Атау бездерінің төмен түспеуі және еркек репродуктивті денсаулығының бұзылуы

Cryptorchidism, also known as undescended testis, is the failure of one or both testes to descend into the scrotum. The word is from Greek κρυπτός (kryptos) 'hidden' and ὄρχις (orchis) 'testicle'. It is the most common birth defect of the male genital tract. About 3% of full term and 30% of premature infant boys are born with at least one undescended testis. However, about 80% of cryptorchid testes descend by the first year of life (the majority within three months), making the true incidence of cryptorchidism around 1% overall. Cryptorchidism may develop after infancy, sometimes as late as young adulthood, but that is exceptional. Cryptorchidism is distinct from monorchism, the condition of having only one testicle. Though the condition may occur on one or both sides, it more commonly affects the right testis. A testis absent from the normal scrotal position may be:
Anywhere along the "path of descent" from high in the posterior (retroperitoneal) abdomen, just below the kidney, to the inguinal ring
In the inguinal canal
Ectopic, having "wandered" from the path of descent, usually outside the inguinal canal and sometimes even under the skin of the thigh, the perineum, the opposite scrotum, or the femoral canal
Undeveloped (hypoplastic) or severely abnormal (dysgenetic)
Missing (also see anorchia). About two thirds of cases without other abnormalities are unilateral; most of the other third involve both testes. In 90% of cases, an undescended testis can be felt in the inguinal canal. In a small minority of cases, missing testes may be found in the abdomen or appear to be nonexistent (truly "hidden"). Undescended testes are associated with reduced fertility, increased risk of testicular germ cell tumors, and psychological problems when fully grown. Undescended testes are also more susceptible to testicular torsion (and subsequent infarction) and inguinal hernias. Without intervention, an undescended testicle will usually descend during the first year of life, but to reduce these risks, undescended testes can be brought into the scrotum in infancy by a surgical procedure called an orchiopexy. Although cryptorchidism nearly always refers to congenital absence or maldescent, a testis observed in the scrotum in early infancy can occasionally "reascend" (move back up) into the inguinal canal. A testis that can readily move or be moved between the scrotum and canal is referred to as retractile. Cryptorchidism, hypospadias, testicular cancer, and poor semen quality make up the syndrome known as testicular dysgenesis syndrome.

Many men who were born with undescended testes have reduced fertility, even after orchiopexy in infancy. The reduction with unilateral cryptorchidism is subtle, with a reported infertility rate of about 10%, compared with about 6% reported by the same study for the general population of adult men. The fertility reduction after orchiopexy for bilateral cryptorchidism is more marked, about 38%, or six times that of the general population. The basis for the universal recommendation for early surgery is research showing degeneration of spermatogenic tissue and reduced spermatogonia counts after the second year of life in undescended testes. The degree to which this is prevented or improved by early orchiopexy is still uncertain.

One of the strongest arguments for early orchiopexy is reducing the risk of testicular cancer. About one in 500 men born with one or both testes undescended develops testicular cancer, roughly a four to 40 fold increased risk. The peak incidence occurs in the third and fourth decades of life. The risk is higher for intra abdominal testes and somewhat lower for inguinal testes, but even the normally descended testis of a man whose other testis was undescended has about a 20% higher cancer risk than those of other men. The most common type of testicular cancer occurring in undescended testes is seminoma. It is usually treatable if caught early, so urologists often recommend that boys who had orchiopexy as infants be taught testicular self examination, to recognize testicular masses and seek early medical care for them. Cancer developing in an intra abdominal testis would be unlikely to be recognized before considerable growth and spread, and one of the advantages of orchiopexy is that a mass developing in a scrotal testis is far easier to recognize than an intra abdominal mass. Orchidopexy was originally thought to result in easier detection of testicular cancer, but did not lower the risk of actually developing cancer. However, recent data have shown a paradigm shift. The New England Journal of Medicine published in 2007 that orchidopexy performed before puberty resulted in a significantly reduced risk of testicular cancer than if done after puberty. The risk of malignancy in the undescended testis is 4 to 10 ten times higher than that in the general population and is about one in 80 with a unilateral undescended testis and one in 40 to one in 50 for bilateral undescended testes. The peak age for this tumor is 15–45 years old. The most common tumor developing in an undescended testis is a seminoma (65%); in contrast, after orchiopexy, seminomas represent only 30% of testicular tumors.

