac silhouette. (bi) Right and (bii) left lateral thoracic radiographs of a dog with pleural fluid secondary to tricuspid valve dysplasia and Ebstein’s anomaly. The lungs are small, retracted from the thoracic boundaries and have scalloped and angled margins. The pleural spaces are expanded and have a fluid opacity that effaces the borders of the heart and diaphragm. Multiple interlobar fissures are visible. (c) Pleural fluid distribution in dorsal recumbency. The lungs are small and retracted away from the body wall and mediastinum in the direction of the arrows. Fluid collects in the dorsal aspect of the left and right pleural cavities and displaces the lungs ventrally. The lungs and fluid are distributed over a wider area than when the animal is in ventral recumbency because the thoracic cavity is wider dorsally and the heart is located ventrally. This allows for greater differential absorption of the X-ray beam between the heart and lungs. (d) VD thoracic radiograph of a dog with pleural fluid secondary to tricuspid valve dysplasia and Ebstein’s anomaly. The lungs are small, retracted from the thoracic boundaries and mediastinum, and have scalloped margins. The pleural spaces are expanded and have a fluid opacity that partially effaces the borders of the heart and diaphragm and makes the mediastinum appear wide. Multiple interlobar fissures are visible. (e) Pleural fluid distribution in ventral recumbency. The lungs are small and retracted away from the body wall and mediastinum in the direction of the arrows. Fluid collects in the ventral aspect of the left and right pleural cavities and displaces the lungs dorsally. The lungs and fluid are distributed over a narrower area than when the animal is in dorsal recumbency because the thoracic cavity is narrower ventrally and the heart is located ventrally. This results in similar absorption of the X-ray beam between the heart and lungs. (f) DV thoracic radiograph of a dog with pleural fluid secondary to tricuspid valve dysplasia and Ebstein’s anomaly. The lungs are small and retracted from the thoracic boundaries, especially in the cranial thorax and both costodiaphragmatic recesses. The pleural spaces are expanded and have a fluid opacity that completely effaces the borders of the heart and diaphragm. Multiple interlobar fissures are visible. L= left; R = right. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. (a, c, e, Redrawn after Suter (1984)) © 2024 British Small Animal Veterinary Association

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11.20 (a) Pleural fluid distribution in left lateral recumbency. The lungs are small and retracted away from the body wall and mediastinum in the direction of the arrows. There is greater collapse of the left lung due to gravity and the heart shifts to the left side as a consequence. Fluid in the left and right pleural cavities will contribute to diffuse increased opacity of the thoracic cavity relating to the volume of fluid present and create wide interlobar fissures. Fluid in the costomediastinal recesses will efface the ventral border of the cardiac silhouette. (bi) Right and (bii) left lateral thoracic radiographs of a dog with pleural fluid secondary to tricuspid valve dysplasia and Ebstein’s anomaly. The lungs are small, retracted from the thoracic boundaries and have scalloped and angled margins. The pleural spaces are expanded and have a fluid opacity that effaces the borders of the heart and diaphragm. Multiple interlobar fissures are visible. (c) Pleural fluid distribution in dorsal recumbency. The lungs are small and retracted away from the body wall and mediastinum in the direction of the arrows. Fluid collects in the dorsal aspect of the left and right pleural cavities and displaces the lungs ventrally. The lungs and fluid are distributed over a wider area than when the animal is in ventral recumbency because the thoracic cavity is wider dorsally and the heart is located ventrally. This allows for greater differential absorption of the X-ray beam between the heart and lungs. (d) VD thoracic radiograph of a dog with pleural fluid secondary to tricuspid valve dysplasia and Ebstein’s anomaly. The lungs are small, retracted from the thoracic boundaries and mediastinum, and have scalloped margins. The pleural spaces are expanded and have a fluid opacity that partially effaces the borders of the heart and diaphragm and makes the mediastinum appear wide. Multiple interlobar fissures are visible. (e) Pleural fluid distribution in ventral recumbency. The lungs are small and retracted away from the body wall and mediastinum in the direction of the arrows. Fluid collects in the ventral aspect of the left and right pleural cavities and displaces the lungs dorsally. The lungs and fluid are distributed over a narrower area than when the animal is in dorsal recumbency because the thoracic cavity is narrower ventrally and the heart is located ventrally. This results in similar absorption of the X-ray beam between the heart and lungs. (f) DV thoracic radiograph of a dog with pleural fluid secondary to tricuspid valve dysplasia and Ebstein’s anomaly. The lungs are small and retracted from the thoracic boundaries, especially in the cranial thorax and both costodiaphragmatic recesses. The pleural spaces are expanded and have a fluid opacity that completely effaces the borders of the heart and diaphragm. Multiple interlobar fissures are visible. L= left; R = right. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. (a, c, e, Redrawn after Suter (1984))

