Erdheim-Chester disease: MR imaging, anatomic, and histopathologic correlation of orbital involvement.

Erdheim-Chester disease (ECD) is a rare form of histiocytosis of unknown origin characterized by tissue infiltration by lipid-laden histiocytes. Typically, the diaphyseal and metaphyseal portions of the tubular bones are affected, leading to a characteristic radiographic pattern of bone sclerosis. Orbital involvement is not infrequent and is manifested by exophthalmos and periorbital xanthomatous lesions, with associated visual problems.