The posterior ligament of the incus (“white dot”): A reliable surgical landmark for the facial recess

Abstract

ObjectiveThere is a void in the literature describing reliable surgical landmarks that aid in the dissection of the facial recess in the absence of skeletonizing the mastoid segment of the facial nerve. The posterior ligament of the incus is a readily distinguishable “white dot” along the incus buttress that has been used to guide dissection in a safe and efficient manner. The goal of our study is to describe a surgical approach that utilizes this surgical landmark to drill the facial recess and to take anatomical measurements demonstrating the safety and reliability of this approach. Materials and methodsAfter cortical mastoidectomies were performed in 10 cadaveric temporal bones, the white dot was identified at the junction of short process of the incus and the incus buttress. Using the white dot for anatomical reference, a 2 mm diamond drill bit was used to open the facial recess without first identifying the facial nerve or chorda tympani nerve. After photographs were taken, the facial and chorda tympani nerves were definitively identified and skeletonized to delineate the confines of the facial recess. Photographs were once again acquired in a consistent manner for comparison. Finally, calibrated anatomic measurements were acquired from the 10 distinct image sets. ResultsThe facial recess was successfully drilled in 10 temporal bones using the posterior ligament as a surgical landmark without injury to the chorda tympani or facial nerve. The median angle taken from the axis of the short process of the incus to the facial nerve - chorda tympani junction was 139.2° (IQR 136.8–141). At the widest point in the facial recess, median distances anterior and posterior to an imaginary line connecting the white dot to the facial nerve - chorda tympani junction were 1.6 mm (IQR 1.5–1.7) and 1.6 mm (IQR 1.6–1.7; p = 0.57), indicating at this point, the white dot reference reliably bisects the facial recess width. Similarly, at the level of the round window niche, median anterior and posterior distances from an imaginary line connecting the white dot to the facial nerve - chorda tympani junction were 1.1 mm (IQR 1.1–1.3) and 1.3 mm (IQR 1.1–1.7; p = 0.07), respectively, once again demonstrating the white dot reliably bisecting the facial recess. ConclusionsThe white dot, representing the posterior ligament of the incus, is a reliable surgical landmark that aids in safe and efficient drilling of the facial recess without first skeletonizing the facial nerve.