Unilateral improvement in glomerular filtration rate after permanent drainage of a perinephric pseudocyst in a cat

Abstract

A 12-year-old, 6 kg, castrated male Siamese-cross cat was referred for investigation of an abdominal mass. The cat was found to have a left perinephric pseudocyst (PNP), accompanied by azotemia, with a small right kidney detected on ultrasound. Glomerular filtration rate (GFR) was determined by renal scintigraphy and was found to be low, with the left kidney contributing 64% of the total GFR. Percutaneous ultrasound-guided drainage of the PNP did not improve the GFR, and fluid reaccumulated within a short period of time. Laparoscopic fenestration of the cyst capsule was performed to allow for permanent drainage. The PNP did not recur, renal values progressively improved, and 8 months after the capsulotomy the GFR of the left kidney had increased by 50%, while renal function remained static on the right side.

Perinephric (or perirenal) pseudocysts (PNPs) have been described in cats in a number of case series and individual case reports (Ticer 1963, Kraft and Kraft 1970, Chastain and Grier 1975, Abdinoor 1980, Carlson and Badertscher 1993, Rishniw et al 1998, Ochoa et al 1999, Hill and Odesnik 2000, Beck et al 2000, Essman et al 2000, Morrow 2005). PNPs are unilateral or bilateral fluid-filled sacs that surround the kidney. The fluid may accumulate in a subcapsular or extracapsular location, and is typically a transudate, although uriniferous pseudocysts have been reported (Geel 1986, Lemire and Read 1998). The cyst is not lined by epithelium, hence the term ‘pseudocyst’. Feline PNPs are often accompanied by chronic renal failure, although the relationship between the two conditions is unknown (DiBartola and Westropp 1997, Ochoa et al 1999, Beck et al 2000). This case report describes unilateral improvement in renal function after surgical treatment of a PNP in a cat.

A 12-year-old, 6 kg, castrated male Siamese-cross cat was referred for investigation of a left-sided abdominal mass. The cat was reported to be bright and eating well, but there was a history of gradual weight loss (13%) over the preceding 4 months. Two months before referral, a serum biochemistry profile revealed a blood urea nitrogen (BUN) of 35.3 mg/dl (12.6 mmol/l) (reference range: 16–35 mg/dl; 5.7–12.5 mmol/l) and a serum creatinine of 2.3 mg/dl (203.3 μmol/l) (reference range: 1.0–2.3 mg/dl; 88.4–203.3 μmol/l). The urine specific gravity was 1.033 at that time. The cat had a history of transient diabetes mellitus that was in remission, was receiving ursodiol (92 mg once daily) for suspected cholangiohepatitis, and an oral chondroprotective agent.

On physical examination the cat was quiet, but alert, and was estimated to be 7–8% dehydrated. The body condition score was 3/5. Abdominal palpation revealed a markedly enlarged, smooth, non-painful, left kidney and a small, irregularly shaped right kidney. A grade IV/VI left apical systolic cardiac murmur was detected on thoracic auscultation. Systolic blood pressure was measured three times sequentially by the Doppler method, and the average value was 148 mmHg.

A serum biochemistry profile showed azotemia with a BUN of 101 mg/dl (36.1 mmol/l) and a creatinine of 8.2 mg/dl (724.9 μmol/l). Phosphorus was elevated at 7.1 mg/dl (2.29 nmol/l) (reference range: 2.2–6.5 mg/dl; 0.71–2.10 nmol/l), and potassium was low at 3.4 mEq/l (reference range: 3.5–5.2 mEq/l). Glucose was mildly elevated at 158 mg/dl (8.8 mmol/l) (reference range: 69–136 mg/dl; 3.9–7.6 mmol/l), and all liver enzyme activities were within normal limits. A complete blood cell count was unremarkable. Urine obtained by cystocentesis had a specific gravity of 1.010, with a trace of protein, occasional erythrocytes and leukocytes, and 1+ (100 mg/dl; 5.6 mmol/l) glucose. No ketones, bilirubin, casts, or crystals were detected in the urine, and there was no growth on aerobic bacterial culture. Serum total thyroxine was normal at 1.4 μg/dl (18.0 nmol/l) (reference range: 1.2–4.8 μg/dl; 15.4–61.8 nmol/l).

The cat was hospitalized for intravenous fluid therapy (Normosol-R [Abbott Laboratories, Abbott Park, Illinois, USA] supplemented with 20 mEq/l of KCl), to correct the initial fluid deficit, and provide for maintenance and ongoing losses. Ursodiol and chondroprotective therapy were continued during hospitalization. Famotidine (3.0 mg subcutaneously once daily) was prescribed for presumptive uremic gastritis.

