Two patients with cerebral lesions: is it tumor or multiple sclerosis? Illustrative cases

BACKGROUND: Multiple sclerosis (MS) is a common demyelinating disease of the central nervous system, usually presenting with multiple small white matter lesions. In some rare cases, it can present as a singular tumefactive white matter plaque. OBSERVATIONS: The patient in case 1 was a 33-year-old woman presenting with a restriction of fine motor skills. Magnetic resonance imaging showed a singular round lesion in the left frontal lobe with ring enhancement and moderate perilesional edema. Assuming the diagnosis of a neoplasm, total resection was performed. Histological examination showed an early active inflammatory demyelinating process. A final diagnosis of MS was made. The patient in case 2 was a 65-year-old woman who had been diagnosed with MS 10 years earlier and was experiencing moderate left hemiparesis. She was found to have a progressive right thalamic lesion with contrast enhancement, perilesional edema, and space-occupying effect. Stereotactic biopsy of the lesion was performed. Histological examination revealed a glioblastoma multiforme World Health Organization grade IV, and concomitant chemoradiation was recommended. LESSONS: On the one hand, tumefactive MS can be a diagnostic challenge because it mimics neoplasms or abscesses. On the other hand, a new lesion in patients with a diagnosis of long-standing demyelinating disease may not necessarily be a new demyelinating lesion and should be closely monitored.