Renal cystadenoma in a domestic shorthair

Abstract

An 11-year-old domestic shorthair was examined after an enlarged left kidney was palpated by the referring veterinarian. No abnormalities were noted on complete blood count, serum biochemical profile and total thyroxine concentration, and the urine specific gravity was 1.039. An abdominal ultrasound identified the presence of a large cystic structure on the caudal pole of the left kidney. No abnormalities of the right kidney were seen. A left ureteronephrectomy was performed, and the cat recovered uneventfully from the procedure and was discharged from the hospital 5 days after surgery. The cat remains clinically normal 16 months postoperatively. Histopathology of the removed kidney demonstrated the presence of a renal cystadenoma. This report describes the successful surgical treatment of a renal cystadenoma. Renal cystadenoma should be considered as a differential diagnosis when renomegaly is noted. To the author's knowledge, a renal cystadenoma has not been previously reported in a cat.

An 11-year-old castrated male domestic shorthair was referred to our clinic for evaluation after an enlarged left kidney was palpated by the referring veterinarian during a routine health examination. The owner reported that the cat was clinically normal, and the vaccination status was current. The physical examination was unremarkable except for an enlarged, firm, and irregular left kidney.

Complete blood count (CBC), serum biochemical profile [blood urea nitrogen (BUN) 23 mg/dl (reference range, 15–32 mg/dl), creatinine 1.8 mg/dl (reference range, 1–2 mg/dl)], and total thyroxine concentration (1.4 ug/dl; reference range, 1–4 ug/dl) were within normal limits. A urinalysis obtained by cystocentesis revealed proteinuria (+3), hematuria (+3), and pyuria (too numerous to count white blood cells per high power field), and the urine specific gravity was 1.039. An aerobic culture of the urine obtained by cystocentesis yielded no bacterial growth.

Abdominal ultrasound revealed that the caudal pole of the left kidney was occupied by a large, smooth-bordered, complex cystic structure which distorted the renal outline. Only a minimal amount of compressed normal renal tissue remained at the cranial pole (Fig 1). The cystic structure was anechoic with multiple internal compartments divided by fine septae. The overall size of the cystic structure was 4.5×2.3×2.1 cm. The left renal pelvis and ureter could not be identified by ultrasound, and the left renal artery and vein were normal. The right kidney measured 4 cm in craniocaudal length (reference range, 3.8–4.4 cm) and had a normal architecture and echogenicity.

Fig 1.

A sagittal ultrasound image of the left kidney of this cat. A large complex cystic structure occupies the caudal pole of the kidney and only a small region of normal renal parenchyma remains at the cranial pole. The cystic structure is divided internally by narrow echogenic septae into anechoic fluid filled compartments. The kidney is enlarged overall, and the region of the renal pelvis is not identifiable.

One of the compartments of the renal cystic structure was drained under ultrasound guidance, using a 22 g, 1.5 in. needle and an extension set. No complications or leakage of fluid into the retroperitoneal space were observed during or following the procedure. The cystic fluid was submitted for cytological analysis and aerobic bacterial culture and sensitivity.

The cystic fluid contained 400 nucleated cells/μl and 69,000 red blood cells/μl and had a specific gravity of 1.035 and total protein count of 13.9 g/dl. Cytological evaluation of the cystic fluid revealed 70% macrophages, 30% small lymphocytes, few neutrophils, few small cohesive clusters of baseloid epithelial cells, and a moderate amount of blood. Macrophages often contained phagocytosed red blood cells or coarse hemosiderin. Infectious agents and atypical cells were not identified. These cytological findings were consistent with a diagnosis of chronic inflammation and hemorrhage. Aerobic culture of the cystic fluid revealed no bacterial growth.

The cat was discharged from the hospital, and amoxicillin/clavulanate (Clavamox; Pfizer) (14 mg/kg (6.4 mg/lb), PO, q12) was prescribed pending the results of the urine and cystic fluid bacterial cultures.

Upon re-examination 2 weeks later, the cat was still clinically normal, and the physical examination was unchanged. Serum biochemical profile, urinalysis, and focal abdominal ultrasound were repeated. The biochemical profile was still normal (BUN 23 mg/dl, creatinine 1.7 mg/dl). Urine specific gravity remained 1.039, and the degree of hematuria (+2) and pyuria (+3) decreased. Ultrasound examination revealed that the complex cystic structure in the left kidney was larger than previously noted (4.5×4.0×3.2 cm) but was unchanged in architecture and shape.

