In recent years, transillumination has become recognized in many pediatric centers as an aid in the diagnosis of subdural collections of fluid in infants under 12 months of age.1,2 The value of the test may be abrogated, however, if rather strict conditions for its application are not observed, and if the test is not interpreted in the light of the total clinical picture. The purpose of this brief communication is to describe the test in detail and to briefly discuss the results of such a test in a variety of clinical conditions.
A standard 2-cell flashlight is modified by molding a cuff of foam rubber about the edge of the illuminating surface. The foam rubber should be approximately 3/8 in. thick and extend 1/2 in. beyond the rim. The rubber may extend for a variable distanc, usually up to 2 in., behind the rim. The foam rubber is then