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Right lateral thoracic radiograph of a cat with congestive heart failure. The cardiac silhouette and pulmonary blood vessels are enlarged and there is pulmonary opacification that is most marked caudodorsally. In addition, the lungs have reduced size and are retracted away from the body wall due to fluid in the pleural cavities. Note the fluid opacity dorsal to the sternum and ventral to the lung (arrowed) and an interlobar fissure (arrowhead). The pulmonary opacification is likely a combination of pulmonary oedema, reduced lung inflation and summation with the pleural fluid. © 2024 British Small Animal Veterinary Association

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11.22 Right lateral thoracic radiograph of a cat with congestive heart failure. The cardiac silhouette and pulmonary blood vessels are enlarged and there is pulmonary opacification that is most marked caudodorsally. In addition, the lungs have reduced size and are retracted away from the body wall due to fluid in the pleural cavities. Note the fluid opacity dorsal to the sternum and ventral to the lung (arrowed) and an interlobar fissure (arrowhead). The pulmonary opacification is likely a combination of pulmonary oedema, reduced lung inflation and summation with the pleural fluid.

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(a) Thoracic ultrasound image obtained using an intercostal window in a dog with pleural effusion. Deep to the body wall, the pleural space is enlarged and filled with a large volume of anechoic fluid, which was a transudate. The fluid surrounds echogenic collapsed lung. (b) Ultrasound image obtained using an abdominal window in a dog with ulcerative haemorrhagic gastroenteritis. The body wall and liver are in the near field. In the far field, a small volume of anechoic fluid (*) is seen cranial to the diaphragm and adjacent to the ventral tip of a lung lobe (arrowed), which is aerated and not collapsed. The location of the fluid is consistent with pleural effusion, and its irregular and triangular shape distinguishes it from pericardial effusion. This pleural effusion was occult, demonstrating the importance of checking cranial to the diaphragm when performing abdominal ultrasonography as this may be the first indication of pleural disease. © 2024 British Small Animal Veterinary Association

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11.23 (a) Thoracic ultrasound image obtained using an intercostal window in a dog with pleural effusion. Deep to the body wall, the pleural space is enlarged and filled with a large volume of anechoic fluid, which was a transudate. The fluid surrounds echogenic collapsed lung. (b) Ultrasound image obtained using an abdominal window in a dog with ulcerative haemorrhagic gastroenteritis. The body wall and liver are in the near field. In the far field, a small volume of anechoic fluid (*) is seen cranial to the diaphragm and adjacent to the ventral tip of a lung lobe (arrowed), which is aerated and not collapsed. The location of the fluid is consistent with pleural effusion, and its irregular and triangular shape distinguishes it from pericardial effusion. This pleural effusion was occult, demonstrating the importance of checking cranial to the diaphragm when performing abdominal ultrasonography as this may be the first indication of pleural disease.

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DV thoracic radiograph of a dog with a large-volume unilateral pleural effusion. The left lung is moderately reduced in size and retracted towards the lung hilus, away from the left body wall and diaphragm. The left pleural cavity is expanded with a homogeneous fluid opacity that effaces the adjacent borders of the cardiac silhouette and diaphragm, and there is also a right mediastinal shift. © 2024 British Small Animal Veterinary Association

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11.24 DV thoracic radiograph of a dog with a large-volume unilateral pleural effusion. The left lung is moderately reduced in size and retracted towards the lung hilus, away from the left body wall and diaphragm. The left pleural cavity is expanded with a homogeneous fluid opacity that effaces the adjacent borders of the cardiac silhouette and diaphragm, and there is also a right mediastinal shift.

