The descent of the testes is a complex process required for the male reproductive system to function correctly. This movement, from the abdomen to the scrotum, is a necessary developmental event. Without this relocation, the reproductive cells would be exposed to the core body temperature, which is too high for their proper development and maturation.
The Timeline of Testicular Descent
The journey of the testes from the abdomen to the scrotum begins during the prenatal period. This developmental process is divided into two main phases. The initial phase, known as the transabdominal phase, sees the testes move from their starting position near the kidneys to the deep inguinal ring, typically occurring around the seventh month of gestation.
The second phase, the inguinoscrotal phase, involves the testes passing through the inguinal canal and into the scrotum, generally completing between 25 and 35 weeks of gestation. For many full-term male infants, the testes are fully descended at birth. If descent has not occurred by three months of age, there is still a chance for spontaneous movement, but if the testes remain undescended by six months, the probability of later spontaneous descent becomes low, and a medical evaluation is recommended.
Hormonal and Mechanical Triggers
Testicular descent is orchestrated by a precise interplay of hormones and physical guidance mechanisms. The initial transabdominal phase is heavily influenced by Insulin-like hormone 3 (INSL3), a hormone produced by the Leydig cells of the testes. INSL3 acts to stimulate the enlargement and swelling of the gubernaculum, a fibrous cord that attaches to the lower pole of the testis.
Simultaneously, the hormone testosterone drives the regression of the cranial suspensory ligament. The later inguinoscrotal phase, which guides the testis through the inguinal canal and into the scrotum, is controlled by androgens, including testosterone and dihydrotestosterone (DHT). These androgens mediate their effect on the gubernaculum, allowing it to guide the testis into the scrotum.
Understanding Undescended Testes
The failure of this process to complete is cryptorchidism, the absence of one or both testes from the scrotum. This condition affects approximately 3 to 5% of full-term male infants at birth, though the incidence naturally decreases to about 1% by six months of age as spontaneous descent occurs. Cryptorchidism is distinct from a retractile testis, where the testicle can be manually moved into the scrotum during examination, often due to an overactive cremasteric reflex.
True undescended testes carry health risks primarily because the higher body temperature impairs the development of reproductive cells. Untreated cryptorchidism can substantially increase the risk of infertility, especially when both testes are affected. Furthermore, there is an increased, though small, lifetime risk of developing testicular cancer.
Diagnosis and Treatment Options
The diagnosis of cryptorchidism is typically made through a physical examination by a pediatrician or urologist, who attempts to gently palpate the testis in the scrotum or along the path of descent. Imaging tests, such as ultrasound, are generally not recommended for routine diagnosis as they rarely add diagnostic accuracy or change the treatment plan. The priority is to confirm the absence of the testis from the scrotum and rule out a retractile testis that moves freely.
Treatment for a truly undescended testis is a surgical procedure called orchiopexy. During this surgery, the testis is located, freed from any surrounding tissue, and secured into its proper position within the scrotum. Orchiopexy is recommended between 6 and 18 months of age, with the latest guidelines favoring completion before 18 months. Early surgical correction is preferred to minimize the potential for long-term damage to the reproductive cells and to allow for easier detection of any future malignant changes. Hormonal treatments are rarely used as the primary treatment due to a lack of strong evidence supporting their effectiveness compared to surgery.