Pathology of meningiomas.

Because meningiomas arise from arachnoid cells present in the meninges, they can occur in any location where meninges or ectopic meninges exist, such as the nasal cavity, the paranasal sinuses, the middle ear, and even the mediastinum. Although the tumors may range in appearance from epithelial to mesenchymal, they are characterized by a uniform distribution of cells with shapes ranging from polygonal epithelial-like to spindled and fusiform. Historically, classification of meningiomas has been based upon cell shapes, cell patterns, cell products, or stroma, implying clinicopathologic differences among the types. Numerous observations have shown that certain conditions may indicate a predisposition for developing meningiomas, prompting extensive studies of meningiomas using cytogenetic techniques. Meningiomas are common neoplasms arising from the central nervous system meninges. They are important because of the morbidity they produce. Their critical intracranial and intraspinal locations make diagnosis and surgical removal difficult.