In the fetus, the testes (testicles) develop within the abdomen. After the testes develop, but typically before birth (usually in the last third of pregnancy—the third trimester), they descend through a tunnel from the abdomen into the groin (the inguinal canal) and then down into the scrotum.
After the testes descend, the tunnel usually closes. If the tunnel does not close completely, an inguinal hernia may develop. The inguinal hernia rarely causes symptoms, but doctors can often feel it.
Sometimes, fluid from the abdomen accumulates around the testes and is trapped in the scrotum after the tunnel closes. This trapped fluid forms a soft lump called a hydrocele, which usually goes away in the first year of life. (See also Scrotal Swelling.)
About 3 of every 100 boys who are born at full term (9 months) have an undescended testis at birth. However, about 30 of every 100 boys born prematurely have an undescended testis. Boys whose family members had undescended testes also are more likely to have the condition. Usually only one testis fails to descend, but in about 10% both testes are affected.
Usually the undescended testis is in the inguinal canal but sometimes it is within the abdomen. About two thirds of undescended testes descend on their own by 4 months of age in full-term infants or, for premature infants, by 4 months after the date they would have been born if they were not premature. Testes that remain in the abdomen at birth are much less likely to descend on their own.
Undescended testes rarely cause symptoms. However, undescended testes can impair sperm production later in life and increase the risk of testicular cancer. Undescended testes in the abdomen can become twisted (testicular torsion), causing severe pain. Most newborns who have an undescended testis also have an inguinal hernia.
Doctors do a physical examination of the scrotum to detect the testes at birth and at each annual well-child visit. If they cannot feel one or both testes, they make sure that the testes are not simply retracted into the inguinal canal (see Retractile testes). Most boys are diagnosed with undescended testes in infancy, but some may be diagnosed later in childhood usually after a growth spurt. If the testes are not in the scrotum, children should be seen by a urologist (a doctor who specializes in the urinary tract and male reproductive system). Rarely, doctors do ultrasonography or magnetic resonance imaging (MRI).
If the testis has not descended by about 6 months of age in full-term infants and by 1 year of age in premature infants, surgery is needed. Depending on the location of the testis, it may be brought down into the scrotum via a surgical procedure through an open incision or by laparoscopy (in which doctors look inside the abdominal cavity using an endoscope). If the infant has an inguinal hernia, that is also repaired.
Because children who have undescended testes are at an increased risk of developing testicular cancer, after puberty they should examine their testes for lumps every month.
Retractile testes (hypermobile testes) are descended testes that easily move back and forth between the scrotum and the inguinal canal. The testes retract as a reflex response to touch, temperature, fear, or laughter. Such a response is common, particularly in infants and children. Retractile testes do not lead to cancer or other complications.
Doctors examine the testes during well-child visits to confirm they are properly positioned in the scrotum as the child grows. The testes usually stop retracting into the groin by puberty because they grow larger. Retractile testes do not require surgery or other treatment.