Left retrosigmoid perspective of the upper cranial nerves with tentorium removed. The left cerebellar hemisphere has been retracted medially. The basilar artery has numerous branches along the trunk including anterior inferior cerebellar arteries (AICA) and pontine perforating arteries, ultimately dividing into the superior cerebellar arteries (SCA) and posterior cerebral arteries (PCA). Cranial nerve III exits the midbrain between the SCA and PCA and courses anteriorly alongside the posterior communicating artery. Cranial nerve IV is visible running from the dorsal midbrain anteriorly toward the cavernous sinus. Cranial nerve V emanates from the anterolateral pons toward Meckel’s cave and has a close relationship to the SCA. Cranial nerves VII is visible here from its origin to the geniculate ganglion, where it turns and courses inferiorly as the mastoid segment giving off the chorda tympani. AICA courses near the root exit zone of the cranial nerve VII-VIII complex. Caudally, cranial nerves IX, X, and XI enter the jugular foramen, while cranial nerve XII is deep and medial and exits the skull via the hypoglossal canal. (Image courtesy of AL Rhoton, Jr.)