Revisiting the Intratemporal Course of the Facial Nerve

Introduction The facial nerve displays a lot of variations and anomalies in its course. Having sound knowledge about the surgical anatomy along with its intricacies is essential in mastoid surgeries. In this study, we have documented the angle of deviation of the mastoid segment of the facial nerve during its intratemporal course and the importance of this angle during mastoid surgeries. Aim and objectives The objectives of this study were to document and assess the orientation of the intratemporal course of the mastoid segment of the facial nerve and to measure the angle of deviation of the mastoid segment of the facial nerve as it traverses from the second genu to the stylomastoid foramen. Methodology A prospective observational study was conducted between December 2023 and June 2024 on 20 wet temporal bone specimens. Following canal wall down mastoidectomy, the facial nerve was explored and completely traced from the second genu to the stylomastoid foramen. High-quality images were captured and uploaded to the GIMP 2.10.36 software. At the second genu, a tangential line was drawn in the sagittal plane. Another line was drawn along the course of the facial nerve until its exit at the stylomastoid foramen. The angle between these two lines was estimated, and the angle of deviation was documented using this software and statistically analyzed. Results The mean angle of deviation at the second genu was found to be 15 (12-18) degrees in all 20 specimens. It was found that as the facial nerve traverses towards the stylomastoid foramen, from its anteromedial course it becomes more lateral and superficial. The anteroposterior angulation between males and females had a p-value of 0.02591, showing that it was significant. Similarly, the medial to lateral angulation between males and females had a p-value of 0.0458, which showed significance. However, the anteroposterior and medial to lateral angles did not show any significance when compared to the standard angle of 15 degrees as per literature, showing a p-value of 0.456 and 0.275 respectively. This helped us understand and document the highly variable course of the mastoid segment of the facial nerve, which can be emphasized during further research. Conclusion This angle of deviation of the mastoid segment of the facial nerve, around 15 degrees, will help surgeons be more careful during mastoid surgeries as it helps in assessing the depth and highly variable course of the facial nerve during its intratemporal course. This further acts as a guiding tool for budding surgeons in preventing inadvertent facial nerve injuries.