American Society for Peripheral Nerve

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Intraoperative Anatomy Associated with Migraines at the Frontal Trigger Site
Ricardo Ortiz, BSc; Lisa Gfrerer, MD, PhD; Marek A. Hansdorfer, MD; Kassandra Nealon, BSc; William G., Jr. Austen, MD
Massachusetts General Hospital, Boston, MA

Previous studies have suggested that the development of migraine headaches may involve the entrapment of craniofacial peripheral nerves at specific trigger sites. Cadaver studies in the general population have confirmed potential anatomic compression points of the supraorbital (SON) and supratrochlear (STN) nerve at the frontal trigger site, including bony supraorbital foramina and tight fascial bands. However, there are limited reports on anatomic compression points in patients undergoing surgery for headaches. In this study, we aim to describe the anatomy of patients undergoing migraine surgery at the frontal trigger site.

Materials and Methods
Subjects scheduled to undergo migraine surgery at the frontal site were enrolled in a prospective fashion. At the time of surgery, the senior author evaluated intraoperative anatomy and notes were made on anatomic variables using an intraoperative anatomy form and detailed operative report. The resulting data was analyzed.

A total of 126 sites (65 left and 61 right) in 67 patients were included in the study. The majority of subjects (80%) described pain from both left and right frontal sites. The SON course was through solely a notch in 50% of sites, a foramen in 48% (isolated foramen in 38%, notch plus foramen in 10%), and through neither a notch or foramen (solely a fascial band inferior to the supraorbital rim) in 1.7% of sites (Fig 1). The senior author noted that the SON and STN appeared compressed at 74% and 39% of sites, respectively. Reasons for suspected compression of the SON included a tight foramen in 38%, a notch with a tight band in 28%, a tight foramen plus notch in 11%, a STN and SON emerging via the same notch in 11%, and "other" in 12% (Fig 2).

The anatomy of the frontal trigger site varies greatly between patients undergoing migraine surgery. We report that the prevalence of foramina at SON sites is 48%, which is greater than any previous cadaver studies of the general population. We also report the most common suspected causes of SON and STN compression in migraine surgery patients, which often include a tight band and tight foramen.

Fig 1: SON emergence routes

Fig 2: Suspected causes of SON compression

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