During the unborn male's development, the testicles (testes) are located in the abdomen and gradually move down into the scrotum during the seventh month of pregnancy. When they descend, they pass through a small passageway that runs along the abdomen near the groin called the inguinal canal. Once through the inguinal canal, the testes reside in the scrotal sac. Since the scrotal sac is cooler than the body temperature, it is the ideal location for the testicles because they function better at this cooler temperature.
Undescended testis (testes –plural) and cryptorchidism refer to a condition in which the testicle has not descended and cannot be brought into the scrotum with external manipulation. This occurs in 3% of newborn males and up to 21% in premature male newborns. Nearly three quarters of these move down on their own by the child's first birthday.
The undescended testis can be located in the abdomen, the inguinal canal or other more unusual locations, but most are located in the inguinal canal (80%). About 10-15% of all cases are bilateral (involve both testicles).
There is a genetic association with this condition. About 14% of boys with this condition come from families in which another male is affected also. Six percent of fathers of males with undescended testis have also had this problem.
It is very important to clarify that "retractile testicles" are not undescended testicles. If a testicle can be brought down into the scrotal sac, even if it retracts again upon release, it is a retractile testis. A reflex pulls the testicle up to protect it when the boy is cold or frightened. These retractile testicles are in the scrotum at other times and do not require treatment.
