A case of central nervous system vasculitis presenting as a mass-like lesion Abstract Vasculitis of the central nervous system presenting as a mass lesion is a relatively uncommon occurrence. Even more uncommon is a vasculitis mimicking a demyelinating lesion. We present here an interesting case of a 15-year-old boy who was found to have a mass-like lesion on neuroimaging involving the left subcortical white matter and deep gray matter. The differential diagnosis for this lesion was primary demyelination versus a glial tumor, the former being more favored over the latter. Biopsy of this lesion however revealed findings compatible with a vasculitis, which was unexpected given the neuroimaging findings. To the authors’ knowledge, case reports in the English literature of a vasculitic lesion mimicking demyelination are scarce. This case also serves as a reminder of the diagnostic difficulty that arises in a pediatric patient with an initial presentation of mass-like lesion.