MRI Anatomy Flashcards · Angiography

Carotid Anatomy

Learn to identify every labeled structure on a Carotid MRI, plane by plane.

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Carotid anatomy, structure by structure

Carotid MRI is really carotid MR angiography (MRA), and reading it starts with knowing the normal vascular roadmap from the aortic arch up into the neck. This reference walks through every vessel in our carotid flashcard deck on the standard coronal maximum-intensity projection (MIP), with a plain-language definition, where each vessel sits and how it courses on the angiogram, and the vascular pathology you will actually run into at the scanner.

Aortic arch and great vessels

The arch and the first-order branches that feed the neck. On the coronal MIP they form the wide base of the angiogram, so trace each vessel upward from where it leaves the arch.

Aortic Arch

The curved top of the thoracic aorta that gives rise to all of the arteries supplying the head, neck, and arms.

On MRI: Forms the broad, bright curve across the bottom of the coronal MRA MIP; the great-vessel branches lift off its superior margin from right to left.

Common pathology: Arch atheroma, aneurysm, and bovine or other branching variants that change how the carotids and subclavians arise; variant arch anatomy is important to flag before any catheter procedure.

Tip: In the standard left arch, the branch order from the patient's right to left is brachiocephalic, then left common carotid, then left subclavian.

Brachiocephalic Artery

The first and largest branch off the aortic arch, which splits into the right common carotid and right subclavian arteries.

On MRI: A short, bright trunk rising from the right side of the arch on the coronal MIP before dividing into two limbs that head up the neck and out to the right arm.

Common pathology: Atherosclerotic stenosis at its origin, and the upstream culprit in proximal subclavian steal; also called the innominate artery.

Right Subclavian Artery

The artery branching from the brachiocephalic that supplies the right arm and gives off the right vertebral artery.

On MRI: Curves laterally toward the right shoulder on the coronal MIP after the brachiocephalic splits, passing below the right vertebral origin.

Common pathology: Proximal stenosis or occlusion causes subclavian steal, where flow reverses down the vertebral artery to supply the arm; look for a signal drop just past the origin.

Left Subclavian Artery

The third arch branch, arising directly from the aorta, that supplies the left arm and gives off the left vertebral artery.

On MRI: The leftmost vessel lifting off the arch on the coronal MIP, then turning laterally toward the left shoulder.

Common pathology: The most common site of subclavian steal; proximal stenosis reverses left vertebral flow and can produce arm-exertion dizziness.

Carotid arteries

The anterior circulation pathway up each side of the neck. The bifurcation of the common carotid into internal and external branches is the single most scrutinized region on any carotid study.

Right Common Carotid Artery

The right-sided neck artery, arising from the brachiocephalic, that ascends and divides into the right internal and external carotid arteries.

On MRI: A long, bright vertical vessel on the right of the coronal MIP, climbing the neck before it splits at the bifurcation around the level of the upper thyroid cartilage.

Common pathology: Atherosclerotic disease and, less often, dissection; the carotid bifurcation just above it is the classic plaque and stenosis site graded for endarterectomy.

Left Common Carotid Artery

The left-sided neck artery, arising directly from the aortic arch, that ascends and divides into the left internal and external carotid arteries.

On MRI: The mirror-image vertical vessel on the left of the coronal MIP, ascending from the arch to its own bifurcation.

Common pathology: Atherosclerosis and dissection; because it usually comes straight off the arch, its origin is a separate stenosis checkpoint from the right side.

Right Internal Carotid Artery

The branch of the right common carotid that ascends without branching in the neck to supply the front of the brain.

On MRI: The more posterior and lateral of the two limbs above the right bifurcation on the coronal MIP, running straight upward toward the skull base with no neck branches.

Common pathology: Bifurcation and proximal ICA atherosclerosis (the prime endarterectomy target), dissection causing a tapered flame-shaped narrowing, and aneurysm.

Tip: On the MIP the internal carotid is the smoother, branchless limb; the external carotid is the busier one giving off twigs in the neck.

Left Internal Carotid Artery

The branch of the left common carotid that ascends without branching in the neck to supply the front of the brain.

