Abstract

Monorchism (also monorchidism) is the state of having only one testicle within the scrotum.

Causes

This can be due to:

- One testicle not descending into the scrotum during normal embryonic or fetal development (3–4% of 'normal' live births), also known as undescended testis or cryptorchidism. In this case the testis is within the abdominal cavity, somewhere along the normal route of descent – most commonly, within the inguinal canal. Such a testis has an increased risk of malignancy.

- One testicle may disappear during development (the so-called vanishing testis) due to some intrauterine insult. This is thought to be most likely vascular, such as testicular torsion.

- One testicle may have been surgically removed through orchiectomy.

- One testicle may be injured.

Monorchism in nonhuman animals

Although extremely rare, monorchism has been observed to be characteristic of some animal species, notably in beetles.

Terminology

An individual having monorchism can be referred to as "monorchid".