Evaluation of the arteries of the neck requires inspection of all segments from the aortic arch to the skull base. All these segments may be affected by atherosclerotic or non-atherosclerotic pathologies. Atherosclerotic plaque of the aortic arch can be a source of cryptogenic stroke, even distal to the origin of the left subclavian artery due to retrograde diastolic flow. Common variants of the aortic arch include arch-origin of the left vertebral artery, common origin of the brachiocephalic and left common carotid artery, and aberrant right subclavian artery.

Stenosis of the proximal arch branches can be important to note for procedure planning and can be flow-limiting. The prime example is stenosis of the proximal subclavian artery with subclavian steal.

Scattered atherosclerosis is common in the common and internal carotid arteries, but the major area of atherosclerotic plaque formation is the carotid bifurcation, where the origins of the ICA and ECA can be involved.

Common variants

plaque, flow imaging

The basic cervical ICA anatomy is fairly consistent, with branches and major congenital variants being uncommon. However, the course of the ICA has several notable variants that can develop with age, including retropharyngeal or retrojugular sweeps. Also kinks, loops, or coils can develop, which are quite common, but seem to have some association with development of dissection and certain connective tissue disorders. ICA size is also fairly consistent, although mild asymmetry can be seen when one (larger) side supplies both A2 segments intracranially. Diffuse smooth ICA narrowing is seen in the setting of reduced inflow due to critical proximal stenosis (slim sign).

Sympathetic nerve fibers course along the cervical ICA explaining the association of a Horner's syndrome with carotid dissection. The mid to distal cervical ICAs and vertebral arteries are common locations of fibromuscular dysplasia (FMD), which is commonly seen in middle aged females with current CTA technology.

The carotid body is an important chemoreceptor situated in the adventitia of the cervical carotid bifurcations bilaterally. This is the source of carotid body tumors.

Variant course, retropharyngeal, retrojugular, loops, kinks.

Dissection, aneurysm, ASO, FMD/SCAD

Volume-rendered MRA exam shows chronic bilateral ICA dissections, which had been essentially stable in appearance for over two years. Such dissections often have a period of evolution in the acute/subacute periods and may stabilize chronically. The imaging findings reflect the patterns of blood flow within different layers of the carotid wall and include true luminal stenosis, pseudoaneurysm formation, intramural blood, and intimal flaps. This case shows multiple pseudoaneurysms in the mid to distal ICA (red arrows). Such dissections typically spare the proximal ICA near the bifurcation.

Even though the ECA branches do not always receive the same deference that the cervical ICA does, ECA arterial supply is extremely important for several reasons. These include arterial supply of ECA-ICA collaterals, collaterals to the orbit, and cranial nerve branches. A common scenario encountered in diagnostic neuroradiology is complete occlusion of the ICA with reconstitution of the intracranial ICA via an ECA-supplied ophthalmic artery. Supply of the nerves and orbit present hazards for the neurointerventional radiologist. In fact, various dangerous collaterals are described in neurointerventional radiology educational resources (these are a must-read before any NIR rotation, but are beyond the scope of this essentials module).

Beyond supplying a reconstituted intracranial ICA, the main clinical significance of ECA arterial supply encountered in clinical practice or board examinations include juvenile nasopharyngeal angiofibroma (JNA) supply via the internal maxillary artery and superficial temporal artery involvement with giant cell arteritis (which can be detected on vessel wall imaging of scalp arteries). Other pertinent conditions include intracranial dural AV fistulae, which are typically supplied via ECA branches (which supply much of the dura) as well as AV malformations of the face.

Although many of the smaller branches are difficult or impossible to see with CTA or MRA unless pathologically enlarged, the main branches of the ECA are typically identifiable (especially on CTA). It is a useful exercise to follow and identify these branches as far distally as possible on CTA.

The vertebral arteries typically arise from the proximal subclavian arteries and consist of 4 main segments designated V1-V4. The V1 (pre-foraminal) segment extends from the artery origin to the foramen transversarium (usually at C6), the V2 (foraminal) segment extends from the lowest level within foramen transversarium to that of C2, the V3 (extradural) segment extends from the C2 transverse process to the dura mater in the foramen magnum, and V4 (intradural) segment extends from the dural piercing to the basilar artery.

The V3 segment is associated with a highly mobile region of the cervical spine and forms a characteristic C-curve with an ascending portion between the C1 and C2 transverse foramen coursing just lateral to the lateral C1-C2 joint and a superior portion arching posteriorly and superior to C1 to then pierce the dura. This configuration is important for interventional procedures including C1-C2 joint injections, C1-C2 epidural injections, and bowhunters syndrome.

Common variants include aortic origin of the left vertebral artery, left or right sided dominance, variable level of entry into the foramen transversarium, and termination of the vertebral artery as a PICA with little or no contribution to the basilar artery. The V3 segment may traverse the variant foramen arcuale (formed by calcification of the posterior atlanto-occipital ligament called the ponticulus posticus) between C1 and the foramen magnum.

Additionally, the vertebral arteries occasionally loop into the adjacent neural foramen, which is a consideration prior to any transforaminal procedure/injection. The vertebral arteries are also common locations for atherosclerosis (especially the origin V4 segments), dissection, and FMD.