Polyorchidism is a very rare condition. Men with this condition are born with more than two testes, also known as testicles or gonads. There are only about 200 known reported cases. In the vast majority of cases, the individuals have three testes. There are fewer than 10 reported cases of someone having four or more testicles.

The additional testicle is usually located within the scrotum. In some cases, though, it may be higher in the inguinal (groin) area, closer to the lower abdominal wall or within the abdomen entirely.

The condition doesn’t necessarily present any health problems, though polyorchidism does slightly increase the risk of testicular cancer.

Polyorchidism often has no symptoms outside of the extra testis. When symptoms are present, they may include pain in the scrotum or lower abdomen, or an obvious mass in the scrotum.

Usually, the additional testis or testes are on the left side. The extra testicle is typically not as large as the two normal testes, making it more likely to go undetected for a long time.

Fertility is often unaffected by polyorchidism. For example, in a 2010 study, a father of three children informed his doctor about a painless mass in his scrotum. Imaging tests were done, but no further treatment was deemed necessary, as there were no related health concerns. A third or fourth testicle may function in the same way as a normal testicle.

If, however, you have been diagnosed with polyorchidism and fertility is becoming a challenge, talk to a fertility specialist. It’s not likely that a third or fourth testicle should interfere with the healthy function of the other two, but you may need further fertility testing just to make sure.

The causes of polyorchidism aren’t well understood. The rarity of the condition makes it difficult to research its origins.

One theory is that polyorchidism follows an abnormal division of the genital ridge early in the development of a male fetus. The genital ridge or gonadal ridge is the precursor to the testicles, and forms within the first two months. For reasons that remain unknown, the genital ridge may divide in such a way that a duplicate testis forms in the scrotum or up in the inguinal area.

Polyorchidism isn’t associated with other developmental or anatomical abnormalities. There does not appear to be a hereditary or environmental link to this rare condition.

In cases of polyorchidism in which there are no symptoms, the condition may be discovered during a self-exam or a physician’s exam that reveals an additional mass within the scrotum. The diagnosis tends to be made during adolescence. However, you could be in your 30s, 40s, or older before polyorchidism is diagnosed.

A doctor may find an additional testicle during an unrelated surgery for an inguinal hernia. That’s a painful condition in which tissue pushes through a weakened part of the abdominal muscles.

If a suspicious mass is found during an external exam, some imaging will be done to determine if it’s an extra testis, a tumor, or something else. A magnetic resonance imaging (MRI) test of the pelvic region may be ordered, as well as an ultrasound. Both screenings are noninvasive and painless. An MRI uses radio waves and a strong magnetic field to create images of soft tissue inside the body. Ultrasound uses sound waves to create pictures of organs and other tissues within the body.

These tests can determine the exact size and location of the testes, as well as reveal important information about them, such as their vascularity and whether there is any sign of testicular cancer.

Doctors divide cases of polyorchidism into two types: type A and type B.

In type A, the extra testicle is drained by a ductus deferens, which transports sperm to the ejaculatory duct. This testicle has reproductive potential. The majority of polyorchidism cases are type A.

With type B polyorchidism, the additional testicle is not drained by a ductus deferens, and therefore serves no reproductive purpose.

Unless there are indications of cancer or other complications related to the additional testicle, no medication or procedure is needed. Once you’ve been diagnosed with polyorchidism, the condition should be monitored as part of an annual checkup. That monitoring will include keeping track of any new symptoms, and receiving MRIs or ultrasounds as determined by the doctor.

There is some debate as to whether a superfluous testicle should be removed, as it raises the risk of cancer. If cancer is suspected through a biopsy of the testicle or from imaging, then an orchiopexy (removal of the additional testicle) may be advisable. Additionally, some doctors recommend removing abdominal testicles, as these have the highest risk of becoming cancerous

If you have been diagnosed with polyorchidism, it will be especially important to do regular self-checks for testicular cancer. You will also need to keep up with doctor appointments and imaging as recommended.

Unless you have symptoms or a test indicates cancer, this unusual condition shouldn’t interfere with your quality of life.