Intracranial Metaplastic Meningioma : Clinical and Radiological Characteristics of 11 Cases

OBJECTIVE: Metaplastic meningioma is an extremely rare subtype of World Health Organization (WHO) grade I meningioma. It has distinctive histological subtypes according to its own mesenchymal components. Owing to its scarcity, clinical or radiological features of a metaplastic meningioma are poorly described. METHODS: Between 2004 and 2018, we analyzed total 1814 cases surgically proven meningioma for 15 years. Among them, metaplastic meningioma was diagnosed in 11 cases. Magnetic resonance images were taken for all patients, and computed tomography scan was taken for 10 patients. RESULTS: WHO grade I meningiomas were 1376 cases (75.9%), 354 cases (19.5%) in WHO grade II, and 84 cases (4.6%) in WHO grade III meningiomas. Metaplastic meningioma was 11 cases as 0.8% of WHO grade I meningioma and 0.6% of entire meningiomas for 15 years. Among the entire 11 metaplastic meningiomas, five tumors (45%) were diagnosed as a lipomatous subtype with rich fat components, four (36%) as an osseous subtype with extensive bone formation and two (18%) as a xanthomatous subtype. There was no cartilaginous subtype metaplastic meningioma in our study. Lipomatous and osseous metaplastic meningioma have peculiar radiological characteristics according to mesenchymal components. CONCLUSION: We investigated a rare metaplastic meningioma subtype based on our 15-year surgical experience with meningiomas. Further investigation will be necessary for the clear clarification of tumor nature of this rare tumor.