Micropenis

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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. The condition is usually 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.

1 Criteria
2 Causes
3 Micropenis in racial groups
4 Treatment
5 See also
6 External links

[edit] Criteria

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 length smaller than 2 cm, and for an adult male a length below 4 cm is a common definition. If penile length follows a normal distribution, about 0.6% of penises will be in the micropenis category. The definition is somewhat arbitrary and different criteria have been used for different purposes.

[edit] Causes

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

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

[edit] Micropenis in racial groups

A study by Pik Shun Cheng and Jean-Pierre Chanoine of the University of British Columbia concluded the following: "We determined whether the existing reference values for the diagnosis of micropenis are appropriate for optimal care of neonates in a multiethnic environment like Vancouver. Methods: The stretched penile length and width were measured in 105 full-term newborn males of Caucasian (n = 40), Chinese (n = 40) and East-Indian origin (n = 25). Results: Mean length -2.5 SD was used for the definition of micropenis and was 2.6, 2.5 and 2.3 cm for Caucasian, East-Indian and Chinese babies, respectively (p < 0.05). This is close to the widely accepted recommendation that a penile length of 2.4- 2.5 cm be considered as the lowest limit for the definition of micropenis. Conclusion: Mean penile length and diameter are slightly but significantly smaller in newborns of Chinese origin compared to newborns of Caucasian and East-Indian origins." (Cheng et al. 2001)

Careful examination and assessment of penile length in the newborn is important because micropenis is associated with hypothalamic disorders. This prospective cross-sectional study was designed to establish the norm of penile length for term Hong Kong Chinese newborns. 4,628 full-term healthy male newborns were enrolled in the study. Penile length was measured from pubic ramus to the tip of the glans penis by placing the end of a straight edge ruler against the pubic ramus. A gestation-associated graph of 3rd, 10th, 25th, 50th, 75th, 90th and 97th centiles for the penile length was created. The penile length was significantly correlated with gestational age, birth weight and body length. When compared with published data for other populations, Hong Kong newborns have significantly shorter penile length. The norm of the penile length is useful in diagnostic and therapeutics for the ethnic Chinese male newborns. Fok et al. 2005)

A lower incidence of alleles believed to cause the micropenis condition have been found in studies of several Asian populations, including Japanese, Chinese (of varying ethnicity) and Vietnamese samples. The presence of a micropenis in these subjects are lower than that of Caucasian populations, and (age range: 0-14, median age: 7) is considered to be 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.

The incidence of alleles related to the micropenis condition in other racial groups has not been subject to medical research, though by the definition of the micropenis condition, it is reasonable to assume that idiopathic-type cases would occur in members of all asian races.

[edit] Treatment

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:

gender identity and sex differences were solely a matter of social learning rather than biology.
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.
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.

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.