Sanchis-Gimeno, Juan A.Orellana-Donoso, MathiasValenzuela-Fuenzalida, Juan JoséArlegi, MikelPaton, Glen J.Nalla, ShahedGómez-Olivencia, Asier2026-09-282026-09-282026-06-29Translational Research in Anatomy, Vol. 44 (2026) pp. 1-7https://hdl.handle.net/20.500.12254/7742Background: The atlas vertebra (C1) has a close anatomical relationship with the vertebral artery through the transverse foramen. Incomplete osseous closure of this canal, described as an unclosed transverse foramen (UTF), may modify the expected bony boundaries around the vertebral artery. Objective: This systematic review and meta-analysis estimated the prevalence of UTF in anatomically modern humans and summarized its anatomical and potential clinical implications. Methods: Searches were conducted in MEDLINE, CINAHL, Web of Science, Scopus and complementary sources following PRISMA 2020 and evidence-based anatomy recommendations. Eligible studies were original human anatomical, osteological, cadaveric, skeletal or imaging-based studies that reported C1-specific UTF with an extractable numerator and denominator. Methodological quality was assessed using the AQUA tool. Pooled prevalence was estimated using a random-effects model with logit-transformed proportions. Results: Six studies were included in the quantitative synthesis. The pooled prevalence of UTF was 8.8%, with negligible between-study heterogeneity. Methodological quality was predominantly favorable. Conclusions: UTF is an uncommon but recurrent anatomical variant of the atlas. Current evidence does not establish isolated UTF as an independent cause of symptoms. The variant should nevertheless be recognized in anatomical description, radiological reporting and preoperative planning for upper cervical procedures.Atribución-NoComercial-CompartirIgual 3.0 Chile (CC BY-NC-SA 3.0 CL)AtlasC1Transverse foramenUnclosed transverse foramenVertebral arteryAnatomical variationMeta-analysisArticlehttps://orcid.org/0000-0002-1781-062Xhttps://doi.org/10.1016/j.tria.2026.1005062214-854X