Brain membrane tumour. Sequence of magnetic resonance imaging (MRI) sagittal scans showing the internal structure in the head of a 53-year-old woman with a para-falcine (parasagittal) meningioma. The front of the head is at left in this side view, and the sequence moves through the head from one side to the other. A meningioma is a tumour that arises from the meninges, the membranes that enclose the brain. This one has arisen in the region of the falx cerebri (cerebral falx), the arched fold of dura mater found in the longitudinal fissure between the cerebral hemispheres. The tumour is the light grey mass at upper centre around the middle of the clip. It appears in the clip between the points where the eyes are shown. It is indenting the corpus callosum, the bundle of nerve fibres in the same region that connects the two hemispheres of the brain. The tumour, which is also distorting the lateral ventricles, was discovered following persistent headaches.