Intraparenchymal Meningioma: Clinical, Radiologic, and Histologic Review

BackgroundAlthough meningiomas are usually attached to the dura matter, intraparenchymal and subcortical meningiomas do not show dural attachment.MethodsA total of 39 cases of intraparenchymal meningiomas including subcortical meningiomas were reviewed.ResultsCompared with ordinary meningiomas, intraparenchymal meningiomas occurred more frequently in males and at younger ages. Unusual magnetic resonance imaging findings such as heterogeneous enhancement and cystic components were frequently recognized. Histologic analysis revealed half of the intraparenchymal meningiomas to be of the fibrous type, and approximately 20% of the tumors were diagnosed as World Health Organization grade II–III disease. Compared with sylvian fissure meningiomas, which also lack dural attachment, patients with intraparenchymal meningiomas were younger than those with sylvian fissure meningiomas. Gross total resection was performed more frequently for intraparenchymal meningiomas than for sylvian fissure meningiomas. More patients with intraparenchymal meningiomas than those with sylvian fissure meningiomas showed malignant phenotypes, and fibrous phenotypes were twice as common among intraparenchymal meningiomas as among sylvian meningiomas.ConclusionsBecause of the unique features described earlier, which contrast with those of ordinary meningiomas, there is a possibility that intraparenchymal meningiomas are not precisely diagnosed. Collectively, the information collected from the study cases may facilitate the appropriate management of these rare tumors.