History
A 14-year-old 2.8-kg (6.2-lb) neutered male domestic shorthair cat was referred because of progressive weight loss and a history of a urinary bladder mass. No other important medical history was reported at the time of referral. The mass was initially detected on abdominal palpation 8 months earlier; abdominal ultrasonography at that time had revealed a severely thickened urinary bladder wall. The cause of the urinary bladder mass had not been determined. Three-view thoracic radiography (only the ventrodorsal and right lateral images are shown) was performed at the time of referral as part of the staging protocol (Figure 1).
Right lateral (A) and ventrodorsal (B) radiographic views of the thorax in a 14-year-old 2.8-kg (6.2-lb) neutered male domestic shorthair cat evaluated for progressive weight loss and a history of a urinary bladder mass.
Citation: Journal of the American Veterinary Medical Association 248, 5; 10.2460/javma.248.5.493
Right lateral (A) and ventrodorsal (B) radiographic views of the thorax in a 14-year-old 2.8-kg (6.2-lb) neutered male domestic shorthair cat evaluated for progressive weight loss and a history of a urinary bladder mass.
Citation: Journal of the American Veterinary Medical Association 248, 5; 10.2460/javma.248.5.493
Right lateral (A) and ventrodorsal (B) radiographic views of the thorax in a 14-year-old 2.8-kg (6.2-lb) neutered male domestic shorthair cat evaluated for progressive weight loss and a history of a urinary bladder mass.
Citation: Journal of the American Veterinary Medical Association 248, 5; 10.2460/javma.248.5.493
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretations
A 3.5-cm-diameter, round, smooth, well-defined soft tissue opaque mass is evident in the caudal aspect of the thorax along the midline and is visible slightly dorsal to the caudal vena cava on the lateral views (Figure 2). The caudal aspect of this mass is silhouetting with the cranial aspect of the diaphragmatic margins, and a thin rim of fat opacity is visible around the mass. The cupula of the diaphragm is mildly flattened ventral to the mass. Smooth bony calluses are evident on the fifth and sixth left ribs, consistent with healed fractures. More recent fractures, without evidence of callus formation, are found on the 8th through 10th and 13th left ribs. A fracture of the spinous process of T6 is observed with surrounding sclerosis and mild remodeling. These findings are consistent with multiple traumatic events.
Same radiographic images as in Figure 1 (A and B) with close-up images of the radiographic lesions (C and D). A and C—A round, smooth, well-defined soft tissue opaque mass is evident in the caudal aspect of the thorax. Notice the opaque rim of fat at the caudal aspect of the mass (arrow) and the mild flattening of the diaphragm (asterisk). B and D—Notice callus formation from multiple healed rib fractures (arrowheads).
Citation: Journal of the American Veterinary Medical Association 248, 5; 10.2460/javma.248.5.493
Same radiographic images as in Figure 1 (A and B) with close-up images of the radiographic lesions (C and D). A and C—A round, smooth, well-defined soft tissue opaque mass is evident in the caudal aspect of the thorax. Notice the opaque rim of fat at the caudal aspect of the mass (arrow) and the mild flattening of the diaphragm (asterisk). B and D—Notice callus formation from multiple healed rib fractures (arrowheads).
Citation: Journal of the American Veterinary Medical Association 248, 5; 10.2460/javma.248.5.493
Same radiographic images as in Figure 1 (A and B) with close-up images of the radiographic lesions (C and D). A and C—A round, smooth, well-defined soft tissue opaque mass is evident in the caudal aspect of the thorax. Notice the opaque rim of fat at the caudal aspect of the mass (arrow) and the mild flattening of the diaphragm (asterisk). B and D—Notice callus formation from multiple healed rib fractures (arrowheads).
Citation: Journal of the American Veterinary Medical Association 248, 5; 10.2460/javma.248.5.493
Differential diagnoses for the intrathoracic mass include primary pulmonary neoplasia of the accessory lung lobe, or metastatic pulmonary neoplasia. However, considering the multiple rib fractures, T6 spinous process fracture, abnormal flattening of the diaphragm, and the rim of fat opacity surrounding the mass, a potential traumatic diaphragmatic rupture with herniation of abdominal contents into the thorax is also considered as the cause of the intrathoracic mass.
