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URETHRAL OBSTRUCTION IN MALE DOGS
Overview of the condition
The urethra is the tube that carries urine from the bladder out of the body. In the male dog, it passes along the back side of the dog and between the rear legs. Within the penis, the urethra lies within a trough of bone- the os penis- and becomes narrower. Calculi ("stones") that develop within the urinary tract (see "Urotlihiasis") will often become stuck within the urethra behind this bone, blocking the urethra. The urethra can also be blocked if the bone is fractured or if the dog develops a tumor of the penis. Scar tissue can also cause partial blockage.
Signs/Clinical presentation
Clinical signs depend on the severity of the blockage. Dogs that have a partial obstruction may urinate small amounts frequently, take along time urinating, or strain to urinate and may have blood in the urine. The urine may come out in drips instead of a strong stream. The dog may urinate in inappropriate places (on the carpet or in its bedding). If the urethra is completely blocked, the dog will strain without producing any urine. It will become painful and lethargic, lose its appetite, and possibly start vomiting. An overly large urinary bladder will be easily felt in the back half of the belly. Dogs with total urethral obstruction will die within 3 to 6 days if the obstruction is not removed.
Risk Factors
Because urinary tract calculi are the most common cause of urethral obstruction in dogs, anything that cause stone formation will increase the risk of urethral blockage (see "Urotlihiasis"). For example, Yorkshire terriers and schnauzers with liver shunts (see "Portosystemic shunts") and Dalmatian dogs are prone to forming urate calculi. Kidney, bladder, and prostate infections can increase the risk of struvite calculi.
Diagnostic tests
Diagnosis of obstruction is usually based on an inability to advance a urethral catheter into the bladder. The veterinarian may feel the catheter pass over the calculli in dogs that are partially obstructed. X-rays of the dog may show small stones within the urethra (Figure 1). The veterinarian can inject contrast material into a urethral catheter during x-rays to see if there is any narrowing of the urethra.
Figure 1. X-ray of a dog's penis and urethra. Two urethral calculi or "stones" (red arrows) are lodged behind the os penis (yellow arrows).
Blood work is evaluated to determine the severity of the dog's illness. Kidney function may be temporarily damaged in dogs with urinary tract blockage. Potassium, which is normally removed from the body through the urine, can also be very high and can cause heart problems, so an electrocardiogram (ECG) is often performed. The urine will be checked for crystals, which may help to determine the type of stone present, and for evidence of infection, and may be submitted for culture.
Differential diagnoses
Straining to urinate can be caused by an enlarged prostate gland, either from a tumor, cyst, infection, or high hormone levels (this happens commonly in older male dogs that have not been castrated). It can also occur in dogs with perineal hernias. (Link here) or bladder infections. Blood in the urine also occurs with bladder, prostate, or kidney disease or infection.
Treatment Options
If the obstruction is caused by a urinary tract calcluli, the veterinarian will try to flush the stone back into the bladder, where it can either be removed surgically through a cystotomy (Figure ), dissolved with medical management (depending on the type), or broken up with lithotripsy (smashing of stones with ultrasonic waves).
Dogs that are unable to be blocked, have a tumor of the penis, or are recurrent stone formers may require surgery to form a new temporary opening ("prescrotal urethrostomy") or permanent opening ("scrotal urethrostomy") to the urethra that will allow urine to exit behind the os penis where the urethra is wider (Figures 2, 3). Scrotal urethrostomies are often required because calclui in the urethra may become trapped in scar tissue and therefore cannot be removed. In dogs with penile tumors, a scrotal urethrostomy is performed and the penis is removed. (Figure 4)
Figure 2. The scrotum has been incised and the urethra is visible (yellow arrows). A new opening will be made in the urethra, which will be sewn to the skin. This dog was already castrated before the procedure.
Figure 3. Final appearance of the scrotal urethrostomy. The urethra has been sewn to the skin with a "whipstitch" to try and prevent bleeding. The other skin sutures will need to be removed in 10-14 days.
Figure 4. One day after surgery, there is swelling but no bleeding at this scrotal urethrostomy site. This dog had a tumor of the penis, and therefore required removal of the penis as well.
When to seek referral
Dogs with complete urethral obstruction require immediate emergency care. Scrotal urethrostomies are often performed by ACVS Veterinary Surgeons because of the risk of complications. (Find an ACVS Veterinary Surgeon)
Potential complications of surgery
The tissue around the urethra has an excellent blood supply, and dogs may have bleeding after the surgery (Figure 5, 6). The risk of bleeding is reduced if the new opening is sewn in a "whipstitch" pattern, which helps to seal the edges. Also, excitement or trauma to the area from licking can increase the risk of bleeding, so dogs wear Elizabethan collars and may require sedation. Because the surgery site is in the area of the scrotum, dogs are castrated during the procedure, which will also help reduce excitement after surgery.
If the opening is made in the wrong area, or the hole scars down and narrows, urine can spray the inside or back of the legs.
Figure 5. Despite the use of very fine suture, this Dalmatian had bleeding for 10 days along its suture line.
Figure 6. The scrotal urethrostomy site in this dog bled every time he was excited, and he eventually required a blood transfusion. He was kept heavily sedated for a week, and bleeding stopped once the sutures were removed.
Aftercare
Most dogs are kept sedated for several days after the surgery to reduce the chance of bleeding. The Elizabethan collar is left on for 7-10 days until the site is healed. If a bladder infection is present, antibiotics will be prescribed. Calculi are sent for analysis to determine whether special diets or medications are needed.
Prevention and prognosis
Urethral obstruction by calculi is prevented by reducing factors that cause stone formation. If you dog is a stone former, you will need to follow your veterinarian's diet and medication recommendations closely, and have your dog rechecked as needed to make sure crystal formation is being controlled.
Prognosis is excellent for dogs that undergo scrotal urethrostomy for urethral blockage, as long as the dogs have not suffered serious kidney or toxic damage from prolonged obstruction.
—Dr. Karen Tobias, DVM, MS
Diplomate ACVS
Posted 8/23/2006
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