Cerebellopontine cistern: microanatomy applied to vestibular schwannomas.

The microanatomy of the cerebellopontine cistern (CPC) is of interest to many surgeons and has been the subject of controversial works especially concerning the study of the subarachnoid space in the internal acoustic meatus (IAM). The CPC lies in the cerebellopontine angle between the brainstem, cerebellum and petrous bone. It contains in its upper part the trigeminal nerve with the superior petrosal vein. The cochleovestibulofacial bundle occupies the middle portion and lies between the pontomedullary sulcus and the IAM. The glossopharyngeal, vagus and accessory nerves are located in the inferior part of the cerebellopontine angle close to the vertebral artery and the posteroinferior cerebellar artery. The acousticofacial cistern is a lateral extension of the CPC in the IAM. The anatomy of the meningeal layers within the IAM is discussed especially concerning 'the arachnoidal cleavage plane' in acoustic neuroma surgery.