What is a Micro Penis (and what can be done about it?)

“Micro penis” is a medical term that refers to 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. This is a condition that usually is recognized shortly after birth.

The term is most often used medically when the rest of the penis, scrotum, and perineum is well-formed, without ambiguity such as hypospadias. (Hypospadias an abnormal positioning of the meatus, the opening from which urine passes. The degree of hypospadias depends on the location of the penis opening. The defect may occur anywhere along the underside of the penis down to the scrotum).

What is considered a micro penis?

Most reference standards for penile length measure the gently stretched, flaccid dorsal length to the tip of the glans.For a full-term newborn infant, a stretched penis length smaller than 2 cm, and for an adult male a penis length below 4 cm is a common definition. If penile length follows a normal distribution, about 0.6% of penises will be labeled in the micropenis category.
The definition is somewhat subjective and different criteria have been used for different purposes.

What causes a micro penis?

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

“Of the abnormal conditions associated with micro penis, 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. “ (found in Wikipedia)

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.

Pediatric endocrinologists are usually the physicians to whom boys with a very small penis are referred. After medical examination to detect any of the conditions described above, a micropenis can often be treated in early years with injections of various hormones, such as human chorionic gonadotropin or testosterone.

Most eight to fourteen year old boys referred for micropenis have a penis concealed in suprapubic fat (extra fat around the pubic area). They have a large bodyframe for which a prepubertal penis simply appears too small.

Is there a treatment for a micropenis?

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, some doctors recommend sex reassignment and surgery.

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. male with a penis too small to put into a vagina could not find a satisfactory social and sexual place in society.
3. a functionally acceptable vagina could be constructed surgically.

The Johns Hopkins Hospital, most known for this approach 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 (mal)practice.
As a result, sexual reassignment is rarely performed today for severe micropenis.

A notable related, although not identical, case was that of David Reimer, a Canadian boy who was subjected to similar gender reassignment surgery after his normal penis was inadvertently destroyed in a botched circumcision.