Pterional Exposure of a Transsylvian Approach. A, Dissection photograph showing (inset) that a right pterional craniotomy has been completed, and the sylvian fissure has been opened to expose the walls of the fissure. The limen insula, anterior part of the insula, the inferior insular sulcus, the temporal pole, and the M1 and M2 segments of the middle cerebral artery have been exposed anterolaterally. This anterolateral exposure accesses the entry point above the amygdala and anterior tip of the temporal horn in the floor of the sylvian fissure that does not cross the optic radiations. B, Dissection photograph showing that the lateral part of the sylvian fissure has been opened to expose the inferior insular sulcus posterior to the limen. This trajectory is more lateral than that shown in A. The site of the amygdala deep to the floor of the medial part of the floor of the sylvian fissure is outlined in green. The incision (yellow line) that opens into the amygdala and the temporal horn carries less risk of damaging the optic radiations than the incision behind the limen (black line) in the inferior insular sulcus. C, Dissection photograph showing that the incision in the inferior limiting sulcus has been completed to expose the head of the hippocampus, the choroidal fissure, and the anterior choroidal artery. An incision that opens directly from above along the inferior insular sulcus, as shown in this dissection, is much more likely to cross the optic radiations than a more anterior incision (yellow line) that exposes the temporal horn through the amygdala (green oval). D, Dissection photograph showing the right transsylvian exposure (A). The middle cerebral artery has been elevated to expose the limen. The gray matter overlying the uncinate fasciculus, which courses deep to the limen, has been removed. E, Dissection photograph showing that a cortical incision has been made on the medial side of the uncinate fasciculus, and a portion of the amygdala, which resides largely in the anterior segment of the uncus, has been removed to expose the hippocampal head. This incision avoids the optic radiations. F, Enlarged view. The head of the hippocampus is exposed in the floor of the temporal horn. The incision can be extended laterally through the limen, uncinate fasciculus, and anterior a few millimeters of the inferior insular sulcus if needed to deal with the pathological features. The incision directed through the amygdala into the temporal horn avoids the optic radiations. (Images courtesy of AL Rhoton, Jr.)