In most full term infant boys with cryptorchidism but no other genital abnormalities, a cause cannot be found, making this a common, sporadic, unexplained (idiopathic) birth defect. A combination of genetics, maternal health, and other environmental factors may disrupt the hormones and physical changes that influence the development of the testicles. Severely premature infants can be born before descent of testes. Low birth weight is also a known factor. A contributing role of environmental chemicals called endocrine disruptors that interfere with normal fetal hormone balance has been proposed. The Mayo Clinic lists "parents' exposure to some pesticides" as a known risk factor. Risk factors may include exposure to regular alcohol consumption during pregnancy (five or more drinks per week, associated with a three fold increase in cryptorchidism when compared to nondrinking mothers. Cigarette smoking is also a known risk factor. Androgen insensitivity syndrome generally manifests itself in Cryptorchidism. In CAIS, the testis are generally located completely undescended where the ovaries usually are, in PAIS, the testis are generally partially undescended. This also occurs with 5α Reductase 2 deficiency (DHT insensitivity) however, the testis generally descend during puberty. In 2008, a study was published that investigated the possible relationship between cryptorchidism and prenatal exposure to a chemical called phthalate (DEHP), which is used in the manufacture of plastics. The researchers found a significant association between higher levels of DEHP metabolites in pregnant mothers and several sex related changes, including incomplete descent of the testes in their sons. According to the lead author of the study, a national survey found that 25% of U. S. women had phthalate levels similar to the levels that were found to be associated with sexual abnormalities. A 2010 study examined the prevalence of congenital cryptorchidism among offspring whose mothers had taken mild analgesics, primarily over the counter pain medications including ibuprofen (e. g. Advil) and paracetamol (acetaminophen). Combining the results from a survey of pregnant women prior to their due date in correlation with the health of their children and an ex vivo rat model, the study found that pregnant women who had been exposed to mild analgesics had a higher prevalence of baby boys born with congenital cryptorchidism.

When one identical twin is born with cryptorchidism, his identical twin also has the trait only 25% of the time, despite sharing their genes and prenatal hormonal environment. Animal studies have found that androgen antagonists during early fetal development cause elevated rates of hypospadias and cryptorchidism, however, in humans these traits rarely occur together. If this marks are sexually antagonistic, and if a subset of these epigenetic marks carry over generations, they are expected to produce mosaicism of sexual development in opposite sex offspring, sometimes producing hypospadias or cryptorchidism when passed from a mother to son (feminizing the external genitalia). Rice's model requires further testing with currently available technology to support or falsify it. The prevalence of this condition can vary depending on species and breed. Evidence of this condition is more likely in companion animals and swine than ruminants. The cause of this condition can vary from a combination of genetics, environment, and epigenetics. This condition is one of the most common congenital defects in purebred dogs (11%), with 14% reported in Siberian Huskies. Although the genetics are not fully understood, it is thought to be a recessive, and probably polygenetic, trait. Some have speculated that it is a sex limited autosomal recessive trait; however, it is unlikely to be simple recessive. 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 teste(s) should be considered for cryptorchid dogs due to the high rate of testicular cancer, especially Sertoli cell tumors. Persians are predisposed. Normally, the testicles are in the scrotum by the age of six to eight weeks. Male cats with one cryptorchid testicle may still be fertile; however, male cats with two cryptorchid testicles are most likely to be sterile. 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 on the penis (which usually regress within six weeks after castration). Most cryptorchid cats present with an inguinal testicle. Testicular tumors and testicular torsion are rare in cryptorchid cats, but castration is usually performed due to unwanted behavior such as urine spraying.

In horses, cryptorchidism is sufficiently common that affected males (ridglings) are routinely gelded. Rarely, cryptorchidism is due to the presence of a congenital testicular tumor such as a teratoma, which has a tendency to grow large.