The anatomy of the greater occipital nerve: implications for the etiology of migraine headaches.

An interest in pursuing new theories of the underlying etiology of migraine headaches has been sparked by previously published reports of an association between amelioration of migraine headache symptoms and corrugator resection during endoscopic brow lift. This theory has further been reinforced by recent publications documenting improvement in migraine headaches following injection of botulinum A toxin. There are thought to be four major "trigger points" along the course of several peripheral nerves that may cause migraine headaches. Among these peripheral nerves is the greater occipital nerve. For this reason, the authors have undertaken an anatomic study of this nerve to determine its usual course, potential anatomic variations, and possible points of potential entrapment or compression. The results of this anatomic study have enhanced further development of techniques designed to address these points of entrapment/compression and potentially lead to relief of migraine headaches caused by this mechanism. Twenty cadaver heads from patients with an unknown history of migraine headaches were dissected to trace the normal course of the greater occipital nerve from the semispinalis muscle penetration to the superior nuchal line. Standardized measurements were performed on 14 specimens to determine the location of the emergence of the nerve using the midline and occipital protuberance as landmarks. On the basis of this information, the location of emergence was determined to be at a point centered approximately 3 cm below the occipital protuberance and 1.5 cm lateral to the midline. This location can, in turn, be used to guide the practitioner performing chemodenervation of the semispinalis capitis muscle in an attempt to provide migraine symptom relief.