External Carotid Artery

1. Overview

The external carotid artery is one of the two main branches of the common carotid artery. It supplies oxygenated blood to the head and neck, providing blood flow to several important structures, including the face, scalp, neck, jaw, and base of the skull. It plays a crucial role in maintaining the circulation to the upper part of the body and is responsible for delivering blood to various organs and tissues that require a steady supply of oxygen and nutrients. The external carotid artery branches out into several smaller arteries that serve the head and neck region. This artery is critical for the vascular supply to the superficial structures of the head and neck.

2. Location

The external carotid artery originates from the common carotid artery at the level of the upper border of the thyroid cartilage (approximately at the level of the C4 vertebra). The common carotid artery bifurcates into the internal carotid artery, which supplies the brain, and the external carotid artery, which supplies the face, scalp, and neck. The external carotid artery ascends in the neck, running along the side of the head, passing through the carotid triangle and dividing into its terminal branches at the level of the neck near the ear, where it divides into the superficial temporal and maxillary arteries.

3. Structure

The external carotid artery is a relatively large artery that has several structural features designed to efficiently supply blood to the head and neck. Some key structural characteristics of the external carotid artery include:

• Origin: The external carotid artery arises from the common carotid artery, typically at the level of the C4 vertebra. It begins at the bifurcation of the common carotid artery.

• Course: The artery travels upward along the side of the neck, passing deep to the digastric muscle and the stylohyoid muscle before reaching the level of the ear, where it bifurcates into its terminal branches.

• Size and Diameter: The external carotid artery is usually about 4-5 mm in diameter, although this can vary depending on the individual and the size of the carotid arteries.

• Branches: The external carotid artery gives rise to several important branches that supply various regions of the head and neck. These branches include:

  • Superior thyroid artery: Supplies the thyroid gland, larynx, and some muscles in the neck.

  • Lingual artery: Supplies the tongue and parts of the floor of the mouth.

  • Facial artery: Supplies blood to the face, including the lips, nose, and cheeks.

  • Occipital artery: Supplies blood to the posterior scalp and the muscles in the back of the neck.

  • Posterior auricular artery: Supplies the ear and the scalp behind the ear.

  • Maxillary artery: Supplies deep structures in the face, including the jaw, teeth, palate, and muscles of mastication.

  • Superficial temporal artery: Supplies the scalp and muscles of the face, including the temporal region.

• Wall Composition: Like all arteries, the external carotid artery consists of three layers:

  • Intima: The innermost layer composed of endothelial cells, which allow for smooth blood flow.

  • Media: The middle layer of smooth muscle cells and elastic tissue that provides strength and flexibility to the artery.

  • Adventitia: The outer layer made of connective tissue, which provides structural support and helps anchor the artery to surrounding tissues.

4. Function

The external carotid artery has the important function of supplying oxygenated blood to the structures of the head and neck. Some of the primary functions of the external carotid artery include:

• Supplying the face and scalp: The external carotid artery delivers blood to the face, scalp, and neck through its branches. This includes supplying the skin, muscles, and tissues of the face, as well as the ears and scalp.

• Supplying the tongue and mouth: The lingual artery, one of the branches of the external carotid artery, supplies the tongue and parts of the mouth, facilitating oral and speech functions.

• Blood supply to the thyroid and larynx: The superior thyroid artery, another branch of the external carotid artery, provides blood to the thyroid gland, larynx, and nearby muscles, supporting endocrine and respiratory functions.

• Blood supply to the deeper facial structures: The maxillary artery, a major branch of the external carotid artery, supplies deep structures in the face, including the jaw, teeth, and palate, as well as muscles involved in chewing and facial expression.

• Scalp and neck muscle blood flow: The occipital and posterior auricular arteries provide blood to the muscles of the neck and the scalp, supporting neck movements and sensory functions for the ear.

5. Physiological Role(s)

The external carotid artery plays several key physiological roles in maintaining normal blood flow to the head and neck:

• Oxygen and nutrient delivery: By supplying blood to various tissues of the face, neck, and scalp, the external carotid artery ensures that these regions receive adequate oxygen and nutrients required for normal cellular function. This is essential for maintaining healthy skin, muscles, and other tissues.

• Facilitation of facial and neck movement: The external carotid artery supports the muscles of the face, jaw, and neck by supplying them with the necessary oxygenated blood to function. This enables essential movements like speaking, chewing, and facial expressions.

• Support of respiratory and endocrine function: The blood supply to the thyroid gland and larynx, provided by branches of the external carotid artery, is critical for proper metabolic regulation and vocalization.

• Support of hearing and sensory functions: The blood supply to the ear and surrounding muscles, provided by the posterior auricular and occipital arteries, supports hearing and other sensory functions in the head.

6. Clinical Significance

The external carotid artery is clinically significant due to its role in supplying blood to critical structures in the head, face, and neck. Various conditions can affect the external carotid artery, leading to serious health complications. Some key clinical conditions associated with the external carotid artery include:

• Atherosclerosis: Atherosclerosis, the buildup of fatty plaques in the arteries, can affect the external carotid artery, leading to narrowing or blockage. This can reduce blood flow to the face, neck, and brain, increasing the risk of stroke, transient ischemic attack (TIA), or peripheral artery disease. Treatment may involve medications, lifestyle changes, and surgical procedures such as angioplasty or bypass surgery.

• Carotid artery stenosis: Carotid artery stenosis occurs when there is a narrowing of the carotid arteries, including the external carotid artery, due to plaque buildup. This condition can impair blood flow to the brain and lead to symptoms such as dizziness, weakness, or sudden vision loss. Management typically includes lifestyle changes, medications, or surgical interventions like carotid endarterectomy or stenting.

• Carotid artery dissection: A carotid artery dissection occurs when there is a tear in the inner wall of the artery, which can result in reduced blood flow to the brain and cause a stroke or TIA. Dissections can affect the external carotid artery and its branches, leading to neurological symptoms. Treatment often involves blood thinners and, in some cases, surgery to repair the tear.

• Temporomandibular joint (TMJ) disorders: Disorders affecting the temporomandibular joint can lead to changes in blood flow to the jaw and face. Although not directly involving the external carotid artery, TMJ disorders can affect the arterial blood supply to muscles and tissues in the jaw, leading to pain and discomfort.

• Trauma to the external carotid artery: Injuries to the external carotid artery, such as from blunt or penetrating trauma to the neck or face, can cause bleeding, hematoma, and potential loss of blood flow to vital structures. Surgical intervention may be required to repair or ligate the damaged artery and control bleeding.

The external carotid artery is essential for supplying oxygenated blood to the head, face, and neck. Disorders such as atherosclerosis, carotid artery stenosis, and dissection can impair its function and lead to serious cardiovascular complications. Early diagnosis and timely treatment are crucial for maintaining proper blood flow and preventing adverse outcomes.