Evaluation of the relationship of the sigmoid sinus with the facial nerve and semicircular canals in terms of mastoid surgery.

Purpose: The location of the sigmoid sinus may change according to the ventilation status of the mastoid bone, in which case the relationship of the sigmoid sinus to the facial nerve and semicircular canals is predicted to change. The purpose of this study was to evaluate the importance of sigmoid sinus distances to the facial nerve and semicircular canals concerning mastoid surgery.

Methods: The relationship of the sigmoid sinus and the facial nerve with the semicircular canals was analyzed from the cone beam computed tomography images of 75 male and 95 female subjects, aged 18-65 years. First, a line drawn from the posterior semicircular canal to the sigmoid sinus on axial CT images was used to assess whether the sigmoid sinus was lateral or medial. Second, sigmoid sinus typing was performed quantitatively on 3D reconstructed images. The distance between the sigmoid sinus-facial canal, sigmoid sinus-semicircular canals and sigmoid sinus-basal part of the cochlea was measured.

Results: The sigmoid sinus was found to be lateral to the posterior semicircular canal in 80.8% of cases and medial in 19.2% of cases. The posterior semicircular canal-sigmoid sinus distance was determined to be 11.76 ± 0.99 mm and 9.99 ± 0.93 mm on the right side and 11.99 ± 0.43 mm and 9.87 ± 0.02 mm on the left side, respectively, according to the sigmoid sinus patterns.

Conclusion: According to our results, it was found that the relationship between the semicircular canals and the facial canal varied according to the location of the sigmoid sinus, and in the medially located sigmoid sinus, the facial canal was very close to all three semicircular canals.