Thevertebral arteries are majorarteries of the neck. Typically, the vertebral arteries originate from thesubclavian arteries. Each vessel courses superiorly along each side of the neck, merging within the skull to form the single, midlinebasilar artery. As the supplying component of thevertebrobasilar vascular system, the vertebral arteries supply blood to the upperspinal cord,brainstem,cerebellum, andposterior part of brain.[1]
The vertebral arteries usually arise from the posterosuperior aspect of the central subclavian arteries on each side of the body,[2] then enter deep to the transverse process at the level of the 6thcervical vertebrae (C6),[1] or occasionally (in 7.5% of cases) at the level of C7. They then proceed superiorly, in thetransverse foramen of eachcervical vertebra.[1] Once they have passed through the transverse foramen of C1 (also known as theatlas), the vertebral arteries travel across the posterior arch of C1 and through thesuboccipital triangle[3] before entering theforamen magnum.[1]
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.[4]
Inside the skull, the two vertebral arteries join to form thebasilar artery at the base of thepons. Thebasilar artery is the main blood supply to thebrainstem and connects to theCircle of Willis to potentially supply the rest of the brain if there is compromise to one of thecarotids. At each cervical level, the vertebral artery sends branches to the surrounding musculature via theanterior spinal arteries.
Segments of vertebral artery anterior projection
The vertebral artery may be divided into four parts:
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 thetransverse process of the axis.
The third (extradural or atlantic) part issues from the C2 foramen transversarium on the medial side of theRectus 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 thesuperior 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 theposterior atlantoöccipital membrane. This part of the artery is covered by theSemispinalis capitis and is contained in thesuboccipital triangle—a triangular space bounded by theRectus capitis posterior major, theObliquus superior, and theObliquus inferior. The first cervical orsuboccipital nerve lies between the artery and theposterior arch of the atlas.
Segments of vertebral artery lateral projectionThe fourth (intradural or intracranial) part pierces thedura mater and inclines medially to the front of themedulla oblongata; it is placed between thehypoglossal nerve and the anterior root of the first cervical nerve and beneath the first digitation of theligamentum denticulatum. At the lower border of thepons, it unites with the vessel of the opposite side to form thebasilar artery.
The vertebral artery runs from base to apex (prior to entering the transverse foramen of 6th cervical vertebra).[citation needed]
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 thecommon carotid artery against the carotid tubercle.[6]
There is commonly variations in the course and size of the vertebral arteries, usually on both sides artery diameters are asymmetrical.[7] For example, differences in size between left and right vertebral arteries may range from a slight asymmetry to markedhypoplasia of one side, with studies estimating a prevalence of unilateral vertebral artery hypoplasia between 2% and 25%.[8] In 3-15% of the population, a bony bridge called thearcuate foramen covers the groove for the vertebral artery on vertebra C1. Rarely, the vertebral arteries enter the subarachnoid space at C1-C2 (3%) or C2-C3 (only three cases have been reported) vertebral levels instead of the atlanto-occipital level.[9]
The portion of vertebral arteries located within the skull (intracranial) have diameters of 3.17 mm. The intracranial length for the left vertebral artery (32.4 mm) is longer than the right (31.5 mm). The angle where vertebral arteries meet thebasilar artery (vertebrobasilar junction), is 46 degrees.[10]
Vertebral artery dominance (VAD) is typically a normal congenital vascular variation of the vertebral arteries. It refers to the asymmetry of the VA diameters on both sides, with the larger diameter being the dominant side and the smaller diameter being the nondominant side.[7]
In one study, the left vertebral artery diameter dominance was present in 54% of cases, while the right diameter was dominant in 30%. In 16% of cases, the left and right arterial diameters were equal.[11]
Typically, blood flow velocities in the carotid artery are measured in terms of peak systolic velocity (PSV) and end diastolic velocity (EDV).[15]
Normally, vertebral artery blood flow velocity can be 63.6 ± 17.5 cm/s during PSV and 16.1 ± 5.1 cm/s during EDV according to a study done by Kuhl et al.[16] Due to vertebral artery dominance, measurements can vary on both sides, for example, another study by Seidel et al. found that the right side had an average of 45.9 cm/s and the left side 51.5 cm/s during PSV, and 13.8 cm/s on the right side and 16.1 cm/s on the left side during EDV.[15][17]
