Prospective Analysis of the Greater Occipital Nerve Location in Patients Undergoing Occipital Nerve Decompression.

Abstract

Migraine surgery and onabotulinumtoxinA injections aim to deactivate neurovascular trigger points implicated in chronic headaches. The greater occipital nerve (GON) is a common trigger point. The 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. We reviewed records of patients who underwent GON decompression by a single surgeon. Intraoperative measurement of the GON location lateral to midline, inferior to the occipital protuberance, and deep to the skin was collected for 2 previously described positions: where GON (a) enters, "point #2," and (b) exits, "point #3," the semispinalis muscle as it travels from deep to superficial (Plast Reconstr Surg. 2010;126:1563-1572; Plast Reconstr Surg. 2004;113:693-697). Thirty-four subjects (60 nerves) were included. The mean depths of the GON were 20 mm (SD, 4) at point no. 3 and 30 mm (SD, 6) at point no. 2. In 26 subjects who underwent bilateral surgery, there was a difference between right and left nerve position lateral to midline at point no. 3 (P = 0.008). Female sex (P = 0.014) and body mass index of 29 kg/m or less (P < 0.001) were associated with a more superficial GON position. Knowledge of the GON depth (eg, mean of 20 mm where it emerges from the semispinalis muscle) may improve accuracy of procedural treatments for migraines. When performing bilateral interventions, nerve position may differ between sides, particularly with respect to lateral distance from midline. Differences in this study compared with previous anatomic studies may reflect the use of live subjects in a prone position compared with cadaver specimens.