Because of the right kidney's ultrasonographic appearance and the lack of urinary-specific clinical signs (e.g. pollakiuria, stranguria), the primary differential diagnosis for the renal mass was neoplastic disease. Primary renal lymphoma
was considered most likely because of the cat's age, but primary renal carcinoma, transitional cell carcinoma, and metastatic
neoplasia were also possible. Granulomatous disease such as noneffusive feline infectious peritonitis was also considered
but was thought to be less likely given the cat's signalment and lack of abnormal findings on the CBC and serum chemistry
profile (e.g. lymphopenia, nonregenerative anemia, neutrophilia with a left shift, hyperglobulinemia). Any of these differential diagnoses
could result in generalized weight loss over several months and might not be associated with specific clinical signs.
Table 2 Urinalysis and Urine Culture Results
Initial dental treatment and additional test results
The owner elected to proceed with the scheduled dental procedures because the cytology results would not be immediately available,
and he felt in retrospect that the dental disease might have been affecting the cat's appetite and quality of life. The cat
was anesthetized for dental examination, radiography, and routine prophylaxis. Feline odontoclastic resorptive lesions were
confirmed; one extraction and two crown amputations were performed on the affected teeth, and the cat recovered well. The
cat received buprenorphine for analgesia and amoxicillin trihydrate-clavulanate potassium to prevent infection after the dental
procedures and for a presumed urinary tract infection, pending urine culture results.
Figure 2. Cytologic examination of an aspirate from the right kidney revealed irregular clusters of malignant epithelial cells
with marked anisocytosis and anisokaryosis. Individual cells showed hyperchromatic staining and a single, prominent nucleolus
(Wright's-Giemsa stain; 100X).
No growth was present on bacterial culture of the urine. The bacteriuria was attributed to misidentification of fat droplets
or other debris in the sediment, particularly since the cat had not been receiving antibiotic therapy at the time of sample
collection. The results of the renal cytologic examination revealed a highly cellular sample that was compatible with a diagnosis
of primary renal cell carcinoma (Figure 2), although this tumor is relatively rare in cats.
The cat was referred to the University of Minnesota Veterinary Medical Center for further evaluation and likely nephrectomy
11 days later. A physical examination revealed a palpably large right kidney but was otherwise unremarkable. Three-view thoracic
radiographs showed no evidence of pulmonary metastases; a mass involving the right kidney was noted on the ventrodorsal view
(Figure 3). The results of a CBC and serum chemistry profile were within reference ranges. Urinalysis revealed concentrated urine with
a specific gravity of 1.035, proteinuria, marked pyuria and hematuria, and normal epithelial cells (unspecified type) (Table 2). No bacteria were seen, and the results of a second urine culture were negative. A serum thyroxine (T4) concentration was within the reference range.
Figure 3. Ventrodorsal (left) and right lateral (right) thoracic radiographs obtained at the initial presentation to the University
of Minnesota. The thoracic structures are normal, but the right kidney is markedly enlarged (arrow).
The cat was anesthetized for an exploratory celiotomy. The anesthesia protocol included premedication with midazolam and buprenorphine,
induction with propofol, and maintenance with sevoflurane in oxygen. Ongoing analgesia was provided by a constant-rate infusion
of fentanyl and lidocaine. Indirect Doppler blood pressure measurements were obtained intermittently, and continuous electrocardiographic
and temperature readings were obtained. Perioperative intravenous crystalloid fluids were supplemented by a single bolus of
intravenous hetastarch to treat an episode of hypotension during the procedure.
The right kidney was an irregular mass that appeared contained within the renal capsule. The remainder of the abdominal organs
appeared grossly normal. A right nephrectomy was performed, and the cat recovered without complications.
The cat was admitted to the hospital for overnight monitoring and was treated with intravenous hydromorphone for analgesia
and lactated Ringer's solution with supplemental potassium chloride. Urine output was estimated to be normal.
On the day after surgery, a renal biochemical profile (BUN, creatinine, calcium, phosphorus, magnesium, total protein, albumin,
globulin, sodium, chloride, potassium, bicarbonate, osmolality, creatine kinase, glucose, and cholesterol) revealed the cat
had mild hypoproteinemia (total protein 5.6 = g/dl; reference range = 5.9 to 8.2 g/dl) and mild hyperkalemia (potassium =
5.5 mmol/L; reference range = 3.9 to 5.3 mmol/L). The mild hypoproteinemia and hyperkalemia were attributed to the intraoperative
and postoperative intravenous fluid therapy.
Histologic examination of the right kidney and associated mass revealed neoplastic transitional cells that had infiltrated
the kidney (especially the medulla) and marked reactive fibrosis (Figure 4). The diagnosis was transitional cell carcinoma, likely originating from the transitional epithelium lining the renal pelvis.
Figure 4. Histologic examination of the right kidney obtained by surgical biopsy revealed nests of neoplastic epithelial cells
resembling transitional epithelium that infiltrated the renal medulla. The tumor cells are fairly well differentiated and
have uniform nuclei with dispersed chromatin and one prominent nucleolus. A marked reactive fibrosis is associated with the
nests of tumor cells (hematoxylin-eosin stain; 2X [inset 10X]).
The cat was discharged the day after surgery with buprenorphine (0.03 mg given sublingually twice daily), and the owner was
told to bring in the cat for a renal biochemical profile and urinalysis two to three weeks after discharge.
Follow-up evaluations and treatment
The referring veterinarian evaluated the cat 11 days after surgery. The cat was doing well and had an improved appetite and
normal activity level. The incision had healed. A renal biochemical profile revealed persistent, mild hyperkalemia (potassium
= 5.5 mmol/L; reference range = 3.3 to 5.4 mmol/L). Urinalysis revealed concentrated urine with a specific gravity greater
than 1.040, trace proteinuria, and an inactive sediment (Table 2).