Patient Positioning

Perineal urethrostomy may be performed in sternal or dorsal recumbency. Although traditionally performed in sternal recumbency, benefits of performing perineal urethrostomy in dorsal recumbency are that no repositioning is required to perform concurrent cystotomy, improved ventilation of the patient due to reduced diaphragmatic compression by abdominal organs, reduced cranial movement of the urinary bladder to maintain adequate urethral exposure, and increased surgeon comfort.^4–7 Dorsal recumbency also provides improved exposure to the area by stretching the skin over the perineum, whereas in sternal recumbency, the prepuce and penis are sometimes more difficult to access due to the skin rolling inward if the caudal thighs cannot be externally rotated. An additional potential benefit of dorsal recumbency is that the urinary bladder may be approached for normograde urethral catheterization if retrograde urethral catheterization is not possible, although in most cases this is not necessary and the procedure can be completed without a urethral catheter. There is no difference in the length of anesthesia or surgery or the risk of short‐ or long‐term complications between perineal urethrostomy performed in sternal compared to dorsal recumbency.⁴ Cats positioned in dorsal recumbency have less vertebral canal narrowing compared to those positioned in sternal recumbency;⁸ however, no differences in neurological status have been found postoperatively between cats positioned in sternal compared to dorsal recumbency.⁹

To perform perineal urethrostomy in sternal recumbency, the patient should be positioned in the perineal position with the tail taped over the back toward the head (Figure 32.1). The pelvic limbs can either hang off the table or can be frog‐legged. With the limbs hanging off the table, it is important to ensure sufficient padding is present to prevent sciatic nerve deficits due to prolonged pinching of the nerve. To perform perineal urethrostomy in dorsal recumbency, the patient should be positioned with the pelvic limbs pulled upwards toward the head (Figure 32.2a,b). If exposure is inadequate, a towel may be placed under the pelvis to increase exposure to the perineal area (Figure 32.2c). The entire perineal area should be shaved, and a pursestring suture should be placed in the anus to prevent leakage due to the proximity to the surgical site (Figure 32.3).

Procedure

A sterile urethral catheter should be placed, when possible, to facilitate palpation of the urethra during the procedure, although in cases with an obstruction that cannot be relieved, a catheter is not required. An elliptical‐ or teardrop‐shaped incision should be made encircling the scrotum and prepuce (Figure 32.4), ensuring to only incise skin at the junction of the perineal and scrotal skin. If too much skin is taken, there may be increased tension on the urethrostomy. Intact cats should be castrated routinely at this time. The subcutaneous tissues should be dissected to the level of the penis and urethra; gentle traction on the prepuce helps to facilitate this dissection (Figure 32.5, Video 32.1). Gelpi retractors may be placed to retract the subcutaneous tissues and assist with dissection by providing exposure and traction on the tissues. Following dissection of the caudal penis, penile attachments to the pelvis should be freed. The first attachments are the ischiocavernosus muscles, which attach the penis to the ischium (Figure 32.6a, Video 32.2). These muscles should be isolated, and an instrument should be able to be passed between the pelvis and the muscle (Figure 32.6b). Isolation can be performed with blunt dissection with curved mosquito hemostats, which are useful for isolating this muscle due to the narrow tip of the jaws. Once the muscle has been isolated, it should be transected at its attachment to the ischium (Figure 32.6c, Video 32.3). This can be performed with Mayo scissors or electrosurgery. It is important to transect this muscle at its tendinous insertion on the ischium to avoid hemorrhage. When using scissors for transection, the scissors should be laid flat against the pelvis prior to transection to ensure the tendinous insertion is transected.

Following transection of the ischiocavernosus muscles, the ventral ligament of the penis should be identified (Figure 32.7a, Video 32.4). This ligament is located on the ventral portion of the penis and attaches the penile body to the pubis. This attachment should be severed sharply at the connection with the pelvis. Once this attachment has been severed, the ventral tissues should be easily dissected with blunt finger dissection until an index finger can be passed through the pelvic canal toward the pubic brim without encountering any soft tissue attachments (Figure 32.7b, Video 32.4). Minimal dorsal and lateral dissection should be performed, as innervation to the urethra enters dorsally. Once the bulbourethral glands are identified proximal and medial to the transected ischiocavernosus muscles, dissection has proceeded to an appropriate level (Figure 32.8, Video 32.5). The bulbourethral glands are spherical glands that are more pronounced in intact males and may be a subtle rounded area in neutered males. At the level of the bulbourethral glands, the urethral diameter is adequate for perineal urethrostomy, and there will be minimal tension to suture the urethra to the skin at this level. Trying to incise the urethra more proximally will not result in a larger urethrostomy diameter; it will simply increase tension of the mucosa‐skin apposition.

