An 11-year-old 14.5 lb (6.6 kg) castrated male domestic shorthaired cat was presented for evaluation of a progressively distended
abdomen. The cat lived exclusively indoors and was receiving insulin (Humulin L; 4 U b.i.d.) and undergoing routine monitoring
for diabetes mellitus that had been diagnosed when the cat was 8 years old. Except for the abdominal distention, the owners
had not noticed lethargy, changes in appetite, or any other clinical signs.
Physical examination and differential diagnoses
The cat was fractious and had to be sedated with a combination of butorphanol tartrate, medetomidine, and ketamine hydrochloride
given intramuscularly. The physical examination revealed a distended abdomen with a large palpable mass. An abdominal radiographic
examination revealed a large mass with soft tissue radiopacity in the area normally occupied by the kidneys (Figure 1). The differential diagnoses included renal neoplasia, hydronephrosis, polycystic kidney disease, pyonephrosis, and a perinephric
Figure 1. A lateral abdominal radiograph demonstrating the large mass.
The results of a complete blood count were normal. The only abnormality on a serum chemistry profile was mild hyperglycemia
(glucose 191 mg/dl; reference range = 63 to 139 mg/dl). All other values were normal, including creatinine (0.9 mg/dl; reference
range = 0.7 to 2.4 mg/dl), blood urea nitrogen (23.4 mg/dl; reference range = 17.2 to 31.1 mg/dl), and phosphorus (7.3 mg/dl;
reference range = 2.7 to 8.1 mg/dl) concentrations. Additional diagnostic tests were not performed because of financial constraints.
The cat's owners opted for exploratory surgery and treatment. Although the owners did not pursue additional diagnostics, a
urinalysis to further evaluate kidney function and abdominal ultrasonography and intravenous pyelography to evaluate the renal
morphology would have been valuable to help narrow the differential diagnoses before exploratory surgery.
Exploratory surgery and treatment
The cat was sent to a referral center for exploratory surgery. The cat was sedated with the same protocol as before followed
by mask induction with isoflurane for intubation and maintenance during surgery. A ventral midline laparotomy was performed.
A fluid-filled structure was readily apparent (Figure 2), and about 500 ml of clear, colorless fluid was removed to allow better exposure. The structure was determined to be a perinephric
pseudocyst of the left kidney. The kidney within the fluid-filled capsule was grossly abnormal with an irregularly depressed
surface. Because there was no clinical evidence of renal disease, a nephrectomy was thought to be in the patient's best interest.
The nephrectomy was uneventful, and the cat recovered well. Postoperative pain was controlled with buprenorphine (0.008 mg/kg
subcutaneously b.i.d.). The cat was discharged from the referral facility to the owners the next day. The owners administered
buprenorphine for three additional days.
Figure 2. An intraoperative view of the perinephric pseudocyst before fluid removal. The pseudocyst contained a total of 800
ml of fluid (transudate).
The pseudocyst contained a total of 800 ml of clear, colorless fluid. Fluid analysis revealed a specific gravity of 1.010
and low cellularity and was consistent with a transudate. On gross examination, the kidney had an irregular shape and several
areas of infarction and hemorrhage (Figures 3 & 4). Histologic examination of the kidney revealed regions with infiltrates of lymphocytes, plasma cells, and macrophages (moderate
multifocal perivascular and interstitial nephritis), as well as mild interstitial and periglomerular fibrosis. Sections of
the cyst wall contained large amounts of collagen and fibroblasts.
Figure 3. The opened perinephric pseudocyst with attachment at the renal hilus.
Because of the cat's fractious nature, the cat was not brought back to the clinic for follow up. But when I did see the cat
again two months later, it was doing well with no signs of renal disease or abdominal distention. No pseudocyst development
in the contralateral kidney was evident. The blood urea nitrogen and creatinine concentrations also remained normal.
Figure 4. The left kidney has been opened longitudinally, showing several areas of infarction and hemorrhage. The surface
of the kidney is irregularly depressed.