Male genitalia

Angel K. Chen

The pediatric physical examination is not complete without a thorough evaluation of the developing genitalia. Routine surveillance of the genitourinary system is equally important in all patient encounters, and when assessment of the genitalia is performed routinely abnormalities can be identified and promptly treated. Many parents, children, and adolescents are concerned and anxious about the genitalia, yet may not feel comfortable expressing those concerns initially. A review of systems in the health history and the routine genital exam offer an opportunity for the parent, child, and/or adolescent to voice concerns, and for the health care provider to offer reassurance and education on normal development. The provider has a role in fostering dialogue between the parent and child regarding reproductive health. Establishing this dialogue early with families forms the basis for healthy discussions on reproductive health during puberty and in the developing adolescent.

Embryological development

The differentiation of the sexual organs begins as early as the third week of embryonic development, dictated by the sex chromosomes at the time of fertilization.¹ The mesoderm is the embryonic layer that becomes smooth and striated muscle tissue, connective tissue, blood vessels, bone marrow, skeletal tissue, and the reproductive and excretory organs. As proliferation of the embryonic layers continues, maturation of the external genitalia in the fetus is established by the twelfth week.¹ The sex-determining region of the Y chromosome (SRY gene) activates the differentiation of the embryonic gonad into a testis, without which the gonad would become an ovary. The antimüllerian hormone (AMH) prevents development of the uterus and fallopian tubes, whereas testosterone stimulates the wolffian ducts to develop into the male reproductive structures, including the epididymis, vas deferens, and seminal vesicles. Testosterone is also the precursor to dihydrotestosterone (DHT), which stimulates the formation of the male urethra, prostate, and external genitalia.¹

Urine production begins between the ninth and twelfth weeks and is excreted into the amniotic cavity through the urethral meatus. During development, the fetus continues the production and excretion of urine, which forms the amniotic fluid. Between the seventeenth and twentieth weeks, the testes, which develop in the abdominal cavity, begin to descend along the inguinal canal into the scrotum, bringing the arteries, veins, lymphatics, and nerves that are encased within the cremaster muscle and spermatic cord.¹ The inguinal canal closes after testicular descent. Incomplete or abnormal embryonic development of the inguinal canal predisposes the newborn to the formation of hydroceles or hernias. Preterm infants are at increased risk for these conditions. At birth, the infant’s genitourinary system is functionally immature with limited bladder capacity, inability to concentrate urine sufficiently and frequent voiding.

Growth of the fetus and differentiation of the sexual organs can be affected by placental function, the hormonal environment during pregnancy, maternal nutrition, maternal infection, and genetic factors or chromosomal abnormalities. A fetal insult from intrinsic or extrinsic factors during the eighth or ninth week of gestation may lead to major abnormalities of the developing external genitalia. The impact of endocrine-disrupting chemicals on the development of the endocrine and genitourinary system is reviewed in Chapter 5.

Anatomy and physiology

Penis

The penis consists of the shaft, glans, corona, meatus, and prepuce. The shaft is composed of erectile tissue called corpora cavernosa (two lateral columns) and corpus spongiosum (ventral column). The anterior portion of the corpus spongiosum forms the glans penis, the border or edge of which is called the corona. The urethra is within the corpus spongiosum, and the orifice, or urethral meatus, is the slitlike opening just ventral to the tip of the penis (Figure 15-1).

FIGURE 15-1 Internal and external genitalia. (From Seidel HM et al: Mosby’s guide to physical examination, ed 7, St. Louis, 2011, Mosby.)

