Schematic drawings of the rearrangement of the arachnoid plane in relation to the tumour growth. Left; 3-dimensional views from the anterior aspect in the cerebello-pontine cistern. Centre; axial sections through the facial and cochlear nerves. Right; sagittal sections through the internal auditory meatus (IAM). Arrowheads indicate the tumour-arachnoid adhesion that takes place at Stage 2 and moves medially as the tumour growth. AICA, anterior inferior cerebellar artery; AM ; arachnoid membrane, V; trigeminal nerve, VII-VIII; facial-cochlear nerves, IX-X; glossopharyngeal-vagus nerves.