Surgical conditions of the male equine reproductive tract (Proceedings)

Traumatic Injuries to the Penis and Prepuce

Lacerations to the Penis and Prepuce

Lacerations to the stallion's penis typically occur when a stallion attempts to breed a mare across a fence, from the mare's tail hair or breeding stitch during coitus, or from improperly fitted stallion rings. Penile lacerations in geldings are the usually the result of trauma or from iatrogenic damage during castrations attempts. Most penile lacerations involve the skin and subcutaneous tissues, however, lacerations into the cavernosal tissues and urethra have been reported. Any horse with a penile laceration should be examined to determine the extent of the laceration. An acute wound should be cleaned, debrided and sutured primarily, if possible. The suture chosen should be of a soft nature, such as Vicryl, to avoid irritating the prepuce when the penis is retracted into the sheath. Any rent or tear in the tunica albuginea should be closed to prevent a shunt from forming between the cavernosal tissues and the penile vasculature. If the urethra is involved, the nature of the laceration determines whether or not surgical repair is necessary. Smaller longitudinal lacerations may close with second intention healing. However, larger longitudinal and transverse lacerations of the urethra will leak urine, creating cellulitis of the soft tissues and possibly form a fistula with the skin or cavernosal tissues. In these cases, primary closure of the urethral defect with diversion of urine via a urinary catheter or proximal urethrostomy will decrease the chances of urethral stricture. If the wound is chronic in nature or grossly infected, it should be cleaned daily and topical antimicrobial ointment applied. In cases of severe, intractable penile injury, amputation may be best option.

Preputial Injuries

Like penile injuries, preputial lacerations are often the result of trauma. All but the most superficial of preputial lacerations should be closed primarily. Due to the ventral nature of the prepuce, open lacerations generally develop cellulitis and swelling. Closure of these lacerations prevents the horse from protruding the penis through the defect in the prepuce. In addition, second intention healing of the prepuce often results in a scarring which limits the ability of the horse to retract its penis into the sheath.

Penile Hematomas

Penile hematomas result from the rupture of the cavernosal tissues or from disruption of the subcutaneous vascular plexus. They frequently occur following a kick from a mare when breeding, a sudden movement of the mare during coitus or from mounting stationary objects. Bleeding occurs rapidly, with the penis and prepuce swelling markedly. Eventually, venous and lymphatic return as well as urination may be affected. Often, the horse is unable to retract the penis into the sheath and paraphimosis results.

In the acute phase, application of a pneumatic tourniquet may limit the degree of hemorrhage. The tourniquet is applied at distal end of the penis and worked proximally. The tourniquet may need to be re-applied as the swelling is reduced. The penis should be returned to the sheath and kept in place by means of a sling support or purse string suture in the prepuce. Hydrotherapy with a cold hose may also be beneficial. Emollient antimicrobial salve should be applied to the penis to prevent the skin from cracking and sloughing. In more chronic cases, the penis may be deviated due to the presence of the hematoma. The use of ultrasound to identify a hematoma in the subcutaneous tissues can aid in surgical evacuation of the hematoma. As with most chronic penile hematomas, the skin is usually too damaged to attempt a primary closure. Urethral patency should be checked in all cases to avoid bladder rupture.

Paraphimosis

Paraphimosis is defined as the inability of the horse to retract its penis into the sheath. It is caused by trauma (such as from a breeding accident), debilitation or illness, spinal cord disease, infectious disease (EHV1, rabies) or as a consequence to administration of phenothiazine tranquilizers or anesthetic agents. Continued protrusion of the penis causes edema, which in turn impairs venous and lymphatic return. Chronic paraphimosis results in fatigue and eventual atrophy of the retractor penis muscle, excoriation of the penile skin and cellulitis. Eventually, damage to the puedendal nerves with resulting fibrosis of the penis occurs. Urination is rarely impeded.

If treated aggressively in the acute stage, paraphimosis can resolve. Treatment is aimed at reducing the edema so as to prevent further damage and supporting the penis against the body wall or within the sheath. The penis should be washed with a gentle soap and an antibiotic-containing emollient applied to prevent cracking and drying of the skin. Silver sulfadiazine is an excellent emollient for this purpose. The following is a list of ingredients used at Texas A&M (Dr. Steve Brinsko) as an emollient:

• 1 lb lanolin

• 70 grams Terramycin

• 80 mg dexamethasone

Hydrotherapy can be performed daily to reduce the edema as well.

