Primary meningeal melanoma masquerading as neurofibromatosis type 2: illustrative case

BACKGROUND: Primary meningeal melanocytic neoplasms are exceedingly rare tumors, representing only 0.06% to 0.1% of all primary brain tumors and ranging in spectrum from benign localized tumors to highly aggressive malignant lesions. The diagnosis of these tumors is often challenging from clinical, radiological, and pathologic standpoints. Equally challenging is the distinction between primary meningeal melanocytic neoplasm and metastatic melanoma. OBSERVATIONS: The authors reported the case of a 41-year-old man with imaging findings diagnostic of neurofibromatosis type 2: bilateral internal auditory canal lesions (most consistent with bilateral vestibular schwannomas), two dura-based lesions presumed to be meningiomas, multiple spinal lesions consistent with peripheral nerve sheath tumors, and one intramedullary spinal lesion consistent with an ependymoma. Biopsy of these lesions revealed melanocytic neoplasms with mild to moderate atypia and a mildly elevated proliferation index, which made the distinction between benign and malignant challenging. In addition, the disseminated nature of these tumors made it difficult to determinate whether they arose from the meninges or represented metastases from an occult primary melanoma. LESSONS: This case illustrated the challenges presented by the diagnosis of meningeal melanocytic neoplasms and highlighted the importance of integrating the clinical and radiographic findings with histologic appearance and molecular studies.