Carotid Arterial System

The carotid arterial system provides blood supply to the head and neck. The arterial system begins as the common carotid artery, which arises directly from the aortic arch on the left side and from the brachiocephalic trunk/artery on the right. The common carotid arteries then ascend through the neck and divide into the internal and external carotid arteries. The former supplies structures within the brain and orbits, whereas the latter supplies the superficial structures and parts of the neck and face.

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Common Carotid Artery

The common carotid artery has different origins on either side of the body:

  • Left: The left common carotid artery arises directly from the aortic arch.
  • Right: The brachiocephalic trunk/artery (1st branch of the aortic arch) bifurcates behind the sternoclavicular joint into:
    • Right common carotid artery 
    • Right subclavian artery

The common carotid artery bifurcates at the level of the thyroid cartilage (C4 vertebra) into:

  • External carotid artery
  • Internal carotid artery
Bifurcation of the carotid artery

Bifurcation of the carotid artery

Image by BioDigital, edited by Lecturio

Carotid body:

  • Oval-shaped cluster of chemoreceptors posterior to the bifurcation 
  • Functions as a sensor for PO2 levels and changes in blood pH
  • Changes the rate and volume of respiration
  • Innervated by the carotid branch of the glossopharyngeal nerve

Carotid sinus:

  • Dilation at the base of the internal carotid artery
  • Baroreceptor: relays information about arterial BP to the hypothalamus
  • Innervated by the carotid branch of the glossopharyngeal nerve
Common carotid artery within the carotid sheath

Common carotid artery within the carotid sheath

Image by BioDigital, edited by Lecturio
Table: Spatial relations of the common carotid artery
Thoracic part (left)Lower neck (both)Higher neck (both)
Anterior
  • Sternohyoid and sternothyroid muscles
  • Anterior part of lungs and pleura
  • Remains of the thymus
  • Left brachiocephalic vein
  • Sternoclavicular joint
  • Superficial fascia
  • Platysma
  • Sternocleidomastoid, sternothyroid, and omohyoid muscles
  • Skin
  • Branches of the cervical plexus
  • Platysma
  • Sternocleidomastoid muscle
Posterior
  • Trachea
  • Esophagus
  • Left recurrent laryngeal nerve
  • Thoracic duct
  • Sympathetic trunk
  • Longus colli, longus capitis, and anterior scalene muscles
Lateral
  • Phrenic nerve
  • Left vagus
  • Left pleura
  • Vagus nerve
  • Internal jugular vein (within the same carotid sheath)
MedialBrachiocephalic trunk/arteryTrachea
  • Larynx
  • Pharynx
  • Thyroid gland

External Carotid Artery

The external carotid artery supplies the following structures:

  • Superficial structures of the neck
  • Face
  • Jaw
  • Scalp
  • Meninges

Origin

Superficial, within the carotid triangle, and at the level of the thyroid cartilage (C4)

Eight major branches

  1. Superior thyroid artery
  2. Ascending pharyngeal artery
  3. Lingual artery
  4. Facial artery
  5. Occipital artery
  6. Posterior auricular artery
  7. Maxillary artery
  8. Superficial temporal artery

To help remember the 8 major branches, use the following mnemonic: Some Anatomists Like Freaking Out Poor Medical Students.

  • Superior thyroid artery
  • Ascending pharyngeal artery
  • Lingual artery
  • Facial artery
  • Occipital artery
  • Posterior auricular artery
  • Maxillary artery
  • Superficial temporal artery
Table: Structures supplied by the 8 major branches of the external carotid artery
BranchStructures supplied
Superior thyroid
  • Thyroid gland
  • Infrahyoid muscles
  • Sternocleidomastoid muscle
Ascending pharyngeal
  • Pharynx
  • Prevertebral muscles
  • Middle ear
  • Cranial meninges
Lingual
  • Intrinsic muscles of the tongue
  • Floor of the mouth
Facial
  • Tonsils
  • Palate
  • Submandibular glands
OccipitalPosterior region of the scalp
Posterior auricular
  • Parotid gland
  • Facial nerve
  • Ear
  • Scalp
Maxillary
  • External acoustic meatus
  • Tympanic membrane
  • Dura mater
  • Calvaria
  • Mandible
  • Gingivae
  • Teeth
  • Temporalis muscles
  • Pterygoid muscles
  • Masseter muscles
  • Buccinator muscles
Superficial temporalTemporal region of the scalp
Major branches of the external carotid artery

Major branches of the external carotid artery

Image by BioDigital, edited by Lecturio

Relations

  • Anterior: skin, superficial fascia, platysma muscle, deep fascia, and anterior margin of the sternocleidomastoid muscle
  • Posterior: superior laryngeal nerve
  • Medial: hyoid bone, pharynx, superior laryngeal nerve, and parotid gland
  • Lateral: internal carotid artery

Internal Carotid Artery

The internal carotid artery supplies the following structures:

  • Frontal lobe
  • Parietal lobe
  • Temporal lobe
  • Diencephalon
  • Eyes
  • Parts of the paranasal sinuses (ophthalmic artery)
  • Contributes to the circle of Willis in the cerebrovascular system

Location

  • Originates within the carotid triangle at the level of the thyroid cartilage (C4)
  • Ascends and enters the skull through the carotid canal (temporal bone)
  • Terminates as the middle and anterior cerebral arteries

Segments

The internal carotid artery is divided into segments:

  • Modern division: 
    • Cervical part: no branches
    • Petrous part
    • Cavernous part: relates to the cavernous sinus
    • Intracranial part
  • Cincinnati classification: 
    • Cervical
    • Petrous
    • Lacerum
    • Cavernous
    • Clinoid
    • Ophthalmic (supraclinoid)
    • Communicating (terminal) segments

Mnemonic: C‘mon Please Learn the Carotid Clinical Organizing Classification

  • Cervical
  • Petrous
  • Lacerum
  • Cavernous
  • Clinoid
  • Ophthalmic
  • Communicating
Segments Internal carotid artery

Segments of the internal carotid artery

Image by BioDigital, edited by Lecturio

Clinical Relevance

  • Carotid artery stenosis: a narrowing of the lumen of the carotid arteries due to fat and cholesterol deposition. Carotid artery stenosis occurs in patients with hypercholesterolemia and atherosclerosis and is a primary risk factor for ischemic stroke. Carotid artery stenosis can be treated with antiplatelet medications or surgical revascularization in severe cases.
  • Dissection of the carotid and vertebral arteries: separation of the tunica media and tunica intima of the carotid artery. The dissection typically presents with the sudden onset of severe headache and neck pain. Focal neurologic deficits can occur secondary to stenosis of the carotid artery or thrombus formation. 
  • Superficial temporal arteritis: inflammation of the superficial temporal artery. Superficial temporal arteritis results in a severe throbbing headache in the affected side of the head with scalp tenderness overlying it. Temporal arteritis is typically treated with NSAIDs or steroids. If untreated, temporal arteritis can result in blindness.

References

  1. Drake, R.L., Vogl, A.W., Mitchell, A.W.M. (2014). Gray’s Anatomy for Students (3rd ed.). Philadelphia, PA: Churchill Livingstone.
  2. Sethi, D., Gofur, E.M., Munakomi, S. (2021). Anatomy, Head and Neck, Carotid Arteries. [Updated 2021 Feb 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing https://www.ncbi.nlm.nih.gov/books/NBK545238/
  3. Vijaywargiya, M., et al. (2017). Anatomical study of petrous and cavernous parts of internal carotid artery. Anatomy and Cell Biology, 50(3):163.

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