NORMAL TESTICULAR DESCENT

Testicular descent into the scrotum is dependent upon a series of complex endocrine and mechanical interactions.

• Stage 1 = Transabdominal migration:
• Occurs at 10-15 weeks gestation.
• Thought to be due to differential growth of the fetus.
• This is thought to be mediated by the Mullerian inhibiting substance.
• Stage 2 = Transinguinal migration:
• Occurs at 26-35 weeks.
• This is androgen dependent and is possibly mediated indirectly through the release from the genitofemoral nerve of the neuropeptide calcitonin gene-related peptide (1).

In a recent review (2), testicular descent was not observed prior to 25 weeks gestation, with 30% of the fetuses having one or both testes descended at 25 weeks and 97% after 32 weeks.

2D image of normal testicular descent	3D image of normal testicular descent

REFERENCES

1. Hutson JM, Baker M, Terada M et.al. Hormonal control of testicular descent and the cause of cryptorchidism. Reprod Fertil Dev 1994;6:151-156.
2. Achiron R, Pinhas-Hamiel O, Zalel Y et.al. Development of fetal male gender: prenatal sonographic measurements of the scrotum and evaluation of testicular descent. Ultrasound Obstet Gynecol 1998;11:242-245.