Canine Urethral and Ureteral Obstruction – NAVLE Study Guide

Overview and Clinical Importance

Urinary obstruction is a life-threatening emergency in dogs that occurs when normal urine outflow is mechanically or functionally impeded. This condition encompasses both urethral obstruction (obstruction of the urethra) and ureteral obstruction (obstruction of one or both ureters). Complete urethral obstruction can be fatal within 2-3 days due to metabolic derangements, particularly hyperkalemia and uremia. This topic is frequently tested on the NAVLE due to its clinical urgency and the critical decision-making required for successful patient management.

In dogs, urolithiasis is the most common cause of urethral obstruction, unlike cats where matrix-crystalline plugs predominate. Understanding the pathophysiology, clinical presentation, diagnostic approach, and treatment options is essential for any veterinarian managing emergency cases.

Etiology and Pathophysiology

Causes of Urethral Obstruction

Urolithiasis is the most common cause of urethral obstruction in dogs. Stones typically form in the bladder and migrate to the urethra, becoming lodged at narrow points, most commonly at the base of the os penis in male dogs. Other causes include neoplasia (particularly transitional cell carcinoma), urethral strictures, prostatic disease, blood clots, and extraluminal compression from pelvic masses.