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(a) DV and (b) lateral thoracic radiographs of a cat with an uneven bilateral pleural effusion due to pyothorax. Both lungs have reduced size and are unevenly retracted from the body wall and diaphragm. The lung margins are noticeably rounded and scalloped, consistent with a reactive or chronic effusion. Restrictive pleuritis is possible. In addition, there is patchy lung consolidation due to concurrent pneumonia. © 2024 British Small Animal Veterinary Association

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11.25 (a) DV and (b) lateral thoracic radiographs of a cat with an uneven bilateral pleural effusion due to pyothorax. Both lungs have reduced size and are unevenly retracted from the body wall and diaphragm. The lung margins are noticeably rounded and scalloped, consistent with a reactive or chronic effusion. Restrictive pleuritis is possible. In addition, there is patchy lung consolidation due to concurrent pneumonia.

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11.26

DV thoracic radiograph of a Dachshund. The shape of the rib cage is typical of what might be seen in some chondrodystrophic dogs. Note the internal deviation of the costochondral junctions creating linear soft tissue opacities that summate with the lateral margins of both lungs. This appearance of the thoracic body wall should not be mistaken for pleural effusion. © 2024 British Small Animal Veterinary Association

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11.26 DV thoracic radiograph of a Dachshund. The shape of the rib cage is typical of what might be seen in some chondrodystrophic dogs. Note the internal deviation of the costochondral junctions creating linear soft tissue opacities that summate with the lateral margins of both lungs. This appearance of the thoracic body wall should not be mistaken for pleural effusion.

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(a) Lateral thoracic radiograph of a normal cat. In cats, the lumbodiaphragmatic recess is located more ventral to the vertebral column than in dogs due to the morphology of the psoas muscle (dashed line) attachments. The resultant soft tissue opacity between the lung margin and vertebral column represents the muscles and not the lumbodiaphragmatic recess, which is part of the pleural cavity. This soft tissue opacity should not be mistaken for a small volume of pleural effusion in cats. (b) Lateral thoracic radiograph of a cat with pleural effusion. Compared to the normal cat (a), the lungs are rounder and more retracted, and the fluid-filled lumbodiaphragmatic recess (arrowed) is larger, creating a fluid opacity that effaces the adjacent border of the psoas muscles. (c) Lateral thoracic radiograph of a normal dog. In contrast to cats, canine lungs extend further dorsally and often summate with the vertebral column due to the morphology of the ribs and their attachment to the vertebral column. © 2024 British Small Animal Veterinary Association

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11.27 (a) Lateral thoracic radiograph of a normal cat. In cats, the lumbodiaphragmatic recess is located more ventral to the vertebral column than in dogs due to the morphology of the psoas muscle (dashed line) attachments. The resultant soft tissue opacity between the lung margin and vertebral column represents the muscles and not the lumbodiaphragmatic recess, which is part of the pleural cavity. This soft tissue opacity should not be mistaken for a small volume of pleural effusion in cats. (b) Lateral thoracic radiograph of a cat with pleural effusion. Compared to the normal cat (a), the lungs are rounder and more retracted, and the fluid-filled lumbodiaphragmatic recess (arrowed) is larger, creating a fluid opacity that effaces the adjacent border of the psoas muscles. (c) Lateral thoracic radiograph of a normal dog. In contrast to cats, canine lungs extend further dorsally and often summate with the vertebral column due to the morphology of the ribs and their attachment to the vertebral column.

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Lateral thoracic radiograph of a cat with a cranial mediastinal mass and pleural effusion. It can be difficult to localize an abnormal, widespread soft tissue opacity to the pleural cavity, mediastinum, cardiac silhouette or some combination. In this cat, the presence of pleural fluid is confirmed based on retraction and rounding of the caudal lung lobes and a fluid opacity external to the lungs that effaces the cranial margin of the diaphragm. Ventrally, falciform fat contrasts with the caudal border of the diaphragm. Radiographic signs of a concurrent mediastinal mass include severe dorsal displacement of the trachea, caudal displacement of the lungs and caudal displacement of the carina to the seventh intercostal space. The radiograph is well positioned without rotation, which supports that these changes are real and not artefactual. © 2024 British Small Animal Veterinary Association

