Double Retrotransverse Foramen of Atlas (C1)

Background: The retrotransverse foramen is a nonmetric variant of C1 that consists of an abnormal accessory foramen on the posterior root of the transverse process. Case Description: During a study on the prevalence of the retrotransverse foramen in 150 dry C1 vertebrae, we observed an exceptional C1 (0.67%) with a right double retrotransverse foramen of the 14 C1 vertebrae (9.3%). This has not been reported previously in the literature. No osteogenic reaction and no degenerative signs were observed in this C1 with the double retrotransverse foramen. Conclusions: Neurosurgeons should be aware of the possible presence of the “conventional” retrotransverse foramen and the “exceptional” double retrotransverse foramen so that they can safely plan to prevent surgical complications. This will thus ensure better patient management by neurosurgeons.