Occipital neuralgia/ migraine: Intra- operative evidence for extracranial pathology
Lisa Gfrerer, MD PhD, Marek A. Hansdorfer, MD PhD, Ricardo Ortiz, Bsc, Kassandra P. Nealon, Bsc, William G. Austen, Jr., MD.
Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
BACKGROUND: Recent clinical and basic scientific data supports a theory that aberrant anatomy and inflammation of structures surrounding peripheral/ extra-cranial sensory nerves can provoke migraines through compression/ irritation. Anecdotally, at the occipital trigger site, intra- operative anatomy of migraine surgery patients is distorted with thickened fascia/ muscle, dilated vessels that are tightly adhered to nerves, and atypical nerve course. This study scientifically evaluated this observation.
METHODS: 92 subjects scheduled to undergo migraine surgery at the occipital trigger site (Greater occipital nerve [GON] release) 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 examined.
RESULTS: Preoperatively, 67% of subjects reported bilateral pain. Pain on both sides was associated with abnormal tissue anatomy bilaterally (0.016). Unilateral pain was not predictive of one-sided tissue aberration. In fact, 19/30 (63%) subjects with pain on one side had abnormal findings on both sides. In 94% of subjects, abnormally thick trapezius fascia was seen, and in 30% of cases the nerve was encased in or compressed by fibrotic tissue at the muscle/ fascia interface. The occipital artery interacted with the GON in 88% of cases and 20% had dilated veins. The GON had an anomalous course in 42% of patients, and appeared crushed/discolored in 32%. CONCLUSIONS: In an ongoing effort to understand the extra-cranial pathophysiology of occipital neuralgia/ migraine, it is critical to describe the anatomic/ tissue changes encountered during migraine surgery. Although nerve compression/ irritation seems the common endpoint, it is currently unclear which tissues are involved in triggering migraine. Interestingly, patients with unilateral pain had bilateral pathology, further highlighting the importance of release on both sides. Pathology varied between subjects with both anatomic abnormalities (aberrant GON course, interaction of the occipital artery and nerve), as well as tissue pathology (thickened fascia and muscle, dilated vessels). Interestingly, the majority of subjects operated on had thickened/ fibrotic appearing trapezius fascia (94%), indicating a much more important role of soft tissues surrounding the nerve than previously implicated. Further, interaction of the occipital artery was seen in 88% of cases. This nerve/ artery interaction has a much higher incidence in migraine surgery patients than previously reported in dissection of cadavers (0-54%). This work is the basis for further research to elucidate pathophysiology of migraine.
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