Morphologic variations of the sigmoid sinus on computed tomography: a classification-based study

PURPOSE: The sigmoid sinus is a vital dural venous structure whose anatomical variability has direct implications for lateral skull base and otologic surgeries. Understanding the sinus's positional variations is considered important for minimizing surgical risks. This study aimed to evaluate the morphological classification of the sigmoid sinus using a surgical reference-based system and to assess its relationship with demographic variables. METHODS: A retrospective analysis was conducted on high-resolution temporal bone CT scans of 241 patients (114 females [47.30%], 127 males [52.70%]) with an age range of 18-92 years (mean age: 47.95 ± 17.84). The morphology of the sigmoid sinus was classified into four types based on the system defined by Dong-Il Sun et al., using three anatomical reference lines. The width and depth of the sigmoid sinus were measured bilaterally and analyzed in relation to age and gender. Statistical analysis included paired tests for bilateral measurements, chi-square tests and ordinal logistic regression for associations with age and sex, and reliability assessment using Cohen's kappa and intraclass correlation coefficients. RESULTS: A total of 241 patients were included. Mean sigmoid sinus depth and width were 6.57 ± 1.73 mm and 14.55 ± 4.06 mm on the right, and 6.33 ± 1.52 mm and 15.18 ± 4.93 mm on the left, respectively. Left-sided width was significantly greater than the right (p < 0.05), whereas depth did not differ. Type 3 and Type 4 configurations predominated bilaterally; Type 1 was not observed. Age was significantly associated with left-sided sigmoid sinus type (p = 0.0048), with more medial configurations in older individuals. Ordinal regression showed decreasing odds of higher-type anatomy with increasing age (OR = 0.84 per decade). Gender was associated with left-sided type distribution but not independently predictive after adjustment. Inter- and intraobserver reliability was excellent. CONCLUSION: The positional morphology of the sigmoid sinus varies significantly with age and gender. The absence of Type 1 and predominance of high-risk configurations in younger individuals suggests the potential relevance of individualized preoperative assessment. This classification system may provide additional anatomical insight for radiologic evaluation; however, its direct impact on surgical decision-making requires further validation.