Case Series: tumefactive demyelinating lesions: a diagnostic challenge.

T umefactive demyelinating lesion (TDL) is defined as a solitary de myelin ating lesion greater than 2 cm. Mass effect and contrast enhancement on neuroimaging make it difficult to distinguish this type of lesion from high-grade gliomas. Multiple sclerosis (MS) accounts for most cases of TDL. Even in patients with established MS, an atypical manifestation of a large lesion can suggest concurrent neoplasm, because the clinical manifestations are often similar. When examined on magnetic resonance imaging (MRI) scans, TDLs have ill-defined borders, mass effect, perilesional edema, central necrosis, cystic degeneration, contrast enhancement and variable involvement of grey matter. Unless specifically requested, pathological exam in ation does not routinely include luxol fast blue staining, which can be used to detect demyelination. The presence of hypercellularity, atypical reactive astrocytes and mitotic figures can lead to an incorrect diagnosis of glial neoplasm. We present 3 cases of tumefactive demyelinating lesions that were clinically and radiologically challenging to distinguish from high-grade neoplasm.