On MRI: The branchless ascending limb above the left bifurcation on the coronal MIP, heading toward the skull base.

Common pathology: Stenosis at the bifurcation and proximal ICA, dissection, and aneurysm; right and left are always compared side to side for asymmetric narrowing.

Right External Carotid Artery

The branch of the right common carotid that supplies the face, scalp, and neck rather than the brain.

On MRI: The more anterior and medial limb above the right bifurcation on the coronal MIP, recognizable because it gives off several small branches in the neck.

Common pathology: Less commonly the primary clinical concern than the ICA, but it provides collateral flow when the ICA is occluded and can be a source of epistaxis or tumor blush.

Left External Carotid Artery

The branch of the left common carotid that supplies the face, scalp, and neck rather than the brain.

On MRI: The branching limb above the left bifurcation on the coronal MIP; its early neck twigs distinguish it from the smooth internal carotid.

Common pathology: An important collateral pathway in ICA occlusion; on the angiogram its branching pattern is the cue that you are looking at the external, not the internal, carotid.

Vertebrobasilar system

The posterior circulation, climbing through the cervical spine and joining in the midline. On the coronal MIP the vertebral arteries run more posteriorly than the carotids and merge into the single basilar artery.

Right Vertebral Artery

The branch of the right subclavian artery that ascends through the cervical transverse foramina to help supply the posterior brain.

On MRI: A thinner vessel on the right of the coronal MIP, arising from the subclavian and climbing in a slightly beaded course through the neck toward the skull base.

Common pathology: Dissection (a common cause of posterior-circulation stroke in younger patients), origin stenosis, and congenital hypoplasia, where one vertebral is normally much smaller than the other.

Left Vertebral Artery

The branch of the left subclavian artery that ascends through the cervical transverse foramina to help supply the posterior brain.

On MRI: The mirror vessel on the left of the coronal MIP rising from the left subclavian; it is the dominant (larger) vertebral in many people.

Common pathology: Dissection, stenosis, and asymmetry from hypoplasia; the left is frequently the dominant vertebral, so do not call a smaller right side abnormal by default.

Basilar Artery

The single midline artery formed where the two vertebral arteries join, supplying the brainstem and posterior circulation.

On MRI: Sits in the midline near the top of the coronal MIP, formed by the V-shaped convergence of the two vertebral arteries as they reach the skull base.

Common pathology: Basilar tip aneurysm, basilar occlusion (a stroke emergency), and dolichoectasia (an elongated, tortuous, dilated basilar).

Frequently asked questions

What structures are seen on a carotid MRA?

A carotid MRA traces the arterial roadmap from the chest to the skull base: the aortic arch and its great-vessel branches (brachiocephalic, right and left subclavian), the common, internal, and external carotid arteries on each side, and the vertebrobasilar system (right and left vertebral arteries joining into the basilar). This page labels all 13 on the coronal MIP with their course and the vascular pathology that matters.

Which plane is best for studying carotid anatomy?

The coronal maximum-intensity projection (MIP) is the workhorse overview: it lays out the aortic arch, both carotid systems, and the vertebral arteries in one front-facing image so you can follow each vessel from its origin to the skull base. Radiologists then rotate the MIP and review thin source slices to grade a specific stenosis without overlapping vessels hiding it.

What sequences are used for carotid MRA?

Carotid MRA is most often contrast-enhanced (CE-MRA) timed to the arterial phase after a gadolinium bolus, which gives a clean arch-to-skull-base map. Time-of-flight (TOF) MRA is a contrast-agnostic alternative that relies on inflowing blood; both render flowing arteries bright and are reconstructed into the MIP, rather than showing T1 or T2 tissue signal.

Why is the carotid bifurcation so important on a carotid study?

The carotid bifurcation, where the common carotid splits into the internal and external carotid arteries, is the classic site of atherosclerotic plaque and stenosis. The degree of narrowing of the internal carotid here is what gets graded to decide on carotid endarterectomy or stenting, so it is the most scrutinized segment on the whole exam.

Do I need an account to use these carotid MRI flashcards?

No. The interactive flashcards and this full labeled reference are open to use, with no account required to start. Creating an account lets you save your progress across devices and track which packs you have mastered.

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