Tumefactive Acute Disseminated Encephalomyelitis.

Tumefactive demyelination is a phenomenon involving the radiographic resemblance of an acute demyelinating process in the central nervous system to neoplasia. Although this has been described and characterized for multiple sclerosis, it has been reported in a few cases in patients with acute disseminated encephalomyelitis (ADEM) within the past decade. While it may be challenging to establish a diagnosis of tumefactive ADEM according to clinical and radiological data alone, a thorough review of the clinical history and following the patient over time can be supportive of the same. The principal diagnostic confounds include neoplastic disease and a first attack of multiple sclerosis. A definitive diagnosis can be made by biopsy, which reveals perivenular demyelination and mononuclear cell infiltration in ADEM, in contrast to confluent plaque-like areas of demyelination in patients with multiple sclerosis. Histopathologic evidence of neoplastic disease includes characteristic features, including nuclear atypia and polymorphism, cellular hyperproliferation, mitoses, necrosis, endothelial proliferation, rosettes, and/or pseudorosettes. ADEM responds excellently to treatment with corticosteroids and is monophasic, with recurrence occurring infrequently. We review the literature on tumefactive ADEM and discuss the clinical manifestations, imaging characteristics, and histopathologic findings used to distinguish it from other conditions.