Arteries of the brain
About fifteen percent (15%) of the daily cardiac output is utilized by the brain. Owing to the high oxygen and nutrient demand of the organ, it is supplied by two arterial systems:
- The anterior circuit is supplied by the internal carotid arteries
- The posterior circuit is supplied by the vertebrobasilar system.
The focus of this article will be to discuss the major arteries that supply the brain. More details about the development, course and their target regions of the individual vessels can be found in their respective articles.
|Development||3rd - 7th gestational weeks|
|Anterior circulation||Internal carotid arteries
Anterior cerebral arteries
Anterior communicating arteries
Middle cerebral arteries
|Carotid artery||Branch of the common carotid artery
Cincinnati classification and Newer 4 part classification
Mnemonic (excludes C1): Please Let Children Consume Our Candy
|Posterior circuit||Posterior cerebral arteries
Posterior communicating arteries
|Vertebral arteries||Branches: posterior inferior cerebral artery (PICA), anterior and posterior spinal, meningeal and medullary arteries|
|Basilar arteries||Branches: Anterior inferior cerebellar, Superior cerebellar, Internal auditory (Labyrinthine). Becomes the posterior cerebral artery|
|Circle of Willis||Union of anterior and posterior circulation
In the subarachnoid space, in the interpeduncular cistern
Surrounds optic chiasm and infundibulum
|Clinical Significance||Anterior circulation stroke
Posterior circulation stroke
- Anterior circulation
- Posterior circulation
- Circle of Wills
- Clinical significance
Although there is a dual supply to the brain, each division shares a common origin. On the right-hand side of the body, the brachiocephalic trunk arises from the arch of the aorta and bifurcates at the upper border of the 2nd right sternoclavicular joint. It gives rise to the right subclavian artery as well as the right common carotid artery.
The left counterparts to these vessels are direct derivatives of the aortic arch. Both the left and right common carotid arteries subsequently bifurcate between the third and fourth cervical vertebra (between the superior horn of the thyroid cartilage and the hyoid bone) to give the internal and external carotid arteries. The derivatives of the internal carotid arteries form the anterior blood supply (anterior circulation) of the brain, which includes the anterior and middle cerebral arteries.
The subclavian artery is divided into three parts based on anatomical landmarks. The first part extends from its origin to the medial border of the scalenus anterior muscle. The vertebral artery originates from this part of the vessel and travels superiorly toward the transverse foramen of the 6th cervical vertebra. After entering the transverse foramen, it continues superiorly within the five preceding foramina. The paired vessels eventually unite to give rise to the basilar artery, which contributes to the posterior blood supply (posterior circulation) of the brain.
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The anterior circulation involves all the arteries that originate from the internal carotid arteries. It is responsible for the blood supply of the anterior and middle aspect of the brain. The arteries of this anterior circuit are:
- The internal carotid arteries
- The anterior cerebral arteries
- The anterior communicating artery
- The middle cerebral arteries
Internal carotid arteries
The internal carotid artery is one of two branches of the common carotid artery. It is responsible for supplying a large portion of the anterior and middle parts of the brain.
A new classification system divides the internal carotid artery into four parts; cervical in the neck, petrous in the base of the skull, cavernous within the cavernous sinus and intracranial above the cavernous sinus.
Previously, the Cincinnati Classification (Bouthillier et. al., 1996) classified the internal carotid artery into seven segments; cervical (C1), petrous (C2), lacerum (C3), cavernous (C4), clinoid (C5), ophthalmic or supraclinoid (C6), communicating or terminal (C7). It is undoubtedly easier to remember the new classification. However, here is a quick mnemonic to remember the C2-C7 intracranial segments of the internal carotid artery according to the Cincinnati classification - Please Let Children Consume Our Candy.
|New classification||Cervical part, petrous part, cavernous part, intracranial part|
|Cincinnati classification||C1 – Cervical Segment
C2 – Petrous Segment
C3 – Lacerum Segment
C4 – Cavernous Segment
C5 – Clinoid Segment
C6 – Ophthalmic (Supraclinoid) Segment
C7 – Communicating (Terminal) Segment
Mnemonic (C2-C7): Please Let Children Consume Our Candy
When comparing the Cincinnati classification with the new system, the following differences can be observed:
- The part of the artery that was considered the lacerum segment is now referred to as a continuation of the petrous segment.
- The intracranial part involves the clinoid, ophthalmic and communicating portions (i.e. C5, C6, and C7)
The petrous part (C2) gives off the caroticotympanic and Vidian arteries. The cavernous segment (C4) gives numerous branches to the walls of the cavernous sinus and the surrounding nerves and dura mater. Of significance, the inferior hypophyseal artery also originates from this segment.