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11.28 Lateral thoracic radiograph of a cat with a cranial mediastinal mass and pleural effusion. It can be difficult to localize an abnormal, widespread soft tissue opacity to the pleural cavity, mediastinum, cardiac silhouette or some combination. In this cat, the presence of pleural fluid is confirmed based on retraction and rounding of the caudal lung lobes and a fluid opacity external to the lungs that effaces the cranial margin of the diaphragm. Ventrally, falciform fat contrasts with the caudal border of the diaphragm. Radiographic signs of a concurrent mediastinal mass include severe dorsal displacement of the trachea, caudal displacement of the lungs and caudal displacement of the carina to the seventh intercostal space. The radiograph is well positioned without rotation, which supports that these changes are real and not artefactual.

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DV thoracic radiograph of a dog with bilateral pneumothorax. Both lungs are small and retracted from the body wall (arrowed). Both pleural spaces are expanded and have a gas opacity (*). Pulmonary blood vessels do not extend to the periphery of the thoracic cavity. © 2024 British Small Animal Veterinary Association

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11.29 DV thoracic radiograph of a dog with bilateral pneumothorax. Both lungs are small and retracted from the body wall (arrowed). Both pleural spaces are expanded and have a gas opacity (*). Pulmonary blood vessels do not extend to the periphery of the thoracic cavity.

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11.30

Sagittal thoracic CT image of a cat in ventral recumbency with pneumothorax and focal inflammatory lung abnormalities (X), displayed in a lung window. The lung lobes are small and retracted from the body wall and diaphragm. The pleural space is expanded and non-attenuating (arrowed). The gas preferentially accumulates in the caudodorsally located lumbodiaphragmatic recess due to gravity. The pleural space also contains a small volume of fluid, which is located ventrally due to gravity (*). The lung margins are rounded, suggesting chronic disease. Free pleural gas can be distinguished from lung gas by the lack of internal architecture when viewed using a lung window. © 2024 British Small Animal Veterinary Association

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11.30 Sagittal thoracic CT image of a cat in ventral recumbency with pneumothorax and focal inflammatory lung abnormalities (X), displayed in a lung window. The lung lobes are small and retracted from the body wall and diaphragm. The pleural space is expanded and non-attenuating (arrowed). The gas preferentially accumulates in the caudodorsally located lumbodiaphragmatic recess due to gravity. The pleural space also contains a small volume of fluid, which is located ventrally due to gravity (*). The lung margins are rounded, suggesting chronic disease. Free pleural gas can be distinguished from lung gas by the lack of internal architecture when viewed using a lung window.

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A transverse section through the thorax showing ultrasound probe placement and movement to estimate the extent of a pneumothorax (blue area) by identifying the lung point, which is where the lung (purple area) regains contact with the costal pleura. Beginning dorsally, move the ultrasound transducer ventrally in the intercostal spaces until a lung point is identified. More severe pneumothorax (right side of the image) will have more ventrally located lung points. 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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11.31 A transverse section through the thorax showing ultrasound probe placement and movement to estimate the extent of a pneumothorax (blue area) by identifying the lung point, which is where the lung (purple area) regains contact with the costal pleura. Beginning dorsally, move the ultrasound transducer ventrally in the intercostal spaces until a lung point is identified. More severe pneumothorax (right side of the image) will have more ventrally located lung points. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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DV thoracic radiograph of a dog with a unilateral (left) pneumothorax following lung lobectomy. The left lung is small, opaque, and severely retracted from the body wall and diaphragm. The left pleural space is severely expanded and has a gas opacity. On both sides of the dog, there are also prominent skin folds that summate with the lateral aspects of the thorax (arrowed). These linear opacities are differentiated from lung margins because they extend beyond the thoracic boundaries and curve in a different direction than interlobar fissures. Skin folds should not be mistaken for signs of pneumothorax. The ribs on the left side are further apart from each other, indicating increased volume on this side of the thoracic cavity. © 2024 British Small Animal Veterinary Association

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11.32 DV thoracic radiograph of a dog with a unilateral (left) pneumothorax following lung lobectomy. The left lung is small, opaque, and severely retracted from the body wall and diaphragm. The left pleural space is severely expanded and has a gas opacity. On both sides of the dog, there are also prominent skin folds that summate with the lateral aspects of the thorax (arrowed). These linear opacities are differentiated from lung margins because they extend beyond the thoracic boundaries and curve in a different direction than interlobar fissures. Skin folds should not be mistaken for signs of pneumothorax. The ribs on the left side are further apart from each other, indicating increased volume on this side of the thoracic cavity.