If the penis can be returned to the sheath, it should be held within the sheath by means of a purse string suture or sling. If the edema is extensive, the application of an Esmarch tourniquet beginning distally and working proximally can be helpful prior to returning the penis to the sheath. If the penis can not be replaced within the sheath, it should be compressed against the ventral abdomen via use of a belly bandage. Light exercise and a non-steroidal anti-inflammatory drug may also be helpful. Diligent and appropriate treatment in the acute phase of paraphimosis can be successful. Preputial scarring may be a sequlea to paraphimosis, which may require segmental posthetomy to correct. Failure of therapy generally results in phallectomy for most horses. Breeding stallions with paraphimosis often retain their libido despite their inability to achieve an erection. Some stallions with paraphimosis can ejaculate and may therefore be trained to collect with an artificial vagina.

Phimosis

Phimosis is defined as the inability of a horse to protrude its penis from the sheath. The causes may be congenital or acquired. Acquired conditions usually result from neoplasia of the penis or prepuce, adhesions between the penis and prepuce or constriction of the preputial orifice. Regardless of the cause, entrapment of the penis within the sheath results in significant urine scalding with subsequent tissue irritation which ppotentiatesfurther scarring. Treatment of phimosis is directed towards the surgical removal of the cicatrix.

Priapism

Defined as a persistent erection without sexual excitement, priapism occurs from a lack of detumescence of the erect penis. Priapism may result from a lack of venous outflow or from an increase in arterial inflow to the corpus carvernosum penis. Causes of priapism in horses include the administration of phenothiazine tranquilizers, general anesthesia and the presence of neoplasia in the pelvic canal. The goal of treatment is to restore venous drainage from the corporeal tissue. Benztropine mesylate (8mg, iv) may be given in the immediate acute phase to reverse the effects of acepromazine. Phenylephrine (10mg in 10 ml of saline) may be injected in to the corpus cavernosum penis directly to resolve priapism. Irrigation of the cavernosal tissues may be performed by placing 14gauge needles in the corpus cavernosum.

Surgical Methods for the Treatment of Penile Disorders

Segmental Posthetomy

Also known as reefing, segmental posthetomy is performed to remove neoplastic lesions on the penis. Lesions must not involve the underlying tunica albuginea. The procedure can performed with the horse standing using light sedation and a ring block proximal to the lesion. The penis is extended by placing a gauze ligature on the glans and applying traction. A standard aseptic prep is performed. Two parallel circumferential incisions are made into the skin and subcutaneous tissues. A longitudinal incision is made on either side of the lesion, connecting the circumferential lesion. The skin and associated lesion are dissected free, avoiding the branches of the external pudendal artery and vein. The skin edges are sutured using soft absorbable suture such as Vicryl.

Phallectomy

Phallectomy is generally regarded as a salvage procedure in stallions when there is irreparable penile damage. Indications for partial phallectomy of the horse include chronic paraphimosis, neoplasia, and stenosis of the distal aspect of the urethra. The procedure may be performed under general anesthesia or as a standing procedure in the sedated horse. Regardless of the method chosen, the technical challenges of phallectomy include closure of the cavernosal tissues and creation of a urethral stoma. Stallions should ideally be gelded several weeks prior to phallectomy. Broad spectrum antimicrobial prophylaxis and anti-inflammatories should be provided in the immediate post-operative period.

Methods of phallectomy for anesthetized horses include Williams', Scott's and Vinsot's techniques. In each case, the horse is placed in dorsal recumbency, a stallion catheter is passed up the urethra and the penis extended by a tying a roll gauze around the glans and applying traction. A tourniquet is applied distally. Following an aseptic prep, an incision is made on the ventrum of the penis. In Vinsot's technique, the incision is triangular in shape and removes the skin, bulsospongiosus muscle and the corpus spongiosum penis. The apex of the triangle is oriented towards the proximal portion of the penis. The urethra is opened and spatulated to the three sides of the triangular in the skin. A tourniquet consisting of umbilical t ape is then placed distal to the urethrostomy and the penis transected. The stump heals by second intention. Vinsot's technique may be also be performed in standing horses using a dorsal ring block on the penis.

