Surgical Landmarks to Locating the Main Trunk of the Facial Nerve in Parotid Surgery: A Systematic Review.

PURPOSE: The purpose of this study was to describe distances from commonly used anatomic landmarks to the main trunk of the facial nerve during parotid surgery.

MATERIALS AND METHODS: A systematic search of the published literature was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. All studies from January 1, 1990 to January 1, 2017 that measured distances to the main trunk of the facial nerve from common anatomic landmarks were eligible. Inclusion criteria were English-language articles with distances measured from the main trunk of the facial nerve to anatomic landmarks. The primary outcome variable was the distance from the respective anatomic landmarks. Other variables included surgical approach, year, and existential status of subject (cadaveric or living).

RESULTS: The search yielded 1,412 studies (1,397 by PubMed, 15 by reference searching), with 10 studies meeting the inclusion criteria. Within the 10 studies, there were 30 reported means and 375 dissected cadavers. The most common incision was the standard preauricular incision; the mean distances to the facial trunk from landmarks were 13.6 ± 11.0 mm (n = 6 reported means) for the tragal pointer, 8.79 ± 3.99 mm (n = 7 reported means) for the posterior belly of the digastric muscle, 10.5 ± 1.4 mm (n = 4 reported means) for the tip of the mastoid process, 14.99 ± 1.68 mm (n = 3 means) for the transverse process of C1, 3.79 ± 2.92 mm (n = 6 means) for the tympanomastoid fissure, 9.80 ± 0 mm (n = 1 mean) for the styloid process, and 11.77 ± 1.42 mm (n = 3 means) for the external auditory meatus. Formal assessment of inter-study variability could not be assessed because of the small number of studies and measurements.

CONCLUSION: There are substantial variations in measurements from anatomic landmarks to the main trunk of the facial nerve in the literature. Therefore, multiple landmarks can be used to identify the main trunk of the facial nerve during parotid surgery. The distances reported in this study can guide surgeons during parotid surgery to decrease the risk of facial nerve damage.