Case Studies

Bella's Bad Kidney (5yo FN Domestic Shorthair)

Bella was referred to The Feline Centre with a one-month history of intermittent vomiting, inappetance and right-sided renomegaly. Biochemistry revealed a moderate elevation of creatinine at 358 umol/l (reference interval 133-175 umol/l) and hyperphosphataemia (2 mmol/l; reference interval 0.95-1.55 mmol/l). Abdominal ultrasound and radiographs revealed a large accumulation of fluid in the subcapsular space of the right kidney resembling a perinephric pseudocyst, moderate right renal pyelectasia and multiple radiopaque ureteroliths along the length of the right ureter. The left kidney was very small left (2.3cm in length). Ninety mls of fluid was drained from the right subcapsular space and was analysed. This revealed that the subcapsular fluid was an accumulation of urine and therefore not a perinephric pseudocyst, as originally suspected. The subcapsular fluid recurred quickly after drainage.

We suspected that Bella had chronic obstruction of her right ureter due to ureteroliths (most likely calcium oxalate stones as she had an acidic urine pH), causing hydronephrosis and leakage of urine into the subcapsular space from the renal pelvis.

Ureteroliths are classically treated medically or, if this is not possible, removed via ureterotomy. There is a risk of ureteral stricture after this surgical procedure. The risk would have been particularly high for Bella as she had several ureteroliths that needed removal. Nephrectomy was not an option for Bella because her left kidney was structurally abnormal and considered unlikely to be properly functional, considering her urine specific gravity was inappropriately concentrated.

We attempted instead to salvage Bella's right kidney via placement of a ureteral stent, which bypasses the obstruction. Placement of a ureteral stent in a cat was described for the first time in 2006. It is therefore a relatively new technique in veterinary medicine, although it is commonly used in humans with ureteral obstruction. A midline celiotomy was performed and the abdomen explored. The left kidney was very small and the right one had a fluid-filled structure around it. The right ureter was dilated and several ureteroliths were palpated in it. A 14 mm hard multifenestrated double pig tail ureteral stent was placed in the right ureter from the bladder to the renal pelvis. The stent was placed via a 2 cm ventral cystotomy, with no need to surgically open the ureter. The right ureter was cannulated from its bladder opening to the renal pelvis with a weasel wire, a dilator was subsequently advanced over the wire and then removed and the stent was then placed. The correct placement of the stent was confirmed with intraoperative fluoroscopy. When the wire is removed the two ends of the stent curl (like a pig tail), securing the stent in the renal pelvis and in the bladder. The cystotomy was closed in 2 layers and the right renal capsule was omentalised. The abdomen was closed routinely.

After stent placement the ureter dilates around the stent (passive ureteral dilation) and the urine can therefore flow in and around the stent bypassing the obstruction. This technique is relatively new and a long term follow up is therefore unavailable. From the case series available in veterinary literature, ureteral stents are generally successful in relieving the obstruction and are well tolerated. Recurrent urinary infections and need to replace the old stent with a new one (infections or obstruction of the stent) are reported complications.

Bella has recovered well post-operatively. Her azotaemia has resolved but she has a persistent mild hyperphosphataemia. She has some evidence of mechanical cystitis due to irritation from the stent, but we are hopeful that this will reduce over time. Bella's chronic kidney disease will be managed in the longer-term with a restricted protein and phosphate wet diet. Although we cannot guarantee that she will not develop further uroliths, the ureteral stent will help to maintain Bella's renal function for as long as possible. Ureteroliths are an increasingly recognised cause of acute kidney disease in mature-senior cats, medical management may help to dislodge ureteral obstruction in 20% of cases, however ureteral stents now offer an alternative means to be able to by-pass an ureteric obstruction and salvage the obstructed kidney.