In Williams' technique, the corpus cavernosum is compressed with large absorbable sutures following creation of a triangular urethrostomy. The apex of the triangle is placed at the distal apex of the penis. The cavernosal tissue compressed along the three sides of the triangle and the urethra is sutured to the skin in similar fashion. In Scott's technique, the cavernosal tissue is compressed in circular fashion and the urethra is spatulated on top of the compression sutures. In each of these methods, it is common for horses to hemorrhage during or at the end of urination for up to three weeks post-operatively.

A modification of Vinsot's technique has been developed for use in the standing sedated horse. The horse is restrained in a stock during the procedure. The tail was wrapped and reflected to the side of the horse with elastic gauze. An aseptic surgical prep consisting of betadine and water is applied to the perineum, penis and scrotum if the horse was a stallion. A urethrostomy is performed either at a subishcial location or more distally between the preputial ring and preputial orifice depending on the extent of penile damage. For horses that received a subischial perineal urethrostomy, the skin is desensitized by instilling mepivacaine HCl subcutaneously on the perineal raphe approximately 2-3 cm distal to the anus. The external portion of the penis is then desensitized with a subcutaneous ring block, using mepivacaine, proximal to the site of partial phallectomy. Horses that receive a distal urethrostomy receive only a penile ring block. A stallion catheter was inserted through the distal urethral orifice into the bladder to facilitate recognition of the urethra during the urethrostomy.

To perform a perineal urethrostomy, a 4-cm long, cutaneous incision is created on the perineal raphe, 2 to 3 cm distal to the ventral aspect of the anus. The incision is extended through the paired retractor penis muscles, the bulbospongiousus muscle, the corpus spongiosum penis, and urethral mucosa overlying the stallion catheter. A permanent urethral stoma is created by suturing the urethral mucosa to the edge of the skin incision with simple interrupted sutures of 2-0 PDS. Distal urethrostomies are created in similar fashion between the preputial ring and preputial orifice on the ventral aspect of the penis, approximately 3 cm proximal to the proposed site of penile amputation without the use of a tourniquet.

After creating the urethrostomy, the stallion catheter is removed, and a latex band was applied using a Callicrate Bander several centimeters proximal to the proposed site of amputation. The Callicrate Bander is comprised of a metal clamp that holds the two ends of the specialized latex tubing in a loop and a locktight clip that configures the latex tubing into a figure-of-eight pattern. The loop is inserted into the nose of the instrument with the crimp positioned seam-side up. The instrument has a ratchet mechanism that tightens the latex loop and a lever to deploy the crimp. The loop is connected to the ratchet mechanism of the instrument by placing the rubber washer on a cord in the loop between the crimp and the metal clap. The clip is held in place while the latex rubber band was pulled forward to expand the size of the loop. The band was then placed over the penis several centimeters proximal to the site of transection and one centimeter distal to the urethrostomy. The ratchet was tightened until the penis is maximally compressed. The crimp lever is deployed to maintain tension on the loop, and the bands are transected adjacent to the metal spool of the ratchet using the band cutter provided by the manufacturer of the device. The penis is transected 2 cm distal to the band. The bands are left in situ to cause necrosis of tissue distal to them. The site of amputation is left to heal by second intention after the band and necrotic segment of penis distal to it have sloughed.

En Bloc Resection

En bloc resection is used to remove the free portion of the penis, the internal and external lamina of the prepuce and the regional lymph nodes affected by neoplasia. The penis may be amputated and anchored to the body wall or retroverted between the hind legs. An elliptical incision is centered over the prepuce and a combination of blunt and sharp dissection is used to remove the penis from the body wall. The large vasculature in the area may be ligated with suture or with a Ligasure. The penis may be amputated using any of the previously described techniques. If the penis is sutured to the body wall with the tunica albuginea, the urethra should be opened and spatulated. If the penis is to be retroverted, it should be drawn through a 6 cm subischial incision and the tunica albuginea sutured to the subcutaneous tissues. If there is enough skin to close the defect primarily, drains may be placed and the skin closed. However, the incision may also be left open to heal by second intention.