Study Design. Observational study using a retrospective single-institute database.
Objective. To investigate the variance of the vertebral artery (VA) V2 segment and the anatomical features of the C7 pedicle with or without VA entry based on computed tomographic (CT) angiography in 919 consecutive Japanese subjects.
Summary of Background Data. Generally, the level of the VA entrance into the transverse foramen is assumed to be C6. Therefore, surgeons tend to pay less attention to VA injury when inserting a C7 pedicle screw. However, anomalies at C7 surely exist and are considered to be 1 of the major risk factors for VA injury during posterior instrumentation.
Methods. Subjects who underwent contrast-enhanced CT or CT angiography from November 2011 to October 2012 were eligible. The entrance into the transverse foramen was reviewed. In addition, anatomical features of C7 with or without VA entrance were measured.
Results. A total of 919 subjects with a mean age of 56.1 years were surveyed. From among 1838 VA courses, VA entered the C6 transverse foramen in 95.6% of specimens (1757 of 1838 VA courses). Sixty-seven of 919 subjects (7.3%) had a unilateral anomaly and 7 (0.8%) had a bilateral anomaly. An abnormal level of entrance was observed in 8.1% of subjects (74 of 919 patients), and 4.4% of specimens (81 of 1838 VA courses), with a level of entrance into the C4, C5, or C7 transverse foramen in 0.5% (n = 10), 3.1% (n = 57), and 0.8% (n = 14) of all specimens, respectively. C7 transverse foramen with a VA entrance was wider in those without a VA entrance, and abnormal cases frequently showed an uneven transverse foramen. Therefore, the C7 pedicle diameter with abnormal VA entrance was significantly narrower in those without VA entrance (P < 0.01; t test).
Conclusion. CT angiography is recommended in cases with an uneven transverse foramen for confirming vascular anomaly.
Level of Evidence: 2