Anatomical assessment of the digastric branch of the facial nerve as a landmark to localize the extratemporal facial nerve trunk.

ABSTRACT

PURPOSE: Localization of the facial nerve trunk (FNT) [i.e., the portion of the facial nerve between the stylomastoid foramen (SMF) and pes anserinus] may be required during various surgical interventions such as parotidectomy and hypoglossal-facial anastomosis. Several landmarks have been proposed for efficient identification of the FNT. We sought to assess the anatomical features of the digastric branch of the facial nerve (DBFN) and its potential as a landmark to identify FNT. METHODS: Fifteen sides of eight cadaveric heads were dissected to find the DBFN. Anatomic features of DBFN including its point of origin relative to SMF, length, and important relationships, as well as the distance between the insertion point on the digastric muscle and mastoid tip were recorded. RESULTS: DBFN was found in all specimens originating from the FNT outside the SMF with an average length (± standard deviation) of 15.4 ± 3.4 mm. In all specimens, the DBFN inserted on the superomedial aspect of the posterior belly of the digastric muscle (PBD). In 8/15 specimens, DBFN was accompanied by the stylomastoid artery on its anteromedial side. Average distance (± standard deviation) between the mastoid tip and the nerve insertion point on PBD was 13.6 ± 2.0 mm (range 10-17). CONCLUSIONS: The DBFN is a reliable landmark for identifying the FNT. It could be consistently identified within 15-20 mm of the mastoid tip on the superomedial aspect of the PBD. The DBFN may be used as a supplementary landmark for efficient localization of the FNT. LEVEL OF EVIDENCE Not applicable (anatomic study).