micropenis

A micropenis or microphallus is an unusually small penis. A common criterion is a dorsal (measured on top) penile length of at least 2.5 standard deviations smaller than the mean human penis size for age. A micropenis in adults is equal to when the erected penis is shorter than 7cm (2.7 inches), measures less than 4cm (1.5 inches) when flaccid, and/or when stretched penile length equal to or less than 1.9cm (0.75 in) in term infants, and 9.3 cm (3.67 in) in adults. The condition is usually recognized shortly after birth. The term is most often used medically when the rest of the penis, scrotum, and perineum are without ambiguity, such as hypospadias. Traditionally, a microphallus describes a micropenis with hypospadias. Micropenis incidence is about 1.5 in 10,000 male newborns in North America.

==Causes== thumb|A closeup of an erect micropenis with a tape measure displaying length Of the abnormal conditions associated with micropenis, most are conditions of reduced prenatal androgen production or effect, such as 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), and other forms of congenital hypogonadism. Micropenis can also occur as part of many genetic malformation syndromes that do not involve the sex chromosomes. It is sometimes a sign of congenital growth hormone deficiency or congenital hypopituitarism. Several homeobox genes affect penis and digit size without detectable hormone abnormalities.