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Lateral (standing/horizontal) thoracic radiograph of a dog with chronic chylothorax. The pleural fluid has accumulated in the ventral aspect of the thoracic cavity according to the effect of gravity, effacing the ventral borders of the cardiac silhouette and diaphragm. This redistribution of fluid demonstrates that the fluid is freely mobile and not compartmentalized, thus allowing the dorsal thoracic structures to be assessed. In the cranioventral thorax, the margin between the lung and pleural fluid should not be mistaken for a horizontal air–fluid interface that may be seen with pneumohydrothorax. © 2024 British Small Animal Veterinary Association

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11.33 Lateral (standing/horizontal) thoracic radiograph of a dog with chronic chylothorax. The pleural fluid has accumulated in the ventral aspect of the thoracic cavity according to the effect of gravity, effacing the ventral borders of the cardiac silhouette and diaphragm. This redistribution of fluid demonstrates that the fluid is freely mobile and not compartmentalized, thus allowing the dorsal thoracic structures to be assessed. In the cranioventral thorax, the margin between the lung and pleural fluid should not be mistaken for a horizontal air–fluid interface that may be seen with pneumohydrothorax.

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(a) VD thoracic radiograph of an 8-year-old Siamese cat with lobar resorption atelectasis (obstructive atelectasis) secondary to a bronchial carcinoma. Most pulmonary neoplasms produce a space-occupying tumour, but the most salient feature in this case is the loss of lung volume because the tumour obstructs airflow to the lobe. Note that the right caudal lung lobe is collapsed with an ipsilateral cardiac shift and an increased opacity that effaces the pulmonary blood vessels and adjacent borders of the heart, diaphragm and body wall. In addition, the left lung may have compensatory hyperinflation. A discrete lung tumour contrasted by gas is not seen because of the border effacement. The increased opacity in the right caudal thorax is unlikely encapsulated or trapped pleural fluid because the cardiac shift is towards the abnormality. (b) VD thoracic radiograph of the same cat in the same position with the table and X-ray tube tilted 25 degrees towards the cat’s head, allowing free fluid to move cranially within the thorax. In the caudal thorax, the size of the abnormality is slightly reduced. There is a mild overall increased opacity in the cranial thorax. This simple and well tolerated manoeuvre helped identify that there was only a small volume of free pleural fluid. © 2024 British Small Animal Veterinary Association

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11.34 (a) VD thoracic radiograph of an 8-year-old Siamese cat with lobar resorption atelectasis (obstructive atelectasis) secondary to a bronchial carcinoma. Most pulmonary neoplasms produce a space-occupying tumour, but the most salient feature in this case is the loss of lung volume because the tumour obstructs airflow to the lobe. Note that the right caudal lung lobe is collapsed with an ipsilateral cardiac shift and an increased opacity that effaces the pulmonary blood vessels and adjacent borders of the heart, diaphragm and body wall. In addition, the left lung may have compensatory hyperinflation. A discrete lung tumour contrasted by gas is not seen because of the border effacement. The increased opacity in the right caudal thorax is unlikely encapsulated or trapped pleural fluid because the cardiac shift is towards the abnormality. (b) VD thoracic radiograph of the same cat in the same position with the table and X-ray tube tilted 25 degrees towards the cat’s head, allowing free fluid to move cranially within the thorax. In the caudal thorax, the size of the abnormality is slightly reduced. There is a mild overall increased opacity in the cranial thorax. This simple and well tolerated manoeuvre helped identify that there was only a small volume of free pleural fluid.

