Urogenital surgery (Proceedings)
The entire urethra is lined with transitional epitheliurn with the exception of a small amount near the tip of the penis or urethral tubercle. Urethral muscle is composed of an inner longitudinal layer of smooth muscle and an outer transverse layer of skeletal muscle that are separated dorsally by a longitudinal raphe.
Blood supplies are mainly from the urogenital and/or internal pudendal arteries depending on whether the dog is a male or female. Venous drainage is primarily through the internal pudendal vein, Autonomic nerves from the pelvic plexus supply the smooth muscle of the urethra. Voluntary control of muscle is mediated by the pudendal nerve.Pathophysiology
Urethral reaction to foreign objects is dependent on many variables; e.g., individual patient response, length of time the foreign objects are lodged, the type of foreign object (calculi, catheter, etc.), and absence or presence of secondary infection. In humans, urethras show some reaction after 2-3 days of indwelling catheter. This reaction is superficial and does not clearly indicate that the degree of submucosal reaction is probably important in breaking down body defense mechanisms to infections as well as in causing scarring of the urethra after the foreign body has been removed.
Surgery of the urethra
Urethral prolapse - the cranial prepuce and surrounding abdomen are clipped and scrubbed. The preputial diverticulum and penis are irrigated with an antiseptic solution prior to scrubbing and draping. When the prolapse is small and not grossly engorged with blood, a conservative repair is indicated. The penis is extended from the sheath and grasped between the thumb and forefingers. A well lubricated catheter of the largest diameter that can easily be inserted is passed up the urethra as an attempt is made to reduce the prolapse. If the prolapse easily reduces, the catheter is inserted a short distance into the urethra and a purse-string suture of 3-0 or 4-0 nylon material is placed around the end of the penis The catheter is sutured to the prepuce to maintain its position in the urethra and bladder for 5-7 days. When the prolapse is severe, amputation of the prolapsed segment is preferred. Again, a well-lubricated catheter is placed in the urethra. To prevent the inner mucosa from retracting, four stay sutures are placed equidistant around the tip of the penis and through the urethral mucosa, The prolapse is excised over the catheter as close to the tip of the penis as possible. Simple interrupted sutures of 4-0 or 5-0 PDS are paced around the tip of the penis approximately 0.25 to 0.5 cm apart, uniting the urethral mucosa to the cranial tip of the penis. The catheter is sutured to the prepuce to maintain its position for 3-4 days.
Post-operative considerations - a urinary antibiotic e.g. chloramphenicol or nitrofurantoin is indicated for treatment of any infection. Antispasmodics and/or tranquilizers may be beneficial. Elizabethan collars are useful in preventing catheter removal and licking at the operative site.
Urethrostomies - creation of a new and permanent urethral orifice are performed as one of three types in the male dog, prepubic, scrotal, and perineal. The perineal region is by far the least desirable because of urine scalding of the perineal skin and scrotum. It is also more difficult to suture deep urethra to the skin, if castration is acceptable, scrotal urethrostomy is preferred. if castration cannot be per-formed, a prepubic urethrostomy is the alternative. The indications for this are recurrent stone formation untreatable or unresponsive to medical management, urethral strictures, and patients where medical management might be harmful.