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 Aortic arch The branchial arches, also known as pharyngeal or visceral arches, are embryonic structures seen in the development of vertebrates that serve as precursors for many structures of the face, neck, and head. These arches are composed of a central core of mesoderm, which is covered externally by ectoderm and internally by endoderm. Branchial Apparatus and Aortic Arches on the left side and from the brachiocephalic trunk/artery on the right. The common carotid arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries then ascend through the neck and divide into the internal and external carotid arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. 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 Aortic arch The branchial arches, also known as pharyngeal or visceral arches, are embryonic structures seen in the development of vertebrates that serve as precursors for many structures of the face, neck, and head. These arches are composed of a central core of mesoderm, which is covered externally by ectoderm and internally by endoderm. Branchial Apparatus and Aortic Arches.
  • Right: The brachiocephalic trunk/artery (1st branch of the aortic arch Aortic arch The branchial arches, also known as pharyngeal or visceral arches, are embryonic structures seen in the development of vertebrates that serve as precursors for many structures of the face, neck, and head. These arches are composed of a central core of mesoderm, which is covered externally by ectoderm and internally by endoderm. Branchial Apparatus and Aortic Arches) 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 Cartilage Cartilage is a type of connective tissue derived from embryonic mesenchyme that is responsible for structural support, resilience, and the smoothness of physical actions. Perichondrium (connective tissue membrane surrounding cartilage) compensates for the absence of vasculature in cartilage by providing nutrition and support. 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 blood pressure to the hypothalamus Hypothalamus The hypothalamus is a collection of various nuclei within the diencephalon in the center of the brain. The hypothalamus plays a vital role in endocrine regulation as the primary regulator of the pituitary gland, and it is the major point of integration between the central nervous and endocrine systems. 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 Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs and pleura Pleura The pleura is a serous membrane that lines the walls of the thoracic cavity and the surface of the lungs. This structure of mesodermal origin covers both lungs, the mediastinum, the thoracic surface of the diaphragm, and the inner part of the thoracic cage. The pleura is divided into a visceral pleura and parietal pleura. Pleura
  • Remains of the thymus
  • Left brachiocephalic vein
  • Sternoclavicular joint
  • Superficial fascia
  • Platysma
  • Sternocleidomastoid, sternothyroid, and omohyoid muscles
  • Skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin
  • Branches of the cervical plexus
  • Platysma
  • Sternocleidomastoid muscle
Posterior
  • Trachea Trachea The trachea is a tubular structure that forms part of the lower respiratory tract. The trachea is continuous superiorly with the larynx and inferiorly becomes the bronchial tree within the lungs. The trachea consists of a support frame of semicircular, or C-shaped, rings made out of hyaline cartilage and reinforced by collagenous connective tissue. Trachea
  • Esophagus Esophagus The esophagus is a muscular tube-shaped organ of around 25 centimeters in length that connects the pharynx to the stomach. The organ extends from approximately the 6th cervical vertebra to the 11th thoracic vertebra and can be divided grossly into 3 parts: the cervical part, the thoracic part, and the abdominal part. Esophagus
  • Left recurrent laryngeal nerve
  • Thoracic duct
  • Sympathetic trunk
  • Longus colli, longus capitis, and anterior scalene muscles
Lateral
  • Phrenic nerve
  • Left vagus
  • Left pleura Pleura The pleura is a serous membrane that lines the walls of the thoracic cavity and the surface of the lungs. This structure of mesodermal origin covers both lungs, the mediastinum, the thoracic surface of the diaphragm, and the inner part of the thoracic cage. The pleura is divided into a visceral pleura and parietal pleura. Pleura
  • Vagus nerve
  • Internal jugular vein (within the same carotid sheath)
Medial Brachiocephalic trunk/artery Trachea Trachea The trachea is a tubular structure that forms part of the lower respiratory tract. The trachea is continuous superiorly with the larynx and inferiorly becomes the bronchial tree within the lungs. The trachea consists of a support frame of semicircular, or C-shaped, rings made out of hyaline cartilage and reinforced by collagenous connective tissue. Trachea
  • Larynx
  • Pharynx
  • Thyroid gland Thyroid gland The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland

