Abstract
Primary central nervous system vasculitis (PCNSV) is rare, and the diagnosis is difficult to make because of its variable radiologic expressions. Early corticosteroid therapy often is effective. Herein we report the case of a 56-year-old man who had a well-enhanced cystic mass with severe edema in the right frontal lobe, which was initially felt to be a malignancy. Histologic examination of tissue removed at craniotomy revealed that it was a PCNSV. Despite early administration of corticosteroids, a new lesion developed within 3 days. The lesions responded to treatment with cyclophosphamide and corticosteroid.