Facial nerve trunk surgical identification: a new approach

Considering the lack of feasible methods for previsualisation of the extracranial portion of facial nerve and the high risk of its iatrogenic injuries, a better understanding of facial nerve identification landmarks is much needed. The aim of this study was to identify reliable landmarks for surgical access to the facial nerve trunk (FNT).

Our study was conducted on 75 hemifaces of adult embalmed cadavers. Prior to anatomical dissection, the cephalometric type of each head was determined and the landmarks identified for study were established.

For the FNT surgical access, eight landmarks were measured and statistically analysed against five criteria: gender, laterality, cephalometric type, branching pattern and its variant (classic/atypical). Six of the examined landmarks showed statistical significance depending on gender (p ≤ 0.05), i.e.: angle of the FNT bifurcation (FNTB); distance between the FNT division and the angle of the mandible (FNTD/AM); distance between the FNT division and the apex of the mastoid process (FNTD/AMP); distance between the FNT origin and the intertragic notch (FNTO/ITN); distance between the FNT origin and the triangular prominence of the cartilage of the external acoustic meatus (FNTO/ΔCEAM); and distance between the FNT origin and the anterior margin of the sternocleidomastoid muscle insertion point (FNTO/AMSCMIP). The angle formed at the intersection of the facial nerve trunk with a vertical line drawn through the anterior margin of the external acoustic meatus (FNT/VEAM), was statistically significant depending on laterality (p = 0.049). The FNT bifurcation angle was also statistically significant depending on the branching pattern (p = 0.005).

Six of the evaluated landmarks (75%) FNTB, FNTD/AM, FNTD/AMP, FNTO/ITN, FNTO/ΔCEAM and FNTO/AMSCMIP were statistically significant depending on gender and FNT/VEAM was significant depending on laterality. Based on the cephalometric type, the highest mean values were observed in the dolichocephalic type and the lowest in the brachycephalic type.