External Carotid Artery

The external carotid artery supplies the following structures:

  • Superficial structures of the neck
  • Face
  • Jaw Jaw The jaw is made up of the mandible, which comprises the lower jaw, and the maxilla, which comprises the upper jaw. The mandible articulates with the temporal bone via the temporomandibular joint (TMJ). The 4 muscles of mastication produce the movements of the TMJ to ensure the efficient chewing of food. Jaw and Temporomandibular Joint
  • Scalp
  • Meninges Meninges The brain and the spinal cord are enveloped by 3 overlapping layers of connective tissue called the meninges. The layers are, from the most external layer to the most internal layer, the dura mater, arachnoid mater, and pia mater. Between these layers are 3 potential spaces called the epidural, subdural, and subarachnoid spaces. Meninges

Origin

Superficial, within the carotid triangle, and at the level of the thyroid cartilage Cartilage Cartilage is a type of connective tissue derived from embryonic mesenchyme that is responsible for structural support, resilience, and the smoothness of physical actions. Perichondrium (connective tissue membrane surrounding cartilage) compensates for the absence of vasculature in cartilage by providing nutrition and support. 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
Branch Structures supplied
Superior thyroid
  • Thyroid gland Thyroid gland The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland
  • Infrahyoid muscles
  • Sternocleidomastoid muscle
Ascending pharyngeal
  • Pharynx
  • Prevertebral muscles
  • Middle ear
  • Cranial meninges
Lingual
  • Intrinsic muscles of the tongue Tongue The tongue, on the other hand, is a complex muscular structure that permits tasting and facilitates the process of mastication and communication. The blood supply of the tongue originates from the external carotid artery, and the innervation is through cranial nerves. Oral Cavity: Lips and Tongue
  • Floor of the mouth
Facial
  • Tonsils
  • Palate Palate The palate is the structure that forms the roof of the mouth and floor of the nasal cavity. This structure is divided into soft and hard palates. Oral Cavity: Palate
  • Submandibular glands
Occipital Posterior region of the scalp
Posterior auricular
  • Parotid gland
  • Facial nerve
  • Ear
  • Scalp
Maxillary
  • External acoustic meatus
  • Tympanic membrane
  • Dura mater
  • Calvaria
  • Mandible
  • Gingivae
  • Teeth Teeth Normally, an adult has 32 teeth: 16 maxillary and 16 mandibular. These teeth are divided into 4 quadrants with 8 teeth each. Each quadrant consists of 2 incisors (dentes incisivi), 1 canine (dens caninus), 2 premolars (dentes premolares), and 3 molars (dentes molares). Teeth are composed of enamel, dentin, and dental cement. Teeth
  • Temporalis muscles
  • Pterygoid muscles
  • Masseter muscles
  • Buccinator muscles
Superficial temporal Temporal 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 Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Structure of Bones, pharynx Pharynx The pharynx is a component of the digestive system that lies posterior to the nasal cavity, oral cavity, and larynx. The pharynx can be divided into the oropharynx, nasopharynx, and laryngopharynx. Pharyngeal muscles play an integral role in vital processes such as breathing, swallowing, and speaking. 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 Paranasal Sinuses The 4 pair of paranasal sinuses include the maxillary, ethmoid, sphenoid, and frontal sinuses. The sinuses are a group of air-filled cavities located within the facial and cranial skeleton; all are connected to the main nasal cavity and nasopharynx. Paranasal Sinuses (ophthalmic artery)
  • Contributes to the circle of Willis in the cerebrovascular system Cerebrovascular system Blood supply to the brain can be divided into an anterior and a posterior circulation, which interconnect to form the circle of Willis. The anterior circulation is derived from the internal carotid arteries and consists mainly of the anterior and middle cerebral arteries. The posterior circulation is derived from the vertebral arteries and consists primarily of the cerebellar and posterior cerebral arteries. Cerebrovascular System

