The Extended Retrosigmoid Approach for High-Riding Posterior Inferior Cerebellar Artery Aneurysms—Part I: A Quantitative Anatomical Analysis of the Glossopharyngo–Cochlear Triangle

Object: An extended retrosigmoid approach can offer sufficient space for clip reconstruction of high-riding posterior inferior cerebellar artery aneurysms. We conducted a quantitative anatomical analysis on the glossopharyngo–cochlear triangle (GCT) and structures within it.

Methods: Extended retrosigmoid craniotomies were performed on ten sides of cadaveric heads, and the GCT was identified in each specimen. The length of the base and the area of the GCT were measured. The depth of the vertebrobasilar system and the abducens nerve to the GCT were measured. The proximal and distal exposable and controllable points on the vertebrobasilar system were identified. The length from those points to the dural entry point of the vertebral artery were measured, and the superoinferior distance from those points to the inferior edge of the foramen magnum were recorded to establish approach algorithms based on the preoperative imaging. Other factors related to accessibility via the GCT were investigated.

Results: The mean (±SD) area of the GCT was 45.7 ± 12.55 mm². Through the GCT, the mean depths of the proximal exposable point, proximal controllable point, distal controllable point, and distal exposable point of the vertebrobasilar system were 12.2 ± 4.79, 14.7 ± 5.22, 18.9 ± 3.68, and 22.3 ± 4.01 mm, respectively; the mean depth of the abducens nerve was 14.3 ± 1.42 mm. The mean lengths between the dural entry point of the vertebral artery to the proximal exposable point, proximal controllable point, distal controllable point, and distal exposable point of the vertebrobasilar system were 30.5 ± 8.09, 33.8 ± 9.00, 43.1 ± 8.74, and 48.0 ± 7.86, respectively; the mean superoinferior distances from the foramen magnum to those points were 23.1 ± 7.39, 24.7 ± 8.25, 30.0 ± 9.56, and 32.6 ± 7.79 mm, respectively. The lower segment of the vertebrobasilar system was more superficial in the setting of a high-lying vertebrobasilar junction (VBJ) than a low-lying VBJ.

Conclusion: We describe the parameters of the GCT in an extended retrosigmoid approach for high-riding posterior inferior cerebellar artery aneurysms and evaluate the spatial relationship of the neurovascular structures within it, its relationship to the position of the vertebrobasilar junction, and the effect of a protruding jugular tubercle on this approach. Finally, two potential algorithms are offered for preoperative patient selection.

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