Unusual CNS relapse of plasma cell leukemia manifesting as multiple extra-axial brain lesions: A case report with literature review.

Central nervous system (CNS) involvement in multiple myeloma (MM) is rare - occurring in approximately 1% of cases - and typically presents as dural-based lesions, leptomeningeal infiltration or solitary parenchymal tumors. Multifocal extra-axial intracranial lesions without systemic relapse are extremely uncommon. We describe a 51-year-old male with plasma cell leukemia who initially presented with headache, hydrocephalus, and suspected meningitis. Magnetic Resonance Imaging (MRI) revealed multiple extra-axial contrast-enhancing lesions in the pineal region, sellar area, tectal plate, and cribriform plate. Cerebrospinal fluid (CSF) flow cytometry and neuro-navigation guided biopsy confirmed central nervous system (CNS) dissemination of plasma cell dyscrasia, bone marrow, serum, and urine studies were negative, confirming that this was an isolated CNS event. He underwent ventriculoperitoneal shunting and resection of the dominant pineal lesion. Despite treatment, follow-up imaging showed persistent intracranial disease along with new, abnormally enhancing nodular lesions within the cauda equine at the L2-L3 level. This case represents a rare case of multifocal extra-axial intracranial involvement of MM without systemic recurrence. It underscores the need for high clinical suspicion in atypical neuro-oncologic presentations and supports early surgical intervention for both diagnosis and symptomatic relief.