Triplication of the lesser occipital nerve.

Triplication of the lesser occipital nerve (LON) was observed bilaterally in an adult male cadaver during routine prosection of the posterior triangle. The three LONs were studied to determine the clinical importance of this variation. The origin of one LON was from a nerve to the trapezius that had a common origin with the trunk of the supraclavicular nerve (C3,4) from the cervical plexus. Such a common origin of a LON may explain the pain referred to the shoulder and arm that is experienced by some patients with cervicogenic headache. Another LON ran across the roof of the posterior triangle, passed through the trapezius and was closely related to the point of exit of the greater occipital nerve (GON) from the trapezius. This LON supplied the nape of the neck, back of the scalp and the auricle. The anomalous course taken by this LON through the trapezius may be an explanation for cervicogenic headache precipitated by neck movement. The close relationship of this variant LON to the exit of the GON from the trapezius seems to be relevant to the management of cervicogenic headache. The authors suggest that the reason for the complete pain relief experienced by some patients with cervicogenic headache by anesthetic blockade of the GON may be because both the GON and LON are blocked simultaneously due to their proximity in these patients.