Orbital gyrusの形態に着目した開放しにくいsylvian fissureの術前評価と手術における留意点

Abstract

Background: The deep-lying cisternal part of the Sylvian fissure stem is structurally complex. A more developed posterior orbital gyrus (pOG) adds complexities to the dissection in that plane because adhesion between the pOG and the temporal lobe is much thicker and stronger in such cases. The purpose of this study was to suggest a method of preoperative estimation of the degree of development of the pOG by using only axial-view computed tomographic (CT) images.Methods: First, we retrospectively classified 32 patients who underwent clipping of the anterior circulation aneurysms via the transsylvian approach at our institution into three types as follows, according to the degree of difficulty of the Sylvian fissure stem dissection evaluated using operative videos: type A, difficult; type B, normal; and type C, easy. Second, we hypothesized that an imaginary line (line D) joining the medial point of the Sylvian fissure with the limen insulae on axial CT images corresponds to the posterior rim of the pOG. Then, we evaluated the characteristics of line D in each case.Results: Five cases were type A, and line D was curved with a backward convexity, with a mean length of 4 cm. Eleven cases were type B, and line D was curved with a backward convexity, with a mean length of 3.5 cm. Sixteen cases were type C, and line D was curvilinear or straight, with a mean length of 3.48 cm.Conclusion: Preoperative evaluation of the morphological feature of the pOG is useful in estimating the degree of difficulty of Sylvian fissure stem dissection via the transsylvian approach.