Persistent Penile Frenulum

During fetal development, the epithelial surfaces of the penis and prepuce are attached by a single lamina of ectodermal cells that is incomplete ventrally. Here, a thin band of connective tissue, the frenulum, unites the penis and prepuce. Androgens secreted by the developing fetal testes cause the lamina to split, forming the preputial cavity. This normally occurs in the fetus or neonate, depending on the species. Androgens may cause thinning but not rupture of the frenulum; rupture of the frenulum is thought to result from mechanical stress early in life. Failure of the frenulum to rupture results in the persistence of a band of connective tissue extending from the ventral tip of the glans penis to either the prepuce or the ventral surface of the penis itself, causing a ventral or lateral deviation of the tip of the glans penis.

Persistent penile frenulum is usually identified during the physical examination of a puppy that has been brought in for its first vaccinations (Fig. 28-1). Owners may also complain that the puppy urinates on its back feet or in other unexpected directions, which may cause secondary dermatitis of the rear leg from urine scald. Additional clinical signs may include inability to extrude the penis from the prepuce during penile engorgement, discomfort or pain with penile engorgement, and repeated licking of the preputial area. If the problem is not identified, the dog may associate pain with sexual excitement and secondarily develop reduced libido and unwillingness to mate.

FIGURE 28-1 Persistent penile frenulum, causing deviation of the distal portion of the penis in a 3-month-old Lhasa Apso. The dog was presented for treatment for urinating in unexpected directions.

A diagnosis of persistent penile frenulum is made by identifying the abnormal band of tissue during visual examination of the penis and prepuce. The frenulum is usually avascular and can easily be transected with a scalpel blade after application of a topical anesthetic. Genetic implications for persistent penile frenulum are unknown, although Cocker Spaniels have been most commonly cited in the literature (Johnston et al, 2001).

Penile Hypoplasia

Penile hypoplasia is a rare disorder that has been reported in the Cocker Spaniel, Collie, Doberman Pinscher, and Great Dane (Johnston, 1989). Penile hypoplasia is a component of some intersex states (see page 893) and may be one of several reproductive abnormalities identified on physical examination. An abnormal karyotype has been identified in some animals with penile hypoplasia. A decrease in penile size may also occur in dogs castrated at an early age. Salmeri and colleagues (1991) found mixed breed dogs castrated at 7 weeks of age had immature genitalia, characterized by significantly smaller penile diameter, decreased size and radiodensity of the os penis, and immaturity of the prepuce, compared with male dogs castrated at 7 months of age or left intact. The mean penile diameter of the dogs castrated at 7 weeks of age was approximately half the penile diameter of the intact dogs; the penile diameter in dogs castrated at 7 months was intermediate between the other two groups.

Penile hypoplasia is usually asymptomatic and an incidental finding on physical examination. Urine pooling and infection inside the prepuce may develop if the dog also has a hypoplastic preputial opening (see page 954). The diagnosis of penile hypoplasia is based on physical examination. If it is identified, intersexuality should be suspected, and karyotyping (see page 893) may be indicated. No treatment is necessary in the asymptomatic dog. Enlargement of the preputial opening and surgical shortening of the prepuce may be necessary if urine pooling and infection are problems.

Hypospadias

Hypospadias is a congenital urogenital defect involving the external genitalia of males. It is characterized by an abnormal termination of the urethra ventral and posterior to the normal opening at the tip of the glans penis. Hypospadias is categorized as glandular, penile, scrotal, or perineal, depending on where the urethra opens (Hayes and Wilson, 1986). The perineal form is the most common and may represent a form of pseudohermaphroditism (see page 897). Hypospadias results from failure of fusion of the genital folds or genital swelling (or both) during fetal development, which may also cause abnormal development of the penis, prepuce, and/or scrotum. A short or deviated penis, malformed os penis, incomplete preputial closure, defects in the development of the scrotum, and other urogenital anomalies have been identified in dogs with hypospadias (see Fig. 24-14, page 898).

In addition to the visual abnormalities, clinical signs may include those related to urinary tract infection (e.g., dysuria, hematuria), urinary incontinence, and urine scalding. The diagnosis of hypospadias is made on visual inspection of the external genitalia and by catheterization of the urethra. The type of surgical correction required, if any, depends on the location and severity of the congenital defect. A thorough evaluation of the urogenital system should be completed before surgical correction is considered, because identification of additional abnormalities may alter the therapeutic plan. Penile amputation, ostectomy of the os penis, scrotal or perineal urethrostomy, or other reconstructive surgery may be necessary. Castration should always be performed because of the likely genetic implications of hypospadias, especially when the condition is present in conjunction with other developmental abnormalities (e.g., intersexuality, cryptorchidism). A familial occurrence in the Boston Terrier has been suggested (Hayes and Wilson, 1986).

