Anatomical and Morphological Structure of the Lesser Occipital Nerve.

Objective To characterize the anatomical features of the lesser occipital nerve，thereby providing an applied anatomical basis for cervical neuralgia and local surgical procedures. Methods This study included both left and right sides of 40 adult formalin-fixed adult human specimens，totaling 80 sides.Routine incision was adopted in the dissection of lateral cervical region and the sternocleidomastoid region. Results The dissection rate of the lesser occipital nerve was 100%.Specifically，67.5%，25.0%，and 7.5% originated from the anterior branch of the third cervical nerve，the ansa cervicalis of the second cervical nerve，and the ansa cervicalis of the third cervical nerve，respectively.Below the accessory nerve，the lesser occipital nerve wraps around the accessory nerve in front of it to the vicinity of the posterior edge of the sternocleidomastoid or its shallow surface.It controls the skin on the upper part of the sternocleidomastoid，the upper part of the posterior cervical triangle，and the middle surface behind the auricle.The lesser occipital nerve specimens were classified into a single branch type （17.5%） and a multi-branch type （82.5%） after coiling around the accessory nerve in the posterior cervical triangle，among which the multi-branch type was dominated by the three-branch type. Conclusions The lesser occipital nerve is mainly a shrub-type nerve without a main trunk，and its distribution range spans the skin on the upper part of the sternocleidomastoid，the posterior cervical triangle，and the middle surface behind the auricle，and its position is superficial.The lesser occipital nerve block point should be at the midpoint of the posterior margin of the sternocleidomastoid and should not be too deep.