Variations in the anatomy of the posterior auricular nerve and its potential as a landmark for identification of the facial nerve trunk: a cadaveric study.

The posterior auricular nerve (PAN) is the first extracranial branch of the facial nerve trunk. It innervates the posterior belly of the occipitofrontalis and the auricular muscles and contributes cutaneous sensation from the skin covering the mastoid process and parts of the auricle. This study was carried out to provide a detailed account of its anatomy and to ascertain its reliability as a surgical landmark for the facial nerve. Eleven facial sides from six formalin-fixed cadavers were dissected. The course and arborisation pattern of the PAN was observed, and its position of emergence from the facial nerve trunk (FNT) was measured. The PAN arose from the posterolateral aspect of the FNT 1.6-11.1 mm from the stylomastoid foramen (5.4 ± 3.3 mm). It arose as a single branch (45.4%), or from a common trunk that divided into two (36.4%) or three branches (18.2%), with the other branches passing into the parotid gland. The PAN continued deep (63%), or lateral to the mastoid process (9.1%), or through the tissue of the parotid gland (27.3%). In all cases the PAN ran in a consistent, superficial location posterior to the external auditory meatus. The PAN takes a variable course; however, its consistent location behind the external auditory meatus makes it easily identifiable in superficial dissection, and therefore a potential surgical landmark for identifying the FNT.