Location

  • Originates within the carotid triangle at the level of the thyroid cartilage Cartilage Cartilage is a type of connective tissue derived from embryonic mesenchyme that is responsible for structural support, resilience, and the smoothness of physical actions. Perichondrium (connective tissue membrane surrounding cartilage) compensates for the absence of vasculature in cartilage by providing nutrition and support. Cartilage (C4)
  • Ascends and enters the skull Skull The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull through the carotid canal (temporal bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Structure of Bones)
  • Terminates as the middle and anterior cerebral arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. 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 Carotid artery stenosis Carotid artery stenosis is a chronic atherosclerotic disease resulting in narrowing of the common and internal carotid arteries. Common risk factors include family history, advanced age, hyperlipidemia, smoking, and diabetes mellitus. Patients may present with or without symptoms of decreased cerebral perfusion. Carotid Artery Stenosis: a narrowing of the lumen of the carotid arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries due to fat and cholesterol deposition. Carotid artery stenosis Carotid artery stenosis Carotid artery stenosis is a chronic atherosclerotic disease resulting in narrowing of the common and internal carotid arteries. Common risk factors include family history, advanced age, hyperlipidemia, smoking, and diabetes mellitus. Patients may present with or without symptoms of decreased cerebral perfusion. Carotid Artery Stenosis occurs in patients with hypercholesterolemia and atherosclerosis Atherosclerosis Atherosclerosis is a common form of arterial disease in which lipid deposition forms a plaque in the blood vessel walls. Atherosclerosis is an incurable disease, for which there are clearly defined risk factors that often can be reduced through a change in lifestyle and behavior of the patient. Atherosclerosis and is a primary risk factor for ischemic stroke Ischemic Stroke An ischemic stroke (also known as cerebrovascular accident) is an acute neurologic injury that occurs as a result of brain ischemia; this condition may be due to cerebral blood vessel occlusion by thrombosis or embolism, or rarely due to systemic hypoperfusion. Ischemic Stroke. Carotid artery stenosis Carotid artery stenosis Carotid artery stenosis is a chronic atherosclerotic disease resulting in narrowing of the common and internal carotid arteries. Common risk factors include family history, advanced age, hyperlipidemia, smoking, and diabetes mellitus. Patients may present with or without symptoms of decreased cerebral perfusion. Carotid Artery Stenosis can be treated with antiplatelet medications or surgical revascularization in severe cases.
  • Dissection of the carotid and vertebral arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. 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 Neck Pain Neck pain is one of the most common complaints in the general population. Depending on symptom duration, it can be acute, subacute, or chronic. There are many causes of neck pain, including degenerative disease, trauma, rheumatologic disease, and infections. Neck Pain. Focal neurologic deficits can occur secondary to stenosis of the carotid artery or thrombus formation. 
  • Superficial temporal arteritis Temporal arteritis Giant cell arteritis (GCA), also known as temporal arteritis, is a type of large-vessel vasculitis that predominantly affects the aorta and its major branches, with a predilection for the branches of the carotid (including the temporal artery). Giant cell arteritis is defined by inflammatory leukocytes in the vessel walls leading to reactive damage, ischemia, and necrosis. Giant Cell Arteritis: inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of the superficial temporal artery. Superficial temporal arteritis Temporal arteritis Giant cell arteritis (GCA), also known as temporal arteritis, is a type of large-vessel vasculitis that predominantly affects the aorta and its major branches, with a predilection for the branches of the carotid (including the temporal artery). Giant cell arteritis is defined by inflammatory leukocytes in the vessel walls leading to reactive damage, ischemia, and necrosis. Giant Cell 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 Temporal arteritis Giant cell arteritis (GCA), also known as temporal arteritis, is a type of large-vessel vasculitis that predominantly affects the aorta and its major branches, with a predilection for the branches of the carotid (including the temporal artery). Giant cell arteritis is defined by inflammatory leukocytes in the vessel walls leading to reactive damage, ischemia, and necrosis. Giant Cell 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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