The head and neck receive the majority of their blood supply through the carotid and vertebral arteries. This article shall explore the anatomy of this arterial system – its anatomical course, branches, and clinical correlations.
The right common carotid artery arises from a bifurcation of the brachiocephalic trunk – the right subclavian artery being the other branch – occurring at approximately the level of the right sternoclavicular joint. The left common carotid artery branches directly from the arch of the aorta. Both the left and right common carotid arteries ascend up the neck, lateral to the trachea and oesophagus, giving off no branches along the way.
At a height of roughly the superior margin of the thyroid cartilage (C4), the carotid arteries split into the external and internal carotid arteries. This point of divergence is located in an anatomical region known as the carotid triangle. At this point, the common carotid and internal carotid arteries are slightly dilated, forming an area known as the carotid sinus. This area contains baroreceptors, specialised sensory cells, which detect stretch as a measure of blood pressure, which is relayed to the brain via the glossopharyngeal nerve to ultimately regulate blood pressure.
Due to the baroreceptors being hypersensitive to stretch in some individuals, external pressure on the carotid sinus can cause slowing of the heart rate and decrease in blood pressure, leading to syncope due to the brain becoming under-perfused. For this reason, it is not advised to check the pulse of such individuals at the carotid triangle.
Externally to the carotid sinus, is a cluster of cells known as the carotid body, which act as peripheral chemoreceptors, detecting the O2 content of the blood and relaying this information to the brain to regulate breathing rate.
The external carotid artery supplies the areas of the head and neck external to the cranium, travelling up the neck, passing posteriorly to the mandibular neck and anteriorly to the lobule of the ear, ending within the parotid gland by dividing into the superficial temporal artery and the maxillary artery. It gives rise to six branches in total – the superior thyroid artery, lingual artery, facial artery, ascending pharyngeal artery, occipital artery, and posterior auricular artery.
Of these, the facial, maxillary and superficial temporal arteries are the major branches of note. The maxillary artery supplies the deep structures of the face, while the facial and superficial temporal arteries generally supply superficial areas of the face. The posterior auricular, occipital and superficial temporal arteries, along with two branches of the internal carotid artery – the supra-orbital and supratrochlear arteries – combine to provide a dense blood supply to the scalp.
Injury to the scalp can lead to excessive bleeding due to various reasons. Firstly, the walls of the arteries are tightly and closely bound to the underlying connective tissue of the scalp, preventing them from constricting to limit blood loss following injury or laceration. Additionally, numerous anastomoses formed by the arteries produce a very densely vascularised area. Deep lacerations involving the epicranial aponeurosis can worsen due to the opposing pulls of the occipital and frontalis muscles.
Though scalp injuries can cause severe bleeding, it is important to note that the bony skull gets its blood from an alternative source – the middle meningeal artery – and so will not undergo avascular necrosis.
The middle meningeal artery is a branch of the maxillary artery, which is unique in that it supplies some intracranial structures – usually the external carotid artery and its branches supply extra-cranial structures. It supplies both the skull and the dura mater, the outer membranous layer covering the brain.
A possible complication of a fracture of the skull, particularly at its weakest point, the pterion, is that it can injure or completely lacerate the middle meningeal artery. As blood collects between the dura mater and the skull, this can cause a dangerous increase in intra-cranial pressure, referred to as an extradural haematoma.
The increase in intra-cranial pressure produces a variety of symptoms, such as nausea, vomiting, seizures, bradycardia, and limb weakness.
The head and neck receive their blood supply through the carotid and vertebral arteries. These arteries are of critical importance to the physiology of the human body and require proper understanding of their anatomy.
To begin our exploration, we shall start at the origin of the Carotid Arteries. The right common carotid artery arises from a bifurcation of the brachiocephalic trunk. This bifurcation occurs roughly at the level of the right sternoclavicular joint. The left common carotid artery branches directly from the arch of the aorta.
The left and right common carotid arteries ascend up the neck, lateral to the trachea and the oesophagus. As they ascend, they do not give off any branches in the neck. Then, at the level of the superior margin of the thyroid cartilage (C4), the carotid arteries split into the external and internal carotid arteries. This bifurcation occurs in an anatomical area known as the carotid triangle.
The common carotid and internal carotid are slightly dilated here, this area is known as the carotid sinus. The carotid sinus is an important area for detecting and regulating blood pressure.
The carotid sinus is a dilated portion of the common carotid artery and proximal internal carotid artery, containing baroreceptors, specialised sensory cells. The baroreceptors detect stretch as a measure of blood pressure, which is then fed to the brain, and used to regulate blood pressure.
In some individuals, the baroreceptors are hypersensitive to stretch. External pressure on the carotid sinus can cause slowing of the heart rate and a decrease in blood pressure, leading to syncope and brain under-perfusion. Therefore, in these cases, checking the pulse at the carotid triangle is not advised.
External to the carotid sinus, there lies a cluster of nervous cells known as the carotid body. It contains chemoreceptors that detect changes in the chemistry of the blood, and send this information to the brain, which is used to regulate breathing. The common carotid and internal carotid do not supply any structures in the neck; they enter the cranial cavity via the carotid canal in the petrous part of the temporal bone, and supply the brain, eyes, and forehead.
The swelling at the bifurcation of the common carotid arteries, the carotid sinus, produces turbulent blood flow. This increases the risk of atheroma formation in this area, with the internal carotid most susceptible. Atherosclerotic thickening of the tunica intima of these arteries will reduce blood flow to the brain, resulting in the development of a variety of neurological symptoms, including headache, dizziness, and muscular weakness. If blood flow is completely occluded, a cerebral ischaemia (stroke) results. If atherosclerosis of the carotid arteries is suspected, a Doppler study can be used to assess the severity of any thickening; severe cases may require the use of a carotid endarterectomy.
