An undescended testicle has not moved into the scrotum, the bag of skin that hangs behind the penis, during the development of a fetus.

The American Urological Association report that 3–4 percent of full-term male newborns and 21 percent of those born prematurely have an undescended testicle. Usually, only one testicle does not descend. Both are undescended in 10 percent of cases.

The more formal medical term for testicles that do not descend is cryptorchidism. It is one of the most common endocrine problems in newborn males and the most common genital condition that doctors can identify at birth.

Cryptorchidism often corrects itself within a few months of birth. However, an infant sometimes needs surgery to relocate the testicle to the scrotum.

This article explores the causes of cryptorchidism, risk factors, and treatment methods.

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The testicles should descend into the scrotum while the fetus is developing.

Cryptorchidism occurs when one or both of the testicles do not descend into the scrotum while the fetus is developing.

During gestation, the testicles form in the abdomen and gradually drop through the inguinal canal into the scrotum at around month 8 of pregnancy.

The scrotum is a small pouch, or sac, of skin that hangs behind the penis.

The testicles are oval-shaped organs that form part of the male reproductive system.

The testicles produce sperm cells, which are vital to reproduction. They also make testosterone, a hormone that plays a key role in male sexual development.

Undescended testicles may be palpable or unpalpable.

Palpable means that a doctor will be able to feel the undescended testicle during a physical examination. About 80 percent of undescended testicles are palpable.

The testicle is usually located at the end of the inguinal canal, a channel that carries the spermatic cord towards the penis and scrotum.

If a doctor cannot feel the undescended testicle, it is unpalpable, and it may be:

  • Abdominal: The least common location for an undescended testicle is in the abdomen.
  • Inguinal: The testicle has moved into the inguinal canal, but not far enough to be detectable by touch.
  • Atrophic or absent: The testicle is either very small, or it has never formed.

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A premature birth increases the risk of cryptorchidism.

The following factors may increase the risk of cryptorchidism:

  • premature birth, with an earlier delivery carrying a greater risk
  • a low birth weight, which may double or triple the risk
  • Down's syndrome and other conditions that slow fetal growth
  • a family history of issues with genital development
  • tobacco consumption by a mother during pregnancy

In the early stages, all fetuses have structures that can develop into male or female reproductive organs.

The child receives sex chromosomes from its mother and father. Sex chromosomes are a pair of DNA molecules. The chromosomes will be XX in a female fetus, and XY if the fetus is male.

As the fetus develops, the XY gene promotes the development of the testes. These produce hormones that encourage the growth of the male reproductive tract, preventing female development.

Scientists maintain that the testicles might begin to develop incorrectly.

Abnormal genital development may also stem from androgen insensitivity syndrome (AIS), a genetic disorder in which XY fetuses do not respond to male hormones, such as testosterone.

A newborn with AIS may have female attributes, such as a short, pouch vagina, but no uterus, ovaries, or fallopian tubes. The testes may be present in the abdomen or the inguinal canal.

Experts believe that most cases of undescended testicles occur when a combination of genetics, maternal health, and some environmental factors disrupt the hormones, cause physical changes, and interrupt the nerve activity involved in the testicles' development.

However, the exact cause of cryptorchidism remains unclear.

To diagnose an undescended testicle, the doctor usually places the infant in a warm place to help him relax. Expanding the skin around the scrotum also makes it easier to perform the examination.

About 20 percent of the time, a doctor cannot locate the undescended testicle until the child is no longer an infant.

If the testicle is unpalpable, an ultrasound scan can often show its location. However, a doctor usually deems this step unnecessary. In some cases, a specialist called a pediatric urologist requests further testing.

The tests may include:

  • An MRI scan with a contrast agent: The doctor injects the agent into the bloodstream to give a clearer picture of whether the testicle is in the groin or abdomen.
  • A laparoscopy: The doctor inserts a tiny tube with an attached camera through a small incision in the abdomen. If necessary, they can also perform corrective surgery using the same tool.
  • Open surgery: In rare, complicated cases, surgeons will use this to explore the abdomen directly.

If both testicles are undescended, the doctor may recommend a genetic test to determine the sex chromosomes.

Some genetically female babies have external male genitalia or ambiguous genitalia. In this case, a doctor may use:

  • ultrasound imaging to check for undescended testicles or ovaries
  • blood and urine tests to measure hormone levels
  • genetic testing to identify sex chromosomes

In around half of all infants with cryptorchidism, the testicle will descend on its own within 3 months.

However, in 1 or 2 of every 100 infants with cryptorchidism, the testicle has not descended by the time the baby reaches 6 months of age. If this occurs, treatment is necessary.

Orchidopexy

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A surgeon may perform an orchidopexy if the testicle has not descended by the time the baby reaches 6 months of age.

A surgeon will often use an orchidopexy procedure, or orchiopexy. This is a procedure to free an undescended testicle and implants it in the scrotum.

A child usually undergoes this surgery when they are between 6 and 18 months old. It is important to perform the procedure before the child is 2 years old because delays may increase the long-term risk of testicular cancer or infertility.

Infertility is a risk because the testicles need to be at a certain temperature to produce sperm. If the testicles remain inside the inguinal canal, for example, the high temperature can impair sperm production.

During an orchidopexy, the surgeon makes a small incision in the abdomen and uses small instruments to move the testicle down the inguinal canal and into the scrotum, which requires a second incision.

The surgeon will usually seal the inguinal canal to stop the testicle from moving back up. In most cases, the infant can return home on the day of surgery.

If a testicle does not descend, its temperature can rise high enough to cause a low sperm count or poor sperm quality.

Testicular cancer is another complication of an undescended testicle, though the risk is lower than 1 percent. The link between the two conditions remains unclear.

Cryptorchidism also increases the risk of testicular torsion. This occurs when the spermatic cord becomes twisted.

The spermatic cord contains nerves, blood vessels, and tubes that carry semen between each testicle and the penis. If a person does not receive quick treatment, they could lose the twisted testicle.

Also, if an undescended testicle is located in the groin, pressure from the pubic bone can damage it.

Finally, as with any surgery on the testicles, an orchidopexy carries a risk of damaging the vas deferens, which is the tube connecting each testicle to the urethra.

Takeaway

Cryptorchidism is a common and treatable condition in which one or both testicles does not drop into the scrotal sac while a male fetus is developing.

The condition resolves in 50 percent of cases without treatment. However, some infants with an undescended testicle require a procedure called an orchidopexy to correct the issue.

If an undescended testicle does not receive treatment soon enough, there is a risk of infertility later in life. While the surgery carries risks, its outlook is good.

Q:

Can adults have undescended testicles?

A:

Yes, though it is rare. For those who receive routine healthcare, this is usually found and repaired at a young age. However, an undescended testicle or testicles can occur in someone who did not receive the appropriate diagnosis and treatment during childhood.

Occasionally, a testicle that was in the scrotum at birth can “ascend” back up into the inguinal canal during childhood, but this does not happen after puberty. In some cases, a testicle can be absent from birth or lost to trauma and may appear to be undescended.

Karen Gill, MD Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.