Urethral Stones

The urethra is the channel that carries urine from the bladder to the outside of the body. In male dogs, it travels along the underside of the body and between the hind legs. Inside the penis, the urethra sits within a bony groove of the os penis and becomes narrower. Urinary tract calculi (stones) (see urinary stones) commonly become lodged in the urethra just behind this bone, creating an obstruction. Blockage may also occur if the os penis is fractured, if a penile tumor develops, or if scar tissue causes partial narrowing.

Clinical signs vary with how severe the obstruction is. With partial obstruction, dogs may:

• urinate small amounts often
• take a long time to urinate
• strain while urinating
• have blood in the urine
• pass urine in dribbles rather than a strong stream
• urinate in inappropriate locations (e.g., carpet or bedding)

With complete obstruction, the dog strains but produces no urine. The dog is typically painful and may become lethargic, stop eating, and possibly vomit. A veterinary professional can usually feel an overly distended bladder in the back half of the abdomen (warning: palpation may be painful). With total obstruction, the bladder can rupture and urine can leak into the abdomen. Dogs with complete urethral obstruction can die within days if it is not relieved. If your pet cannot urinate, they should be examined by a veterinarian immediately.

Urinary stones are the most frequent cause of urethral obstruction in dogs, and anything that promotes stone formation increases the risk (see urinary stones). For example, Yorkshire Terriers and Schnauzers with liver shunts (see portosystemic shunts) may form ammonium biurate stones. Dalmatians have a genetic tendency to form urate stones. Infections of the kidneys, bladder, or prostate can increase the likelihood of struvite stone formation.

Obstruction is most often diagnosed when a urethral catheter cannot be advanced into the bladder. In partially obstructed dogs, the veterinarian may feel the catheter pass over stones. Radiographs (x-rays) may reveal small stones in the bladder and/or urethra (Figures 1a, 1b, and 2). During radiography, contrast material may be injected through a urethral catheter to identify urethral narrowing that could suggest a tumor or scar tissue.

Ultrasound may be recommended to evaluate the bladder for tumors, blood clots, or stones that are not visible on x-ray, and to assess the rest of the urinary tract (kidneys and ureters) as well as the prostate in male dogs. Blood tests are used to gauge how ill the dog is.

Urinary blockage can cause temporary or permanent kidney damage. Potassium—normally excreted in urine—may become dangerously elevated and can trigger cardiac abnormalities, so an electrocardiogram (ECG) is often performed. The urine is examined for crystals (which may help indicate stone type) and for signs of infection, and may be submitted for culture.

Figure 1a. Abdominal radiograph of a dog with many calculi in the urinary bladder and urethra.
Figure 1b. Abdominal radiograph of a dog with many calculi in the urinary bladder and urethra.
Figure 2. Radiograph of a dog’s penis and urethra. Two urethral stones (red arrows) are trapped behind the os penis (yellow arrows).

If stones are causing the obstruction, the veterinarian will attempt to flush them back into the bladder. Once in the bladder, stones can be removed surgically, dissolved with medical therapy (depending on stone type), or fragmented using lithotripsy (breaking stones with ultrasonic waves or lasers). If the dog is severely ill, surgery may be postponed and a urinary catheter may be left in place to drain the bladder for a day or two until the dog is stable enough for general anesthesia and surgery.

Surgical removal of bladder stones is performed via cystotomy. Under general anesthesia, the bladder is reached through a small incision in the abdomen. The bladder is opened, stones are removed, and the urinary tract is thoroughly flushed to confirm no stones remain. If urethral stones cannot be pushed back into the bladder, a separate incision into the urethra may be required. Stones removed during surgery are sent for chemical analysis and, in some cases, bacterial culture. Any abnormal bladder tissue may also be biopsied.

Male dogs with an obstruction that cannot be relieved, dogs with penile tumors, or dogs that repeatedly form stones may need a procedure that creates a new permanent urethral opening called a scrotal urethrostomy. This may be necessary because stones can become trapped within scar tissue and cannot be removed. A scrotal urethrostomy allows urine to exit from a point behind the os penis where the urethra is wider (Figures 2, 3). The opening is designed so small stones can pass through, although very large stones in the bladder or upper urethra can still cause obstruction. In most cases, the penis remains, so the dog’s appearance while walking does not change, but urination occurs through the new opening where the scrotum used to be (Figures 3, 4). If the dog has a penile tumor, the procedure is combined with penile removal (Figure 4). Because the surgical site is in the scrotal region, dogs are neutered (castrated) during the operation.

Figure 3. Final appearance of a scrotal urethrostomy. The urethra is sutured to the skin with a “whipstitch” to reduce bleeding. Other skin sutures are removed in 10–14 days.
Figure 4. One day after surgery, swelling is present but bleeding is not seen at this scrotal urethrostomy site. This dog had a penile tumor and required penile removal as well.

After an abdominal surgery, dogs need restricted activity for several weeks. Following cystotomy, the bladder may be slightly smaller for a few weeks due to sutures, so the dog may urinate more frequently. Increased urgency and accidents can occur. Mild blood-tinged urine is common; active dripping of frank blood is abnormal and should prompt a call to your surgeon. An Elizabethan collar is worn for 10–14 days until the incision is healed to prevent licking or chewing. Oral pain medication is typically prescribed. If a bladder infection is present, antibiotics are given. Stones are analyzed to determine whether special diets or medications are needed.

Because tissues around the urethra have a strong blood supply, bleeding can occur for several days after a scrotal urethrostomy. Excitement or licking-related trauma can worsen bleeding risk, so dogs must wear an Elizabethan collar and may need sedation for a few days to reduce bleeding.

Complications of urinary obstruction may include tears in the urethra or bladder with urine leakage, bladder dysfunction, incontinence, or scarring within the urethra that leads to re-obstruction. After cystotomy, potential postoperative complications include temporary bloody urine, urine leakage from the bladder suture line into the abdomen (uroabdomen), hernia at the abdominal incision, and infection.

After scrotal urethrostomy, potential complications include early postoperative bleeding, urine scald (skin irritation from urine), scarring or narrowing of the new opening causing obstruction, urine spray onto the legs, and infection.

Preventing recurrence of calculi-related obstruction depends on reducing the factors that promote stone formation. If your dog forms stones, you must follow dietary and medication plans recommended by your veterinarian and return for rechecks as advised to ensure crystals and stones are controlled.

Overall prognosis is excellent for dogs treated with cystotomy, with or without scrotal urethrostomy, provided the dog has not suffered severe kidney injury or toxin-related damage from prolonged obstruction.