In some cases, a testicle does not descend to the scrotum because it is absent (anorchia or anorchidism) or is malformed (dysgenesis). Absent or malformed testicles may be caused by a problem with the development of the testicle during fetal growth. In some cases, an absent testicle may be caused when the testicle shrinks (atrophies) because of problems in development, lack of proper blood supply, or other factors. In 3% to 5% of males who have testicles that can't be felt (nonpalpable), one or both testicles are absent.
An absent testicle on one side (unilateral) is called monorchidism ("single testicle"). It occurs in about 1 out of 5,000 males.
Absence of both testicles (bilateral anorchia) is very rare, occurring in only about 1 out of 20,000 males. Lack of both testicles poses a serious health problem for normal development. Boys who do not have testicles must take hormone therapy when they reach puberty because their bodies do not have the hormones that are normally produced by the testicles and that are needed for normal development. Absence of both testicles also may indicate an intersex disorder, in which a baby develops characteristics of the opposite sex because of abnormalities in the chromosomes or endocrine system.
Surgery is usually needed to distinguish an undescended testicle that cannot be felt during a physical exam (nonpalpable) from an absent or malformed testicle. In some cases, an undescended testicle is present but has not developed properly (dysgenesis). If the testicle is present but is found to be malformed, most doctors recommend removing it (orchiectomy) rather than trying to place it in the scrotum.