## 4 Discussion  
Based on the CTA studies, this study reported the various types of variations in vertebral anatomy and analyzed the incident rates based on sex and laterality. While racial differences in VA variations have been reported in the literature [6, 8, 9, 10, 11, 20, 23, 24], to the best of our knowledge, very few studies from the Middle Eastern region [23, 24] and no study from Oman have reported incidences of different kinds of VA variations. We report for the first time the incidence of VA variations in Omani subjects, particularly in the V2 and V3 segments, and discuss their clinical importance. In previous CTA studies, the incidence of UE-V2 varied from 4.4% to 12.5% (Table 2). Studies from Korea [9], Japan [8], and France [6] reported an incidence of 6.5%, 4.4%, and 7%, respectively. Two recent studies from China reported an incidence of 9.16% and 8.3% [10, 11]. Other imaging studies reported an incidence of 7.8% in Germany [19], 12.5% in Republika Srpska [31], 7.5% in Turkey [32], and 5.3% of left VA and 0.8% of right VA in Thailand [20]. A study reported an incidence of 7% among 50 Saudi patients [23]. The reported incidence of UE-V2 in Omani subjects is slightly higher than that reported in most of the studies [6, 8, 9, 19, 20, 23, 32]. The characteristics of the UE-V2 observed in the present study were compared with those of previous studies and presented in Table 2. Consistent with previous studies, in the present study, the transverse process of C5 is the common entrance point. In studies by [PERSON] et al. (2016) [9] and [PERSON] et al. (2014) [8], the sequence of UE-V2 levels incidence was found to be C5 > C4 > C7 > C3 and C5 > C7 > C3, respectively. In a recent study, in Chinese subjects, the sequence was C5 > C4 > C7 > C3 [10]. We observed a similar incidence of sequence for UE-V2 levels observed in Chinese subjects [10]. The UE-V2 variation is also often referred to as an extra-foxarinal VA anomaly. When such variation is present, the subaxial cervical spine procedures need to be performed with more caution as below the entrance, the artery is unprotected by the bone. The UE-V2 segment is at high risk of injury during surgeries in the cervical region, such as tumor resection and stellate ganglion block. Prior knowledge of baseline data and the characteristics of this variation is essential for successful surgeries and the prevention of life-threatening events [33]. The variability in UE-V2 incidences among different populations could be attributed to the racial influences on the embryonic development of VA. The development of VAs begins at the distal ends of the seventh intersegmental dorsal arteries, which usually give rise to \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline Author \& Year & [PERSON] et al., 2006 [6] & [PERSON] et al., 2008 [7] & [PERSON] et al., 2014 [8] & [PERSON] et al., 2016 [9] & [PERSON] et al., 2018 [31] & [PERSON] et al., 2022 [10] & Present study \\ \hline Country & France & Korea & Japan & Korea & Republic & China & Oman \\  & & & & & & & \\ \hline Total Patients (_n_), & 250 (20 MRI, & 50 CT) & 350 (CTA) & 919 (CTA) & 2207 (CTA) & 112 (CTA) & 223 (CTA) & 579 (CTA) \\ \hline Overall Unusual & \multirow{2}{*}{7\% (35/500)} & \multirow{2}{*}{5.1\% (36/700)} & \multirow{2}{*}{4.4\% (81/1838)} & \multirow{2}{*}{6.5\% (286/4414)} & \multirow{2}{*}{12.5\% (28/224)} & \multirow{2}{*}{8.2\% (37/446)} & \multirow{2}{*}{10.4\% (121/1158)} \\ Entrace (”c) & & & & & & & \\ \hline C3\% & 2.9\% & - & - & 0.3\% & - & 2.7\% & 0.8\% \\ \hline C4\% & 14.3\% & 30.6\% & 12.3\% & 18.2\% & 3.1\% & 29.7\% & 20.7\% \\ \hline C5\% & 71.4\% & 63.9\% & 70.4\% & 74.8\% & 8.9\% & 56.8\% & 71\% \\ \hline C7\% & 11.4\% & 5.5\% & 17.3\% & 6.7\% & 0.4\% & 10.8\% & 7.4\% \\ \hline Right (_n_)/Left (_n_) & 17/18 & 16/16 & 40/41 & 150/135 & 16/12 & 22/15 & 72/49 \\ \hline Unilateral (\%) vs. Bilateral (\%) & 94 vs. 6 & 94 vs. 6 & 91 vs. 9 & 86.5 vs. 13.5 & NA & NA & 85 vs. 15 \\ \hline \hline \end{tabular}
\end{table}