Fig. 3.

Histopathological examination of the mass reveals tumor growth in the intertrabecular space and whorl patterns of spindle-shaped cells (hematoxylin-eosin stain, original magnification, ×4 [A] and ×20 [B]). The tumor is marked with ossification (arrow) and lipomatous tissue (dashed arrow) inclusions, which are different from the pre-existing bone trabeculae and bone marrow fat. Immunohistochemistry shows that the tumor cells express epithelial membrane antigen (C) and progesterone receptor (D), but they are negative for MIB-1 (not shown here). Given these findings, the final diagnosis is intraosseous metaplastic meningioma (World Health Organization Grade I).