A coronal section of the brain through the brain at the level of the lenticular nuclei. A large mass between the hemispheres markedly distorts the brain. The mass is separable from the brain parenchyma. This is characteristic of a meningioma, which arises from the arachnoid cells.
Meningiomas arise from arachnoid cells.
Their cause is not known but occasionally they arise at sites of trauma or irradiation or in some hereditary tumor diatheses such as neurofibromatosis. The tumor grows from arachnoid cells when there has been loss of tumor suppressor genes and activation of protooncogenes. They are more comman in women than men, probably related to their tendency to have estrogen and progesterone receptors. They are the only truly benign tumor in that they usually do not recur after complete surgical removal. Meningiomas have a smooth bosselated external surface which is usually pink-tan in color.