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11.36

Thoracic ultrasound images of a cat with a cranial thoracic mass and pleural fluid obtained using multiple acoustic windows with the cat in ventral recumbency. The results of fine-needle aspiration (FNA) analysis were highly suggestive of lymphoma. (a) The pleural space is expanded and contains a large volume of echogenic fluid that fills the costodiaphragmatic recess (arrowed). The echogenicity of the fluid is supportive of an exudate. Collapsed lung (*) and liver (X) are marked for reference. (b) The cranial thorax contains a space-occupying lesion (X) that is heterogeneously echogenic and surrounded by a small volume of the pleural fluid (arrowed). The fluid has displaced aerated lung (*), providing an acoustic window for FNA. (c) Extending from the thoracic mass, the presence of a fibrin tag (arrowed) supports the reactive nature of the fluid and the possible presence of pleuritis. (d) Material in the pleural fluid has settled out in the ventral aspect of the thorax due to gravity, creating an interface within the fluid (arrowed). (e) The caudal vena cava (*) is seen at the level of the caval foramen. Cranial to the diaphragm, the caudal vena cava is surrounded by pleural fluid (arrowed). © 2024 British Small Animal Veterinary Association

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11.36 Thoracic ultrasound images of a cat with a cranial thoracic mass and pleural fluid obtained using multiple acoustic windows with the cat in ventral recumbency. The results of fine-needle aspiration (FNA) analysis were highly suggestive of lymphoma. (a) The pleural space is expanded and contains a large volume of echogenic fluid that fills the costodiaphragmatic recess (arrowed). The echogenicity of the fluid is supportive of an exudate. Collapsed lung (*) and liver (X) are marked for reference. (b) The cranial thorax contains a space-occupying lesion (X) that is heterogeneously echogenic and surrounded by a small volume of the pleural fluid (arrowed). The fluid has displaced aerated lung (*), providing an acoustic window for FNA. (c) Extending from the thoracic mass, the presence of a fibrin tag (arrowed) supports the reactive nature of the fluid and the possible presence of pleuritis. (d) Material in the pleural fluid has settled out in the ventral aspect of the thorax due to gravity, creating an interface within the fluid (arrowed). (e) The caudal vena cava (*) is seen at the level of the caval foramen. Cranial to the diaphragm, the caudal vena cava is surrounded by pleural fluid (arrowed).

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11.37

(a) Thoracic ultrasound image of a 3-year-old Siamese cat with pleural effusion. The image depicts the cranial thorax and was obtained at the level of the costochondral junctions using a linear transducer oriented in a dorsal plane. The near field contains the thoracic wall and two ribs (R). There are acoustic shadows associated with the ribs. In the far field, the left (nearer) and right (further) pleural spaces are markedly expanded and contain slightly echogenic fluid. Between the two pleural cavities, the ventral part of the cranial mediastinum is seen as a narrow hyperechoic band (arrowed). (b) Long-axis ultrasound image of the cranial thorax of a 1-year-old cat with feline infectious peritonitis. The near field contains the thoracic wall and two ribs (R). In the far field, the left and right pleural spaces are markedly expanded and contain echogenic fluid on either side of the cranial vena cava (CrVC). © 2024 British Small Animal Veterinary Association

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11.37 (a) Thoracic ultrasound image of a 3-year-old Siamese cat with pleural effusion. The image depicts the cranial thorax and was obtained at the level of the costochondral junctions using a linear transducer oriented in a dorsal plane. The near field contains the thoracic wall and two ribs (R). There are acoustic shadows associated with the ribs. In the far field, the left (nearer) and right (further) pleural spaces are markedly expanded and contain slightly echogenic fluid. Between the two pleural cavities, the ventral part of the cranial mediastinum is seen as a narrow hyperechoic band (arrowed). (b) Long-axis ultrasound image of the cranial thorax of a 1-year-old cat with feline infectious peritonitis. The near field contains the thoracic wall and two ribs (R). In the far field, the left and right pleural spaces are markedly expanded and contain echogenic fluid on either side of the cranial vena cava (CrVC).

