550 CHAPTER 15 Pediatric urology

Hypospadias

Definition

Hypospadias is a congenital deformity in which the opening of the urethra (the meatus) occurs on the underside (ventral) part of the penis, anywhere from the glans to the perineum. It is often associated with a hooded foreskin and chordee (ventral curvature of the penile shaft).

It occurs in 1 in 250 live male births. There is an 8% incidence in offspring of an affected male, and a 14% risk in male siblings.

Classification

Hypospadias can be classified according to the anatomical location of the urethral meatus (Fig. 15.4).

•Anterior (or distal)—glandular, coronal, and subcoronal (~50%)

•Middle—distal penile, midshaft, and proximal penile (~30%)

•Posterior (or proximal)—penoscrotal, scrotal, and perineal (~20%)

Etiology

Hypospadias results from incomplete closure of urethral folds on the underside of the penis during embryological development. This is related to a defect in production or metabolism of fetal androgens, or the number and sensitivity of androgen receptors in the tissues.

Chordee is caused by abnormal urethral plate development, and the hooded foreskin is due to failed formation of the glandular urethra and fusion of the preputial folds (resulting in a lack of ventral foreskin but an excess of dorsal tissue).

Diagnosis

A full clinical examination will make the diagnosis. However, it is also important to seek out associated abnormalities that will need treatment (undescended testes, inguinal hernias, and hydroceles).

Patients with absent testes and severe hypospadias should undergo chromosomal and endocrine investigation to exclude intersex conditions.

Treatment

Surgery is indicated where deformity is severe, interferes with voiding, OR is predicted to interfere with sexual function. Surgery is now performed between 6 and 12 months of age. Local application of testosterone for 1 month preoperatively can help increase tissue size.

The aim of surgery is to correct penile curvature (orthoplasty), reconstruct a new urethra, and bring the new meatus to the tip of the glans using urethroplasy, glanuloplasty, and meatoplasty techniques.

Severe cases may require staged procedures. Common operations for anterior hypospadias include meatal advancement and glanuloplasty (MAGPI), meatal-based flaps (Mathieu procedure), and tubularization of the urethral plate.

Posterior defects require free grafts (buccal mucosa), on-lay grafts, and preputial transfer flaps.

HYPOSPADIAS 551

Complications

These include bleeding, infection, urethral strictures, meatal stenosis, urethrocutaneous fistula, urethral diverticulum, and failed procedures requiring reoperation.

Anterior Glanular

(Distal) Coronal Subcoronal

Distal penile

Middle Midshaft

Proximal penile

Penoscrotal

Posterior Scrotal (Proximal)

Perineal

Figure 15.4 The anatomical classification of hypospadias according to the location of the urethral meatus. This figure was published in Walsh PC, et al. Campbell’s Urology, 8th Edition, p. 2287. Copyright Elsevier 2002.

552 CHAPTER 15 Pediatric urology

Normal sexual differentiation

Sexual differentiation and gonadal development is determined by the sex chromosomes (XY male, XX female). The gonads produce hormones that influence the subsequent differentiation of internal and external genitalia (Figs. 15.5 and 15.6).

Both sexes

Gonads develop from the genital ridges (formed by cells of the mesonephros and coelomic epithelium). At 5–6 weeks, primordial germ cells migrate from the yolk sac to populate the genital ridges. Primitive sex cords are formed, which support germ cell development.

From 4 weeks, the mesonephric (Wolffian) ducts are incorporated into the genital system, when renal function is taken over by the definitive kidney. At 6 weeks, coelomic epithelium creates the paramesonephric (Müllerian) ducts, which develop laterally and are fused to the urogenital sinus at their bases.

Males

The testis-determining gene (SRY) is located on the Y chromosome and stimulates medullary sex cords in the primitive testis to differentiate into Sertoli cells, which produce Müllerian inhibiting substance (MIS) at 7–8 weeks. This triggers regression of the paramesonephric ducts, testosterone secretion from Leydig cells of the testis, and the initial phase of testicular descent.

During weeks 8–12, mesonephric ducts differentiate into epididymis, vas deferens, seminal vesicles, and ejaculatory ducts. The prostate is formed from mesenchyme (capsule) and urethral endoderm.

After week 23, the testes rapidly descend from the abdomen (via the inguinal canal during weeks 24–28) and into the scrotal sac, guided by the gubernaculum. The scrotum is created by fusion of labioscrotal folds.

Testosterone and dihydrotestosterone (DHT) androgens are responsible for masculinization. DHT is made from testosterone by 5-D-reductase enzyme in the tissues.

Development of the external genitalia occurs from week 7. Urogenital folds develop around the opening of the urogenital sinus, and labioscrotal swellings form either side. The penile shaft and glans are formed by elongation of the genital tubercle and fusion of urogenital folds.

Incomplete production or activity of DHT in the male fetus will result in incompletely virilized male genitalia.

Females

The genital ridge forms secondary sex cords (primitive sex cords degenerate) that surround the germ cells to create ovarian follicles (week 15). These undergo meiotic division to become primary oocytes, which are later activated to complete gametogenesis at puberty.