Background: Knowledge concerning variability of the facial nerve trunk (FNT) direction after its exit through the stylomastoid foramen is of a great clinical significance for maxillofacial surgeons, otorhinolaryngologists, oncologists, specialists in plastic and aesthetic surgery. The aim of our study was to establish the variation of the FNT direction and its peculiarities depending on the branching pattern, gender, anthropometric type and side of the head.
Materials and methods: The direction of the FNT and its branching pattern were studied on 75 dissected hemifaces of adult formalised cadavers (59 male/ /16 female), and the morphometry of the FNT length, width and bifurcation angle was carried out.
Results: Seven branching patterns of the facial nerve were established: type I - 18.7%, type II - 14.7%, type III - 20%, type IV - 14.6%, type V - 5.3%, type VI - 18.7%, and type NI - 8% (bizarre types). The FNT had a descending direction in 73.3% of cases; ascending FNT - 9.3% (including 5.3% of very short diffuse branching trunks and 1.3% of arch-shaped FNT); horizontal FNT - 10.7%; number variants - 6.7%. The male/female ratio of the descending FNT was 69.5%/87.4%; ascending - 10.2%/6.3%; horizontal - 11.9%/6.3%; number variants - 8.4% (only in male). The right/left ratio of the descending FNT was 62.9%/82.5%; ascending - 11.4%/7.5%; horizontal - 11.4%/10%; number variants - 14.3% (only on the right side). The ratio of the descending FNT in mesocephalic type (MCT)/brachycephalic type (BCT)/dolichocephalic type (DCT) was respectively 70.6%/100%/66.7%; ascending - 12.1%/0%/0%; horizontal - 12.1/0%/11.1%. Numerical variants in MCT - 5.2%, in DCT - 22.2%. The mean number of FNT in MCT/BCT/DCT was respectively 1.07/1.0/1.22.
Conclusions: Three main directions are characteristic of the FNT: the descending, ascending and horizontal ones, which vary depending on the branching pattern, gender, shape and side of the head.
Keywords: branching types; facial nerve; morphometry; peculiarities; variation.