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tFAST is performed on both sides of the thorax with the patient in either ventral or lateral recumbency. The locations for probe placement are indicated: CTS = chest tube sites, dorsal seventh–ninth intercostal spaces; PCS = pericardial sites (same location as parasternal cardiac windows); DH = diaphragmaticohepatic site (abdominal approach through the diaphragm). The CTS are best for detecting pneumothorax and the PCS and DH are best for detecting pleural fluid. 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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11.38 tFAST is performed on both sides of the thorax with the patient in either ventral or lateral recumbency. The locations for probe placement are indicated: CTS = chest tube sites, dorsal seventh–ninth intercostal spaces; PCS = pericardial sites (same location as parasternal cardiac windows); DH = diaphragmaticohepatic site (abdominal approach through the diaphragm). The CTS are best for detecting pneumothorax and the PCS and DH are best for detecting pleural fluid. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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11.39

DV thoracic radiograph of a cat with pyothorax and a large pleural abscess. In the right caudal aspect of the thorax, the abscess can be seen as a large mass with a homogeneous fluid opacity that effaces the adjacent body wall and diaphragmatic borders and displaces the right lung medially. These findings are consistent with an area of encapsulated pleural fluid (F), but a capsule is not apparent on this image. © 2024 British Small Animal Veterinary Association

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11.39 DV thoracic radiograph of a cat with pyothorax and a large pleural abscess. In the right caudal aspect of the thorax, the abscess can be seen as a large mass with a homogeneous fluid opacity that effaces the adjacent body wall and diaphragmatic borders and displaces the right lung medially. These findings are consistent with an area of encapsulated pleural fluid (F), but a capsule is not apparent on this image.

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Transverse thoracic CT image of a 2-year-old German Shepherd Dog with suppurative pleuritis, obtained at the level of the tenth thoracic vertebra and displayed in a lung window. An inciting cause for the inflammation was not determined. The dog had purulent fluid in both pleural cavities consistent with pyothorax (pleural empyema) and gas in both cavities consistent with pneumothorax. The pleural gas contrasts with the pulmonary (visceral) and parietal pleurae. The pulmonary pleura is diffusely mildly thick, which is consistent with pleuritis. The left parietal pleura contains multiple small nodules (arrowed) consistent with marked focal pleuritis or abscesses. The caudoventral mediastinal reflection is also thick and irregularly margined, consistent with mediastinitis (*). © 2024 British Small Animal Veterinary Association

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11.40 Transverse thoracic CT image of a 2-year-old German Shepherd Dog with suppurative pleuritis, obtained at the level of the tenth thoracic vertebra and displayed in a lung window. An inciting cause for the inflammation was not determined. The dog had purulent fluid in both pleural cavities consistent with pyothorax (pleural empyema) and gas in both cavities consistent with pneumothorax. The pleural gas contrasts with the pulmonary (visceral) and parietal pleurae. The pulmonary pleura is diffusely mildly thick, which is consistent with pleuritis. The left parietal pleura contains multiple small nodules (arrowed) consistent with marked focal pleuritis or abscesses. The caudoventral mediastinal reflection is also thick and irregularly margined, consistent with mediastinitis (*).

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Transverse post-contrast thoracic CT image of a dog with pleural mesothelioma, displayed in a lung window. The right cranial lung lobe is small and retracted from the body wall. The right pleural cavity is expanded dorsally and has a gas attenuation. The left pleural cavity has a small volume of trapped gas and fluid ventrally, creating a horizontal gas–fluid interface. The neoplasm forms multiple irregular wide-based contrast-enhancing nodular tumours along the parietal and pulmonary pleurae of both pleural cavities (arrowed). The tumours are contrasted by pleural gas, pulmonary gas or both. The pneumothorax may have occurred during drainage of severe bilateral pleural effusion or may have been pre-existing due to intrathoracic disease (pleural masses). © 2024 British Small Animal Veterinary Association

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11.41 Transverse post-contrast thoracic CT image of a dog with pleural mesothelioma, displayed in a lung window. The right cranial lung lobe is small and retracted from the body wall. The right pleural cavity is expanded dorsally and has a gas attenuation. The left pleural cavity has a small volume of trapped gas and fluid ventrally, creating a horizontal gas–fluid interface. The neoplasm forms multiple irregular wide-based contrast-enhancing nodular tumours along the parietal and pulmonary pleurae of both pleural cavities (arrowed). The tumours are contrasted by pleural gas, pulmonary gas or both. The pneumothorax may have occurred during drainage of severe bilateral pleural effusion or may have been pre-existing due to intrathoracic disease (pleural masses).