The prepuce, or foreskin, is the fold of skin at the tip of the penis that covers the glans penis in the uncircumcised male and forms the secondary fold of skin from the urethral meatus to the coronal region of the penis called the frenulum. The skin of the penis is thin, does not contain subcutaneous fat, and is loosely tied to the deeper layer of the dermis and fascia. Often, the skin of the shaft is more darkly pigmented, particularly in children or adolescents with darker pigmentation or darker skin. The skin of the glans penis does not contain hair follicles, but does have small glands and papillae that form in the epithelial cells to produce smegma, the white oily material made up of desquamated epithelial cells trapped under the foreskin, which is normal and often mistaken as pathological ² (Figure 15-2). The foreskin is generally nonretractable at birth, because of adherence of the inner epithelial lining of the foreskin and glans.²^,³ Desquamation of the tissue layers continues until the separation of the prepuce and glans penis is complete secondary to intermittent erections and keratinization of the inner epithelium, generally by 5 to 6 years of age. Partial adhesions of the foreskin to the prepuce may produce smegma along the coronal region, which often persists throughout childhood.

FIGURE 15-2 Smegma. (From Godbole P: General paediatric urology, Surgery (Oxford) 26(5):223-227, 2008.)

Scrotum and testes

The scrotum is made up of a thin layer of skin that forms rugae (folds) and contains the testes. The epididymis is the thin palpable structure along the lateral edge of the posterior side of the testes. Sperm production occurs within the seminiferous tubules in the testes, which connect to the epididymis. The vas deferens is the cordlike structure that is continuous with the base of the epididymis and stores sperm. The spermatic cord extends from the testes to the inguinal ring and is felt only on deep palpation of the testicular sac. The right spermatic cord is shorter in some males, which causes the right testis to hang higher than the left.

The male accessory organs include the seminal vesicles, which lay deep in the abdominal cavity alongside the vas deferens and secrete liquid into the semen as it passes from the testes. The opening of the seminal vesicles joins the vas deferens to form ejaculatory ducts and drains to the posterior urethra. The Cowper glands, or bulbourethral glands, lie along the urethra in the male genitalia. These are exocrine glands that produce a viscous secretion that lubricates the urethra for the passage of sperm. It also neutralizes the acidic urethral secretions that could otherwise damage the spermatozoa in the semen. The prostate gland is the small, firm mass that lies within the pelvic cavity. It first becomes palpable on manual examination in the adolescent male. The prostate gland surrounds the posterior urethra and secrets an alkaline secretion during ejaculation to promote fertilization. The smooth muscle within the prostate gland assists with urinary elimination. An enlarged prostate gland may cause urinary obstruction.

Physiological variations

Table 15-1 presents the physiological variations of the male genitalia in the pediatric age-group from infancy to early childhood.

TABLE 15-1

Physiological Variations of the Male Genitalia

Age-Group	Variation
Preterm infant	Rugae absent on scrotum in low birth weight infant Testes undescended in ∼20% of infants weighing <2500 g*
Newborn	Rugae present from 37 weeks’ gestation Note and evaluate any discoloration of scrotum at birth Testis: volume 1 to 2 ml Length of penis in term infant: 2.5 to 3.5 cm; size should be palpated during exam Shaft may appear short or retracted in infants with significant suprapubic fat pad
Infancy/early childhood	Foreskin partially retractable over glans penis Testes present in scrotal sac Initial sexual arousal and erection occur with normal sexual exploration or exposure of genitalia

^*Data from Thureen PJ, Hall D, Deacon J, Hernandez JA: Assessment and care of the well newborn, ed 2, Philadelphia, 2005, Saunders.

Physiological changes in puberty

Puberty has a gradual onset and although it is marked by a growth spurt, it may be difficult to ascertain when the first changes in the male begin in the transition to secondary sexual characteristics (Figure 15-3). In males, sexual development, or true gonadal activation, begins with an increase in size of the testicles, which is often difficult to determine. Testicular volume should be evaluated and is the most accurate measurement of the progression of puberty in the developing male. In some boys, this begins around 10 years of age and is complete in about 3 years, with the normal range extending to 5 years.⁴ The sexual maturity rating (SMR) scale, also known as Tanner stages, helps to classify physical pubertal maturation⁴ (Figure 15-4 and Table 15-2). Genital development and pubic hair may develop at different rates. Ejaculation usually occurs at SMR 3 during the midpoint of sexual development. Fertility is established by SMR 4, although sperm are present in some quantity with ejaculation during SMR 3.

TABLE 15-2

Developmental Changes in Puberty