Background: Reports of a correlation between relief of migraine headaches and resection of corrugator muscles or injection of botulinum A toxin have renewed interest in finding the cause of migraine headaches and identifying the trigger sites. Four trigger sites have been described. One of these is along the course of the greater occipital nerve. Recent anatomical studies of this nerve have defined its location with respect to external landmarks, leading to new studies with gratifying results. There is a subset of patients who undergo chemodenervation or surgical release of the greater occipital nerve and note improvement or elimination of the symptoms along the greater occipital nerve course but who experience an emergence of migraine headache symptoms laterally. The authors propose the lesser occipital nerve as the source of pain in those who experience headaches laterally and involvement of the third occipital nerve in those who notice residual symptoms in the midportion of the occipital region.
Methods: To test this hypothesis anatomically, 20 cadaver heads were dissected to trace the course of the lesser occipital nerve and third occipital nerve and define the location of these nerves with respect to external landmarks. The midline and a line drawn between the inferiormost points of the external auditory canals were used to obtain standardized measurements of these nerves.
Results: The location of emergence of the lesser occipital nerve was determined to be an area centered 65.4 ± 11.6 mm from midline and 53.3 ± 15.6 mm below the line between the external auditory canals. The third occipital nerve was found 13.2 ± 5.3 mm from midline and 62.0 ± 20.0 mm down from the line between the two external auditory canals.
Conclusions: This information can be used to conduct clinical trials of chemodenervation of these nerves in an attempt to eliminate migraine symptoms in the subset of patients who continue to experience residual symptoms after surgical release of the greater occipital nerve.