BILATERAL VARIATION IN THE COURSE OF VERTEBRAL ARTERY

Address for Correspondence: Dr Jaideo Manohar Ughade, Associate Professor, Department of Anatomy, Late Lakhiram Agrawal Memorial Government Medical College, Raigarh, India. The vertebral artery arises from the first part of subclavian artery and courses within the bony canals of the cervical vertebrae, and then it lies on the upper surface of the posterior arch of the atlas before piercing the dura to enter the cranium. The intracranial part of the vertebral arteries unites at the caudal border of the pons to form the basilar artery. Vertebral artery contributes in supplying posterior part of the brain. In the present case, both the vertebral arteries had normal origin from the first part of subclavian artery. However, the cervical part of the right vertebral artery ascended through the transverse foramina of seventh cervical vertebrae and the left vertebral artery ascended through foramina of fifth cervical vertebrae. Incomplete knowledge of variations of the vertebral artery may lead to serious implications during surgical procedures such as transpedicular fixation technique which is safely performed at the seventh cervical vertebra, in which the vertebral artery is not usually present at the transverse foramen.

vertebral arteries ascend through the transverse foramina of the first six cervical vertebrae.The atlantic part of the vertebral arteries perforate the dura and arachnoid and pass through the foramen magnum.The intracranial part of the vertebral arteries unites at the caudal border of the pons to form the basilar artery.The vertebrobasilar system is clinically referred as posterior circulation of the brain [1].Incomplete knowledge of variations of the vertebral artery may lead to serious implications during angiography and surgical procedures such as vertebral artery stents.Stabilization of the cervical spine is commonly used for treating unstable spine resulting from trauma, Blood supply to the brain accounts for about 2.5% of body weight, it receives about one-sixth of the cardiac output.Vertebral artery gains its importance by forming posterior circulation of the brain.The vertebral arteries are unique because they have long course, greater length, small diameter, asymmetry, segmental branches, division into four parts depending on its course and embryology, formation of single basilar artery by fusion of paired vertebral arteries.The vertebral artery begin in the root of neck as the first branch of the first part of subclavian artery on both the sides.The cervical parts of the neoplasia or degenerating conditions.Transpedicular fixation technique is safe only when performed at the seventh cervical vertebra, in which the vertebral artery is not usually present at the transverse foramen [2].In some cases the vertebral artery is found inside the transverse foramen of seventh cervical vertebrae.Damage to vertebral artery in such cases can lead to various neurological deficits such as Wallenberg syndrome.An abnormal course of the vertebral artery may lead to potential complications during these procedures, alter the cerebral hemodynamics and predispose the patient to intracranial aneurysms [3].

MATERIALS AND METHODS
During routine dissection of head and neck region in the dissection hall, a bilateral variation in the course of vertebral artery was observed in a 60 years old embalmed male cadaver.Dissection was performed as per Cunnin-gham's manual of practical anatomy.Sternocleidomastoid was cut to expose scalenovertebral triangle.Both the vertebral arteries had normal origin from the first part of subclavian artery.The cervical part of the right vertebral artery ascended through the transverse foramina of seventh cervical vertebrae and the left vertebral artery ascended through foramina of fifth cervical vertebrae.After removal of larynx and oesophagus, anterior surface of the cervical vertebral column was exposed, prevertebral fascia covering the prevertebral muscles (longus colli and longus capitis muscle) was seen.Both the vertebral arteries were seperated from sorrounding loose connective tissue attachments from its origin up to the transverse foramen of the cervical vertebra [4].During dissection the first costal cartilage was located there by first thoracic vertebra (T1) was identified which lies at the same level.The seventh (C7) and sixth (C6) cervical vertebrae were identified by counting above T1.
OBSERVATIONS longus colli and scalenus anterior muscle.The cervical part of the right vertebral artery ascended through the transverse foramina of seventh cervical vertebrae and the left vertebral artery ascended through foramina of fifth cervical vertebrae.After its anomalous course from second (vertebral) part both the arteries reached up to the transverse process of C1 vertebra.From the foramen transversarium of axis to that of atlas, the arteries passed upwards laterally making convex outward loop.Third part of the artery then winded backward around the lateral mass of atlas and appeared in suboccipital triangle.Finally they entered the vertebral canal below the lower arched border of the posterior atlanto-occipital membrane and continued as the fourth part.The fourth part of the artery pierced dura and arachnoid maters.Then both the arteries passed upward and medially through foramen magnum in front of the first tooth of ligamentum denticulatum.At the lower border of pons artery from both the sides fused to form basilar artery.
During our routine dissection bilateral variation was noted in the course of the vertebral artery.On both the sides the vertebral artery arose from first part of the subclavian artery.The right and left vertebral artery then passed through scalenovertebral triangular space between In the present case cervical part of the right vertebral artery ascended through the transverse foramina of seventh cervical vertebrae and the left vertebral artery ascended through foramina of fifth cervical vertebrae.Such anomalous course may lead to altered hemodynamics and predispose to intracranial aneurysm 3 .This information is important for vascular or cardiothoracic surgical planning such as treating aneurysms, removal of craniocervical junction masses, bony decompression of the vertebral artery, vertebral endarterectomy and vertebral artery bypass 11 .Knowledge of such variation CONCLUSION

Fig. 1 :
Fig. 1: Showing the bilateral variations of the vertebral artery.