Abdominal radiographs and ultrasonography were performed on the day of presentation. Radiographs demonstrated a small right kidney, and a rounded mass in the region of the left kidney. Ultrasonography revealed that the left kidney was surrounded by anechoic fluid, and measured 4.3 cm in length (normal range: 3.8–4.4 cm: Walter et al 1987). The parenchyma of the left kidney was relatively hyperechoic, which was attributed to its location within a fluid-filled structure. The right kidney was small (2.8 cm in length) with poor corticomedullary differentiation and an irregular contour.

Echocardiography was performed and showed a mild concentric left ventricular hypertrophy pattern, trivial mitral valve insufficiency, and normal systolic and diastolic functions. There was no left ventricular outflow obstruction, and the murmur was attributed to mildly increased pulmonary artery outflow velocities.

A 5 ml sample of clear yellow fluid was aspirated from around the left kidney, and analysis revealed a nucleated cell count of 270 cells/μl, with 91% lymphocytes, 8% large mononuclear cells, and 1% neutrophils. The protein concentration was 1.70 g/dl (17 g/l), creatinine was 7.60 mg/dl (671.8 μmol/l), and potassium was 2.9 mEq/l. Bacterial culture was negative. These findings were consistent with a transudate. Based on the abdominal ultrasound findings, the fluid analysis, and the serum biochemistry results, the cat was diagnosed with a left PNP with concurrent acute-on-chronic renal failure.

Two days after admission to the hospital, serum BUN and creatinine were 77 mg/dl (27.5 mmol/l) and 7.0 mg/dl (618.8 μmol/l), respectively. At that time, glomerular filtration rate (GFR) was determined by scintigraphy using Tc-99m-diethylenetriaminepenta-acetic acid (DTPA), applying a modified Gates' method (Gates 1982, Uribe et al 1992). Tc-99m-DTPA (1.2 mCi) was administered intravenously; images were acquired on a GE Millennium VG camera using a low energy all-purpose collimator, and processed with GE Xeleris software. Global GFR was determined to be 1.04 ml/min/kg (Table 1). The reported normal range for GFR in feline patients is 2.5±0.6 ml/min/kg, when measured by DTPA scintigraphy (Kerl and Cook 2005). The right kidney was determined to be contributing 36% of the total GFR (0.37 ml/min/kg), while the left kidney (with the associated PNP) was contributing 64% of the GFR (0.67 ml/min/kg). After completion of the GFR study, a total of 120 ml of fluid was removed from around the left kidney by ultrasound-guided fine-needle aspiration.

Table 1.

Serial serum BUN, creatinine, and GFRs measurements

Day after initial referral	Day after laparoscopic capsulotomy	Serum BUN, reference range: 16–35 mg/dl (5.7–12.5 mmol/l)		Serum creatinine, reference range: 1.0–2.3 mg/dl (88.4–203.3 μmol/l)		Global GFR, reference range: 2.5±0.6 ml/min/kg	Left kidney GFR, % of global (ml/min/kg)	Right kidney GFR, % of global (ml/min/kg)
		mg/dl	mmol/l	mg/dl	μmol/l
Day 0		101	36.1	8.2	724.9
Day 1				7.3	645.3
Day 2		77	27.5	7.0	618.8	1.04	64% (0.67)	36% (0.37)
Day 3				5.7	503.9
Day 10		53	18.9	5.4	477.4	0.94	58% (0.55)	42% (0.39)
Day 22		45	16.1	4.3	380.1
Day 23	0			3.5	309.4
Day 24	1			3.3	291.7
Day 50	27	40	14.3	2.4	212.2
Day 78	55	50	17.9	2.6	229.8
Day 129	106	42	15.0	3.0	265.2
Day 232	209	39	13.9	2.9	256.4
Day 261	238	39	13.9	2.9	256.4	1.37	73% (1.00)	27% (0.37)
Day 416	393	44	15.7	3.4	300.6
Day 620	597	41	14.6	3.3	291.7

Day 0 is the day of initial referral. Laparoscopic capsulotomy was performed on day 23.

The patient was discharged after 3 days of hospitalization. At that time he was bright, hydrated, and eating well. Blood glucose levels had remained normal, and serum BUN, creatinine (Table 1), phosphorus and potassium values had improved. Oral famotidine (2.5 mg once daily) and subcutaneous fluids (100 ml Normosol-R once daily) were prescribed.