The ophthalmic segment (C6) gives of the ophthalmic artery and the superior hypophyseal artery. The communicating segment (C7) gives off the anterior cerebral (ACA), middle cerebral (MCA) and the anterior choroidal (AChA) arteries. The AChA supplies mesencephalic, diencephalic, and telencephalic derivatives.
Anterior cerebral artery
The anterior cerebral artery (ACA) is a much smaller branch of the internal carotid artery (when compared to the middle cerebral artery). It begins at the terminal portion of the internal carotid artery (after the ophthalmic branch is given off) on the medial part of the Sylvian fissure. It travels in an anteromedial course, superior to the optic nerve (CN II) towards the longitudinal cerebral fissure. Here it anastomoses with the contralateral counterpart via the short anterior communicating artery (AComm). The paired arteries then travel through the longitudinal cerebral fissure along the genu of the corpus callosum.
The anterior cerebral artery also gives off central and cortical branches. Central branches arise from the AComm to perfuse the optic chiasma, lamina terminalis, hypothalamus, para-olfactory areas, cingulate gyrus, and anterior columns of the fornix.
The cortical branches are named for the regions they supply. They are responsible for the somatosensory and motor cortices of the lower limbs.
- Frontal arteries supply the paracentral lobule, medial frontal and cingulate gyri, and the corpus callosum.
- Parietal branches perfuse the precuneus
- Orbital branches supply the frontal lobe (olfactory cortex, medial orbital gyrus, and gyrus rectus)
Anterior communicating artery
The anterior communicating artery (AComm) is a short, slender vessel that runs horizontally between the anterior cerebral arteries. The vessel crosses the ventral aspect of the median longitudinal fissure and is located anterior to the optic chiasm and posteromedial to the olfactory tracts. This vessel forms the anterior bridge between the left and right halves of the anterior circuit. It also completes the anterior part of the anastomotic ring known as the circle of Willis.
Middle cerebral artery
The middle cerebral artery (MCA) is the largest terminal branch of the internal carotid artery. It travels through the Sylvian (lateral) fissure before coursing in a posterosuperior direction on the island of Reil (insula). It subsequently divides to supply the lateral cortical surfaces along with the insula.
The vessel gives numerous tributaries to both central and cortical regions of the brain. The central branches are relatively small and include the lenticulostriate arteries that pass through the anterior perforated substance to supply the lentiform nucleus and the posterior limb of the internal capsule.
The cortical branches include the frontal, orbital, parietal, and temporal branches:
- The frontal arteries perfuse the inferior frontal, middle, and precentral gyri.
- The lateral orbital parts of the frontal lobe, as well as the frontal gyrus, are supplied by the orbital branches.
- The inferior parietal lobe, the inferior part of the superior parietal lobe, and the postcentral gyrus receive blood from the parietal branch.
- Several temporal arteries then go on to perfuse the lateral aspect of the temporal lobe.
The posterior circulation refers to all the blood vessels that arise from the vertebrobasilar system. These blood vessels supply the hindbrain and the occipital lobe of the cerebrum. The vessels of the posterior circuit include:
- The vertebral arteries
- The basilar artery and its branches
- The posterior cerebral arteries
- And the posterior communicating arteries
- Gives off a posterior inferior cerebellar artery
- Contributes to the formation of the anterior spinal artery via tributaries that converge in the midline anterior to the medulla oblongata
- Contributes meningeal branches near the foramen magnum that supplies the falx cerebelli and the surrounding bone
- May give off the posterior spinal artery; although this vessel usually arises from the posterior inferior cerebellar artery
- Gives off medullary arteries that perfuse the medulla oblongata
The vertebral arteries unite in the midline at the pontomedullary junction to form the basilar artery.
The basilar artery is an important vessel found in the pontine cistern. It is posterior to the clivus and anterior to the pons, as it ascends in the basilar groove. Its branches are responsible for supplying the pons, cerebellum, internal ear, and other nearby structures. There are three major branches of the basilar artery:
- Anterior inferior cerebellar
- Superior cerebellar
- Internal auditory (Labyrinthine)
There are also smaller pontine and posteromedial (paramedian) arteries that arise from the lateral surface and distal bifurcation of the artery, respectively. The basilar artery ends by dividing into two posterior cerebral arteries. These vessels unite with the posterior communicating arteries to complete the circle of Willis, posteriorly.
Posterior cerebral artery
The posterior cerebral arteries (PCA) are terminal branches arising from the bifurcation of the basilar artery. The division takes place behind the dorsum sellae. It is separated from the superior cerebellar artery by the oculomotor nerve (CN III). The artery continues in a course lateral to the midbrain (adjacent to the trochlear nerve, CN IV). It gives off the posterior communicating artery, which completes the circle of Willis. The vessel then continues to course around the cerebral peduncles toward the tentorial aspect of the cerebrum. Here, it supplies the occipital and temporal lobes.