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Thoracic ultrasound image of a dog. The body wall is seen in the near field and consolidated lung with some gas (arrowed) and anechoic fluid (arrowhead) is seen in the mid field. Between the body wall and lung, the pleural surface is irregular, indicating the presence of pleuritis or neoplasia. The results of fine-needle aspiration analysis confirmed the presence of carcinoma. © 2024 British Small Animal Veterinary Association

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11.42 Thoracic ultrasound image of a dog. The body wall is seen in the near field and consolidated lung with some gas (arrowed) and anechoic fluid (arrowhead) is seen in the mid field. Between the body wall and lung, the pleural surface is irregular, indicating the presence of pleuritis or neoplasia. The results of fine-needle aspiration analysis confirmed the presence of carcinoma.

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Thoracic ultrasound image of a 2-year-old Labrador Retriever with a rare neoplasm, telangiectatic osteosarcoma. The neoplasm formed multiple irregular pleural masses (M) and a large volume of haemorrhagic pleural fluid. The masses are cauliflower-like, homogeneously echogenic and surrounded by the fluid. © 2024 British Small Animal Veterinary Association

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11.43 Thoracic ultrasound image of a 2-year-old Labrador Retriever with a rare neoplasm, telangiectatic osteosarcoma. The neoplasm formed multiple irregular pleural masses (M) and a large volume of haemorrhagic pleural fluid. The masses are cauliflower-like, homogeneously echogenic and surrounded by the fluid.

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Ventrodorsal (left decubitus/horizontal) thoracic radiograph of a 2-year-old mixed-breed dog with pneumothorax. Gas redistributes according to gravity. This radiographic view is used to improve detection of pneumothorax. The right lung is small and retracted from the body wall (arrowheads) and the right pleural cavity contains free pleural gas (A). © 2024 British Small Animal Veterinary Association

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11.45 Ventrodorsal (left decubitus/horizontal) thoracic radiograph of a 2-year-old mixed-breed dog with pneumothorax. Gas redistributes according to gravity. This radiographic view is used to improve detection of pneumothorax. The right lung is small and retracted from the body wall (arrowheads) and the right pleural cavity contains free pleural gas (A).

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Intercostal ultrasound images from different locations in the same dog as in Figure 11.42, that developed a pneumothorax following lung lobectomy. (a) Gas (*) is seen deep to the pleural line (arrowed), between the ribs. On this static image, it is impossible to differentiate free pleural gas from normal air-filled lung. During dynamic imaging, the absence of a glide sign confirmed the presence of pneumothorax. (b) Gas and a B-line (arrowed) are seen deep to the pleural line. If B-lines are identified, then lung is present at that location (B-lines arise from interactions between the sound beam and the pleural surface of the lung). In this image, the pleural line also forms a rougher hyperechoic interface than that produced by the free gas in (a), indicating concurrent pleural or pulmonary changes. (c) The extent of pneumothorax can be estimated by identifying the location of lung points on the body. A lung point is formed where the pulmonary pleura reconnects with the parietal pleura. In this case, identification of the lung point (arrowed) was facilitated by the roughened pulmonary pleura. © 2024 British Small Animal Veterinary Association

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11.46 Intercostal ultrasound images from different locations in the same dog as in Figure 11.42, that developed a pneumothorax following lung lobectomy. (a) Gas (*) is seen deep to the pleural line (arrowed), between the ribs. On this static image, it is impossible to differentiate free pleural gas from normal air-filled lung. During dynamic imaging, the absence of a glide sign confirmed the presence of pneumothorax. (b) Gas and a B-line (arrowed) are seen deep to the pleural line. If B-lines are identified, then lung is present at that location (B-lines arise from interactions between the sound beam and the pleural surface of the lung). In this image, the pleural line also forms a rougher hyperechoic interface than that produced by the free gas in (a), indicating concurrent pleural or pulmonary changes. (c) The extent of pneumothorax can be estimated by identifying the location of lung points on the body. A lung point is formed where the pulmonary pleura reconnects with the parietal pleura. In this case, identification of the lung point (arrowed) was facilitated by the roughened pulmonary pleura.