A, Posterior view with the left and part of the right half of the cerebellum removed. The SCAs (yellow) are intimately related to the superior half of the fourth ventricular roof and the cerebellomesencephalic fissure; the AICAs (orange) are intimately related to the cerebellopontine fissures and the lateral recesses; and the PICAs (red) are intimately related to the caudal half of the roof and the cerebellomedullary fissure. The SCAs pass around the midbrain above the trigeminal nerve and divide into rostral and caudal trunks. The branches of these trunks loop deeply into the cerebellomesencephalic fissure and give off the precerebellar arteries, which pass along the superior cerebellar peduncles to the dentate nuclei. The PICAS arise from the vertebral arteries and pass between the glossopharyngeal, vagus, and accessory nerves to reach the cerebellomedullary fissure. After passing near the caudal pole of the tonsils, where they form a caudal loop, they ascend through the cerebellomedullary fissure, where they are intimately related to the caudal part of the ventricular roof. They pass around the rostral pole of the tonsil and through the telovelotonsillar cleft, where they form a cranial loop. In their course around the tonsils, they divide into medial and lateral trunks. They give off branches to the dentate nuclei near the superior pole of the tonsils. The AICAs arise from the basilar artery and pass near or between the facial and vestibulocochlear nerves and are intimately related to the cerebellopontine fissures, the flocculi, and the lateral recesses. The AICAs divide into rostral and caudal trunks before reaching the facial and vestibulocochlear nerves. The rostral trunk passes between the nerves and along the middle cerebellar peduncle near the cerebellopontine fissure. The caudal trunk passes below the nerves and near the lateral recess to supply the lower part of the petrosal surface. The AICA and the PICA give rise to the choroidal arteries, which supply the tela choroidea and attached choroid plexus. B, Lateral view with the left half of the cerebellum re-moved to expose the fourth ventricle. The SCAs (yellow) are intimately related to the superior half of the fourth ventricular roof and the cerebellomesencephalic fissure; the AICAs (orange) are intimately related to the cerebellopontine fissures and the lateral recesses; and the PICAs (red) are intimately related to the caudal half of the roof and the cerebellomedullary fissure. The SCAs pass around the midbrain above the trigeminal nerve and divide into rostral and caudal trunks. The branches of these trunks loop deeply into the cerebellomesencephalic fissure and give off the precerebellar arteries, which pass along the superior cerebellar peduncles to the dentate nuclei. The PICAS arise from the vertebral arteries and pass between the glossopharyngeal, vagus, and accessory nerves to reach the cerebellomedullary fissure. After passing near the caudal pole of the tonsils, where they form a caudal loop, they ascend through the cerebellomedullary fissure, where they are intimately related to the caudal part of the ventricular roof. They pass around the rostral pole of the tonsil and through the telovelotonsillar cleft, where they form a cranial loop. In their course around the tonsils, they divide into medial and lateral trunks. They give off branches to the dentate nuclei near the superior pole of the tonsils. The AICAs arise from the basilar artery and pass near or between the facial and vestibulocochlear nerves and are intimately related to the cerebellopontine fissures, the flocculi, and the lateral recesses. The AICAs divide into rostral and caudal trunks before reaching the facial and vestibulocochlear nerves. The rostral trunk passes between the nerves and along the middle cerebellar peduncle near the cerebellopontine fissure. The caudal trunk passes below the nerves and near the lateral recess to supply the lower part of the petrosal surface. The AICA and the PICA give rise to the choroidal arteries, which supply the tela choroidea and attached choroid plexus. (Images courtesy of AL Rhoton, Jr.)