Primary intrathoracic meningioma: histopathological, immunohistochemical and ultrastructural study of two cases

Meningiomas are common, usually benign slow-growing neoplasms of the centra l nervous system thought to arise from meningocytes capping arachnoid villi . Primary ectopic meningiomas are exceedingly rare extracranial and extrasp inal tumors of controversial origin; they are usually limited to the head a nd neck region or to the paravertebral soft tissues. Only one mediastinal e ctopic meningioma and few pulmonary ectopic meningiomas have been described in the literature until now. Because of their rarity and their intriguing pathogenesis, we report here a second case of primary mediastinal meningiom a and an additional case of primary pulmonary meningioma. Their possible or igin and differential diagnosis are discussed.