Abnormal origin of vertebral artery may also favour cerebral disorder because of alterations in cerebral hemodynamic. The prevertebral segment of LVA of aortic origin is frequently affected by atherosclerosis. The segment of the artery from its origin at subclavian artery to its respective transverse foramen is called the pretransverse or prevertebral segment. The vessel takes a vertical posterior course to enter into the foramen transversarium of sixth cervical vertebra. The vertebral arteries arise from the superoposterior aspect of the first part of subclavian artery. In the present study the left sixth segmental artery might have persisted as the first part of vertebral artery, or there is increased absorption of embryonic tissue of LSA between origins from the aortic arch to the origin of vertebral artery resulting in direct origin of the LVA from aortic arch. The second part is derived from longitudinal communications of the postcostal anastomosis. ĭevelopmentally the first part of LVA develops from proximal part of dorsal branch of seventh cervical segmental artery proximal to postcostal anastomosis. The incidence of LVA taking origin from AA between origin of LCCA and LSA was significantly high in our study in comparison to previous studies in different population group ( Table 3). The four branches include BCT, LCCA, LVA, and LSA from right to left. The next common pattern of branching of AA in our study was four-branche pattern. Sometimes such AA anomalies are clinically useful, as catheterization of LCCA originating from BCT or CT can be achieved without catheter exchange. Nonrecognition of a critical AA at surgery may cause fatal consequences. The approximation of LCCA to BCT is an important observation while invading the AA and its branches with instrument as all cases are susceptible to surgical attack. If the aortic sac fails to bifurcate, then the LCCA will connect to aortic sac directly, resulting in bicarotid trunk or common trunk giving origin to BCT and LCCA as observed in 19.2% cases in our study. Left limb of aortic sac forms the part of arch that intervenes between the origin of BCT and LCCA. Aortic sac normally bifurcates into left and right limbs. Developmentally the two-branch pattern of the AA may be explained as follows.
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