The testes are initially part of the urogenital ridge and begin to undergo differentiation at 6-7 weeks, then migrating to the inguinal region. At 28 weeks and again at 35 weeks, further migration occurs until the testes descend into the scrotum from 35 weeks. It is not clear what controls or affects testicular descent. Proposed mechanisms include pulling of the testes into the scrotum by the gubernaculum or the cremaster muscle or increasing abdominal pressure pushing the testes through the inguinal canal. Mullerian duct inhibiting substance (MIS) is thought to provide hormonal control of descent into the inguinal region, while testosterone is thought to be involved with subsequent descent into the scrotum.


Cryptorchidism is diagnosed if one or both testes have not descended into the scrotum by birth. At term it is found in approximately 2-3% of liveborn males, and is more common in premature infants (15-30%). It is most often an isolated finding. The scrotum may be small and flat. Bilateral cryptorchidism may be associated with other malformations; especially renal anomalies (3-5%), horseshoe kidney, or posterior urethral valves such as megacystis, and Prune Belly syndrome.

Differential Diagnosis

The presence of a uterus may suggest a masculinised female fetus with congenital adrenal hyperplasia. In inguinal hernia, testes may be found in the canal.

Sonographic Features

Failure to visualize testes within the scrotum

May not be diagnosed until the third trimester; 10% of male fetuses will still have undescended testes in the early-to-mid 3rd trimester

Associated Syndromes

  • Noonan
  • Prune Belly
  • Trisomy 13
  • Trisomy 18
  • Trisomy 21


  1. Fleischer AC, Romero R, Manning FA, Jeanty P, James AE, Jr In: Principles & Practice of Ultrasound in Obstetrics and Gynecology Appleton & Lange: Norwalk, p269
  2. Birnholz JC Determination of Fetal Sex N Engl J Med 309:942
    Stevenson R, Hall T, Goodman R In: Human Malformations and Related Anomalies Vol II Oxford University Press: New York, p559-560