Undescended testicle (aka cryptorchidism, from Greek "crypto" meaning "hidden", and "orchis" meaning "testicle" is the congenital absence of testes (one or both) from the scrotum.
Note that a testis in early infancy can occasionally "reascend" into the inguinal canal. A testis which can readily move between the scrotum and canal is referred to as retractile.
Pathophysiology
A testis absent from the normal scrotal position can be found:
Along the path of descent from the high in the posterior (retroperitoneal) abdomen, just below the kidney, to the inguinal ring
In the inguinal canal
Ectopically, i.e. to have wandered from its path, usually outside the inguinal canal and sometimes even under the skin of the thigh, the perineum, the opposite scrotum, or the femoral canal
Undeveloped (hypoplastic) or severely abnormal (dysgenetic)
To have vanished (anorchia)
DDx
Monorchism, the condition of having only 1 testicle
Tx
Usually self limiting
To reduce risk, undescended testes can be brought into scrotum in infancy using surgery, known as orchiopexy
Complications
Associated with:
Reduced fertility
Increased risk of testicular germ cell tumors
Psychological problems when the boy is grown
Increased risk of:
Testicular torsion (and subsequent infarction)
Inguinal hernias
Prognosis
80% of undescended testes descend by the 1st year of life, with the majority within 3 months, making the true incidence of non-self limiting undescended testes 1%
Epidemiology
Most common birth defect of the male genetalia
Can develop later in life, often as late as young adulthood
3% of full term, and 30% of premature infants are born with at least 1 undescended testis
66% of cases are unilateral, 33% involve both testes
In 90% of cases, the undescended testis can be felt in the inguinal canal; only a minority are in the abdomen or nonexistent (truly hidden)
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