Transillumination of the Scrotum: Purpose and Procedure

Closeup of doctor performing transillumination of the scrotum and testicles

What Is Scrotal Transillumination?

Transillumination is when a doctor shines a bright light through the scrotum to check for abnormalities. The test is performed in a darkened room, and by holding a light behind the scrotum the doctor can easily determine whether any masses are present, and whether they are fluid-filled or solid (fluid in the scrotum will transilluminate, but solid masses won’t).

For example, hydrocoeles and large epididymal cysts will typically transilluminate, while tumors will not.

Scrotal transillumination can be performed with other tests in order to diagnose certain conditions, such as an ultrasound, blood test, or testicular biopsy.

The test is a quick and simple way for your doctor to examine the interior of your scrotum. It’s also completely pain-free and needs no special preparation. If your doctor notices something abnormal, he or she will perform additional tests to get a better indication of any potential condition you may have in order to make a complete diagnosis.

Why It’s Performed

Transillumination can assist with diagnosing certain medical conditions. However, it’s most frequently used along with other forms of testing in order  to confirm a diagnosis. For instance, transillumination may be used with a scrotal ultrasound and a testicular biopsy.‌

Here are some of the conditions that can be detected by a doctor using transillumination.


hydrocele is a swelling of the scrotum caused by the accumulation of fluid around one or both testicles. Hydroceles occur more frequently among male infants, but can occur in older boys and men due to injury or inflammation of the scrotum.

Hydroceles are typically not painful or dangerous and may not need any treatment. When using transillumination, a clear fluid that surrounds the testicle will be visible.


spermatocele is a cyst that develops in the epididymis ( a tube on the testicle that stores and transports sperm). Spermatoceles are not cancerous, and are usually painless and filled with fluid that might contain sperm.

Although it’s not known exactly why spermatoceles occur, it’s possible that they might develop due to a blockage in the epididymis, which receives and transports sperm from the testicle.

Spermatoceles are common and don’t usually affect fertility or need treatment. In some cases, surgery may be recommended if a spermatocele becomes large enough to become painful.

If you have a spermatocele in your scrotum, transillumination will show that the mass is filled with fluid rather than solid. The light will shine through the fluid-filled spermatocele, whereas a solid testicle (for example) will not allow much light to pass.‌


varicocele is swelling in the veins that transport blood from the testicles. They look similar to varicose veins that can occur in some people’s legs.

This condition often does not require any treatment and is usually harmless, causing little or no discomfort. In certain situations, however, varicoceles can be painful, lead to fertility issues, or slow the growth of the testicle. Varicoceles in these cases can often be surgically repaired.

Varicoceles are typically easy to detect using transillumination, as they appear as solid when exposed to light.

Inguinal Hernia

An inguinal hernia occurs when a small portion of the intestine descends into the scrotum, forming a lump. There are 2 kinds of inguinal hernias.

Indirect inguinal hernias occur in baby boys when the open lining does not close before birth, leaving a weak area in the groin. Pressure can cause the intestine to push through and bulge out. This type of hernia can happen soon after birth or much later in life.

Direct inguinal hernias are somewhat common in older men and can occur from exerting pressure, such as from straining during bowel movements, heavy lifting, or obesity). This pressure pushes part of the intestine through the weakened area in the groin.

Inguinal hernias seen through transillumination testing usually will not appear transparent (transilluminate).

Testicular Cancer

Compared with other types of cancer, testicular cancer is rare. However, testicular cancer is the most common type of cancer in men between the ages of 20-40 years old.

Tumors that occur from testicular cancer are typically painless lumps that form on the testicle. They appear as a solid, irregular mass that does not transilluminate.

To confirm cancer, the doctor will perform additional testing. This may include a blood test, ultrasound, X-ray, or a CT scan.

There are two types of testicular cancer: Seminoma cancer, which grows slowly, and nonseminoma cancer, which grows quickly. It is also possible to have both types at once.

Testicular cancer is highly treatable, even when the cancer has spread beyond the testicle. You may receive one of several different treatments, or a combination of treatments, depending upon the type and stage of the cancer.


In a darkened room, the doctor will shine a pen torch or special flashlight through the skin of the scrotum. The area being tested will light up brightly where there is fluid, or fluid-filled masses such as a cyst. If a testicle is absent it will also allow light to pass through the skin and will appear bright as well.

Solid masses will appear dark and and will not allow much light, if any, to pass through.

After transillumination, your doctor will let you know you if the results indicate any abnormalities. He or she will schedule you for additional testing to confirm the diagnosis.‌‌


Transillumination allows your doctor to check your scrotum for abnormalities quickly and easily. It’s important to remember that testicular transillumination is only an initial step and is used in combination with other tests.

If transillumination indicates any abnormalities, your doctor will schedule you for more tests to confirm a diagnosis.

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