Morphometric analysis of the C2 transverse foramen and vertebral artery using computed tomography angiography.

BACKGROUND: The anatomical relationship between the C2 transverse foramen (TF) and the vertebral artery (VA), particularly at the superior and inferior openings of the C2 TF, is clinically important in upper cervical spine surgery because of the potential risk of VA injury. This study aimed to quantify the morphology of the C2 TF and VA using computed tomography angiography (CTA), compare the superior and inferior openings, and evaluate the correlation between TF area and VA area. MATERIALS AND METHODS: Head and neck CTA images from 80 subjects were retrospectively analyzed. Curved multiplanar reconstruction (CPR) was used to measure the maximum and minimum diameters of the superior and inferior openings of the bilateral C2 transverse foramina. TF area, VA area, and the artery-to-foramen area ratio were calculated. Side-to-side and superior-inferior differences were compared, and correlations between TF area and VA area were analyzed. C2-level VA dominance was determined using the bilateral difference in mean equivalent VA diameter. RESULTS: The left C2 TF and VA areas were larger than those on the right side. VA area and the artery-to-foramen area ratio were higher at the superior opening than at the inferior opening. Bilateral symmetry was the most common C2-level VA dominance pattern, observed in 45 cases (56.3%), followed by left dominance in 27 cases (33.8%) and right dominance in 8 cases (10.0%). TF area was moderately correlated with VA area (r = 0.498, p < 0.001). CONCLUSIONS: The C2 TF and VA showed side- and level-dependent morphometric differences. Combined CTA assessment of C2 TF morphology, VA area, artery-to-foramen area ratio, and C2-level VA dominance may provide useful information for preoperative anatomical assessment before upper cervical spine surgery.