MRI in multifocal eosinophilic granuloma: staging disease and monitoring response to therapy.

Multifocal eosinophilic granuloma is part of the spectrum of histiocytosis X, in which the unifying feature is the proliferation and infiltration of histiocytes. Central nervous system (CNS) involvement has a predilection for the hypothalamic nuclei, and these infiltrates appear as high signal foci on T2-weighted magnetic resonance (MR) images that completely resolve after effective chemotherapy. Intradiploic skull lesions are well delineated with MRI, and the relation to underlying brain may be confidently assessed. MRI is the procedure of choice for staging multifocal eosinophilic granuloma in the skull and CNS, as well as for monitoring response to therapy.