1245. Transmuscular Exposure of the Occipital Artery During the Retrosigmoid Approach – A New Simple Technique Based on Anatomic Findings

Authors: Leandro Borba Moreira; Ali Tayebi Meybodi, MD; Xiaochun Zhao, MD; Michael Lawton; Mark Preul (Phoenix, AZ)

Introduction: Harvesting the occipital artery during the retrosigmoid approach can be challenging. The traditional method involves finding the OA subcutaneously near the superior nuchal line and following it proximally. However, this requires a larger incision and risks the superficially located OA distally. We assessed the anatomic feasibility and safety of suboccipital OA segment exposure through a limited retromastoid skin incision and transmuscular approach. Methods: 14 OAs were harvested though a 3cm-long incision placed 3cm posterior to the mastoid process. Muscular layers of the craniovertebral junction were sequentially cut and recorded before OA exposure. Changes in orientation of muscle fibers were used as a roadmap to expose OA without damage. Varieties of relationships between OA and muscular layers were recorded. Results: OA was successfully exposed without damage in all specimens by considering fiber orientation of two consecutive muscle layers: sternocleidomastoid and splenius/longissimus complex. Following skin incision, vertically-oriented fibers of the sternocleidomastoid muscle were the first exposure layer. One level deeper, anteroposteriorly-oriented fibers of the splenius capitis were exposed. In 10 specimens, OA was found underneath the deep fascial layer of the second layer. In remaining 4 specimens, OA was found underneath the longissimus capitis deep fascia. However, since the orientations of fibers of the longissimus and splenius capitis were similar, OA was successfully exposed without injury by deeper dissection as long as the muscle fibers ran anteroposteriorly. Conclusion: This innovative transmuscular technique of OA harvest is reliable based on the orientation of muscle fibers exposed from superficial to deep, before the OA is exposed along its retromastoid course. This technique may facilitate exposure and protection of the OA during the retrosigmoid approach, and obviate the need for larger incisions when a bypass is planned to the posterior circulation vessels through a retrosigmoid craniotomy, such as the anterior inferior cerebellar artery.