Anterior Opening of the Sylvian (Lateral) Fissure
Trochlear Nerve|Superior Cerebellar Artery|Oculomotor Nerve|Optic Nerve|Optic Chiasm|Optic Tract|Anterior Cerebral Artery (A2)|Anterior Communicating Artery|Internal Carotid Artery|Middle Cerebral Artery (M1)|Anterior Cerebral Artery (A1)|Middle Cerebral Artery (M2)|Posterior Cerebral Artery|Medial Lenticulostriate Artery|Anterior Choroidal Artery
Anterior opening of the Sylvian (lateral) fissure. Mobilization of the temporal and frontoparietal lobes expose the basilar artery and its superior cerebellar and terminal posterior cerebral arteries. The oculomotor nerve is seen emerging from the anterior midbrain and coursing forward in the subarachnoid space between these two vessels. The trochlear nerve is seen wrapping around the midbrain from its dorsal midbrain origin. Both proceed forward into the roof and lateral wall, respectively, of the cavernous sinus. The optic nerve system is also exposed, with the optic nerves, chiasm, and tracts revealed. The intradural portion of the left internal carotid artery gives rise to the posterior communicating artery to the posterior cerebral artery and slightly more distally, the anterior choroidal artery. The latter vessel usually courses along the lateral aspect of the optic tract to the lateral geniculate body. The left middle cerebral artery, the larger of the two terminal branches of the internal carotid artery, is shown entering the Sylvian (lateral) fissure where it progressively divides into four M segments; M1 and M2 segments shown here. The anterior cerebral artery, the smaller terminal branch of the ICA, courses medially around the optic tract as the A1 segment before this vessel gives rise to the anterior communicating artery connecting the right and left anterior cerebral arteries. In its proximal segment it gives rise to small anterior perforating arteries (provided also from anterior choroidal and middle cerebral arteries) that enter the anterior perforating substance to supply the internal capsule, caudate nucleus, putamen, and globes pallidus. The A2 segment begins distal to the communicating artery and it enters the longitudinal interhemispheric fissure. (Image courtesy of PA Rubino)