Arterial Vascular Structures Running Through Retrotransverse Foramen and Retrotransverse Groove of the Atlas Vertebrae.

OBJECTIVE: Retrotransverse foramen (RTF) and retrotransverse groove (RTG) are anatomic variations of the atlas (C1) vertebrae. RTF contains an anastomotic vein connecting atlanto-occipital and atlanto-axodian venous sinuses. The purpose of this study was to analyze the arterial vascular structures running though the RTF and RTG. METHODS: Three-dimensional volume rendered computed tomography angiography (3D VR CTA) images of 427 patients (264 men, 163 women; age 17-87 years) were reviewed and evaluated using the RadiAnt DICOM Viewer (version 5.0.2; Medixant, Poznan, Poland). The incidence of RTF or RTG, the incidence of the V3 segment of vertebral artery variants, and the artery vascular structures inside the RTF and RTG anatomic variation of C1 were analyzed. RESULTS: Fifty (11.7%) atlases presented RTF anatomical variant; 113 (26.5%) atlases presented RTG anatomical variants. The incidence of the V3 segment of vertebral artery variants was 0.94% (4 of 427). Three (0.7%) were persistent first intersegmental artery and 1 (0.2%) was the fenestration of the vertebral artery on left side. In 4 cases of C1 vertebral artery V3 segmental variants, there were no RTF and RTG. No artery vascular structure was found in RTF or RTG. CONCLUSIONS: The RTF or RTG of C1 was a common anatomical variant. No arterial vascular structure runs though the RTF or RTG. The presence of C1 RTF and RTG variants had no effect on the V3 segmental course of the vertebral artery. Preoperative understanding of these variations using 3D CTA are helpful for the safe execution of the upper cervical posterior approach surgeries.

Retrotransverse Foramen and Retrotransverse Groove Anatomic Variations of the Atlas Vertebra in the Chinese Population.

OBJECTIVE: To analyze the prevalence of retrotransverse foramen (RTF) or retrotransverse groove (RTG) anatomic variations in Chinese atlas vertebra (C1). METHODS: Three-dimensional volume-rendered computed tomography angiography images of 427 subjects (264 males, 163 females; 17-87 years old) were reviewed and evaluated using dedicated software. The prevalence of RTF and RTG anatomic variation of C1 was analyzed. RESULTS: RTF anatomic variants were present in 50 (11.7%) atlases. Bilateral RTF, unilateral left RTF, and unilateral right RTF were present in 16 (3.8%), 20 (4.9%), and 14 (3.3%) vertebrae. Comparison between males and females revealed differences in bilateral RTF (P = 0.010) and unilateral left RTF (P = 0.008). RTG anatomic variants were present in 113 (26.5%) atlases. Bilateral RTG, unilateral left RTG, and unilateral right RTG were present in 39 (9.1%), 30 (7.0%), and 44 (10.3%) vertebrae. Comparison between males and females revealed differences in RTG (P = 0.000), bilateral RTG (P = 0.006), and unilateral left RTG (P = 0.034). RTF was detected in 36 cases on the left and 30 cases on the right. RTG was detected in 69 cases on the left and 79 cases on the right. There were no side differences in the prevalence of RTF and RTG. CONCLUSIONS: The incidence of RTG is higher than the incidence of RTF. Incidence of bilateral RTF, bilateral RTG, unilateral left RTF, unilateral left RTG, and RTG differed between males and females. Preoperative understanding of these variations using three-dimensional computed tomography angiography is helpful for safe execution of upper cervical posterior approach surgery.