Carotid bifurcation !

The carotid bifurcation is where the carotid artery splits in the neck; plaque often builds up here and is a major source of strokes.

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What it is

Where the common carotid splits into internal and external, with a pressure sensor (carotid sinus).

What it does

Plaque builds up here; it is the site of carotid endarterectomy.

Key facts

Origin: Common carotid artery divides at the upper border of the thyroid cartilage (C3–C4)
Branches: Internal carotid (posterolateral, no branches in the neck) and external carotid (anteromedial)
Supplies: Carotid sinus (blood pressure sensor, IX) and carotid body (oxygen sensor); common plaque site

Relations

Superficial: Anterior border of the sternocleidomastoid, the common facial vein joining the internal jugular vein (tied to expose the bifurcation) and, just above, the hypoglossal nerve crossing both carotids
Lateral: Internal jugular vein, with the vagus nerve behind, between vein and artery
Medial: Larynx and pharynx; the branches of the superior laryngeal nerve pass deep to the arteries
Behind: Sympathetic trunk on the prevertebral fascia, over the longus capitis and the cervical transverse processes

How to find it

It lies under the anterior border of the sternocleidomastoid, roughly level with the top of the thyroid cartilage and below the angle of the mandible, where the carotid pulse is strongest. In carotid endarterectomy it is exposed through an incision along that border after the common facial vein is tied.

Examination

Carotid sinus massage with ECG and blood pressure monitoring: a pause of 3 seconds or more or a systolic fall of 50 mmHg or more that reproduces symptoms supports carotid sinus hypersensitivity; it is avoided with a bruit or recent stroke
Neck auscultation: a bruit is a poor guide to the degree of stenosis, and a very tight stenosis can be silent

On imaging

Duplex ultrasound is the first test: grey-scale shows the plaque and Doppler peak systolic velocity grades the stenosis. CT or MR angiography confirms it and shows the arch and intracranial vessels. A carotid body tumour widens the angle between the two carotids and enhances intensely.

Clinical notes

Carotid endarterectomy removes plaque through an incision in the artery across the bifurcation; nerves at risk are the hypoglossal nerve, vagus nerve, superior laryngeal nerve, the marginal mandibular branch and the great auricular nerve
Carotid stenting is an alternative in selected patients; stretching the bulb can trigger the baroreflex and slow the heart
Carotid body tumours are graded by how much they encase the arteries (Shamblin I–III); larger ones put the vessels and lower cranial nerves at risk at removal

Anatomical variants

Its height varies: a high bifurcation, near the hyoid or the angle of the jaw, makes endarterectomy harder; a low one may lie near the cricoid
The superior thyroid artery may arise from the bifurcation itself or from the common carotid artery instead of the external carotid artery

Development

The common carotid and the first part of the internal carotid come from the third pharyngeal arch arteries, the external carotid buds from them, and the carotid body forms from neural crest cells in the third arch.

Test yourself

Think of the answer, then tap the question to see it.

Where does plaque build up at the carotid bifurcation, and why there?

On the outer wall of the carotid bulb, opposite the flow divider, where flow separates and wall shear stress is low.

What are the carotid sinus and carotid body, and which nerve carries their signals?

The sinus is a stretch receptor for blood pressure; the body is a chemoreceptor for O2, CO2 and pH; both signal through the glossopharyngeal nerve (IX).

Which nerves are at risk in carotid endarterectomy at the carotid bifurcation?

The hypoglossal, vagus and superior laryngeal nerves, the marginal mandibular branch of the facial nerve and the great auricular nerve.

What is a carotid body tumour and how does it present?

A paraganglioma at the bifurcation: a painless, slow-growing lump at the angle of the jaw, more frequent with chronic hypoxia such as at high altitude.

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): bifurcatio carotidis TA2 4368
Official Spanish (DeCS): Bifurcación carotídea DeCS D002346
English (TA2): Carotid bifurcation

Sources: Terminologia Anatomica (TA2); DeCS; Anatomy, Head and Neck: Carotid Arteries; Anatomy, Head and Neck: Carotid Sinus.

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Representative model, for educational purposes only.