## 4 Discussion

Table 2: The unusual entrance of vertebral artery variation incidences in different studies. subclavian arteries [3]. The anastomoses between the 1 st and 6 th dorsal intersegmental arteries will form the rest of the VAs [34]. Additionally, VA can anastomose with either the ascending or deep carotid arteries. Unusual entrance depends on the dominance of ascending or deep carotid artery anastomoses. If the longitudinal intersegmental anastomosis is completed by the ascending cervical artery, the developing VA will follow the ascending cervical artery and enter the transverse foramen at a higher level than the usual C6 level. On the other hand, if the longitudinal intersegmental anastomosis is completed by the deep cervical artery, then the VA will follow the deep cervical artery and enter into the transverse foramen at the usual C6 vertebral level [10; 35]. The course of VA close to the midline in the V2 segment is referred to as MM. The incidence of MM observed in the present study is 1.29%. In a recent study, MM was observed in 2.63% of cases [11]. In another study, it was observed in 3.8% of cases ([PERSON] et al., 2009). Similar to the results observed by [PERSON] et al. (2009) [12], MM in the present study was seen predominantly in the older age group. Long-term degenerative and post traumatic changes in the cervical spine are possible logical mechanisms that explain the MM variation of VA [12; 36]. The MM variation is known to be associated with sub-axial cervical spine surgeries. In this intra-foraminal variation, VA is at high risk of injury, particularly in routine corpetomy surgery [12]. Hence, preoperative identification of MM is crucial to avoid unexpected complications during surgeries and for successful outcomes. Relatively high racial differences were observed in V3 segment variations when compared to V2 segment variations [7; 37; 38]. The occurrence of PFIA is due to the developmental failure of its obliteration [37]. Failed obliteration could be associated with genetic, hemodynamic, and environmental factors [37]. Two different studies reported a high incidence of 5% to 10% PFIA in Asian populations [7; 38]. Another recent study reported 4.4% PFIA incidence in the Chinese population [11]. In contrast, we observed this only in 0.17% of cases. Similar to the present study, a low incidence of 0.01% was observed in the American population [37]. The differences in incidences of VA anomalies could be attributed to genetic variations between the populations. The paracodylar process is the other variation of the V3 segment. This developmental anomaly is usually formed due to partial proatlas somite assimilation into the occipital bone [39]. In anthropological studies, PP incidence was reported in Maltese skulls (2.02%), South African skulls (0.9%), South Indian skulls (2.1%), and North Indian skulls (10.5%) [40; 41; 42]. In a recent study, PP incidence was reported in 5.9% of cases in Chinese subjects. Comparatively, a low incidence of PP (0.6%) was observed in the present study. Generally, it is an incidental finding [43], asymptomatic, and can be detected unilaterally or bilaterally [44]. In a few instances, PP may compress the C1 spinal nerve, causing occipito-cervical pain [45]. More often, PP mimics a calcified stylohyoid ligament. However, this ligament can be easily differentiated in coronal-reformatted CT [44]. In the present study, there were no sex or side differences in all the types of VA variations occurrence. Similar results were reported in previous research [11; 46] except MM variation which was significantly higher in female [11]. This indicates that variations in the V2 and V3 segments of the VA are not substantially impacted by the individual's sex or the investigated side of the body. Hence, more investigations with a larger sample may require a conclusive result in this regard. Generally, the VA is left-dominant, and its diameter is typically larger than that of the right VA. In general, left VAD is found in 50% of people.