Ureteral Obstruction in Dogs and Cats

71 Ureteral Obstruction IntRoduCtIon The ureters are fibromuscular ducts carrying urine from the kidney to the urinary bladder by peristaltic activity, which is transmitted from one muscle cell to the next (1). The ureters originate in the renal pelvices and travel retroperitoneally along the aorta and vena cava towards the urinary bladder. Near the pelvis they join the lateral ligament of the bladder and insert into the dorsolateral aspect of the urinary bladder (2). Ureteral obstructions can be classified as intraluminal, intramural and extramural. Ureteral obstructions can also be classified as acute or chronic, static or dynamic, unilateral or bilateral, and as partial or complete. Correct classification is crucial, because the nature of the obstruction along with the patient’s medical condition are the major determinants of the treatment plan. Although congenital ureteral obstructions have been described in the veterinary literature, these are relatively rare and acquired ureteral obstructions occur more frequently (27). Cats are predisposed to ureteral obstruction due to their small ureteral lumen (0.4 mm in diameter) (8). The incidence of ureteral obstructions in cats has increased dramatically over the past decades all over the world, and became the leading cause of acute uremia in North America (9). The incidence of ureteral obstruction in Israel is unknown but is seems to be increasing as well (personal observation). As any emerging disease, it is possible that the disorder is initially not recognized by clinicians unfamiliar with it, and thus the perceived incidence is lower than the actual incidence. Intraluminal obstruction is the most common cause for ureteral obstruction in dogs and cats, thus most of the discussion in the review will focus on intraluminal ureteral obstruction. Nevertheless, the guidelines for the management of intramural and extramural obstruction follow the same principles. Intraluminal obstructions are usually caused by ureteral calculi, which in cats are almost exclusively composed of calcium oxalate (6), however, blood clots and inflammatory debris may also obstruct the ureter, particularly in cats (6). Intramural ureteral obstruction can result from a stricture, neoplasia (primary or metastatic), ureterocele, fibroepithelial polyp and proliferative ureteritis. Among those, ureteral strictures seem to be the most common cause of intramural ureteral obstruction. Strictures can be associated Ureteral Obstruction in Dogs and Cats