Microsurgical resection of a primary mixed intramedullary-extramedullary thoracic meningeal melanoma.

Background: Primary meningeal melanoma is an exceedingly rare malignant neoplasm arising from leptomeningeal melanocytes, accounting for only 0.06-0.1% of all central nervous system tumors. These melanocytes, derived from neural crest cells, typically localize within the ventral leptomeninges of the spinal cord and brainstem. Lesions most often occur in the cervical or thoracic spine and may mimic meningioma, schwannoma, or metastasis. Due to its rarity and nonspecific imaging features, diagnosis relies on histopathologic and molecular confirmation following surgical resection. Complete excision with adjuvant radiation remains the mainstay of treatment, though long-term outcomes are poorly defined due to limited reports. Case Description: We present a 61-year-old woman with a multi-segmental thoracic lesion spanning T8-T12 causing progressive genital and low-back pain, paraparesis, and sensory deficits. Magnetic resonance imaging revealed a contrast-enhancing intradural lesion with ventral extramedullary and intramedullary components. The patient underwent T7-T12 laminectomies for microsurgical resection with continuous neuromonitoring. Following dural opening, the tumor was identified in the ventrolateral extramedullary space with focal invasion into the spinal cord. Resection of the extramedullary component of the tumor was first undertaken until the tumor coursed into the intramedullary compartment. Sharp dissection and meticulous pial entry allowed circumferential mobilization and safe removal of the intramedullary portion while preserving the spinal vasculature. A gross total resection was achieved. The patient had a transient exacerbation of her right lower extremity weakness, which improved back to baseline within a few weeks from surgery. Histopathology revealed a densely cellular melanocytic tumor with focal necrosis and low proliferative index. Genetic testing identified a guanine nucleotide binding protein, alpha q (GNAQ) missense variant, confirming primary meningeal melanoma. With no systemic disease, adjuvant fractionated radiation was planned. The patient's recovery was stable, and she was discharged to rehabilitation on postoperative day 9. Conclusion: This case highlights the surgical nuances and diagnostic considerations involved in treating rare mixed intramedullary-extramedullary meningeal melanomas of the thoracic spine.