Subcutaneous Ureteral Bypass Device
As veterinarians gain experience in the discipline of interventional endourology we find that there are challenges in some of our patients that are not experienced in human endourology. One of these challenges is the feline ureter. In the healthy state it is a very thin and narrow structure averaging about 0.4mm in diameter. Ureteral stents for felines are avialbale as small as 2 and 2.5 Fr and for dogs as large as 6 Fr. The obstructed ureter may distend to perhaps a centimeter at its widest point, but usually it is less than that and is often tortuous in nature. Additionally the cause for ureteral obstructions is often calcium oxalate uroliths which may become embedded in the wall of the ureter making removal impossible, and also making passage of a stent around the stone quite challenging. Another cause of ureteral obstruction is a stricture at a previous site of urolith lodgment or urolith removal.
The clinicians and scientists at Norfolk Vet Products have recently patented a device based upon systems used in human medicine to bypass a diseased ureter. This device is the “SUBTM , a subcutaneous ureteral bypass system. This system utilizes a locking loop pigtail nephrostomy tube, a subcutaneous vascular access device and a tube cystostomy catheter.
This system brings the surgeon and the internist or interventional radiologist into the same room. It highlights the team approach to veterinary medicine.The device is simple to place. The surgeon isolates the kidney. Using fluoroscopy, the nephrosotomy tube is guided into the renal pelvis, engaged and locked in place (Figure 1). The cystostomy tube is placed in the bladder and sutured in place. A vascular access port is buried subcutaneously and secured to the body wall. Injection of iohexol contrast agent ensures that there is no leakage at the nephrostomy tube , that the shunt is patent, and that there is no leakage at the cystostomy tube (Figure 2). Urine flows from the kidney through the shunting port and into the bladder, bypassing the ureter. If the affected ureter is still partially patent, urine may still flow in a natural direction.
Foster Hospital clinicians recently placed this device in a cat that had presented with acute on chronic kidney injury secondary to pyelonephritis, severe ureteritis, chronic kidney disease, nephrolithiasis and ureteroliths. The cat required continuous renal replacement therapy in addition to a prolonged course of antibiotics. He became polyuric after renal replacement therapy had begun; however, the ureter was so diseased that there was concern about the feasibility of safely passing a stent while maintaining ureteral integrity. A SUBTM was considered the best option for this patient (Figure 3). The cat is doing well at home with IRIS stage 3 chronic kidney disease with a creatinine of 3 mg/dl. He is urinating well and has a negative urine culture at this time. Thus far he continues to produce large volumes of urine and the bypass device is working well.