Ten days after initial presentation, the patient returned for a second GFR study. Ultrasound examination at this time revealed accumulation of a small volume of fluid around the left kidney, and 35 ml was removed with ultrasound guidance. In addition, a 5 mm diameter intraparenchymal cyst was noted at the caudal pole of the right kidney. The global GFR was assessed after fluid drainage, and was essentially unchanged at 0.94 ml/min/kg. The right kidney was contributing 42% of the GFR (0.39 ml/min/kg), and the left was contributing 58% of the GFR (0.55 ml/min/kg). Serum BUN and creatinine values showed continued improvement (Table 1). Mildly elevated phosphorus was noted (6.6 mg/dl; 2.13 nmol/l) and aluminum hydroxide was prescribed as a phosphate binder.

As the PNP fluid had reaccumulated over a short period of time, the patient returned for laparoscopic fenestration of the capsule, 23 days after initial presentation. This approach was selected to allow for drainage of the fluid into the abdominal cavity. Prior to the procedure, a further 36 ml of transudate was removed from the pseudocyst with ultrasound guidance. Laparoscopy identified the pseudocyst and a 2 cm window was removed from the sac. The tissue was submitted for histopathology, which revealed dense fibrous connective tissue with multiple lymphocyte-cuffed vessels. Aerobic culture of the tissue produced no bacterial growth.

The patient was re-evaluated at regular intervals (Table 1) following the laparoscopic procedure, and no abnormalities were reported by the owner. Management of chronic renal failure included a low protein diet, administration of aluminum hydroxide or sucralfate as a phosphate binder, and subcutaneous fluids; the latter were discontinued 1 month following the laparoscopy. Diabetes mellitus and cholangiohepatitis did not recur. Repeated ultrasound examinations showed no recurrence of the PNP. A final GFR study was performed 238 days after the laparascopic fenestration procedure. This showed a global GFR of 1.37 ml/min/kg with the right kidney contributing 27% of the GFR (0.37 ml/min/kg) and the left contributing 73% of the GFR (1.00 ml/min/kg). This represented an overall increase of 32% in total GFR, with essentially no change in the GFR of the right kidney, and a 50% improvement in GFR of the left kidney, when compared to the first study. The BUN and creatinine were 39 mg/dl (13.9 mmol/l) and 2.9 mg/dl (256.4 μmol/l), respectively, at the time of the final GFR study, and blood pressure remained normal at 130 mmHg.

Management options for PNP include intermittent percutaneous fluid removal (Chastain and Grier 1975, Ochoa et al 1999, Beck et al 2000, Essman et al 2000), capsulotomy or capsulectomy (Abdinoor 1980, DiBartola and Westropp 1997, Ochoa et al 1999, Beck et al 2000), omentalization of the pseudocyst (Hill and Odesnik 2000), and nephrectomy (Ticer 1963, Rishniw et al 1998, Ochoa et al 1999, Morrow 2005). Many cats with PNPs have concurrent chronic renal failure, and this should be addressed while managing the PNP. Assessment of GFR can assist in selecting the best treatment option for these patients. In the case described here, the GFR of the left kidney (with the associated PNP) was significantly higher than that of the right kidney. The decreased GFR, small size, and ultrasonographic appearance of the right kidney suggested chronic disease for which the left kidney was compensating. Therefore, left-sided nephrectomy was contraindicated for therapy of the PNP in this case.

Measurement of GFR (by plasma clearance of DTPA) after treatment of PNP has been previously described. Ochoa et al (1999) reported a low global GFR of 0.85 ml/min/kg in a cat prior to ultrasound-guided percutaneous drainage of a PNP. One week after drainage, the global GFR was 0.72 ml/min/kg. Essman et al (2000) noted an approximately 20% improvement in global GFR 4 days after bilateral surgical capsulectomy in a cat with bilateral PNPs. In the present case report, GFR was not improved in the short-term, after percutaneous drainage of the PNP. However, 8 months after permanent drainage was achieved by laparoscopic capsulotomy, GFR was significantly improved in the left kidney, in the face of stagnant renal function on the right side. In addition, BUN and creatinine values steadily improved in this patient (Table 1). As there was no evidence of concurrent reversible renal disease, such as obstruction or infection, this improvement was attributed initially to correction of prerenal azotemia, and then to resolution of the PNP. These findings suggest that permanent drainage of PNPs may provide long-term benefit in the management of chronic renal failure in feline patients.