Evidence in favor of the mechanical (intrauterine torsion) theory over the endocrinopathy (cryptorchidism) theory in the pathogenesis of testicular agenesis.

There are 2 competing theories regarding the pathogenesis of testicular agenesis--the endocrinopathy/cryptorchidism and the mechanical/intrauterine torsion theories. We compare the number of Leydig cells, total number of germ cells and the transformation of adult dark spermatogonia into primary spermatocytes in semithin sections of testicular biopsies from 59 contralateral descended testes of patients with testicular agenesis with those in the contralateral descended testes from 250 patients with unilateral cryptorchidism. The contralateral descended testes from boys with testicular agenesis demonstrated higher numbers of Leydig cells, higher numbers of total germ cells and a higher rate of transformation of adult dark spermatogonia into primary spermatocytes than did the contralateral descended testes from the patients with unilateral cryptorchidism. These findings favor the mechanical/intrauterine torsion theory over the endocrinopathy/cryptorchidism theory in the pathogenesis of testicular agenesis.