Micropenis: what is it, causes, symptoms, treatment

What is micropenis?

Micropenis(micropenia) is the unusually small size of the male penis. The general criterion is the dorsal (measured from above) length of the erect penis that is at least 2.5 standard deviations less than the average size of a human penis, or less than about 7 cm (2 3⁄4 inches) for an adult compared to an average erection of 12.5 cm (5 inches). Micropenia is usually recognized shortly after birth. This term is most often used in medicine, when the rest of the penis, This term is most often used medically when the rest of the penis, scrotum and perineum are not abnormal, For example, hypospadias. Micropenis occurs in about 0.6% of men.

Causes and risk factors

In humans, the chromosomal sex combination is defined at fertilization as either female (XX) or male (XY). At the beginning of the fetus's life, the embryo has both a mesonephric duct (male) and a paramesonephric (female). Depending on the presence or absence of a gene 

SRY (located on the Y chromosome) regression or development of one of these ducts will continue during organogenesis. Gene SRY stimulates the differentiation of the gonads into testicular tissue. At this early stage of development, the testes release three hormones that are very important in the process of male sexual differentiation:

• Anti-Müllerian hormone (AMH): a regression function for the development of paramesonephric ducts.
• Testosterone: a function that stimulates the development of the mesonephral duct into the internal male structures (seminal vesicle, vas deferens and epididymis).
• Dihydrotestosterone (DHT): Stimulates the growth of male sexual characteristics (maturation of the scrotal sac, increase in penile length and testicular size).

Under the influence of these three hormones, the male reproductive and genitourinary systems begin to develop at the end of the third third of the first trimester (8 to 12 weeks of gestation). Human chorionic gonadotropin (hCG) stimulates Leydig cells to secrete testosterone. Further intrauterine metabolism converts testosterone to dihydrotestosterone. The high level of fetal androgens in the second trimester further accelerates the growth of the penis. In the postpartum period, the further development of male sexual characteristics occurs under the influence of hormones regulated by the hypothalamic-pituitary system (gonadotropin-releasing hormone (GnRH), follicle-stimulating hormone (FSH) and luteinizing hormone (LH)). The highest postnatal androgen levels are observed between the first and third months of life. Signs of under-virilization and micropenis usually result from a violation of any of these stages. This distribution can occur in any of the following cases:

• Kallman syndrome (hypogonadotropic hypogonadism, osteoporosis, hearing impairment and anosmia);
• hypopituitarism (hypoglycemia, hypogonadotropic hypogonadism and growth disorders);
• Prader-Willi syndrome (hypotension, obesity, mental retardation, undescended testicles, micropenis, small arms and legs);
• growth hormone deficiency;
• androgen receptor defect and / or resistance;
• anorchia (absence of testicles);
• Klinefelter syndrome (47, XXY syndrome) (small testicles, infertility, gynecomastia, poor coordination and reading difficulties);
• trisomy of chromosomes 8,13,18 and 21;
• Noonan syndrome (hypertelorism, short neck, low-set ears, skeletal malformations, bleeding disorders and pulmonary valve stenosis);
• dysgenesis of the gonads;
• deficiency of 5-alpha-reductase;
• rare types congenital adrenal hyperplasia (deficiency of steroidogenic acute regulatory protein (STAR), 3-beta-hydroxysteroid dehydrogenase (3β-HSD), 17-α-hydroxylase);

In some cases, the etiology of the micropenis remains unclear even after extensive examination.

Epidemiology

The incidence of micropenis is about 1.5 per 10,000 male newborns. Studies show a small statistical difference in the average length of the penis between white newborns - 2.6 cm, East Indian - 2.5 and Chinese - 2.3.

Diagnostics

The clinical diagnosis of a micropenis is often made after a detailed history and physical examination. Once the diagnosis is made, further testing is needed to identify associated abnormalities and possible etiology.

A detailed maternal history is the first step in assessing the micropenis. Consanguinity and family history of ambiguous genitalia make hereditary conditions more likely on the differential. It is necessary to learn about the mother's medication use, as antiandrogenic drugs (flutamide, testolactone, enzalutamide, and spironolactone) can interfere with intrauterine virilization.

