Anatomical Position and Classification of the Sigmoid Sinus on High-Resolution Computed Tomography Temporal Bone: A Retrospective Cross-Sectional Study

Background The sigmoid sinus demonstrates considerable anatomical variability, which is of critical importance during otologic and lateral skull-base surgeries. Variations in its position may increase the risk of intraoperative complications, including hemorrhage and limited surgical access. Objective To evaluate the anatomical position and classification of the sigmoid sinus on highresolution computed tomography of the temporal bone and determine associated demographic and radiological variations. Method A retrospective cross-sectional study was conducted at the Department of ENT-HNS, Dhulikhel Hospital. High-resolution computed tomography temporal bone scans performed between January 2024 and December 2025 were retrospectively reviewed. Patients with adequate imaging quality and complete demographic data were included, while those with prior temporal bone surgery, congenital malformations, fractures, or distorted anatomy were excluded. Sigmoid sinus anatomy was classified according to the system proposed by Sun et al. using standardized anatomical landmarks on axial and coronal high-resolution computed tomography images. Data were analyzed using SPSS version 22. Result A total of 212 patients' temporal bone scans were analyzed from patients aged 3 to 82 years (mean age: 31.5 ± 17.1 years). Type 3 Sigmoid Sinus was most common on the right side (31.1%), whereas Type 4 predominated on the left side (33-34%). Age demonstrated a significant association with left-sided Sigmoid Sinus (p = 0.010), but not with the right side. No significant association was observed with sex or ethnicity. Sigmoid sinus dehiscence was identified in approximately 15% of cases without significant side predominance. Conclusion Significant anatomical variability exists in sigmoid sinus position and morphology. Preoperative high-resolution computed tomography evaluation and standardized classification are essential for improving surgical planning, radiological reporting, and operative safety in otologic practice.