On Day 101 after surgery, the cat was anesthetized for a computed tomography (CT) scan of the brain and thorax to further
evaluate the Horner's syndrome and characterize the extent of any metastatic disease. A mild patchiness to the cerebral parenchyma
was present, but this change was considered unlikely to be clinically relevant and possibly artifactual. No structural abnormalities
in the brain were seen. A large (3-x-3-x-5-cm), lobulated, cranial mediastinal mass was present immediately ventral to the
trachea and esophagus; it exhibited complex contrast enhancement (Figure 6). Moderate sternal lymphadenopathy was also present. The most likely differential diagnosis was metastasis from the primary
renal transitional cell carcinoma. The pulmonary parenchyma was unremarkable, with no evidence of nodular or diffuse metastases.
Based on these findings and the cat's recent weight loss, the owner declined further diagnostic testing or treatment and elected
Figure 6. A transverse CT image through the cranial mediastinum obtained on Day 101 after surgery (soft tissue window). A
large, lobulated mass with complex contrast enhancement (short arrow) is seen immediately ventral to the trachea (long arrow)
and esophagus (arrowhead).
A complete necropsy was performed. The cat had a body condition score of 2/5. Minimal autolysis had occurred. A firm, nodular,
left-sided mass (1 x 1 x 2 cm) at the thoracic inlet compressed the esophagus and surrounded the vagosympathetic trunk. This
mass invaded the musculature on the left side of the vertebrae. Two similar masses were found within the mediastinum, near
the heart base and close to the trachea. The hilar lymph nodes were moderately enlarged and firm. The left kidney was moderately
enlarged but otherwise grossly normal. Dense fibrotic tissue was present near its cranial pole and surrounded the left adrenal
gland. The urinary bladder and urethra were normal. No marked macroscopic abnormalities were present in the vertebral column,
spinal cord, brain, heart, lungs, spleen, skin, eyes, gastrointestinal tract, urinary bladder, or urethra.
Figure 7. Histologic examination of the cranial mediastinal mass revealed a sclerotic tumor with bands of fibrous tissue surrounding
islands (arrows) of neoplastic epithelial cells (hematoxylin-eosin stain; 10X).
Tissue samples were fixed in neutral-buffered 10% formalin, routinely processed, cut to 5-µm thickness, and stained with hematoxylin
and eosin for examination by light microscopy. Histologic examination of the cranial mediastinal mass revealed a sclerotic
tumor with small, scattered clusters of neoplastic epithelial cells surrounded by large amounts of fibrous tissue (Figure 7). Several nerves were identified within the tumor. The other mediastinal masses and the hilar lymph node showed similar morphology.
The tissue near the cranial pole of the left kidney was composed of similar sclerotic tumor with large lymph vessels filled
by metastases, surrounding a normal adrenal gland (Figure 8). The sublumbar lymph nodes contained large metastases within the medulla. Histologic examination of the lungs revealed numerous
small metastases in the subserosa and around large blood vessels (Figure 9). Mild lymphocytic inflammation was present in the lamina propria of the left third eyelid. No microscopic abnormalities
were found in the brain. The final diagnosis was widely metastatic transitional cell carcinoma arising from the right kidney.
Figure 8. Histologic examination of the left adrenal gland and surrounding tumor mass revealed large lymph vessels (long arrow)
filled with metastases within the sclerotic tumor tissue that extends to the normal adrenal tissue (short arrow) (hematoxylin-eosin