Abdominal exploratory surgery via a ventral midline laparotomy was performed. The left kidney was enlarged, dark brown-red in color, and contained multiple fluid filled cysts. No other gross abnormalities were identified in the abdomen. A left ureteronephrectomy was then performed. The left ureter was identified and traced from the bladder to the hilus of the left kidney. Using sterile cotton tip applicators and a right angle Mixter forceps, the perirenal fat was dissected off of the hilus of the kidney. An incision was made in the peritoneum over the ventral aspect of the kidney. The left kidney was removed from the retroperitoneal space with blunt and sharp dissection. The left kidney was retracted ventrally and medially to expose the renal artery and vein. The left renal artery and vein were individually double ligated with 3–0 silk (Perma-Hand silk suture; Ethicon) and were transected. The left ureter was identified and removed from the retroperitoneal space. At the urinary bladder, the ureter was double ligated with 3-0 polydioxane (PDS II; Ethicon) and was transected. The left kidney and ureter were removed en bloc. A sample of the cystic fluid from the left kidney was submitted for aerobic and anaerobic bacterial culture and sensitivity. The left kidney and ureter were submitted for histopathological examination.

Postoperatively, an indwelling urinary catheter and jugular central line were placed. The cat recovered uneventfully from anesthesia and was transferred to the intensive care unit. Central venous pressures and urinary output were monitored for 36 h after surgery and were within normal limits. BUN, serum creatinine concentration, and serum potassium concentration were evaluated the day after surgery and were within normal limits. On the second day after surgery, the urinary catheter and central line were removed, and the cat was transferred out of the intensive care unit. Five days after surgery, the cat was discharged from the hospital. The cat was prescribed amoxicillin/clavulanate (14 mg/kg (6.4 mg/lb), PO, q12) at discharge to be given for one more week.

Bacterial cultures of tissue from the cystic structure associated with the left kidney revealed no aerobic or anaerobic bacterial growth. Histopathological examination of the kidney identified a cystadenoma (Figs 2 and 3). The cystadenoma was well encapsulated and did not invade the surrounding parenchyma of the kidney. This lesion within the left kidney was multiloculated and lined by a single layer of cuboidal epithelium. There were multifocal papillary proliferations of the tubular epithelium into the lumina of the cysts. Small nests and tubules of epithelial cells were evident within the fibrous cores of the projections. The epithelial cells had round hyperchromatic nuclei with minimal pleomorphism and rare mitotic activity.

Fig 2.

Kidney. A multiloculated cystic lesion within the kidney of the cat. The lesion is well demarcated from adjacent renal parenchyma and subdivided by thin fibrous trabeculae. Hematoxylin and eosin ×2.

Fig 3.

Kidney. The epithelial lining of the cystic lesion is simple cuboidal with uniform round nuclei that exhibit minimal pleomorphism or mitotic activity. Multifocal papillary proliferations of the tubular epithelium and epithelial nests are noted in the lumina of the cysts. Hematoxylin and eosin ×10.

At follow-up examination 5 months after surgery, the cat remained clinically normal and biochemical parameters were within normal limits. Telephone follow-up 16 months postoperatively demonstrated that the cat was clinically normal.

To the authors' knowledge, a feline renal cystadenoma has not previously been reported. Renal cystadenomas have been reported in dogs and children (Savanelli and D'Armiento 1981, Lium and Moe 1985, Cosenza and Seely 1986, Gilbert et al 1990, Atlee et al 1991, Perry 1995). In certain breeds of dogs, the presence of renal cystadenoma is closely associated with nodular dermatofibrosis which is thought to be a paraneoplastic process (Gilbert et al 1990, Atlee et al 1991, Perry 1995). Nodular dermatofibrosis was not identified in the cat reported here.

Canine renal cystadenoma has been reported as an incidental finding at the time of physical examination or necropsy. Many of the affected dogs have normal renal biochemical values and no clinical signs associated with renal disease, and the contralateral kidney has been found to be normal (Gilbert et al 1990, Perry 1995). The renal cystadenoma in this cat was also an incidental finding on physical examination.

Renal function tests were not performed on the right kidney as it was suspected that the function of the left kidney was minimal, and the normal renal values were maintained by the normal function of the right kidney. Ureteronephrectomy was pursued because the cystic structure was expanding and acute rupture was a concern.

Renal cystadenoma in cats should be considered based on abdominal palpation of an enlarged kidney and ultrasonographic identification of a complex cystic structure within the kidney. This benign tumor should be included with malignant renal neoplasia, polycystic kidney disease, abscess, hematoma, and granuloma as a differential diagnosis for cats with a unilateral renal mass. In contrast to some of these differential diagnoses, nephrectomy may be curative for cases of renal cystadenoma.