Undescended testis or cryptorchidism is the most common genitourinary disorder in boys. The true undescended testis has stopped along the pathway of normal descent. The ectopic testis is in an aberrant location, such as the base of the penis, the superficial inguinal pouch, the medial aspect of the upper thigh, or the contralateral scrotal sac.

The undescended testis is more common among preterm, low-birthweight,and twin infants. It can be associated with features of congenital,chromosomal, or intergender disorders. Cryptorchidism must be differentiated from the retractile testis,which is not in the scrotum but can be manipulated without tension into the scrotum. Retractile testes normally descend by puberty.

The testis usually begins its inguinal-scrotal descent at 28 weeks’gestation. Endocrine, mechanical,and neural factors are believed to play a role. After birth, as circulating maternal estrogens decrease,pituitary gonadotropins are stimulated. This produces a surge of testosterone,with levels peaking at 60 days. This event accounts for...

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