Clinical meaning
Cryptorchidism (undescended testis) is the failure of one or both testes to descend from the retroperitoneal space through the inguinal canal into the scrotum. Testicular descent occurs in two phases: transabdominal (weeks 10-15, guided by insulin-like factor 3/INSL3 from Leydig cells) and inguinoscrotal (weeks 25-35, dependent on androgens and the gubernaculum). The undescended testis is exposed to the higher core body temperature (37°C vs 33°C in scrotum), which impairs spermatogenesis (requires cooler temperature) and increases malignant transformation risk. Germ cell degeneration begins by age 6 months in undescended testes, and by 1-2 years, histological changes include decreased germ cells, Leydig cell hyperplasia, and delayed maturation. The risk of testicular cancer is 4-8x higher in undescended testes, with seminoma being the most common malignancy.