The safe zone of posterior semicircular canal resection in suboccipital retrosigmoid sinus approach for acoustic neuroma surgery.

The aim of the study was to find the safe zone of posterior semicircular canal resection that can avoid structure damage in suboccipital retrosigmoid sinus approach for acoustic neuroma. One hundred twenty subjects (72 male and 48 female subjects) were involved in this study anonymously. Five parameters are measured in computed tomography: L1 is the line that goes through the common bony crus and parallel to the plane that contains posterior semicircular canal at axial plane. L2 is the middle sagittal line at axial plane. A is the point of posterior wall of the internal auditory canal at the level of the common bony crus. B is the intersection point of L1 and posterior wall of auditory canal. L3 is the line that goes through the plane that contains posterior semicircular canal at coronary plane. L4 is the middle sagittal line at coronary plane. C is the common bony crus. D is the ampulla. E is the most posterior point of posterior wall of auditory canal at the plane that goes through the posterior semicircular canal. The angle between L1 and L2 was 41.76 (SD, 5.64) degrees on the right and 43.40 (SD, 5.25) degrees on the left (P = 0.003). The distance between A and B was 0.59 (SD, 0.13) cm. The angle between L3 and L4 was 16.57 (SD, 6.51) degrees on the right and 17.57 (SD, 6.98) degrees on the left (P = 0.017). The distance between C and D was 0.60 (SD, 0.05) cm. The distance between E and line CD was 0.48 (SD, 0.09).