Anatomy revisited

The CPA is an inverted, triangular subarachnoid space containing cranial nerves (5–11) and blood vessels bathed in cerebrospinal fluid (CSF), located in the lateral aspect of the posterior fossa (figure 1). The tentorium forms the base of the triangle and the posterior temporal bone forms its lateral boundary. The pons is located medially and the cerebellum is posterior. The cistern extends into the petrous bone as the internal auditory canal, its medial aperture being known as the porus acousticus. The trigeminal nerve crosses the superior aspect of the cistern from the lateral pons to Meckel's cave. The facial and vestibulocochlear nerves arise from low in the CPA cistern at the lateral aspect of inferior medulla; they emerge at the level of the foramen of Luschka and ascend to the porus acousticus. The facial nerve lies anterior and superior to the vestibulocochlear nerve. Both are intimately related to the anterior inferior cerebellar artery, which in two-thirds of people loops into the internal auditory canal on at least one side.

Cranial nerves 9–11 arise from the medulla and upper cervical cord, cross the inferolateral aspect of the …