Abstract
Tumefactive demyelinating lesions (TDLs) are atypical presentations of various demyelinating diseases. They can mimic brain tumors in their clinical and radiological features and usually respond favorably to corticosteroid therapy. We report a case of a 17-year-old girl with a single TDL suddenly increasing in size even under steroid therapy. She underwent very strict follow-up examinations with conventional magnetic resonance and diffusion-weighted imaging, perfusion-weighted imaging, proton-magnetic resonance spectroscopy. The behavior of the lesion during the different follow-up sessions posed a diagnostic challenge as it expanded its size during the final examination, in stark contrast to what we forecast. Diagnosis of TDL was initially hypothesized, but the aggressive behavior of the lesion required biopsy.