P. 620

An Urban Experience
R. Dorsch1
1Medizinische Kleintierklinik, Department für klinische Tiermedizin, München, Germany
Management of ureteral Obstructions in cats
Roswitha Dorsch, Dipl. ECVIM-CA, Dr. med. vet., Dr. habil.
Center for Clinical Veterinary Medicine, Ludwig Maximilian University Munich
Over the last 15 years, veterinarians are increasingly faced with the problem of ureteral obstruction in cats. Osborne et al. 2009 described a tenfold increase in upper urinary tract stones over the last 20 years (1). The higher incidence of upper urinary tract stones
is complicated by the fact that the vast majority of
these stones are calcium oxalate stones for which medical dissolution is not an option. If they do not pass spontaneously and instead cause obstruction, diversion of urine is warranted. Stones are the most common cause of ureteral obstruction (65-80%) followed by ureteral strictures (ca. 20%) (2). Other less common reasons are dried solidi ed blood calculi that can also not be managed by medically dissolution, bladder neoplasia that obstruct urine out ow, accidental ligation of the ureter and in rare cases obstruction of the ureter with in ammatory products in cases of pyelonephritis.
Ureteral obstruction can be partial or complete, unilateral or bilateral. Studies in dogs have shown that complete ureteral obstruction decreases the renal blood  ow to 40% within the  rst 24 hours and to 20% within two weeks (3). The GFR declined permanently to 65%,
56% and 0% after 7, 14 and 40 days, respectively. If both ureters are completely obstructed, this will be fatal within 48 to 72 hours (4). In another experimental study investigating partial ureteral obstruction in dogs, relief of obstruction after 7 days, 28 days and 60 days, resulted in recovery of GFR to 100%, 35% and 8%, respectively (5). These are experimental studies in dogs with no preexisting azotemia. Many cats that are presented with ureteral obstruction due to ureteroliths already have compromised renal function due to CKD. Treatment should therefore be implemented as soon as possible to avoid further damage to the obstructed kidney. Unilateral obstruction leads to compensatory hypertrophy of the contralateral kidney. Such a compensatory response is however not possible in cats with preexisting CKD or in cats with bilateral ureteral obstruction.
Clinical signs in cats with ureteral obstruction are anorexia, lethargy and vomiting as a consequence
of acute uremia. Other clinical signs are weight loss, polydipsia/polyuria, signs of abdominal pain, vocalization, hematuria and pollakiuria. On physical examination,
cats show signs of abdominal pain and the kidneys are typically asymmetrical with one kidney enlarged and painful and the other kidney being small and irregular in shape (“big kidney - little kidney” presentation). Bilateral renomegaly is less common, and can be identi ed in cases of bilateral ureteral obstruction. Cats with unilateral partial obstruction and good functioning of the second kidney can be asymptomatic (2, 6, 7).
Most cats with ureteral obstruction are azotemic
even when unilateral obstruction is present (2, 6, 8). This is certainly also due to the fact that more than
50% to 70% of cats have preexisting chronic kidney disease. In addition to azotemia, metabolic acidosis, hyperphospatemia and varying degrees of hyperkalemia can also be seen. A complete blood count shows anemia in two thirds of affected cats (8). A urinalysis including a urine culture should be performed in all
cats. If the bladder is empty due to bilateral ureteral obstruction, a urinalysis and culture can be performed using urine obtained from the renal pelvis during surgical intervention.
The diagnosis of ureteral obstruction is based on physical examination  ndings and con rmed by diagnostic imaging of the abdomen. Abdominal ultrasound is the primary imaging method and should be performed in
all cats with suspected ureteral obstruction. Ultrasound also allows to evaluate the intrarenal architecture, geometry and to assess whether chronic alterations are present. In addition, ultrasound can be used to monitor the treatment response by evaluating the renal pelvis and ureter size after medical and surgical intervention. Plain abdominal radiographs should be performed in
all cats to look for radiodense stones in the kidney and ureter and for renal asymmetry. In 20 – 30% of cats no discrete calci ed material is identi ed with ultrasound or plain abdominal radiographs. In these cases, antegrade pyelography can be performed to evaluate the patency of the ureter and to identify non radiodense material in the ureter and ureteric strictures. In the author´s facility this
is usually performed immediately before an interventional therapy. Contrast CT and MRI can also be used to evaluate ureteral patency.
Treatment options include medical treatment, traditional surgery, ureteral stent implantation and subcutaneous ureteral bypass.

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