Fulminant Leptomeningeal Dissemination of Primary Intracranial Malignant Melanoma Following Surgical Resection

Primary intracranial malignant melanoma (PIMM) is exceptionally rare and prone to misdiagnosis due to its nonspecific radiologic features. A 32-year-old female presented with a left frontal mass, initially diagnosed as meningioma on imaging. Gross total resection was performed. Histopathology revealed PIMM with an exceptionally high mitotic count (33/2 mm²). Within 5 days postoperatively, she developed hydrocephalus and consciousness disturbance. Cerebrospinal fluid cytology confirmed malignant cells, and spinal MRI demonstrated diffuse leptomeningeal dissemination, indicating rapid cerebrospinal fluid spread. This case highlights the highly aggressive nature of PIMMs with elevated mitotic activity, the risk of misdiagnosis as meningioma, and the potential for surgery to precipitate devastating early leptomeningeal spread. It underscores the need for heightened preoperative suspicion and early postoperative vigilance in similar cases.