Acoustic nerve tumour. Coloured axial (horizontal) magnetic resonance imaging (MRI) scan of the head of a patient with a tumour (red) on the acoustic nerve of the left ear. The scan is at the level of the ears, showing the base of the brain (lower centre) and the bony structures of the face (upper centre). Between these areas, are the internal ear structures (centre left and right). A nerve tumour is a neuroma. An acoustic neuroma is a benign and slow-growing tumour of the sheath of the balance (vestibular) part of the vestibulocochlear nerve. It eventually affects the auditory (cochlear) part of the nerve, causing tinnitus and hearing loss. Excessive growth may warrant surgical removal.