Alastair R. Coomer, BVSc, MS, DACVS
Veterinary Specialist Group @ Unitec, Mt. Albert, Auckland, New Zealand
Elective, or non-elective, castration (neuter, orchiectomy etc.) is by far the most common surgical condition of the male genital tract you will encounter in practice. All other conditions mentioned here are uncommon, but important to identify accurately.
Most urogenital conditions and procedures involve small, delicate tissues, where meticulous surgical technique is essential. Therefore, I wear magnifying surgical loupes for all urogenital surgery. Loupes are expensive, but they make microsurgery appear like macrosurgery. Equally important is the value of an E-collar. Even the best surgery can be undone in an instant by a curious pet. Therefore $10–30 invested in an E-collar, placed at the time of anaesthetic recovery, is the most valuable part of any urogenital surgery.
The penis is divided into three distinct regions: the root, the body and the glans. The root is attached to the tuber ischii by the left and right crura. Each crus is composed of the respective corpus cavernosum and associated ischiocavernosus muscle. The body of the penis extends from the confluence of the crura to just beyond the proximal end of the os penis, and is composed predominantly of corpus cavernosum and corpus spongiosum. The corpus spongiosum surrounds the penile urethra, which lies ventral to the os penis. The glans penis is divided into the bulbus glandis and the pars longa glandis. The bulbus glandis surrounds the proximal part of the os penis and has the greatest potential for expansion.
The rigid axis of the glans penis is supported by the os penis. The penile urethra lies within the urethral groove, along the ventral aspect of the os penis. Because the urethra within the urethral groove cannot expand to the same degree as the remaining penile urethra, uroliths often lodge at the proximal entrance to the groove.
The primary blood supply to the penis is provided by three branches of the artery of the penis, which arises from the internal pudendal artery. These branches are the artery of the bulb, the deep artery of the penis and the dorsal artery of the penis. All branches of the artery of the penis anastomose with one another. Venous drainage occurs through the internal and external pudendal veins. Innervation of the penis is supplied by the paired pudendal nerve and pelvic nerve, which arise from the pelvic and sacral plexuses.
The prepuce is a complete tubular sheath that covers the, non-erect, glans penis. It is attached to the skin of the ventral abdominal wall and consists of external and internal laminas, which are continuous at the ostium preputiale. The preputial muscle is a small strip of cutaneous trunci muscle, which maintains preputial coverage of the glans penis. The blood supply to the prepuce is derived from the dorsal artery of the penis, the external pudendal artery and the caudal superficial epigastric artery.
Priapism is the presence of a persistent erection, without sexual excitement. Parasympathetic stimulation of the penis via the pelvic nerve normally results in penile erection. Therefore, spinal cord injury, thromboembolic occlusion or mass effect in the sublumbar region can result in priapism.
Importantly, priapism must be differentiated from paraphimosis (see later). This can easily be done, as the penis can be replaced into the prepuce with priapism. Accurate diagnosis of the underlying cause of priapism is the best step in defining appropriate treatment. Many cases will resolve spontaneously, and penile amputation is therefore overkill/unnecessary in these cases! When used to treat refractory priapism, penile amputation should be complete, and be combined with scrotal ablation and scrotal urethrostomy.
Phimosis is the inability to extrude the penis from the prepuce, and is almost exclusively associated with an abnormally small preputial orifice. The most common cause of (temporary) phimosis, in my experience, is an accumulation of debris (uroliths, smegma, preputial hair etc.) at the preputial orifice. This is obviously very easy to treat symptomatically.
Permanent phimosis may be acquired secondary to trauma/fibrosis, inflammation, oedema, neoplasia, or infection. Congenital phimosis can be present in dogs with preputial stenosis or intersex states. We see a few kittens every year, referred for congenital phimosis. While congenital phimosis has been reported once in a cat, I don't think this condition is actually congenital. Rather, I have seen about a dozen kittens (4–10 weeks of age) that have suffered severe preputial trauma secondary to exuberant and misdirected suckling from their littermates. This inflammation results in granulation tissue formation at the preputial orifice, and subsequent preputial contraction/stricture and phimosis. In these cases, the urethral orifice and distal penis are often incorporated in the scar tissue.
In either cats or dogs, phimosis is readily treated with surgical enlargement of the preputial orifice. In dogs, a triangular, full-thickness, wedge of preputial skin-to-mucosa is resected from the craniodorsal aspect of the preputial orifice, and each side of the resection is then sutured to itself to recreate the mucocutaneous junction. The wedge is oriented dorsally, to prevent inadvertent paraphimosis, which can occur with ventral wedge resections. The surgical technique is similar for kittens, though I make a circumferential excision, rather than a wedge.
Paraphimosis is the inability to retract the penis into the preputial sheath. Congenital paraphimosis can result from preputial hypoplasia, and a small preputial orifice with a short prepuce. Acquired paraphimosis can result from constriction of the preputial orifice with hair etc., trauma, masturbation, coitus, and venous occlusion of the cavernous tissues with persistent glans engorgement.
Paraphimosis is an emergency, and should be treated seriously. Inappropriate management can ultimately require penile amputation due to ischaemia, gangrenous necrosis, self-trauma or urethral occlusion. The goal of treatment is to reduce the size of the penis, allowing it to be replaced into the prepuce. This can be achieved in a number of ways, including sedation with acepromazine, lubrication of the penis, removal of preputial debris, placing hygroscopic agents (mannitol/sugar) on the penis, and gentle massage.
