vertebral artery

The vertebral arteries are major arteries of the neck. Typically, the vertebral arteries originate from the subclavian arteries. Each vessel courses superiorly along each side of the neck, merging within the skull to form the single, midline basilar artery. As the supplying component of the ''vertebrobasilar vascular system'', the vertebral arteries supply blood to the upper spinal cord, brainstem, cerebellum, and posterior part of brain.

Structure

The vertebral arteries usually arise from the posterosuperior aspect of the central subclavian arteries on each side of the body, then enter deep to the transverse process at the level of the 6th cervical vertebrae (C6), or occasionally (in 7.5% of cases) at the level of C7. They then proceed superiorly, in the transverse foramen of each cervical vertebra. Once they have passed through the transverse foramen of C1 (also known as the atlas), the vertebral arteries travel across the posterior arch of C1 and through the suboccipital triangle before entering the foramen magnum.

Nunziante Ippolito, a Neapolitan physician, identified the "angle of Nunziante Ippolito" to find the vertebral artery, between the anterior scalene muscle and the longus colli muscle.

Inside the skull, the two vertebral arteries join to form the basilar artery at the base of the pons. The basilar artery is the main blood supply to the brainstem and connects to the Circle of Willis to potentially supply the rest of the brain if there is compromise to one of the carotids. At each cervical level, the vertebral artery sends branches to the surrounding musculature via the anterior spinal arteries.

The vertebral artery may be divided into four parts:
* The first (preforaminal) part runs upward and backward between the anterior scalene and the longus colli muscles. In front of it are the internal jugular and vertebral veins, and is crossed by the inferior thyroid artery; the left vertebral is also crossed by the thoracic duct. Behind it are the transverse process of the seventh cervical vertebra, the sympathetic trunk and its inferior cervical ganglion
* The second (foraminal) part runs upward through the transverse foramina of the C6 to C2 vertebrae, and is surrounded by branches from the inferior cervical sympathetic ganglion and by a plexus of veins which unite to form the vertebral vein at the lower part of the neck. It is situated in front of the trunks of the cervical nerves, and pursues an almost vertical course as far as the transverse process of the axis.
* The third (extradural or atlantic) part issues from the C2 foramen transversarium on the medial side of the Rectus capitis lateralis. It is further subdivided into the vertical part V3v passing vertically upwards, crossing the C2 root and entering the foramen transversarium of C1, and the horizontal part V3h, curving medially and posteriorly behind the superior articular process of the atlas, the anterior ramus of the first cervical nerve being on its medial side; it then lies in the groove on the upper surface of the posterior arch of the atlas, and enters the vertebral canal by passing beneath the posterior atlantoöccipital membrane. This part of the artery is covered by the Semispinalis capitis and is contained in the suboccipital triangle—a triangular space bounded by the Rectus capitis posterior major, the Obliquus superior, and the Obliquus inferior. The first cervical or suboccipital nerve lies between the artery and the posterior arch of the atlas.
* The fourth (intradural or intracranial) part pierces the dura mater and inclines medially to the front of the medulla oblongata; it is placed between the hypoglossal nerve and the anterior root of the first cervical nerve and beneath the first digitation of the ligamentum denticulatum. At the lower border of the pons, it unites with the vessel of the opposite side to form the basilar artery.

Triangle

Triangle of the vertebral artery is a region within the root of the neck and has following boundaries:
* Medial border of anterior scalene muscle (lateral)
* Lateral border of longus colli muscle (medial)
* Carotid tubercle (apex)
* First part of subclavian artery (base)

The vertebral artery runs from base to apex (prior to entering the transverse foramen of 6th cervical vertebra).

The carotid tubercle separates the vertebral artery which passes directly behind it from the common carotid artery which lies directly in front of it. The ideal site for palpating the carotid pulse is to gently press the common carotid artery against the carotid tubercle.

Variation

There is commonly variations in the course and size of the vertebral arteries, usually on both sides artery diameters are asymmetrical. For example, differences in size between left and right vertebral arteries may range from a slight asymmetry to marked hypoplasia

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