The physical examination is the most important part of evaluating the micropenis. Insufficient verlization associated with low blood pressure and tachycardia, may indicate adrenal insufficiencyassociated with rare forms congenital adrenal hyperplasia (VGN). Accurate measurement of the length of the penis is critical during a physical examination. The shaft of the penis should be as stretched as possible. The distance is measured from the pubic symphysis (after pressing on the suprapubic fat) to the tip of the head (with the foreskin maximally abducted) dorsally. The average of multiple measurements can improve accuracy.

Specific length of the penis less than two and a half standard deviations from the mean for the corresponding age confirms the diagnosis. Suggested lower limits for penile length in centimeters based on age:

• Premature babiesthose born in the 30th week of pregnancy; 1.5.
• Premature babies born at 34 weeks of gestation; 2.
• Full-term babies; 2,5.
• One year; 2,6.
• Five years; 3.5.
• Ten year old; 3.8.
• Adults; 9,3.

Careful palpation of the gonads is another step in the diagnosis of micropenia to narrow down the differential diagnosis. The appearance and maturity of the scrotum, the presence and location of the urethral passage, the curvature of the shaft of the penis, and any dysmorphic signs require careful evaluation.

Differential diagnosis

The most important difference is the exclusion of pseudomicropenis. In this disorder, the penis appears small due to the protrusion of the surrounding tissue or the web of the penis that attaches the penis to the underlying skin. To rule out pseudomicropenis and avoid invasive diagnostic evaluation and psychological stress in patients and their families, doctors perform a thorough physical examination. Curvature of the penis is another surgical condition that results in an abnormally curved shaft of the penis, which can underestimate the length of the penis.

Treatment

The goals of micropenis treatment include:

• Minimizing the social embarrassment associated with micropenia.
• The ability to achieve normal sexual function.
• Normal urinary function while standing.

There have been trials of medical or surgical interventions with varying responses. Primary etiology, age at treatment, degree of atrophy and the desired outcome determine the approach to treatment. A reasonable treatment plan for a micropenis is to try drug therapy first, and then surgery if drug treatment does not work.

- Hormonal treatment.

Penile growth both before birth and during childhood and puberty is strongly influenced by testosterone and, to a lesser extent, growth hormone. However, later endogenous hormones are mainly of importance in the treatment of micropenis caused by hormone deficiency such as hypopituitarism or hypogonadism.

Regardless of the cause of a micropenis, if recognized during infancy, a short course of testosterone (usually no more than 3 months) is often given. This usually causes small growth, which confirms the likelihood of further growth of the penis during puberty, but the organ rarely reaches its normal size. During childhood, no additional testosterone is prescribed to avoid unwanted virilization and bone maturation. (There is also some evidence that premature testosterone administration can lead to a decrease in penile size in adults.)

In adolescence, testosterone therapy is only resumed in hypogonadal boys. Penile growth is completed at the end of puberty, similar to the completion of male growth, and additional testosterone in post-pubertal adults results in little further growth or absence.

- Surgery.

Since hormonal treatment rarely helps the penis reach a medium size, it has been developed and implemented several surgical techniques similar to phalloplasty to increase penis; but these procedures are generally not considered successful enough to be widespread and are rarely performed during childhood.

In extreme cases, the micropenis has almost no shaft, and the head appears to be almost adjacent to the skin of the pubis. From the 1960s to the late 1970s, it was common practice to recommend gender reassignment and surgery. This was especially likely if the response to supplemental testosterone and testosterone was expected to be poor during puberty. With the approval of his parents, the boy became a girl, an operation was performed to remove the testicles and build an artificial vagina. This was based on the questioned idea that gender identity is completely formed as a result of socialization and that a man with a small penis cannot find an acceptable place in society.

Today, sex reassignment is rarely performed with severe micropenis (although the issue of raising a boy to a girl is sometimes still discussed).

Forecast

If early treatment of micropenis is unsuccessful, it is difficult for the boy and his family to cope with the disease.

In all cases, psychological counseling and social services are likely to be required to help the boy and his family emotionally.