Coloured magnetic resonance imaging (MRI) scan of a large acoustic neuroma tumour (red) affecting the vestibulocochlear nerve (8th cranial nerve) in the brain of a 37 year old male patient. This nerve carries signals from the ear, which are responsible for balance and the sense of hearing. The growth of the tumour can lead to ringing in the ears (tinnitus), deafness and a loss of balance. The tumour is non-cancerous, and does not invade surrounding tissues. However, due to the symptoms, and the danger that it might put pressure on brain structures, it is often surgically removed, although this leads to deafness on the affected side.