If reduction of paraphimosis cannot be readily achieved, urethral catheterization and surgical correction is indicated. As stated previously, penile amputation is necessary only for cases with severe penile damage. That said, penile amputation is very effective at preventing recurrence of paraphimosis! More common surgical techniques include castration, narrowing of the preputial orifice (temporary with a purse-string suture, or permanent), enlargement of the preputial orifice or preputial lengthening/advancement.
Phallopexy creates a permanent adhesion between the dorsal preputial mucosa and the dorsal surface of the penile shaft. This adhesion thereby prevents paraphimosis and penile trauma. A lateral incision is made through the prepuce, at the junction of the body wall and the prepuce. Through this incision, a linear section of dorsal preputial mucosa is resected. A similar incision is made on the dorsal surface of the penis (be careful - this incision only needs to be superficial!), either through the preputial approach, or by extruding the penis through the preputial orifice. The penile and preputial mucosae are then apposed, beginning at the cranial extent of the incisions to ensure that the penis cannot be extruded from the preputial orifice. Layered appositional closure of the lateral preputiotomy completes the procedure.
Preputiotomy is often used in conjunction with other surgical procedures for the correction of paraphimosis, or to assist with partial penile amputation. Preputiotomy can be performed laterally (as described above) or cranially via either dorsal or ventral approaches. During layered appositional closure, the preputial orifice can be reconstructed to achieve a larger or smaller opening (as desired).
Advancing the prepuce cranially, with the penis normally being tethered caudally by the bulbospongiosus and ischiocavernosus muscles, can be used to treat paraphimosis and preputial hypoplasia. A crescent-shaped piece of ventral abdominal skin and underlying preputialis muscle, are excised. The base of the crescent is located adjacent to the preputial orifice. While this technique has been reported with fair success, I have had poor results due to relaxation of the advancement over time. Further, care must be taken not to damage the preputial vessels during dissection.
Partial Penile Amputation
Partial penile amputation is only indicated for treating paraphimosis that is refractory to all other treatments, and in cases with severe/irreversible damage to the penis. In these cases, the extent of amputation is dictated by the amount of damaged tissue, or the minimum amputation necessary to ensure the penis cannot be extruded from the prepuce.
Persistent Penile Frenulum
During development, it is normal for the penis to be fused ventrally with the prepuce. This adhesion can persist until puberty in cats and dogs, and is relatively simple to treat. Because the adhesion is mostly avascular fibrous tissue, sharp transection of the frenulum will rapidly release the tethering effect, and does not bleed much. Cocker spaniels, Pekinese and miniature poodles are over-represented.
Any soft-tissue or cutaneous neoplasm can occur at the prepuce, and being a mucocutaneous junction, the prognosis is often worse for this location compared to others. Most infamous, and common, is preputial mast cell tumour (MCT). Because wide excision is required for surgical treatment, total/penile amputation may also be necessary, to ensure the penis remains covered by preputial mucosa.
Tumours of the penis come in all shapes and sizes, and include both malignant and benign neoplasia. As with all masses, accurate local diagnosis should be achieved with impression or aspiration cytology, or with local tissue biopsy. Further, these animals (usually dogs) should be staged for metastatic disease with abdominal ultrasound and thoracic radiographs (at a minimum). Based on these findings, and honest consultation with the owners, partial or complete penile amputation may be considered as either a palliative or curative-intent surgery.
Although rare, I have also seen osteosarcoma of the os penis, and osteomas and chondrosarcomas are also reported.
Because the penis and prepuce are in a superficial and dependent location, they are susceptible to trauma. Trauma can obviously vary widely in magnitude, and the recommended treatment can vary from conservative management (for small lacerations), to penile amputation. Haemorrhage is of immediate concern with most penile injuries, and can be controlled with sedation (to reduce excitement), a temporary tourniquet, or by suturing the tunica albuginea. If the urethra is also lacerated, it must be repaired (if transected) or catheterized for ~ 10 days (if lacerated longitudinally).
Small and minimally displaced fractures of the os penis can be managed conservatively, as long as the penile urethra is patent. In any case with urethral obstruction, or severe displacement of the fracture fragments, the os penis must be stabilized. The easiest way to achieve this is with an indwelling urethral catheter, but small (mini) bone plates can also be used in large dogs.
Hypospadias is a congenital defect whereby the urethral meatus opens at a location caudal and ventral to the normal urethral orifice. It can occur anywhere along the length of the penis, and results from failure of the urogenital folds to fuse. Hypospadias are classified according to the location of the urethral meatus, as either glandular, penile, scrotal or perineal. This condition can also occur concurrent with other penile malformations.
Depending on the location and severity of the hypospadias, these deformities may be incidental findings, or related to (and causing) recurrent urinary tract infections. Very small and incidental hypospadias rarely justify treatment. In dogs with urine scald, UTI's, incontinence or self-trauma, surgery should be considered. Surgery involves amputation of all urogenital tissue distal/cranial to the scrotum, reconstruction of the perineal urethra (as necessary), scrotal urethrostomy and castration.
All the surgical conditions of the male genitourinary tract are both fascinating, and at times challenging. With adequate haemostasis, instrumentation and visualization, these surgeries can also be very rewarding.
References are available upon request.