Infectious diseases of the brain.

Magnetic resonance imaging is the modality of choice for the characterization of intracranial inflammation, by defining ependyma, white matter, gray matter, and leptomeningeal involvement. Hemorrhage is well shown, but calcification is difficult to identify. Intravenous Gd-DTPA is useful in the evaluation of B-b barrier abnormalities. Although it is not often possible to make a specific microbiologic diagnosis, MR appearances are usually helpful in excluding other abnormalities, such as neoplasm or infarction. Knowledge of the number and size of individual lesions is invaluable in monitoring therapy.