An undescended testicle, also called cryptorchidism, is a testicle that has not moved down into the scrotum. Early in pregnancy, the testicles begin developing deep within the abdomen, influenced by several hormones. At 32 to 36 weeks' gestation, the testicles begin to descend into the scrotum. In 30% of premature and approximately 3% of full-term male infants, one or both of the testicles have not completed their descent at the time of birth. Most of these will then descend spontaneously during the first three to six months of life. By 6 months of age, less than 1% of babies still have the problem. Either one or both testicles can be affected.
An undescended testicle increases the risk of infertility (not being able to have children), testicular cancer, hernias and testicular torsion (twisting). An empty scrotum also can cause significant psychological stress as the boy gets older. For these reasons, early treatment is very important.
Some boys have a normal descended testicle at birth that then appears to move back up into the abdomen when they are between 4 and 10 years old. This condition is called an acquired undescended testicle. This is thought to occur when, for unknown reasons, the spermatic cord attached to the testicle does not grow as quickly as the rest of the child does.
Sometimes, a temporary situation called a retractile testicle is mistaken for an acquired undescended testicle. In this condition, a testicle that has descended fully into the scrotum occasionally retracts into the abdomen. The retraction is caused by an overactive reflex in the cremasteric muscle that pulls the testicle out of the scrotum. Boys who are anxious or ticklish during a testicular exam may have this overactive reflex. A retractile testicle does not increase the risk of infertility or testicular cancer because it always comes back down into the scrotum.