Micropenis is a medical term that describes an unusually small penis in a human male. A common criterion is a dorsal penile length at least 2.5 standard deviations smaller than the mean penis size; if penis length follows a normal distribution, about 0.6% of penises will be in the micropenis category.

The condition is usually recognized shortly after birth, when the stretched flaccid penis of a full-term infant boy measures less than 1.9 cm from base to tip. The term is most often used medically when the rest of the penis, scrotum, and perineum is well-formed, without ambiguity such as hypospadias.

Causes

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Micropenis can have a variety of causes. Since it is defined statistically, a large proportion of males with micropenis are simply normal but in the lowest percentile of normal size. As for many other conditions, the term "idiopathic" is often used when a cause cannot be determined.

Of the abnormal conditions associated with micropenis, most are conditions of reduced prenatal androgen production or effect. Examples include abnormal testicular development (testicular dysgenesis, Klinefelter syndrome, Leydig cell hypoplasia), specific defects of testosterone or dihydrotestosterone synthesis (17,20-lyase deficiency, 5α-reductase deficiency), androgen insensitivity syndromes, inadequate pituitary stimulation (gonadotropin deficiency) or other forms of congenital hypogonadism. Micropenis can also occur as part of many genetic malformation syndromes not involving the sex chromosomes. It sometimes is a sign of congenital growth hormone deficiency or congenital hypopituitarism. Finally, several Homeobox genes have been identified which affects penis and digit size without detectable hormone abnormalities.

Pediatric endocrinologists are usually the physicians to whom these boys are referred. After evaluation to detect any of the conditions described above, micropenis can often be treated in infancy with injections of various hormones, such as human chorionic gonadotropin or testosterone.

Most eight to fourteen year old boys referred for micropenis have

1. a penis concealed in suprapubic fat (extra fat around the pubic area).
2. a large body and frame for which a prepubertal penis simply appears too small.
3. delayed puberty with every reason to expect good future growth.

Micropenis in Asian Populations

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A high incidence of micropenis has been found in several Asian populations, including Japanese, Chinese (of varying ethnicity) and Vietnamese samples, considered due to a higher mutation rate for the SRD5A2 gene, which encodes for the enzyme 5{alpha}-reductase-2 and plays a role in male sex differentiation (Sasaki et al. 2003). The mutation led to decreased expression of the enzyme, which in turn results in penises with erect lengths of -2.5 standard deviations. In the case of the Japanese sample, hormone treatments were also studied and found to be effective, resulting in penis lengths at nearly the average of age-matched Japanese controls.

Treatment

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A number of surgical techniques for penis enlargement have been devised and performed but are not generally considered successful enough to be widely adopted and are rarely performed in childhood.

In extreme cases of micropenis, there is barely any shaft, and the glans appears to sit almost on the pubic skin. From the 1960s until the late 1970s, it was not unusual for sex reassignment and surgery to be recommended. This was especially likely if evidence suggested that response to additional testosterone and pubertal testosterone would be poor. If parents accepted, the boy would be reassigned and renamed as a girl, and surgery performed to remove the testes and construct an artificial vagina. This was based on three now questioned assumptions:

1. gender identity and sex differences were solely a matter of social learning rather than biology.
2. a male with a penis too small to put into a vagina would be unlikely to find a satisfactory social and sexual place in society.
3. a functionally acceptable vagina could be constructed surgically.

The center most known for this approach (Johns Hopkins Hospital) performed twelve such reassignments between 1960 and 1980. By the mid-1990s reassignment was less often offered, and all three premises had been challenged. Former subjects of such surgery, vocally dissatisfied with adult outcome, played a large part in discouraging this practice. As a result, sexual reassignment is rarely performed today for severe micropenis. Much inaccurate or exaggerated folklore on this topic is available on the internet. See History of intersex surgery for a more complete discussion of this issue.

See also

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• Penis size
• Hypogonadism
• Intersex

External links

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• Micropenis FAQ from the University of Virginia
• Into the Hands of Babes, by Melissa Hendricks, Johns Hopkins Magazine
• Gender Self Reassignment in an XY Adolescent Female with Ambiguous Genitalia, from Pediatrics (PDF)
• Effect of penile size on nocturnal erections: evaluation with NPTR testing with men having micropenis from the International Journal of Impotence Research

Andrology | Penis

Mikropenis | Micropene | Micropénis | Mikropenis