Facial nerve trunk variations with surgical implications: A cadaveric study

• We consider the maxilla and mandible as a single biomechanical unit and recommend it for future research in this area.
• We describe that digital palpation can be applied to identify the upper border of the PBM, thus locating the FNT as it coursed in a parallel direction to the PBM.
• We consider bony landmarks are more useful than soft tissue landmarks for deducing the position of the FNT, with only some sex-related differences.

Purpose: Anterograde identification of facial nerve trunk (FNT) identification is paramount, because FNT injury causes substantial morbidity. This study reexamines controversial landmarks and considers the importance of gender and dentition in landmark choice.MethodsDistances from key landmarks to FNT were measured and compared by side, gender and dentition (92 specimens). Landmarks included posterior belly of digastric muscle (PBM), tragal pointer (TP), mastoid process (MP), external acoustic meatus (EAM) and transverse process of axis (TPA).ResultsTwo-sample T tests showing longer distances from: MP/TPA to FNT in men than in women (14.8 ± 2.2 mm vs. 13.5 ± 1.6 mm, P = 0.004; 37.6 ± 4.4 mm vs. 32.7 ± 4.2 mm, P = 0.001); EAM to FNT on occlusal sides than on the counterparts (14.2 ± 1.8 mm vs. 16.0 ± 3.8 mm, P = 0.020). One-sample T tests showing longer distances from: TP to FNT on right than on left side (21.4 ± 2.7 vs. 19.9 ± 2.9, P = 0.006); MP to FNT on the less dentulous maxillae than on the counterpart (14.4 ± 2.1 vs. 13.0 ± 1.6, P = 0.027); PBM/EAM to FNT on the less dentulous mandible than on the counterpart (9.8 ± 1.6 vs. 7.8 ± 2.5, P = 0.039; 16.4 ± 3.0 vs. 14.1 ± 1.5, P = 0.020).ConclusionSurgeons should be aware that distances of MP, PBM and EAM, to FNT, are lengthened in less dentulous patients, especially when maxilla and mandibles are non-occlusive. Overall, soft landmarks are less reliable than osseous landmarks.