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Congenital absence of the penis (apenia) is extremely rare. In this condition, the urethra generally opens on the perineum or inside the rectum.

Patients with apenia should be considered for assignment to the female gender. Castration and vaginoplasty should be considered in combination with estrogen treatment as the child develops.


The penis enlarges rapidly in childhood (megalopenis) in boys with abnormalities that increases the production of testosterone, for example, interstitial cell tumors of the testicle, hyperplasia, or tumors of the adrenal cortex. Management is by correction of the underlying endocrine problem.


Micropenis is a more common anomaly and has been attributed to a testosterone deficiency that results in poor growth of organs that are targets of this hormone. A penis smaller than 2 standard deviations from the norm is considered a micropenis (see Table 41–1). The testicles are small and frequently undescended. Other organs, including the scrotum, may be involved. Early evidence suggests that the ability of the hypothalamus to secrete luteinizing hormone-releasing hormone (LHRH) is decreased. The pituitary–gonadal axis appears to be intact, since the organs respond to testosterone, although this response may be sluggish at times. Studies have shown that topical application of 5% testosterone cream causes increased penile growth, but its effect is due to absorption of the hormone, which systemically stimulates genital growth. Patients with micropenis must be carefully evaluated for other endocrine and central nervous system anomalies. Retarded bone growth, anosmia, learning disabilities, and deficiencies of adrenocorticotropic hormone and thyrotropin have been associated with micropenis. In addition, the possibility of intersex problems must be carefully investigated before therapy is begun.

Table 41–1. Size of Unstretched Penis and Testis from Infancy to Adulthood.

The approach to management of micropenis has undergone gradual change in recent years, but androgen replacement is the basic requirement. The objective is to provide sufficient testosterone to stimulate penile growth without altering growth and closure of the epiphyses. A regimen of 25 mg orally every 3 weeks for no more than four doses ...

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