Anatomical features of the mastoid segment of the facial canal

Abstract

Background: Considering the tortuous course of the facial canal that houses the facial nerve, the stylomastoid artery, and the homonymous vein, its morphological features are of great clinical significance in otologic, maxillofacial, oncologic, reconstructive and plastic surgery of the head and neck. The aim of this paper was to determine the individual specific features of the mastoid segment of the facial canal and of the stylomastoid foramen.

Materials and methods: The study was carried out on 82 temporal bones (41 right/41 left), at the Department of Anatomy and Clinical Anatomy of Nicolae Testemitanu State University of Medicine and Pharmacy of the Republic of Moldova. The morphometry of the mastoid segment of the facial canal and of the stylomastoid foramen was performed. The morphometric parameters were statistically analysed by descriptive and inferential statistics methods.

Results: The mastoid segment exited the facial canal at obtuse, right and sharp angles, with a mean value of 113.1 ± 21.80° (right/left - 112.1 ± 23.85°/114.1 ± 19.76°), p = 0.701. The mean length of the mastoid segment was 15.1 ± 3.78 mm (right/left - 15.7 ± 3.66 mm/14.5 ± 3.84 mm), p = 0.153. The longitudinal diameter of the stylomastoid foramen had a meanof 3.0 ± 0.93 mm (right/left - 3.3 ± 0.96 mm/2.7 ± 0.81 mm), p = 0.007. The transverse diameter had a mean of 2.6 ± 0.74 mm (right/left - 2.9 ± 0.80 mm/2.4 ± 0.60 mm), p = 0.012.

Conclusions: In otologic surgery, particularly in mastoidectomy, it should be taken into consideration that the mastoid segment of the facial canal could exit the temporal bone at sharp, right and obtuse angles. This peculiarity, along with high morphological variability of the stylomastoid foramen, might be a predisposing factor for Bell's palsy.

Keywords: anatomical variations; facial canal; facial nerve; morphometry.