The cerebellar arteries.

Optimizing operative approaches to the posterior fossa requires an understanding of the relationship of the cerebellar arteries to the cranial nerves, brainstem, cerebellar peduncles, fissures between the cerebellum and brainstem, and the cerebellar surfaces (45). When examining these relationships, three neurovascular complexes are defined: an upper complex related to the superior cerebellar artery (SCA); a middle complex related to the anteroinferior cerebellar artery (AICA); and a lower complex related to the posteroinferior cerebellar artery (PICA) (Figs. 2.1 and 2.2) (35). Other structures, in addition to the three cerebellar arteries, occurring in sets of three in the posterior fossa that bear a consistent relationship to the SCA, AICA, and PICA are the parts of the brainstem (midbrain, pons, and medulla); the cerebellar peduncles (superior, middle, and inferior); the fissures between the brainstem and the cerebellum (cerebellomesencephalic, cerebellopontine, and cerebellomedullary); and the surfaces of the cerebellum (tentorial, petrosal, and suboccipital). Each neurovascular complex includes one of the three parts of the brainstem, one of the three surfaces of the cerebellum, one of the three cerebellar peduncles, and one of the three major fissures between the cerebellum and the brainstem. In addition, each neurovascular complex contains a group of cranial nerves. The upper complex includes the oculomotor, trochlear, and trigeminal nerves that are related to the SCA. The middle complex includes the abducens, facial, and vestibulocochlear nerves that are related to the AICA. The lower complex includes the glossopharyngeal, vagus, accessory, and hypoglossal nerves that are related to the PICA. In summary, the upper complex includes the SCA, midbrain, cerebellomesencephalic fissure, superior cerebellar peduncle, tentorial surface of the cerebellum, and the oculomotor, trochlear, and trigeminal nerves. The SCA arises in front of the midbrain, passes below the oculomotor and trochlear nerves and above the trigeminal nerve to reach the cerebellomesencephalic fissure, where it runs on the superior cerebellar peduncle and terminates by supplying the tentorial surface of the cerebellum. The middle complex includes the AICA, pons, middle cerebellar peduncle, cerebellopontine fissure, petrosal surface of the cerebellum, and the abducens, facial, and vestibulocochlear nerves. The AICA arises at the pontine level, courses in relationship to the abducens, facial, and vestibulocochlear nerves to reach the surface of the middle cerebellar peduncle, where it courses along the cerebellopontine fissure and terminates by supplying the petrosal surface of the cerebellum. The lower complex includes the PICA, medulla, inferior cerebellar peduncle, cerebellomedullary fissure, suboccipital surface of the cerebellum, and the glossopharyngeal, vagus, spinal accessory, and hypoglossal nerves. The PICA arises at the medullary level, encircles the medulla, passing in relationship to the glossopharyngeal, vagus, accessory, and hypoglossal nerves to reach the surface of the inferior cerebellar peduncle, where it dips into the cerebellomedullary fissure and terminates by supplying the suboccipital surface of the cerebellum.