Can MDCT Scan of the Temporal Bone Looking at Pneumatization Predict Surgical Vulnerability of the Facial Nerve?

Abstract

Objectives: The aim of this study is to investigate the scutum–cochleariform process (CP) and scutum–promontorium distances according to the mastoid pneumatization condition. Methods: Two hundred temporal multidetector computed tomography scans (90 males and 110 females) were evaluated retrospectively. The scutum-CP and scutum–promontorium distances were measured. Facial canal dehiscence (FCD) in the tympanic segment and mastoid pneumatization were also evaluated. Results: The distances between scutum-CP and scutum–promontorium were not different between males and females and between right and left sides. Facial canal dehiscence in the tympanic segment was detected: 5.6% (right) and 7.8% (left) in males and 5.5% (right) and 10.0% (left) in females. Grade 4 (100%) pneumatization was detected mainly in 55.6% to 57.8% of the patients in both genders. Grade 0 (0%) pneumatization (sclerosis) was detected in 22.2% to 28.2% of both males and females. In more pneumatized mastoids, the scutum-CP and scutum–promontorium distances increased. In sclerotic mastoids, the scutum-CP and scutum–promontorium distances decreased. Facial canal dehiscence rates were not related to the mastoid pneumatization levels. Conclusion: Cochleariform process is an important landmark to localize the tympanic segment of the facial canal. In sclerosed mastoids, scutum-CP and scutum–promontorium distances decreased. There was no relationship between FCD rates and mastoid pneumatization levels. It may be due to the development of FCD that occurs during the intrauterine period. In endoscopic and classic ear surgeries, mastoid pneumatization must be evaluated preoperatively to avoid facial nerve injuries.