Meningioma. Coloured magnetic resonance imaging (MRI) brain scan showing a meningioma (yellow, upper left), a benign (non-cancerous) tumour. The front of the brain, seen in horizontal (axial) section, is at top. The two hemispheres that form the brain's cerebrum are green. Meningiomas arise from the arachnoid mater, the central of the three meninges membranes that cover and protect the brain and spinal cord. A large tumour like this may be compressing the brain, impairing mental function and causing headaches and vomiting. Most meningiomas are easy to surgically remove.