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Cryptorchidism is a disorder where either one or both testes fail to descend and are therefore absent from the scrotum.  This usually occurs during foetal development when the testes begin their movement or descent from an abdominal position through the inguinal canal into the scrotum. Because the testes have failed to descend and therefore remain within the body, the temperature is too hot for sperm production to occur, rendering the male infertile.

There are however varying levels of cryptorchidism:

  • Undescended testicles may later fully descend (usually within 1 year) leaving the male without fertility problems
  • Testicles which have not fully descended but have partially reached the scrotum may be able to produce some sperm
  • Only on testicle may not descend, but as the other will have fully descended the male will be fertile
  • If both testicles fail to descend (bilaterally cryptorchid testes) then the male is infertile

Only sperm production is affected however (due to the high body temperature) which means that the natural hormone production of the testes are unaffected, the male will still behave normally therefore and express normal sexual behaviour.

The possible outcomes of testes failure to descend:

  • Testis could be found anywhere along the “path of descent” from high in the posterior (retroperitoneal) abdomen, just below the kidney, to the inguinal ring
  • Testis could be found in the inguinal canal
  • Testis could be ectopic, that is, found to have “wandered” from that path, usually outside the inguinal canal and sometimes even under the skin of the thigh, the perineum, the opposite scrotum, and femoral canal
  • Testis could be undeveloped (hypoplastic) or severely abnormal (dysgenetic);
  • Testis could have vanished – May therefore be anorchid or monorchid (Not formed)

Consequences of Cryptorchidism

Cryptorchid testes are more liable to tumours in later life, compared to normally descended testes. Cryptorchidism is believed to have a genetic component (as observed in horses and pigs), therefore to protect the health of future breeds, any animal displaying cryptorchidism should be excluded from breeding programs.

Undescended testes are associated with reduced fertility. Undescended testes are also more susceptible to testicular torsion and infarction and inguinal hernias. To reduce these risks it is possible to move undescended testes into the scrotum by a surgical procedure called an orchiopexy.

Cryptorchidism in Animals


Cryptorchidism is common in male dogs, occurring at a rate of to 10%. Dog testes usually descend by ten days of age and it is considered to be cryptorchidism if they do not descend by the age of eight weeks. Cryptorchidism can be either bilateral (causing sterility) or unilateral, and inguinal or abdominal (or both). Because it is an inherited trait, affected dogs should not be bred and should be castrated. The parents should be considered carriers of the defect and a breeder should thoughtfully consider whether to breed the carrier parent or not. Littermates may be normal, carriers, or cryptorchid. Castration of the undescended testes/testis should be considered for cryptorchid dogs due to the high rate of testicular cancer. The incidence of testicular cancer is 13 times higher in dogs displaying cryptorchidism.  Surgical correction is by palpation of the retained testicle and subsequent exploration of the inguinal canal or abdomen.

A list of the most commonly affected breeds:

  • Boxer
  • Chihuahua
  • Dachshund
  • Bulldog
  • Maltese
  • Miniature Schnauzer
  • Pekingese
  • Pomeranian
  • Poodle
  • Shetland Sheepdog
  • Whippet
  • Yorkshire Terrier


Cryptorchidism is more rare in cats than dogs. In one study 1.9 percent of intact male cats were cryptorchid. Normally the testicles are present in the scrotum by the age of six to eight weeks. Urine spraying is one indication that a cat with no observable testicles may not be neutered; other signs are the presence of enlarged jowls, thickened facial and neck skin, and spines present on the penis (which usually regress within six weeks after castration). Testicular tumours and testicular torsion are rare in cryptorchid cats, but castration is usually performed due to unwanted behaviour such as urine spraying.


In horses, cryptorchidism is sufficiently common that affected males (ridgelings) routinely are gelded.

The types of cryptorchidism are still as above, but they can be much more expensive to treat in the horse. Uncastrated males will still show aggressive stallion behaviour


Causes of Cryptorchidism

Typically cryptorchidism is thought of as an idiopathic disease, without a fully known cause. However theories are that the disease is inherited, although a mechanism for its inheritance is unknown – even still, males expressing cryptorchidism should not be bred. Other theories include environmental chemicals (more applicable in humans – such as alcohol), deficiencies in androgens, or more specific causes such as:

  • Prematurely born humans can be born before the decent of the testicles, however it is likely that the testicles will later descend
  • Horses foetal testes grow rapidly before shrinking again before birth, therefore it is possible that the testes do not shrink enough before they move through the inguinal canal.

Mechanism of Testes Descent

Normal testicular descent sees the testes pass from the abdomen, through the inguinal ring and down the inguinal canal into the scrotum. However in a cryptorchid, the testes or just one testis may be retain anywhere along this path. They may be retained in the abdomen or if they are retained in the inguinal canal, then they are known as inguinal testes.

Abdominally retained testes are usually smaller and ‘flabby’ and lie just inside the deep inguinal ring (the entrance to the inguinal canal). It is possible however for abdominal testes to become enlarged, which is due to cyst or teratoma formations. In the abdomen, the testes consist of islands of spermatogenic tubules with associated interstitial cells in a sea of loose connective tissue. Do to their location within the body (high temperature) the spermatogenic cells rarely progress beyond the primary spermatogonia phase. The proportion and density of the fibrous tissue increases with age.

Inguinal retained testes are usually smaller than scrotal testes (like the abdominal testes) yet their behaviour is much closer to normal function. Inguinal testes are more likely to spontaneously descend to the scrotum if their retention was due to delayed maturity – if this is the case, this type of retention is known as temporarily retained testes. The proportion of the testis furthest away from the scrotum appears most immature – spermatogenic tubules occupy most of the testis, with a few interstitial cells. As the testis gets closer to the scrotum, it appears more mature and normal – some spermatozoa production can be observed in some tubules.

When retention is permanent and inguinal, the number of interstitial cells within the testes will increase and cells will become vacuolated and aggregate around the periphery of the tubule (these are signs of degeneration).