A challenging case: A cat with weight loss and an abdominal mass - Veterinary Medicine
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A challenging case: A cat with weight loss and an abdominal mass
This cat's cranial abdominal mass was identified on a preanesthetic physical examination performed before scheduled dental work. Follow along with these clinicians as they uncover an invasive disease.


VETERINARY MEDICINE



Table 2 Urinalysis and Urine Culture Results
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.

Initial dental treatment and additional test 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).
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.

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.

Referral examination


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 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.

Surgery

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.

Definitive diagnosis

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.


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]).
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.

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).


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