Ultrasonography was performed for further assessment of the urinary bladder and the intrathoracic mass. Severe urinary bladder wall thickening was observed, and the previously documented urinary bladder mass was viewed at the level of the urinary trigone. Bilateral dilation of the renal pelves was also evident, along with bilateral dilation of the ureters, secondary to obstruction of the ureterovesical junctions by the urinary bladder mass.
An approximately 4 × 2-cm, heterogeneous, non-vascularized mass was identified in the caudal aspect of the thorax, abutting the diaphragm. The mass did not move with respiration and contained anechoic, fluid-filled, round and linear regions. The echotexture of the mass was distinctly different and hyperechoic, compared with that of the adjacent liver. At the level of the mass, a small discontinuity in the diaphragm was evident (Figure 3), but color flow Doppler ultrasonography failed to reveal existing vascularization between the thoracic mass and the adjacent liver parenchyma. On the basis of the ultrasonographic findings, a diaphragmatic rupture with herniated fat was considered the most likely differential diagnosis for the intrathoracic mass. Neoplasia, either transitional cell carcinoma or lymphoma, was the primary differential diagnosis for the urinary bladder mass. Transitional cell carcinoma is the most common tumor of the urinary bladder,1 with lymphoma of the urinary bladder being reported much less commonly.2 Neither of these tumor types were thought to be a likely cause of the intrathoracic mass.
Transverse abdominal ultrasonographic image at the level of the diaphragm of the cat in Figure 1. Notice the distinct echotexture of the mass (asterisk) that is hyperechoic, compared with the echogenicity of the adjacent liver. In this image, the hyperechoic line of the diaphragm (arrow) cannot be followed, indicating a diaphragmatic discontinuity. Image was obtained transabdominally with a 4- to 8-MHz microconvex transducer.
Citation: Journal of the American Veterinary Medical Association 248, 5; 10.2460/javma.248.5.493
Transverse abdominal ultrasonographic image at the level of the diaphragm of the cat in Figure 1. Notice the distinct echotexture of the mass (asterisk) that is hyperechoic, compared with the echogenicity of the adjacent liver. In this image, the hyperechoic line of the diaphragm (arrow) cannot be followed, indicating a diaphragmatic discontinuity. Image was obtained transabdominally with a 4- to 8-MHz microconvex transducer.
Citation: Journal of the American Veterinary Medical Association 248, 5; 10.2460/javma.248.5.493
Transverse abdominal ultrasonographic image at the level of the diaphragm of the cat in Figure 1. Notice the distinct echotexture of the mass (asterisk) that is hyperechoic, compared with the echogenicity of the adjacent liver. In this image, the hyperechoic line of the diaphragm (arrow) cannot be followed, indicating a diaphragmatic discontinuity. Image was obtained transabdominally with a 4- to 8-MHz microconvex transducer.
Citation: Journal of the American Veterinary Medical Association 248, 5; 10.2460/javma.248.5.493
Treatment and Outcome
The cat was euthanatized because of its worsening clinical status, including severe azotemia, and the grave long-term prognosis. Additional diagnostic testing was not performed, and the cat was submitted for necropsy.
Necropsy and histologic evaluation of the urinary bladder revealed a transitional cell carcinoma involving the trigone, right ureter, and proximal portion of the urethra. Iliac lymphadenopathy was also found; histologic evaluation of the enlarged iliac lymph node was consistent with metastatic transitional cell carcinoma. Micrometastases of the transitional cell carcinoma were also found in the adrenal glands and the liver. Multifocal, chronic rib fractures were evident grossly. A paraesophageal hiatal diaphragmatic defect was also found, which was considered likely secondary to a traumatic event causing the rib fractures. The intrathoracic mass was determined to be a biliary cystadenoma, which had herniated through the diaphragmatic defect. The cystadenoma also contained a small focus of transitional cell carcinoma.
