Lateral and posterolateral foraminal variations of the atlas: A meta-analysis

The lateral (LF) and posterolateral (PLF) foramina are anatomical variants of the atlas. Both variants have been implicated in multiple neurological conditions including vertebrobasilar insufficiency, with symptoms such as dizziness, syncope, auditory and visual disturbances and paresis. The aim of this study was to conduct a systematic meta-analysis on the prevalence and anatomical characteristics of the LF and PLF. An extensive search of the major electronic databases was conducted to identify all studies that reported relevant data on the LF and PLF. No date or language restrictions were applied. Data on the prevalence, type (complete and incomplete), side, gender, and laterality of the LF and PLF, when available, were extracted and pooled into a meta-analysis. A total of 33 studies (n=10,190 subjects) were included in the quantitative analysis. The overall pooled prevalences of complete LF and PLF were 2.6% (95%CI: 2.1-3.1) and 1.2% (95%CI:0.6-2.0), respectively, while the overall pooled prevalence of the incomplete LF was 2.7% (95%CI:1.3-4.4) and the incomplete PLF was 0.7% (95%CI:0.0-1.8). When there was a complete PLF, a contralateral PLF (complete or incomplete) was found in 32.8% of cases. The geographical distribution of both variants was variable. The findings of this study provide an evidence-based foundation of anatomical knowledge of the two variants of the atlas. We recommend that physicians consider the possible role of the LF and PLF during the diagnosis of various neurological disturbances, especially in situations when all other possible explanations for the symptoms have been excluded.