Brain membrane tumour. Sequence of magnetic resonance imaging (MRI) axial 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 top in this view from below, and the sequence moves through the head from bottom to top. 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 white mass at centre that appears briefly just after the middle of the clip, just above the level of the eyes. 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.