Erdheim-Chester disease with extensive intraaxial brain stem lesions presenting as a progressive cerebellar syndrome.

We report a rare case of Erdheim-Chester disease (ECD) presenting as a progressive cerebellar syndrome and diabetes insipidus. On magnetic resonance imaging, a 7-mm extraaxial, enhancing mass was seen enveloping the right vertebral artery and was confirmed at autopsy to represent an adventitial xanthoma with lipid-laden, foamy histiocytes. The cerebellar syndrome most likely resulted from extensive histiocytic infiltration of the pons, particularly the basis pontis and middle cerebellar peduncles.