Origin Meningiomas originate from special meningothelial cells of the arachnoid membrane or the arachnoid granulations. These cells are found in the skull, the spinal canal, the choroid plexus and the arachnoid around cranial nerves. Most meningiomas are attached to the dura in areas where arachnoid villi are numerous. Most meningiomas are spherical masses, with broad implantation on the underlying dura mater. Meningiomas are not invasive, with evidence of a well-delineated interface between the tumor and the brain.
Most meningiomas have a firm consistency.
In case of calcification the tumor can even be very hard. Cysts within meningioma can be due to central necrosis, however peripheral true cysts can be secondary to reactive change, while pseudocysts are formed by entrapped CSF spaces. Edema can be focal or can involve an entire hemisphere. The latter is probably vasogenic in origin, due to venous mechanical obstruction or tumor hypervascularity. Meningiomas are typically highly vascularized.