Monorchidism is a rare developmental condition in which the affected individual only develops one testicle. It is important to note that this condition is often confused with unilateral (one-sided) cryptorchidism, which is a condition where there are two testicles, but only one descends into the scrotum, while the other is retained in abdomen.

Monorchidism is caused by a genetic abnormality and is uncommon. Affected individuals usually show no signs of illness, although the pet has only one descended testicle. Tests must be performed to confirm the diagnosis of monorchidism and exclude other disorders.

Diagnosis

A complete and thorough examination of the scrotum, as well as inguinal (groin) and abdominal palpation, is necessary in order to identify testicular tissue that may be present. Additional tests may include:

Abdominal and inguinal ultrasound to locate a testicle that is otherwise hard to palpate

Plasma (blood) testosterone levels are significantly lower in dogs that lack one or both testes, and help differentiate monorchidism from cryptorchidism.

Treatment

Castration (removing the existing testicle) is the treatment of choice.

Home Care and Prevention

Monorchid individuals should never be used for breeding and affected individuals should be neutered. These pets otherwise lead normal, healthy lives.