Congenital Deformity of the Os Penis

Deformity of the os penis may result in deviation of the penis and, depending on the severity, inability to retract the penis fully into the preputial sheath. Some males are predisposed to urethral obstruction. Persistent exposure of a portion of the glans penis to the environment may result in desiccation, trauma, and necrosis of exposed tissue. Mild deformities of the os penis (e.g., bends or excessive shortness) may result in misdirected copulatory efforts, inability to achieve vaginal penetration, and apparent infertility.

Treatment depends on the severity of the deformity and the intended use of the dog. Severe deviations may require fracturing and straightening of the os penis. An excessively shortened or deviated os penis that impairs the dog’s ability to copulate may necessitate the use of artificial insemination if breeding is desired. Therapy is probably not indicated if the dog is not intended for breeding and if paraphimosis or dysuria is not present.

Duplication of the Penis

Penile duplication (diphallia) is an extremely rare congenital anomaly that has been reported in a 5-month-old Pointer, a 6-month-old Poodle-cross, and a 5-month-old mixed breed dog with concurrent polymelia (Johnston, 1989; Zucker et al, 1993). All these dogs had multiple anomalies of the urogenital system (e.g., hydronephrosis, cryptorchidism, duplication of the urinary bladder and prostate gland). Diphallia may result from anomalous longitudinal duplication of the cloacal membrane, followed by ventral migration of primitive streak mesoderm around two cloacal membranes to form two genital tubercles. The diagnosis is made by visual inspection. There is no treatment.

Phimosis

Phimosis is the inability of the male dog to extrude the penis from the prepuce as a result of an abnormally small preputial orifice. Phimosis may be a congenital abnormality (i.e., congenital preputial stenosis, intersex dogs), or it may occur secondary to inflammation, edema, neoplasia, or scar tissue formation after trauma, chemical irritation, or infection.

The clinical signs depend on the severity of the defect. Complete congenital occlusion of the preputial orifice obstructs urinary outflow, resulting in neonatal death. Small openings may interfere with urination and cause accumulation of urine in the preputial cavity. Constant urine dribbling, an abnormal stream of urine during micturition, perpetual preputial swelling, and secondary bacterial infections and balanoposthitis may develop. More commonly, phimosis interferes with the extrusion of the penis during mating. Inability to copulate is quickly obvious. Pain may be associated with mating behavior, resulting in decreased libido.

The clinician can make the diagnosis relatively easily in severe cases by simply demonstrating that the flaccid penis cannot be extruded from the prepuce. Observation of the male during sexual excitement may be required to obtain a diagnosis if the phimosis interferes with extrusion of the penis only during periods of engorgement.

Any predisposing factors should be corrected in dogs with acquired phimosis. The need for surgical intervention to widen the preputial orifice depends on the severity of the phimosis and the intended use of the dog. Therapy is probably not indicated in an asymptomatic dog not intended for breeding. Surgical reconstruction of the preputial orifice is indicated if the phimosis interferes with urination or with extrusion of the engorged penis in a dog intended for breeding. Congenital preputial stenosis has been observed in a litter of mixed breed dogs and in multiple related Golden Retriever litters, which suggests that this condition may be heritable (Johnston, 1989).

Paraphimosis

Paraphimosis is the presence of an engorged or edematous penis that cannot be retracted into the preputial sheath (Fig. 28-2). Interference with venous drainage of the cavernous tissues during engorgement results in progressive enlargement of the glans penis, interference with circulation to the penis, exposure desiccation, ischemic necrosis, and eventually the development of urethral obstruction and gangrene. Paraphimosis is most commonly associated with coitus, in which preputial hairs become entangled around the base of the glans penis, forming a restrictive band, or the protruding penis becomes trapped as the preputial orifice adheres to the penis and is pulled into the preputial cavity when the erection subsides. Other causes of paraphimosis include mild phimosis, foreign objects (e.g., rubber bands), fracture of the os penis, chronic priapism (i.e., penile engorgement without associated sexual excitement), trauma, neoplasia, and chronic balanoposthitis (Greiner and Zolton, 1980).

FIGURE 28-2 Postcoital paraphimosis in a 4-year-old German Shepherd dog. Paraphimosis developed after preputial hairs around the glans penis became entangled.

Other conditions may result in chronic exposure of the glans penis and may be mistaken for paraphimosis. These include paralysis of the retractor penis muscle, congenital deformation of the os penis, an abnormally large preputial opening, or congenital shortening of the prepuce (Fig. 28-3). These conditions can be differentiated from paraphimosis by the lack of an engorged penis and the length of time the problem is observed (i.e., chronic condition).

FIGURE 28-3 Congenitally shortened prepuce, resulting in persistent exposure of the glans penis. The lack of engorgement of the penis and the chronic nature of this problem help differentiate it from paraphimosis.