The retractor penis, located on the dorsal surface of the penis, should then be dissected free along the length of the penis to the bulbourethral glands with dissection using scissors or mosquito hemostats and then should be sharply transected proximal to the bulbourethral glands (Figure 32.9, Video 32.6). It is important to remove this muscle, as it overlies the urethra and will interfere with the urethrostomy apposition if not excised. Once exposure is deemed adequate, the urethra should be incised on dorsal midline. For surgeons performing this procedure in both sternal and dorsal recumbency, it is imperative to be certain which side of the urethra is dorsal prior to incising. A #11 or #15 blade should be used to initiate the incision in the mid‐to‐distal penis (Video 32.7). Once the catheter is identified or the urethral mucosa is identified, this incision may be continued with iris or Stevens tenotomy scissors to the level of the bulbourethral glands, at which point there will be a palpable change in the feel of cutting the urethral wall with higher collagen density (Figure 32.10, Video 32.8). Hemorrhage can be quite impressive due to transection of the cavernous tissue of the penis and the extensive blood supply to the urethra. Once the incision has been made to the level of the bulbourethral glands, a mosquito hemostat should be able to be inserted easily to the level of the box lock, which indicates sufficient urethral diameter for perineal urethrostomy (Figure 32.11, Video 32.9). Alternatively, some clinicians may use an 8‐Fr red rubber catheter to ensure adequate urethrostomy diameter, which can also be used to lavage the urinary bladder of any additional debris, if present, and if a cystotomy is not being performed concurrently.

Closure

Suturing the ischiocavernosus muscles to the lateral subcutaneous tissues with an interrupted cruciate or horizontal mattress suture with a monofilament absorbable suture helps to facilitate exposure of the urethra, reduce the distance from the urethra to the skin, and reduce tension on the anastomosis while suturing (Figure 32.12). The urethral mucosa should be sutured to the skin with 4‐0 or 5‐0 rapidly absorbed monofilament suture on a taper needle, such as poliglecaprone 25 or glycomer 631. Historically, nonabsorbable suture was used for perineal urethrostomy, but this requires suture removal two weeks postoperatively, which often requires sedation to accomplish. Use of a rapidly absorbed monofilament suture does not increase the risk of complications;¹⁰ thus, many clinicians prefer to use absorbable suture to avoid the need for suture removal.

The dorsal‐most sutures should be placed first and may be placed as stay sutures to ensure accurate apposition. These are generally placed at a 45° angle at the 10 and 2 o’clock position (with 12 o’clock being straight dorsal, Figure 32.13). It is important to ensure accurate apposition of the urethral mucosa to the skin, and the skin sutures should be aligned as an intradermal bite with the needle going through the skin and exiting in the subcuticular layer (above the subcutaneous layer). Bishop Harmon forceps are helpful for handling of the delicate tissues and surgical eye spears are an excellent tool to use for hemostasis during suturing. Once these first two sutures are tied, additional sutures can be placed on either side to form a drain board that helps to prevent urine scald and reduce the risk of stenosis. The urethra should be sutured for 1–1.5 cm in length. These sutures may be simple interrupted or simple continuous in nature; if the continuous pattern is chosen, three to four interrupted sutures are performed on each side followed by a continuous pattern for the drain board (Figure 32.14). Figure‐of‐eight sutures are ideal for all interrupted sutures on the anastomosis, as they keep knots away from the incision line while still maintaining excellent apposition (Figure 32.15). Once the drain board has been established, a mattress suture is placed through the skin on one side, through the most ventral aspect of the cavernous tissues, through the skin on the opposite side, and then back through the skin on the opposite side, this time taking a bite through the dorsal‐most aspect of the cavernous tissues before exiting in the skin on the side in which the suture was started (Video 32.10). The distal penis is then amputated sharply (Video 32.10). Alternatively, a modified transfixation suture can be placed around the penile body prior to amputating the distal penis. Any skin remaining open should be closed dorsal and ventral to the urethrostomy site, as needed (Figure 32.14). In most cases, only the ventral portion of the skin incision requires separate closure.