Investigating the importance of the vertebral artery V3 segment and atlas (C1) variations in craniovertebral junction approaches

Objective: The complex anatomy of the craniovertebral junction (CVJ), the relationship between bone and vascular structures, and the frequent occurrence of variations in both make this region complex in terms of safe surgery. In addition, the existence of differences in the prevalence of variation between populations necessitates the determination of frequencies specific to each population. Our aim in this study is to determine the prevalence of vertebral artery V3 segment and atlas (C1) variations in Turkish population, analyze their relationship with each other, make morphometric measurements according to certain landmarks, compare the results with the literature, offer appropriate suggestions and contribute to the literature. Methods: From October 1, 2018, to October 1, 2023, computed tomography angiography (CTA) scans of a cohort comprising two hundred individuals (one hundred women and one hundred men, aged 18-65, who had not undergone CVJ surgery) from the Department of Neurosurgery at Hacettepe University Faculty of Medicine were analyzed through 3-D reconstruction and modeling. The identified atlas and VA-V3 segment were scanned for variations, and their morphometric relationships were evaluated. In addition, atlas and V3 segment variation examination was performed in the dissection of ten cadavers. The detected variations were used to support positive radiological results with real anatomy. Results: The prevalence of posterior arch defect of atlas (PAAD) was 3% (n = 5 Type A, n = 1 Type B) in 200 individuals. There was no significant relationship between it and any V3 segment variation (p=0.57). Type A PAAD was in only one cadaver. The prevalence of ponticulus posticus (PP) – ponticulus lateralis (PL) was 16.7% (n=67/400) out of four hundred. The presence of V3 segment variation was found to increase the prevalence of PP-PL (p = 0.01). Considering three variations of the V3 segment (persistent first intersegmental artery (PIFA), fenestration of vertebral artery (VAF), extradural origin of posterior inferior cerebellar artery (ed-PICA)), the prevalence is 3.3% (n=13/400), and considering seven variations (additional vertebral artery atresia (continuation of V3 as PICA (V3-PICA)), dominancy of vertebral artert (VAD), hypoplastic vertebral artery (VAH), suboccipital artery of Salmon (SAS)), it is 14.8% (n=59). /400) was determined. The most common was VAD (9%) and the least was PIFA (0.3%). PIFA variation was detected in 1 cadaver, and an important contribution was made since anatomical PIFA dissection could not be detected in the literature. While the prevalence of VAF was observed to be (1%), it was not detected in cadavers. The frequency of ed-PICA was found to be 2% (n=8/400). ed-PICA was detected in 1 cadaver. It was noticed that, unlike atlas bone variations, the prevalence of vascular variations increased from West to East. The prevalence of VA atresia (V3-PICA) was found to be 0.5% (n=2/400). The frequency of VAD was 9.5% (n=36/400), and VAH was 3.5% (n=14/400). Although left dominance was observed, this difference was not statistically significant (p=0.08). The prevalence of SAS was 7.3% (n=29/400), and it was detected in 25% of cadaveric sides. Parameter A (𝑥̅=12.86  1.62 mm); Parameter B was found as (𝑥̅=20.17  2.34 mm). It was concluded that a bilateral distance of 12 mm on the superior surface of the arch and 18 mm on the posterior surface would be a safe area. As parameter C (𝑥̅=32.56  2.66 mm) and parameter D (𝑥̅=6.65  2.16 mm), these values were found to be lower in VAHs and higher in VADs (p<0.001). The parameter was found to be F (𝑥̅=4.34  2.26 mm), and it was concluded that this distance increased significantly when PP-PL, that is, it could protect VA. Conclusion: With the results obtained, atlas and VA V3 variation prevalence analysis specific to the Turkish population, mutual morphometric measurements of these two structures were made, and their importance in CVJ surgery was examined. Anatomical variations obtained with cadaver dissection have strengthened the connection between virtual 3-D radiological results and reality, and a rare example of PIFA dissection has been introduced to the literature. Preoperative CTA examination has been found to be useful in detecting significant variations and is an important method for safe surgery. Artificial intelligence and machine learning, which have become an important part of today's world, leave no doubt that these modalities will also play a role in future healthcare delivery. The data we obtained from our study will provide an important database for the implementation of safe interventions in humans in the future.