The Subcutaneous Ureteral Bypass (SUB) in Cats for Non-Malignant Ureteral Obstruction
Learning objective: To understand the indications for placement of a SUB device and the technical procedural aspects of SUB placement.
Ureteral obstructions in cats are a frustrating condition to diagnose, manage and treat effectively. The onset of clinical signs are often vague and non-specific, especially if partial or unilateral obstruction is present.
Diagnosis is made by abdominal radiography and ultrasonography. Ultrasonography is the preferred imaging modality as it allows assessment of the kidney parenchyma and renal pelves, ureters and bladder. Importantly it allows for detection of radiolucent uroliths as well as obstructions or non-urolith obstructions of the ureters.
Cats with a diagnosis of ureteral obstruction should initially be treated medically with intravenous fluid therapy, analgesia and correction of any electrolyte or acid-base disturbances, especially hyperkalemia.
Ureteral obstruction is most commonly due to urolithiasis with calcium oxalate being the most common form of urolith identified. Other causes of ureteral obstruction include tumours, strictures and blood clots and circumcaval ureteral anatomy. The normal feline ureter is only 2–3 mm in diameter.
Surgical options to treat urethral uroliths include; ureterotomy or retrograde flushing the urolith to the renal pelvis and then urolith removal by pyelotomy or nephrotomy. Both of these surgical options had a high risk of urine leakage or ureteral stenosis. If the stone is relatively distal in the ureter, ureteral transection and reimplantation into the bladder is a possibility.
The subcutaneous ureteral bypass (SUB) device was developed to provide an alternate pathway for urine to flow from the renal pelvis to the bladder. SUBs are placed during an open abdominal surgery using fluoroscopy. The SUB device consists of a pigtail catheter that is placed through the renal parenchyma into the renal pelvis with the aid of a guidewire and intraoperative fluoroscopy. This catheter exits the abdominal cavity through the body wall and is connected to a flushing port located in a paramedian subcutaneous position. The other end of the port is connected to another catheter that enters the abdomen and is placed in the bladder, thus providing an ‘artificial ureter’ bypass pathway for urine to flow from the renal pelvis to the bladder.
Potential complications with the SUB device include: blockage of the catheters with urolith or calcium oxalate encrustation recurrent urinary tract infections and kinking of the SUB tubes. The SUB device should be flushed via the subcutaneous port at the end of surgery and within the first month after surgery and then every 3–6 months for life. A recently special flushing mix and kit is now available. The flushing is normally done with any light sedation and the renal pelvis is imaged with ultrasonography to document renal pelvis dilation during flushing patency which indicates patency of the nephrostomy catheter.