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

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

Transillumination is also sometimes used to find blood vessels.

No preparation is necessary for this test.

There is no discomfort associated with this test.

This test may be done along with other tests to diagnose:

• Hydrocephalus in newborns or infants
• Hydrocele in males
• Breast lesions or cysts in adult females

In newborns, a bright halogen light may be used to transilluminate the chest cavity if there are signs of a collapsed lung. (Transillumination through the chest is only possible on small newborns.)

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

Areas filled with abnormal air or fluid will light up when they should not. For example, in a darkened room, the head of a newborn with possible hydrocephalus will light up when this procedure is done.

When done on the breast:

• Internal areas will be dark to black if there is a lesion and bleeding has occurred (because blood does not transilluminate).
• Benign tumors tend to appear red.
• Malignant tumors are brown to black.

There are no risks associated with this test.

In general, transillumination is not a particularly good test for any of these above-mentioned disorders, and further tests, such as an x-ray or ultrasound, are needed to confirm the diagnosis.