The CPA is the wedge-shaped space formed anteriorly by the dural-coated face of the petrous temporal bone, and posteriorly by the ventral surfaces of the pons and cerebellum. It contains the superior CSF cistern, which is traversed by the trigeminal, abducens, facial and vestibulocochlear nerves, the anterior inferior cerebellar artery (AICA) and the superior petrosal vein with its tributaries. The CPA has important relationships with surrounding structures. The cisterna ambiens, containing the trochlear nerve and the superior cerebellar artery, is located superiorly. Inferiorly lies the cerebellomedullary (inferior cerebellopontine) cistern containing the glossopharyngeal, vagal, accessory and hypoglossal nerves, along with the vertebral artery, origin of the PICA and the inferior petrosal vein. Medially lies the prepon-tine cistern which invests the basilar artery and the origin of the abducens nerve.
The cerebellar hemisphere wraps itself around the postero-lateral aspect of the pons forming the V-shaped cerebellopontine fissure. The middle cerebellar peduncle, flocculus and foramen of Luschka lie in the floor of the apex of the cerebellopontine fissure. The latter, with its tuft of protruding choroid plexus, is an important landmark for the emergence of the VII and VIII cranial nerves in CPA surgery.
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