The vertebral arteries are paired vessels which arise from the subclavian arteries, just medial to the anterior scalenes. They ascend the posterior aspect of the neck, passing through holes in the transverse processes of the cervical vertebrae (known as foramen transversarium). The vertebral arteries enter the cranium via the foramen magnum and converge to form the basilar artery – which continues to supply the brain. The vertebral arteries do not supply any branches to the neck or other extra-cranial structures.
The neck is also supplied by arteries other than the carotids. The right and left subclavian arteries give rise to the thyrocervical trunk. From this trunk, several vessels arise and supply the neck:
Minor cases of haemorrhage may be treated by diuretics, while more extreme cases may require surgery such as drilling burr holes into the skull. Overall, the anatomy of the carotid and vertebral arteries of the neck is essential to the understanding of the physiology of the human body and related clinical correlations.
The external carotid artery is situated in the neck and supplies the areas that lie external to the cranium. It originates from the common carotid artery and then travels up posteriorly to the mandibular neck and anteriorly to the lobule of the ear, ultimately dividing into the superficial temporal artery and the maxillary artery within the parotid gland. It gives rise to six branches in total: the superior thyroid artery, the lingual artery, the facial artery, the ascending pharyngeal artery, the occipital artery and the posterior auricular artery. Of these, the facial, maxillary and superficial temporal arteries are the major branches, with the maxillary artery supplying the deep structures of the face, whereas the facial and superficial temporal arteries generally supply the superficial areas.
The scalp receives its blood supply from the posterior auricular, occipital and superficial temporal arteries, as well as two branches of the internal carotid artery – the supra-orbital and supratrochlear arteries. Because the artery walls are tightly and closely bound to the underlying connective tissue of the scalp, they are unable to constrict to limit blood loss following injury or laceration. Furthermore, the numerous anastomoses formed by the arteries produce a very densely vascularised area, meaning that even deep lacerations can cause excessive bleeding.
It is important to note, however, that the bony skull gets its blood from a different source – the middle meningeal artery – and so will not undergo avascular necrosis.
The maxillary artery is unique in that it supplies some intracranial structures, such as the middle meningeal artery (MMA). When the skull is fractured at its weakest point – the pterion – the MMA can be injured or completely lacerated, causing a collecting of blood between the dura mater and the skull and an increase in the intra-cranial pressure. This is known as an extradural haematoma, and can result in a variety of symptoms, including nausea, vomiting, seizures, bradycardia and limb weakness. Treatment depends on the severity of the haematoma, ranging from diuretics for lesser cases to drilling burr holes into the skull for more extreme ones.
The internal carotid arteries merges with the carotid canal in the petrous part of the temporal bone to enter the cranial cavity. Once there, it supplies the brain, eyes and forehead; providing an essential blood supply for these structures.
The swelling at the bifurcation of the common carotid arteries, known as the carotid sinus, produces turbulent blood flow which increases the risk of atheroma formation in this area, with the internal carotid being most susceptible. Atherosclerotic thickening of the tunica intima of these arteries can reduce blood flow to the brain, resulting in headache, dizziness and muscular weakness. In extreme cases, this can cause a cerebral ischaemia (stroke).
If atherosclerosis of the carotid arteries is suspected, then a Doppler study can be used to assess the severity of any thickening, and in severe cases the artery can be opened and the atheromatous tunica intima removed in a carotid endarterectomy.
The vertebral arteries are paired vessels that arise from the subclavian arteries, located just medial to the anterior scalenes. They ascend the posterior aspect of the neck, passing through the foramen transversarium of the cervical vertebrae, before entering the cranium via the foramen magnum and conjoining to form the basilar artery, continuing to supply the brain.
These cells act as peripheral chemoreceptors, detecting the oxygen content of the blood and relaying this information to the brain to regulate breathing rate.
The vertebral arteries do not supply any branches to the neck or other extra-cranial structures.
The neck is supplied by arteries other than the carotids. The right and left subclavian arteries give rise to the thyrocervical trunk. The thyrocervical trunk is the source of several vessels that supply the neck.
The anatomy of the head and neck arterial system is of great clinical importance due to its involvement with the blood supply to the scalp, the possibility of extradural haematoma, and the clinical relevance of carotid sinus hypersensitivity. The head and neck arterial system is composed of the internal carotid artery, the vertebral arteries, as well as the external carotid artery and its branches. Atherosclerosis of the carotid arteries is a major cause of stroke and other vascular diseases of the neck.
Other arteries of the neck include the occipital artery, posterior auricular artery, superior thyroid artery, lingual artery, facial artery, and ascending pharyngeal artery. All of these arteries are responsible for providing oxygen-rich blood to parts of the head and neck, and they play an important role in the prevention of stroke, cardiovascular disease, and other health issues that are caused by blocked or reduced blood flow.
The carotid arteries, which run alongside the neck on both sides, are particularly prone to atherosclerosis, or hardening of the arteries. This form of cardiovascular disease can reduce blood flow to the head and neck and lead to stroke, heart attack, or other serious health issues. The carotid arteries are typically monitored for blockages and atherosclerosis with ultrasound, magnetic resonance imaging (MRI), or computed tomography (CT) scan. Treatment for carotid artery disease may involve medications, lifestyle changes, and, in some cases, surgery.
Certain factors can increase one’s risk of developing carotid artery disease, such as age, smoking, diabetes, high blood pressure, and high cholesterol. It’s important to be aware of these risk factors as well as the potential symptoms, which can include dizziness, vision problems, and stroke-like symptoms, such as speech difficulty, difficulty walking, and numbness or weakness in the face, arm, or leg. Early diagnosis and treatment of carotid artery disease can help to prevent serious health complications.