Comments
The case described in the present report highlights the importance of complete review of the entire radiograph and a broad list of differential diagnoses encompassing all likely diagnoses to explain the diagnostic imaging findings. Because the presence of a urinary bladder mass suggested malignant neoplasia, the possibility that the intrathoracic mass represented a metastatic tumor warranted consideration. The pattern of metastasis of transitional cell carcinoma in cats is not well studied, but pulmonary metastasis does not appear to be a common finding.2 One study1 revealed that 15% of cats with transitional cell carcinoma had pulmonary metastasis without regional lymph node involvement at the time of diagnosis, but the thoracic radiographic findings were not described in these cats.1 The most common radiographic pattern of pulmonary metastasis, in cats, appears as masses or nodules along with a bronchial infiltrate.3 Other radiographic findings in cats with pulmonary metastasis include ill-defined pulmonary nodules, alveolar infiltrates, and pleural effusion.4 Evaluation of thoracic radiographs of the cat in the present report revealed a single large pulmonary soft tissue opacity, not a typical pattern for pulmonary metastasis in cats.
Radiographic findings of rib fractures and fracture of the spinous process of T6 implied the possibility of traumatic injury as a potential cause of the radiographic intrathoracic mass effect. In addition to the fractures, other findings from thoracic radiography and abdominal ultrasonography, including location and imaging appearance, were consistent with a traumatic diaphragmatic hernia. Radiographic signs that can be consistent with traumatic diaphragmatic hernias include soft tissue opacities located ventrally within the thorax, which often appear as well-defined, discrete masses, resulting from containment by the parietal pleura.5 Abdominal ultrasonography can be used in cases of suspected diaphragmatic hernia to evaluate the integrity of the diaphragm, although small defects can often be missed, as imaging the entire extent of the diaphragm can be difficult.5 In the cat of the present report, ultrasonography revealed a discrete mass in the caudal aspect of the thorax, along the midline and adjacent to the diaphragm, and a diaphragmatic discontinuity. It was suspected that peritoneal fat was herniated through the diaphragm and that the fat might be necrotic because of the intralesional cystic areas observed on ultrasonography and the appearance of a soft tissue opacity on the thoracic radiographs. Hepatic origin was deemed less likely because of the lack of blood flow on color flow Doppler ultrasonography between the liver and the mass.
A diaphragmatic hernia was confirmed on necropsy; a biliary cystadenoma had herniated through a small rent (2.5 × 1 cm) in the diaphragm. In retrospect, the ultrasonographic appearance of the mass in the caudal aspect of the thorax was consistent with a cystadenoma, which typically contain multilocular, thin-walled cysts that contain clear, watery fluid. Cholangiocellular cystadenomas are solitary, well-circumscribed tumors that are variable in size and often compress the surrounding hepatic parenchyma.6 Cystadenomas need to be distinguished from ductal plate malformations and anomalies (ie, von Myenberg complexes), which can cause cytic lesions in the liver that are typically multiple and are considered congenital, but are most commonly observed in mature animals. Both cystadenomas and congenital cystic diseases are often considered incidental findings at necropsy and do not typically cause clinical signs.
References
1. Wilson HM, Chun R, Larson VS, et al. Clinical signs, treatments, and outcome in cats with transitional cell carcinoma of the urinary bladder: 20 cases (1990–2004). J Am Vet Med Assoc 2007; 231: 101–106.
2. Schwarz PD, Greene RW, Patnaik AK. Urinary bladder tumors in the cat: a review of 27 cases. J Am Anim Hosp Assoc 1985; 21: 237–245.
3. Geyer NE, Reichle JK, Valdéz-Martínez A, et al. Radiographic appearance of confirmed pulmonary lymphoma in cats and dogs. Vet Radiol Ultrasound 2010; 51: 386–390.
4. Forrest LJ, Graybush CA. Radiographic patterns of pulmonary metastasis in 25 cats. Vet Radiol Ultrasound 1998; 39: 4–8.
5. Voges AK, Bertrand S, Hill RC, et al. True diaphragmatic hernia in a cat. Vet Radiol Ultrasound 1997; 38: 116–119.
6. Adler R, Wilson DW. Biliary cystadenoma of cats. Vet Pathol 1995; 32: 415–418.
