Transillumination is the shining of a light through a body cavity or organ.

How the test is performed
The room lights are dimmed or turned off so that the appropriate part may be seen more easily. A bright light is then pointed at a cavity or organ, typically the head, scrotum, or chest of a premature or newborn infant; the breast of an adult female; or the scrotum of an adult male.

How to prepare for the test
No preparation is necessary for this test.

How the test will feel
There is no discomfort associated with this test.

Why the test is performed

This test is most commonly performed on newborns or infants with hydrocephalus, or males suspected of having a hydrocele. The test may also be performed on breast tissue to detect lesions and/or cysts. In newborns, a bright halogen light may be used to transilluminate the chest cavity if it is suspected they have a pneumothorax.

Transillumination through the chest is only possible on small newborns. Diagnosis of pneumothorax is always confirmed by chest x-ray. In general, transillumination is not a particularly good test for any of these disorders, and further tests, such as an X-ray or ultrasound, are needed to confirm the diagnosis.

Normal Values
Normal findings depend on the area being evaluated, and the normal tissue of that region.

What abnormal results mean

Areas filled with air or fluid that is not supposed to be in that location have increased light transmission and transilluminate when they should not. For example, in a darkened room, a newborn infant’s head can be seen to light up brightly when transilluminated if there is excess fluid present (suggesting hydrocephalus).

Results specific to the breasts include:

  • If there is a lesion and bleeding has occurred, those internal areas will be dark to black, because blood does not transilluminate.  
  • Benign tumors tend to appear red.  
  • Malignant tumors are brown to black.

What the risks are
There are no risks associated with this test.

Johns Hopkins patient information

Last revised: December 3, 2012
by Gevorg A. Poghosian, Ph.D.

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