Left Transsylvian Transchoroidal Approach to the Basal Cisterns. A, Left frontotemporal exposure. The inset shows the position of the head and skin incision for the frontotemporal craniotomy. The sylvian fissure has been opened and the temporal operculum has been retracted to expose the anterior half of the insula. The M2 branches have been retracted to show the position of the incision (dashed black line) along the inferior limiting sulcus. The cortical incision through the inferior limiting sulcus begins approximately 1 to 2 cm posterior to where the anterior end of the long gyrus fuses with the temporal pole and extends posteriorly approximately 1.5 to 2 cm. The anterior one half of the inferior limiting sulcus is devoid of larger perforating arteries. The incision is made lateral to the inferior MCA trunk between the M2 branches, which run parallel to the inferior limiting sulcus. The cortical incision along the inferior limiting sulcus can be located medially, as shown in this photograph, or lateral to the posterior insular vein without sacrificing the vessel. B, The cortical incision, at a depth of approximately 0.5 cm in most hemispheres, provides access to the anterior portion of the temporal horn. The amygdala is located at the anterior edge of the cortical incision in the anterior wall of the temporal horn. This approach exposes the head and body of the hippocampus. The inferior choroidal point, the site at which the anterior choroidal artery passes through the choroidal fissure, is located near the middle of the exposure. The distance between the inferior limiting sulcus and inferior choroidal point is approximately 11 mm. C, The choroidal fissure has been opened by dividing the attachment of the choroid plexus to the fimbria of the fornix, and the choroid plexus has been elevated toward the thalamus. This approach exposes the hippocampus and collateral eminence in the floor of the temporal horn. The upper portion of the medial edge of the parahippocampal gyrus is exposed medial to the hippocampus. Opening the choroidal fissure exposes the branches of the PCA in the ambient cistern. D, The choroid plexus has been retracted to the thalamic side to expose the lateral geniculate body, basal vein, and P2 segment of the PCA. E, The PCA has been elevated to expose the branches of the PCA in the depths of the ambient cistern. (Images courtesy of AL Rhoton, Jr.)