What Is Transillumination?

Transillumination is a test used to identify abnormalities in an organ or body cavity. The test is performed in a dark room, with a bright light shined at a specific body part to see the structures beneath the skin.

The test is simple and easy, and offers a quick way for your doctor to check your body or organs. It’s also completely painless and requires no special preparation. If your doctor sees something wrong, they will order more tests to make a complete diagnosis.

Transillumination can help diagnose certain medical conditions. However, it’s most often used with along with other procedures to confirm a diagnosis. For example, it may be used with other imaging tests, such as an ultrasound or MRI, and may precede a biopsy.

Certain conditions may be visible with transillumination, including:

  • cysts or lesions in a woman’s breast
  • spermatocele, a cyst that develops in the coiled tube of the upper testicle
  • a collapsed lung in newborn babies
  • hydrocele, an opening between the scrotum and the peritoneal cavity in newborn males
  • hydrocephalus, a fluid accumulation in the brain of an infant
  • hydranencephaly, the absence of brain matter in an infant
  • cracked teeth
  • diseases of the eye


Hydrocele primarily affects premature babies. The hole between the scrotum and peritoneal cavity does not close on its own and fluid leaks out around the testicles. The hole may eventually close on its own or may require surgical repair.


Hydrocephalus can be genetic or the result of an infection. The goal of treatment is to drain fluid from around the brain. Shunts may be placed in the brain to drain excess fluid. Hydrocephalus can be fatal if left untreated.


Hydranencephaly is a rare and fatal disorder in which an infant is born without a portion of its brain. Most babies die within a few days or weeks of birth. The cause of this condition is unknown.

Cracked Teeth

Transillumination of teeth can identify fractures, especially after restorations are removed.

Eye Diseases

Transillumination is used to check for various diseases in the eye, including cysts and tumors. It’s also useful in checking your iris and the overall health of your eyes.

Your doctor will dim the lights in the exam room to perform the transillumination test. They’ll place a bright light very close to the body part being examined, such as the breast, scrotum, head, or chest. The combination of lighted areas, dark spots, and colors that appear can help your doctor determine if more testing is needed.

The area being tested will light up brightly if air, fluid, or non-solid masses such as cysts are present. The absence of an organ will allow light to pass through the skin and will also appear bright. Solid masses will appear dark and normal.

Your doctor will notify you if the results show any abnormalities. They’ll schedule you for further testing to confirm the diagnosis.

Transillumination offers a quick and simple way to check your organs and body for abnormalities. Keep in mind that transillumination is a first step and is used in conjunction with other tests. If transillumination yields abnormal results, your doctor will order more tests to confirm a diagnosis.