Cryptorchidism is a condition characterized by one or both testes being undescended. An undescended testis does not remain at the bottom of the scrotum after the cremaster muscle has been fatigued by overstretching. Cryptorchidism is commonly confused with a retractile testis. A retractile testis may not always lie in the scrotum but will stay at the bottom of the scrotum after overstretching the cremaster.


  • 3% of full-term newborn boys have cryptorchidism.
  • This percentage falls to 1% by 3 months of age.
  • There are two peaks for detection of undescended testes: at birth and at 5 to 7 years of age. The latter group probably represents those patients with low undescended testes that become apparent with linear growth.
  • Bilateral undescended testes occur in 10% of patients with undescended testicles.
  • Unilateral anorchia is found in 5% of patients with cryptorchidism.

Risk Factors


  • Of boys with undescended testes, 4% of their fathers and 6–10% of their brothers also had undescended testes. There is a 23% prevalence of cryptorchidism in family members of cases compared to 7.5% in relatives of controls.
  • Abnormalities in HOXA10, HOXA11, HOXD13, ESR1, INSL3, and the LGR8/GREAT receptor genes account for only 2–3% of patients with nonsyndromic cryptorchidism. Androgen receptor gene mutations are not linked to isolated cryptorchidism. A genome-wide association study failed to identify significant genetic markers.


  • Normal testicular descent occurs during the 7th month of gestation.
  • The majority of testes that are undescended at birth but descend spontaneously will do so by 3 months of age, possibly due to the gonadotropin surge that is responsible for germ cell maturation.
  • The undescended testis fails to show normal maturation at both 3 months and 5 years of age.
    • At 3 months of age, the fetal gonocytes are transformed into adult dark spermatogonia.
    • At 5 years of age, the adult dark spermatogonia become primary spermatocytes.
    • Both of these steps are abnormal in the undescended testis and, to a lesser extent, the contralateral descended testis.
    • It was previously believed that the undescended testis was normal between birth and 1 year of age. However, this is incorrect because these data were derived from counts of all germ cells without taking into account whether maturation was occurring.
    • After 5 years of age, thermal effects on the testis left out of position are seen independent of the endocrinologic effects.


  • Multifactorial mechanisms involving two theories have been postulated:
    • Hypogonadotropic hypogonadism
    • Abnormal mechanical factors (gubernaculum, epididymis, genitofemoral nerve innervation, intra-abdominal pressure)
  • Although boys with undescended testes do have abnormal attachment of the gubernaculum, the mechanical theories do not consistently explain the testis histology found in cryptorchidism.
  • Many boys with cryptorchidism have lower morning urinary luteinizing hormone and a decreased luteinizing hormone/follicle-stimulating hormone response to gonadotropin-releasing hormone, corresponding to the abnormal germ cell development in both the undescended and contralateral descended testis.
  • The normal initial postnatal gonadotropin surge at 60 to 90 days of age is absent or blunted in some boys with cryptorchidism. Without this surge, Leydig cells do not proliferate, testosterone does not increase, germ cells do not mature, and infertility may develop. This indicates that a mild endocrinopathy is responsible, and cryptorchidism may be a variant of hypogonadotropic hypogonadism.
  • Exposure to the environmental antiandrogen polybrominated diphenyl ether is linked to an increased cryptorchidism risk, with an odds ratio of 1.5 to 1.9.
  • Secondary undescended testes can occur after inguinal surgery, either due to scar tissue or difficulty in diagnosing an undescended testis in a young boy with a hernia.

Commonly Associated Conditions

  • Patients with prune belly, Klinefelter, Noonan, and Prader-Willi syndromes have a higher likelihood of undescended testes.
  • Cryptorchidism associated with hypospadias should also raise the possibility of a disorder of sex development (DSD), which occurs in 30–40% of patients, mainly due to defects in gonadotropin or testosterone synthesis.

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