Brain cancer. Coloured magnetic resonance imaging (MRI) scan of a coronal (vertical) section through the head of a child with a glioma brain cancer (pink). This is a tumour of the glia, the connective cells that make up about 40% of the volume of the brain. Glioma is the most common type of tumour originating in the brain. Low- malignancy gliomas press against healthy brain tissue as they grow, causing loss of brain function, including sensory disturbances, speech problems and muscle weakness. Highly-malignant gliomas invade and destroy new areas of brain. MRI scans are slice images through the body made using a strong magnet and pulses of radio waves.