[Multiple sclerosis mimicking brain tumor: an unusual presentation].

Multiple sclerosis (MS) is almost always diagnosed in current medical practice on the basis of clinical, biologic and imaging criteria without need for tissue diagnosis. There are, however, rare pseudo tumoral cases of MS with atypical clinical and imaging features that suggest initially a neoplastic or an infectious processes and in which a stereotactic brain biopsy becomes needed for the diagnosis. We report the case of a 28-year-old man who presented with a right hemiparesis of rapid onset. Magnetic resonance imaging (MRI) of the brain showed a left contrast enhancing fronto-parietal mass lesion with important peripheral edema and displacement of the lateral ventricle. The patient underwent stereotactic biopsy of the mass. The pathologic examination revealed gross architectural disorganization of the white matter with massive infiltration by numerous foamy macrophages and a few lymphocytes consistent with a demyelinating disease. Despite a standard corticoid therapy regimen with initial clinical improvement, the patient was readmitted to the hospital three weeks later for relapse of right hemiparesis. Two months later, he recovered almost entirely except for a slight residual weakness in his right arm and a mild dysarthria. The MRI at that time showed a marked decrease in size of the brain lesion. The stereotactic brain biopsy remains to date the most dependable means for diagnosing the rare pseudotumoral forms of MS and differentiating them from their neoplastic and infectious mimickers.