OBJECTIVE The foramen arcuale (FA) is a bony bridge located over the vertebral artery on the posterior arch of the atlas. The presence of an FA can pose a risk during neurosurgery by providing a false impression of a broader posterior arch. The aim of this study was to provide the most comprehensive investigation on the prevalence of the FA and its clinically important anatomical features. METHODS Major electronic databases were searched to identify all studies that reported relevant data on the FA and the data were pooled into a meta-analysis. RESULTS A total of 127 studies (involving 55,985 subjects) were included. The overall pooled prevalence of a complete FA was 9.1% (95% CI 8.2%-10.1%) versus an incomplete FA, which was 13.6% (95% CI 11.2%-16.2%). The complete FA was found to be most prevalent in North Americans (11.3%) and Europeans (11.2%), and least prevalent among Asians (7.5%). In males (10.4%) the complete FA was more common than in females (7.3%) but an incomplete FA was more commonly seen in females (18.5%) than in males (16.7%). In the presence of a complete FA, a contralateral FA (complete or incomplete) was found in 53.1% of cases. CONCLUSIONS Surgeons should consider the risk for the presence of an FA prior to procedures on the atlas in each patient according to sex and ethnic group. We suggest preoperative screening with computerized tomography as the gold standard for detecting the presence of an FA.
Keywords: C1LMS; C1LMS = C-1 lateral mass screw; FA = foramen arcuale; atlas screw placement; cervical; foramen arcuale; foramen arcuate; ponticulus posticus.