A 9-year-old male castrated domestic shorthair cat was presented to its local veterinarian for coughing and waxing and waning peripheral edema. Thoracic radiographs revealed pleural effusion. After three thoracocentesis events that each recovered between 300 and 420 cm3 of fluid, the cat was referred to the study institution.
At presentation the cat weighed 4.4 kg and had a body condition score of 4/9. A moderate amount of peripheral edema was present in its inguinal region. The cat exhibited increased respiratory effort, and decreased breath sounds were appreciated ventrally. A grade II/VI left parasternal systolic heart murmur was ausculted. Pleural effusion was detected bilaterally via thoracic ultrasound, and bilateral thoracocentesis drained 362 cm3 of translucent fluid from the pleural space. The fluid was classified as a pure transudate (protein 3 kg/m3, total nucleated cell count 90/mm3) and contained a creatinine of 29 g/m3, glucose of 1.32 kg/m3, and potassium of 2.7 mol/m3. Complete blood count showed a moderate normocytic, normochromic, nonregenerative anemia (hematocrit 22.8%; RR: 30-50%). Serum biochemistry panel revealed azotemia [consistent with IRIS stage 2 chronic kidney disease (CKD)] characterized by a creatinine of 28 g/m3 (RR: 12-22 g/m3) and BUN of 540 g/m3 (RR: 180-330 g/m3). Urinalysis revealed a specific gravity of 1.031 with proteinuria (750 g/m3) and glucosuria (10,000 g/m3). Lactate dehydrogenase (LDH) evaluation was as follows: < 0.01 IU/cm3 in the effusion, 0.092 IU/cm3 in the urine, and 0.188 IU/cm3 in the blood. A NT-proBNP test (IDEXX, Westbrook, ME) was normal. Abdominal ultrasound showed bilaterally decreased renal corticomedullary distinction with cortical cysts and scant peritoneal effusion. Echocardiography revealed a mild myocardial irregularity and an impaired relaxation pattern of left ventricular diastolic filling (possibly age related or early heart disease).
Renal scintigraphy was performed using 99mTc diethylenetriamine penta-acetic acid (Tc-DTPA) to investigate for presence of urothorax. In this case, 2.25 millicuries Tc-DTPA were administered intravenously and 60 s static images were acquired using a low-energy, all-purpose collimator at 5 min, 20 min, and hourly until 4 h following injection (Figures 1, 2). Initially, there was blushing of the renal silhouettes as the Tc-DTPA accumulated within the kidneys with immediate extension of radiopharmaceutical in the urinary bladder. Over the next 4 h, technetium progressively accumulated within the pleural space, demonstrating a communication between the urinary tract and pleural space.
Multiphase contrast-enhanced CT of the thorax and abdomen was performed with multiple post-contrast sequences (Figures 3A-C). On venous phase images, both kidneys had a thin outline of subcapsular contrast media with mild extravasation of the contrast into the retroperitoneal space. On delayed phase images, there was progressive accumulation of contrast media in the retroperitoneal effusion as well as an increase in Hounsfield units (from 8 to 16) of the pleural effusion. The pleura was mildly thickened, consistent with pleuritis from chronic pleural effusion, and fluid could be seen on either side of the plica vena cava. There were multiple small contrast filling defects within the renal cortical tissue consistent with renal cortical cysts, and no ureteral abnormalities were detected. Subcutaneous edema was noted in the pelvic limbs and perineal region.
Exploratory celiotomy revealed minimal translucent peritoneal effusion. No visible or palpable defects were identified in the substance of the diaphragm or at the caval foramen, esophageal hiatus, or aortic hiatus. The retroperitoneum appeared gelatinous bilaterally. After retroperitoneal incision, leakage of fluid was traced to circular defects in the cranial aspect of the renal capsules bilaterally. Retroperitoneal fat was adhered to the exposed renal parenchyma (Figure 4) and local retroperitoneal fibrosis was detected in these regions. Fluid was observed to be leaking from these defects and gentle probing revealed a lack of connection of the renal capsule surrounding the defects to the underlying renal parenchyma. Ultrafiltrate fluid was observed accumulating in this space before leaking into the retroperitoneal space. No ureteral or bladder leaks were identified.
No reconstructive options were available, so the retroperitoneum was incised from the level of each kidney to the diaphragm to encourage drainage of fluid from the retroperitoneum into the peritoneum and thereby minimize tracking into the pleural space. Due to the subsequent instability of the renal attachments to the body wall, bilateral nephropexies were performed between the retroperitoneal sublumbar musculature and caudal pole of each kidney using 3-0 polypropylene in a cruciate pattern. The abdomen was closed in routine fashion. A biopsy of the right renal capsule adjacent to the capsular defect revealed minimal chronic lymphocytic and plasmacytic perinephritis. The cat received a packed red blood cell transfusion during the procedure and recovered from anesthesia without complications.
The cat returned 11 days postoperatively for a recheck examination. No clinical signs of pleural effusion were exhibited, though a brief ultrasound scan revealed a moderate amount of pleural effusion and pockets of free peritoneal fluid. The cat presented again 16 days later with an increased respiratory effort and respiratory rate of 40 breaths per minute. A brief ultrasound exam revealed a moderate amount of pleural effusion and a scant amount of peritoneal effusion. Thoracocentesis was performed and 294 cm3 of clear fluid was removed.
The cat continued to produce small amounts of pleural effusion, and intermittent peripheral edema was reported during periods of increased pleural effusion. The owner elected to place a pleural drainage catheter and port system ~2 months after the initial surgery. Pleural effusion was managed for 2 additional years, at which time the cat was euthanized due to progressive CKD (IRIS stage 4) and an associated decline in quality of life. Necropsy revealed bicavitary effusion with severe CKD changes (including interstitial fibrosis and lymphoplasmacytic nephritis), multifocal, nodular, pulmonary interstitial fibrosis without inflammation (suspect idiopathic feline pulmonary fibrosis), cardiac interstitial fibrosis (concentric ventricular myocardial hypertrophy), and parathyroid hyperplasia as well as bone marrow erythroid hypoplasia (suspect secondary to renal disease). The underlying cause of the bicavitary effusion was not grossly or histologically apparent.