Intracranial Metaplastic Meningioma : Clinical and Radiological Characteristics of 11 Cases

Abstract

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.

Keywords: Meningioma of metaplasia · Magnetic resonance imaging · Lipomatous.

Fig. 1.

Distribution of surgically proven meningioma cases from 2004 to 2018 according to WHO grade. There were 1376 (75.9%) WHO grade I benign meningioma cases; 354 (19.5%) and 84 cases (4.6%) were WHO grades II and III, respectively. Among the WHO grade I meningioma, meningothelial subtype was the most common, occurring in 644 of 1376 cases (46.8%). The second most common subtype was transitional meningioma (372 cases, 27.0%), followed by fibrous, microcystic, and psammomatous subtypes. Relatively rare with less than 2% incidence were sclerosing, secretory, metaplastic and lymphocyte-rich meningiomas. Metaplastic meningioma was diagnosed in 11 cases, representing 0.8% of WHO grade I meningioma and 0.6% of all meningiomas during the 15-year study period. The rarest was lymphocyte-rich subtype, with only three cases (0.2%). WHO : World Health Organization.

Fig. 2.

A-D : Preoperative CT and MR images of lipomatous meningioma (case 1). White arrow suggesting the involvement of fatty components. E-H : Osseous meningioma (case 9). CT : computed tomography, MR : magnetic resonance.

Fig. 3.

Gross photo of the surgically resected specimen (formalin-fixed overnight). B : Representative microscopic image shows admixed meningioma tumor cells and fat component (hematoxylin & eosin stain, ×40). C : Membrane immunoreactivity of epithelial membrane antigen immunohistochemical stain observed (×100). D : Ki-67 immunohistochemical stain reveals low proliferative index of tumor cells (Positive in 5%, ×100).