The Potential Morphological Stenosis Pattern of the Arcuate Foramen.

: The arcuate foramen (AF), an osseous foramen, is probably formatted from the ossification of the posterior atlanto-occipital membrane. When this morphologically ossified variant exists, it encloses the vertebral artery (VA) third segment (V3). This close relationship may cause compression to the VA with concomitant vertebrobasilar insufficiency, vertigo, headaches, or neck pain. In the published literature, no studies investigate the abovementioned potential compression pattern. The present study examines the AF ossification pattern (complete or partial type) and the variable VA diameter at the atlantal part (V3), concluding a potential risk for VA compression after correlating the relative diameters (AF and VA diameters). : One hundred and fifty dried first cervical vertebrae (atlases) and one hundred fifty computed tomography (CT) scans were obtained for the present study. The presence of a complete or incomplete AF was evaluated, and when present, its diameter was measured. To correlate these findings with the vessel, 50 computed tomography angiographies (without AF presence) were obtained to measure the V3 segment diameter. : Out of the total 600 ( = 600) sides, 111 sides had incomplete AF (18.2%), and 67 sides had complete AF (11.1%). The AF mean diameter was 6.41 (1.12) mm. The diameter of the V3 segment ranged between 5.0 and 6.0 mm; therefore, three morphological stenosis patterns were identified. A low risk of compression (over 6.0 mm) was identified in 61.2% ( = 109 sides), a moderate risk (between 5.0-6.0 mm) was observed in 29.2% ( = 52 sides), and a high risk (under 5.0 mm) was recorded in 9.6% ( = 17 sides). There was no statistically significant correlation regarding sexes and age for the potential compression patterns. : The present study revealed the morphological stenosis pattern of the AF to the V3 segment. The variation had a high risk of compression to the vessel in 9.6% of sides, indicating that it is not infrequent. Knowledge of these details is essential for clinicians when investigating vertebrobasilar insufficiency.