Effect of Sigmoid Sinus Position on the Difficulty and Approaches to Cochlear Implantation Surgery

Abstract

Objectives: To assess the effect of the position of the SS on CI regarding the ability to perform posterior tympanotomy, round window visibility, and mastoid pneumatization.

Materials and methods: This is a prospective study, including 65 adult patients with CI performed at our center during 2017. We used 3 methods to assess SS position using a computed tomography (CT) scan. Lee's line passing through the tympanic segment of the facial nerve. Park's line passing through the facial nerve and round window membrane. Our proposed method using a parallel line from the external auditory canal and passing through the facial nerve. Relation to mastoid pneumatization on CT and to intraoperative round window visibility were assessed in relation to intraoperative position of the SS.

Results: The method by Park et al. was statistically significant (p<0.001); however, a cutoff point could not be set. Lee's method was statistically insignificant (p=0.091). Our proposed method was statistically significant with a cutoff point at ≤2.46 mm (p=0.001). SS position did not affect pneumatization nor round window visibility.

Conclusion: The position of SS preoperatively using a CT might suggest the inability to perform posterior tympanotomy and the need to change side or approach. However, it does not affect neither mastoid pneumatization nor visibility of the round window niche through the facial recess.

Figure 1

Left: Park’s method for sigmoid sinus position (right ear). Right: Lee’s method (left ear)

Figure 2

Left axial CT showing our proposed method for sigmoid sinus position. A line of the plane of the external auditory canal, blue dot: tympanic annulus, red dot: bony cartilaginous junction. B line parallel to A passing through anteromedial surface of the mastoid FN