Male cats, especially those that have been neutered, can easily develop obstruction of the urethra because the urethral diameter is so small. The obstructions are often the result of mucous plugs of inflammatory material, or small crystals, calculi or “stones” that have passed down into the bladder and are now attempting to pass through the urethra. The exact cause of the inflammatory materials and stone formation it not completely understood, though viral and/or bacterial infections and diet may play a role.
Most affected cats are within 1 to 10 years of age. Initially cats may show signs of urinary tract inflammation, such as straining to urinate, frequent urination, blood in the urine, painful urination, or inappropriate urination (urinating somewhere other than the litter box). These bouts usually resolve in 5-7 days but will recur in many cats within 6-12 months. Once the cats become obstructed, they may attempt to urinate in the litter box or elsewhere but will produce no urine. Many owners may mistakenly believe that the cat is constipated. They may cry, move restlessly, or hide because of discomfort, and eventually will lose their appetites and become lethargic. Other signs of obstruction include depression, weakness, vomiting, and a lack of appetite, dehydration, and collapse. Complete obstruction can cause death of the cat in as little as a few days. In addition to the above clinical symptoms, a cat with a urethral obstruction will have a large, painful bladder that is easily felt in the back half of the abdomen.
While the precise cause of the urethral obstruction may vary from cat to cat, the exact etiology has not been completely determined. Factors that may play a role in the development include viruses, bacterial infections, stress, strict confinement, genetics and diet. Cats that eat dry diets (and therefore get less water) or diets high in mineral content (magnesium, ammonium, phosphate, calcium), protein, or salt may be at an increased risk for developing urethral obstruction. Uroliths and urethral plugs are composed of variable quantities of matrix and a variety of minerals (including struvite, calcium oxalate, ammonium urate, calcium phosphate, and cystine). Knowledge of nutritional factors associated with the pathophysiology of uroliths and urethral plugs facilitates the modification of diets for the dissolution of several minerals contained within them.
In cats with signs of urinary tract inflammation and/or obstruction, complete blood work is performed to evaluate kidney function and to determine if there is any evidence of infection or other systemic illnesses. A urinalysis is evaluated for crystal formation and the presence of infection and may be submitted for culture. Radiography is performed to determine if calculi (stones) or other material are present in the kidneys or bladder. In some cases, contrast enhanced radiography and/or ultrasound evaluation may be indicated to determine if there are any anatomic causes for straining and bloody urination, such as cancer, a bladder wall defect or a stricture of the urethra.
Fortunately, most cats are successfully unblocked. Occasionally a cat is brought in soon after blocking and achieves an excellent urinary stream immediately after unblocking. These cats may be able to proceed without having to spend a few days in the hospital or without having to have the urinary catheter sewn into place. Most blocked cats do not fit into this category but is important to realize that some cats are able to avoid more aggressive treatment. In the majority of cases, after receiving an anesthetic, a urinary catheter is sewn in place and will stay in place for 2-3 days while the cat is hospitalized. Cats that are unable to urinate can have severe abnormalities in their kidney values and electrolyte levels. For these reasons, hospitalized patients receive intravenous fluid therapy to correct the acid-base, electrolyte, and renal abnormalities, as well as receiving pain management, antibiotic therapy and monitoring of the heart for abnormal rhythms. Unfortunately, some patients suffer irreversible kidney damage due to a prolonged obstruction. Often a urinary collection bag is attached to the catheter so that urine production can be measured. Sometimes, the bladder is filled with sterile fluid and flushed out to remove crystals, inflammatory debris, and blood.
If the cat is successfully unblocked, routine post obstructive management includes the administration of medications (antibiotics, pain management), dietary change, and consistent monitoring for signs of straining to urinate, bloody urination, and to be aware of the urine volume being produced and of bladder size, if possible. Because of the amount of stretching that can occur when an animal is completely obstructed, the bladder may be incapable of contracting for some time. Medications can be administered to help this condition once the risk of re-obstructing has decreased. Any loss of appetite or vomiting should be reported to the veterinarian at once. If there is any concern about re-blocking, the veterinarian can determine fairly easily if the cat has re-blocked. It is crucial to realize that the cat is at risk for re-blocking for at least a week or two from the time of discharge. This is because the irritation syndrome that led to blocking in the first place is still continuing and as long as the episode continues, blocking is a possibility.
Cats which have experienced multiple episodes of urethral obstruction requiring hospitalization and catheterization and in those cases where the obstruction cannot be relieved with the passage of a urethral catheter require a surgical procedure called a perineal urethostomy. In this surgery, the distal part of the penis is removed and the more expanded section of the urethra then is opened up and sutured to the surrounding skin to widen the urethral orifice. A perineal urethrostomy will decrease the likelihood of future obstruction but will not prevent the symptoms of cystitis or lower urinary tract disease that already may be present. The potential complications of surgery include the development of bleeding or swelling at the surgery site (usually transient) and stricture (scarring and narrowing) of the urethrostomy site. This last complication may occur if the cat traumatizes the surgery site or if an incomplete dissection of the urethra to a point proximal enough to provide a wide stoma was not performed appropriately. In addition, urine leakage under the skin because of self induced trauma or an incomplete suture closure may result in bruising, infection, scar formation and stricture. To prevent self induced trauma, an Elizabethan collar is placed on the cat to prevent the cat from licking at the surgical site until the sutures are removed. If the surgery is performed properly, it is unlikely that the cat will develop subsequent urinary obstructions. Though postoperative urethral strictures and secondary complications may be minimized by proficiency with an effective surgical technique, the removal of the distal urethra may result in recurrent bacterial urinary tract infections in some patients after surgery. Urinary tract infections caused by urease-producing microbes may induce struvite urolith formation. In other words, the surgery does not affect the formation of crystals (which result in the plug to begin with), but provides a wider passageway for their release outside the body. Thus, blockages should not recur, but bladder infections might. Thus, the prophylactic benefits of minimizing recurrent urethral obstruction by urethrostomy must be weighed against a long-term predisposition to recurrent bacterial urinary tract infection and urolith formation. For this reason, perineal urethrostomy should be limited to those patients with a history of multiple obstructive episodes and those in which successful relief of obstruction via passage of a urethral catheter is unsuccessful.
In summary, urethral obstruction is a medical and potential surgical emergency. If the symptoms are noticed early and professional treatment is obtained immediately, a combination of medical and potential surgical intervention usually results in successful management of the condition and will prevent the subsequent development of life threatening symptoms.