Risk factor analysis and decision-making of surgical strategy for V3 segment anomaly: significance of preoperative CT angiography for posterior C1 instrumentation

Background ContextAwareness of vascular anomalies is crucial to avoid iatrogenic injuries during surgical procedure. Although V3 segment anomaly has been well described, the incidence of V3 segment anomaly has been rather variable in the literature, and there are few reports regarding the adequate surgical strategy for each type of V3 segment anomaly.PurposeThis study aimed to analyze the incidence of V3 segment anomaly and demonstrate the importance of recognizing vertebral artery (VA) anomaly in deciding the surgical strategy for C1 screw placement.Study DesignA retrospective cohort study was carried out.Patient SampleThe sample included 147 patients who underwent C1 posterior instrumentation and preoperative three-dimensional computed tomography angiography (3D CTA).Outcome MeasuresThe primary outcome of this study was the incidence of V3 segment anomaly using preoperative CTA, and the secondary outcome was the risk factor analysis of the V3 segment anomaly.MethodsThere were 147 patients who underwent C1 posterior instrumentation to treat various kinds of upper cervical disease. The 3D CTA of the patients were assessed preoperatively to identify the anomaly of the VA. Each surgical technique of C1 posterior instrumentation was decided upon the shape and the course of the VA around the atlas.ResultsDuring the study period, 11 cases of V3 segment anomaly (7.5%) were found on 3D CTA. Persistent intersegmental artery was found in nine cases and was the most common variant of VA anomaly. Early branch of posterior inferior cerebellar artery was found in three cases. Most of V3 segment anomaly was found unilaterally, but there were two cases with bilateral V3 anomaly. Seven cases (63.6%) were associated with congenital bony abnormality around craniovertebral junction (CVJ), such as occipital assimilation, Klippel-Feil syndrome, and os odontoideum. V3 segment anomaly was significantly common in the cases with bony abnormality (29.2% (7/24) vs. 3.6% (4/123), p<.05). Compared with patient without bony abnormality, the odds ratio was 10.78 (95% CI: 2.88–40.37) for those with congenital bony abnormalities. Rheumatoid arthritis was not a risk factor of V3 segment anomaly (p=.391).ConclusionsThe course of the VA is heterogenous, and the V3 segment anomaly of the VA is more common in the cases with congenital bony abnormalities around CVJ. Therefore, preoperative radiological studies should be performed to identify V3 segment variations and reduce the risk of VA injury. To avoid significant morbidities associated with VA, surgical technique of C1 posterior instrumentation should be decided depending upon the V3 segment anomaly. A more optimal entry point and trajectory for C1 fixation can be selected.