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OBJECTIVE: The authors examined the clipping of middle cerebral artery (MCA) aneurysms using the endoscopic transorbital approach (ETOA) with cadavers and in clinical cases to clarify which patients are good candidates based on preoperative imaging data. METHODS: To determine the indications for MCA clipping using an ETOA with superior-lateral orbital rim osteotomy, 10 sides of 5 cadavers were investigated. The clippable range, defined as the horizontal range, and exposure of the middle cranial fossa base, defined as the vertical extent area, were evaluated. To assess the ETOA trajectory in the MCA, the superior and inferior maximal angles based on the nasion-sella line were evaluated during cadaveric dissection. To test the surgical properties for actual use, 2 clinical cases were evaluated. RESULTS: The bases of the middle cerebral fossa, which were located below the sphenoid ridge, were accessible in all 5 cadavers. The suction tip and clip applier did not conflict with each other when access was made approximately 17.6 ± 3 mm (mean ± SD) laterally from the cranial midline and 6 ± 2 mm from the median temporal bone margin (clippable range). The superior angle was 16.7° ± 7.8°, and the inferior angle was 18.7° ± 9.6°. Two clinical cases underwent procedures using the ETOA. The aneurysms were at the MCA bifurcation in the anterior direction. The clippable ranges of the patients were 29 mm and 31 mm, respectively, and the distances from the midline to the median temporal bone margins were 32 mm and 36 mm. The M1 lengths were 14.5 mm and 17.2 mm, and the maximal diameters of the aneurysms were 3.58 and 3.67 mm. CONCLUSIONS: Clipping using an ETOA is appropriate for MCA aneurysms with anterior, superior, and inferior dome projections. Aneurysms with a horizontal boundary from the anterior clinoid process to the lateral bone margin of the orbital ball and a vertical boundary around and below the sphenoid ridge can be properly clipped using the ETOA.
Yoon et al. (Mon,) studied this question.