Abstract: Intraoperative Location of the Greater Occipital Nerve in Patients Undergoing Migraine Surgery

PURPOSE: Migraine headaches are debilitating and widely prevalent. Newer treatment options for migraines include onabotulinum toxin A injections and migraine surgery. The greater occipital nerve (GON) is a common trigger point. For optimal results, both injection and decompression require knowledge of GON anatomy, and the average depth of this nerve has not been previously described. The purpose of this study was to report the intraoperative location, including depth, of the GON in human subjects undergoing migraine surgery to optimize future nerve identification. METHODS: We reviewed records of patients who underwent GON decompression by a single surgeon. Intraoperative measurement of the GON location in the x-, y-, and z-axes (e.g. distance, in millimeters (mm) lateral to midline, inferior to the occipital protuberance, and deep to the skin) was collected for two previously described positions: where the GON (a) exits (“point #3”) and (b) enters (“point #2”) the semispinalis muscle.1,2 Means were compared using independent t-tests. A p-value of < 0.05 was deemed statistically significant. RESULTS: Thirty-four subjects (60 nerves) were included, with a mean age of 41 years (SD 10) and mean BMI of 29 (SD 7) at time of surgery. The mean depths of the GON were 20 mm (SD 4) where the nerve exits the sempispinalis at point #3 and 30 mm (SD 6) at point #2. In 26 subjects who underwent bilateral surgery, there was no difference between right and left nerve depth at either point (p=0.720, p=0.534). There was a difference between right and left nerve position lateral to midline at point #3 (p=0.008). Female gender (p=0.014) and BMI < 29 (p<0.001) were associated with a more superficial GON position. CONCLUSION: The treatment of migraines requires a multidisciplinary, collaborative approach. The GON can be found approximately 20 mm deep to the skin where it exits the semispinalis muscle, an important consideration when performing targeted injection, diagnostic nerve blocks, and/or migraine surgery. Nerve position may be affected by BMI and gender, which should be considered prior to injection and/or dissection. When performing bilateral interventions, nerve position may differ between sides, particularly with respect to lateral distance from midline. Differences in this study compared to previous cadaver studies may reflect the inclusion of live subjects in prone position compared to cadaver specimens. Reference Citations: 1. Janis JE, Hatef DA, Ducic I, Reece EM, Hamawy AH, Becker S, Guyuron B. The anatomy of the grater occipital nerve: part II. Compression point topography. Plast Reconstr Surg 2010;126(5):1563–72. 2. Mosser SW, Guyuron B, Janis JE, Rohrich RJ. The anatomy of the greater occipital nerve: implications for the etiology of migraine headaches. Plast Reconstr Surg 2004;113(2):693–7.