Histiocytic meningioma: A distinctive subtype of meningioma?

Meningioma with extensive histiocytic changes is rare. We describe a case of histiocytic meningioma which occurred in a 55-year-old woman. The patient had a progressive headache and a decline in fine motor coordination and memory for the past four years. Magnetic resonance imaging demonstrated a well-demarcated, dura-based and contrast-enhancing mass lesion in the right superior frontoparietal region. Histopathologically, the tumor showed neoplastic meningothelial proliferation with extensive and multifocal histiocytic infiltration. The histiocytic component constituted approximately half of the entire tumor. Immunohistochemically, both meningothelial and histiocytic cells showed immunoreactivity for epithelial membrane antigen (EMA), while the histiocytic cells were also positive for CD4 and CD68. In addition, there were scattered S100-positive histiocytes throughout the tumor. Proliferative index highlighted by Ki67 immunostain was 1.6%. There were no high-grade changes such as frequent mitoses, necrosis, or brain parenchymal invasion in the specimen. With review of the literature, we propose that this type of meningioma should be considered as a separate subtype of meningioma. The biological basis and differential diagnosis are discussed.