Transinsular Transchoroidal Approach to the Perimesencephalic Cisterns. A, Specimen showing right orbitozygomatic craniotomy with exposure of the frontal and temporal lobes along the sylvian fissure. The inset shows the site of the scalp incision and craniotomy. B, The sylvian fissure is widely opened to expose the insular cortex and insular branches of the M2 segment of the middle cerebral artery. C, Specimen showing enlarged view. The inferior limiting sulcus of the insula has been exposed. D, Specimen showing cortical incision through the anterior portion of the inferior limiting sulcus parallel to M2 branches opening into the temporal horn and exposing the choroid plexus and head of hippocampus. The temporal horn usually lies approximately 0.5 cm deep to the inferior limiting sulcus. E, Specimen showing choroidal fissure opened by dividing the attachment of the choroid plexus to the fimbria of the fornix and retracting the choroid plexus toward the thalamus to expose the lateral geniculate body, basal vein, and P2p. F, Specimen showing P2p elevated to expose the depths of the ambient cistern and an inferior temporal branch of the P2p passing to the lower surface of the temporal lobe. (Images courtesy of AL Rhoton, Jr.)