Micropenis

Micropenis is a term used to describe a penis that is less than 2 standard deviations from the norm in the absence of any other visible pathology associated with underdevelopment of the penis (e.g. hypospadias, hermaphroditism).

The size of the penis is usually measured by pulling it from the base to the tip along the dorsal surface. The normal size of the penis in a newborn is about 3.5 cm. Micropenis - a penis less than 2 cm (2 SD less than normal).

Causes micropenis

The main growth of the penis begins in the second half of the intrauterine period. Therefore, in premature births, the penis of newborn boys will be shorter than that of full-term babies, but this does not mean that micropenis is present. Tuladhar et al. (1998) derived a formula for the relationship between penis length and gestational age for children born between the 24th and 36th weeks of pregnancy:

Penis length (cm) = 2.27 + 0.16 x weeks of pregnancy.

After birth, the dimensions change slightly until puberty, which is not due to the influence of sex hormones, but to general somatic growth. Tables of length standards depending on age have been developed.

Intrauterine synthesis of testosterone and its conversion to dihydrotestosterone are necessary for the normal development of the external genitalia of the male fetus. At the beginning of gestation, under the influence of hCG, which binds to the LH receptor, the initial differentiation and development of the genitals occurs. Approximately from the 14th week, the fetus's own hypothalamic-pituitary system is activated, therefore, with a defect in this system, the fetus's penis development occurs normally (since the main influence on the development is exerted by maternal hCG), but the penis will not grow, and a micropenis will develop. On the other hand, a violation of the development of the gonads, which occurs in the 7th-10th week of intrauterine development, will also lead to the absence of its growth. Thus, the main causes of underdevelopment are as follows:

• hypergonadotropic hypogonadism - a disorder of gonadal development (anorchism, Klinefelter syndrome, gonadal dysgenesis, Leydig cell hypoplasia, a consequence of a defect in the LH gene or LH receptor);
• defects in testosterone biosynthesis;
• deficiency of 17.20-lyase activity;
• 3beta-hydroxysteroid dehydrogenase deficiency (30-HSD);
• 17β-hydroxysteroid dehydrogenase deficiency;
• defect in dihydrotestosterone synthesis - 5a-reductase deficiency;
• androgen receptor insensitivity;
• hypogonadotropic hypogonadism (hypopituitarism, Kallmann syndrome, septo-optic dysplasia, idiopathic hypogonadotropic hypogonadism);
• familial form (men in the family have a small penis or micropenis in the absence of other disorders).

In addition to the above reasons, micropenis is found in various syndromic diseases and chromosomal defects (Prader-Willi syndrome, Barder-Biedl syndrome, Noonan syndrome, Robinow syndrome, Rud syndrome, CHARGE syndrome).

"False micropenis" - in obese patients, a shortening of the penis can be visually determined due to the overhanging fold of fat over its base - the so-called sunken penis.

Symptoms micropenis

When examining a patient with complaints of underdevelopment or micropenis, it is necessary to collect a family history: death in the neonatal period, short stature in the family, pathologies of the development of the external genitalia among relatives.

Diagnostics micropenis

Inspection and physical examination

The child's height is measured and the growth rate is determined. Any stigmas of dysembryogenesis or combined malformations of other systems are excluded.

If micropenis is combined with hypoglycemia in the neonatal period and growth retardation in older age, this requires the exclusion of hypopituitarism. Olfactory impairment allows one to suspect Kallmann syndrome (anosmia and hypogonadotropic hypogonadism, micropenis). The presence of developmental defects or stigmas of embryogenesis requires consultation with a geneticist to exclude chromosomal pathologies and other genetic syndromes.

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Laboratory and instrumental studies

Karyotyping and chromosomal analysis are indicated if chromosomal pathology and the presence of dysembryogenesis stigmas are suspected.

Determination of LH and FSH content: in the period from 1 to 2 months of life, their concentration corresponds to puberty, therefore, overestimated or underestimated values will indicate hypergonadotropic or hypogonadotropic hypogonadism (respectively). Testosterone, dihydrotestosterone. The T/DHT ratio in the sample with chorionic gonadotropin allows to exclude 5a-reductase deficiency.

Thyroid hormone levels, cortisol, IGF-1, glucose - studies are indicated if hypopituitarism is suspected, especially if a child with micropenis had an attack of hypoglycemia.

Treatment micropenis

It has been proven that testosterone therapy in children with its deficiency is effective and allows for the effective treatment of micropenis, increasing the size of the penis to generally accepted norms. Testosterone is used in various forms (gels, patches, injections). Bin-Abbas (1999) showed that a course of three testosterone injections of 25-50 mg at intervals of 4 weeks in infants allows for reference sizes to be achieved.

Surgical treatment of micropenis

If a true micropenis is present, phalloplasty is used.