Megalocephaly and hypodense extracerebral fluid collections.

Computed tomographic (CT) scans were identified and reviewed for 25 pediatric patients with enlarged heads and extracerebral fluid collections that showed cerebrospinal fluid-like attenuation. Mild to moderate enlargement of the subarachnoid space over the convexity, interhemispheric fissure, and the lateral ventricles was observed in most of the cases. The CT findings are not specific, and it is not always possible to determine the nature of the extracerebral fluid, whether it lies in the subarachnoid space, the subdural space, or both. The differential diagnosis included subdural effusions, hygromas, preclinical or external hydrocephalus, hypodense subdural hematomas, megalocephaly, and possibly a normal variant. CT remains the method of choice for the initial study of these patients and for subsequent follow-up in selected cases.