The branches of the posterior cerebral artery bring oxygenated blood to the following areas:
Posterior communicating artery
The posterior communicating artery (PComm) is a long, slender vessel originating from the posterior cerebral artery. It is much longer than its anterior counterpart - the anterior communicating artery. The vessel is medial to the uncus of the temporal lobe and lateral to the mammillary bodies of the hypothalamus. The distal part of the vessel may overlap the proximal part of the optic tract.
The posterior communicating artery completes the circle of Willis posteriorly. Additionally, it gives tributaries to the optic tract, cerebral peduncles, internal capsule, and thalamus.
Circle of Wills
There is a point at which the anterior and posterior arterial circuits of the brain unite or anastomose. This area is known as the circle of Willis. It is a central communication that unites the internal carotid and vertebrobasilar systems.
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The circle of Willis is a polygonal structure that surrounds the optic chiasm and infundibulum, as it rests within the chiasmatic and interpeduncular cisterns. The anastomosis provides an alternative route for blood flow in the event of vascular occlusion. Additionally, it is also believed that it functions as a pressure relief system to accommodate increased blood flow in instances of raised intracranial pressure.
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Finally, we'll present the development of the brain blood vessels for all the neuroanatomy geeks out there who want to know just everything about the this interesting topic!
There are six pairs of primitive branchial arch arteries that appear during the early stages of development via vasculogenesis (formation of new blood vessels from stem cells). During the third week (around day 24), the internal carotid artery is the first of the cerebral vessels to arise. It is the product of the fusion of the 3rd branchial arch arteries along with the distal components of the dorsal aortae (which is also a paired structure). The ventral pharyngeal artery – which is a derivative of the ventral aspect of the 2nd branchial arch – fuses with the proximal region of the internal carotid artery to form the common carotid artery. For completion, the distal region of the ventral pharyngeal artery continues as the external carotid artery.
During the 4th gestational week, the internal carotid artery bifurcates into the anterior and posterior components. The former will differentiate into the middle and anterior cerebral, and the anterior choroidal arteries; while the latter will form the fetal posterior cerebral and posterior choroidal arteries. Note that prior to forming the anterior cerebral and anterior choroidal arteries, the anterior division of the internal carotid artery supplies the olfactory and optic regions of the primitive brain by way of primitive branches.
In the 5th gestational week, a plexiform vascular network originates near the anterior cerebral artery; this is the primitive middle cerebral artery. Although at this point it is not a true artery, it is the primary supplier of blood to the cerebrum. Late in the 6th gestational week, the plexus fuses to form the adult middle cerebral artery. Between the 6th and 7th gestational weeks, the anterior cerebral artery gives off the olfactory artery before continuing medially in the direction of the opposite anterior cerebral artery. By the late 7th gestational week, the anterior communicating artery forms. This process completes the anterior component of the circle of Willis.
The development of the posterior is initiated by the growing brain stem and occipital lobe. Within the 4th gestational week, the superior cerebellar artery perfuses the primitive cerebellum without any assistance. The posterior division of the internal carotid artery will become the posterior communicating artery. It fuses with the fetal posterior cerebral artery to form the upper part of the basilar artery. Two parallel neural channels unite during the 5th gestational week to form the trunk of the basilar artery. Subsequently, they were fed by vessels of the carotid-vertebrobasilar anastomoses (hypoglossal, otic, proatlantal, and the trigeminal arteries). The hypoglossal, otic, and trigeminal arteries break down after the posterior communicating artery initiates contact with the distal basilar artery.
The intersegmental arteries (from the proatlantal artery) and the 6th intersegmental artery fuse in the 5th gestational week, to form the vertebral artery. The sixth intersegmental artery merges with the subclavian artery to form the origin of the adult vertebral artery. The proatlantal artery is the most caudal of the pre-segmental arteries mentioned earlier. It persists longer than the others and is later incorporated into the distal parts of the occipital and vertebral arteries.
A stroke is the result of decreased blood flow to one or more parts of the brain. The underlying pathology involves a hypoxic-ischemic injury that results in tissue death (infarction). The decrease in blood flow can result from either obstruction of the blood vessels (atherosclerotic plaque formation) or rupture of a blood vessel (hemorrhagic stroke). Strokes can be isolated to the anterior or posterior circulation depending on the vessels affected. Patients will experience symptoms based on the part of the brain that is affected.
Anterior circulation infarction
The anterior circulation can be damaged at different levels, resulting in the manifestation of a variety of symptoms. Lesions of the solitary perforating arteries of the basal ganglia can result in pure sensory, pure motor, or sensory-motor strokes, or ataxic hemiparesis. These symptoms are characteristic of lacunar infarcts (LACI). Patients presenting with two of the following symptoms are believed to have suffered an infarct in the middle cerebral artery (M3 or M4) and would be diagnosed with a partial anterior circulation infarct (PACI):
- Homonymous hemianopia
- Ipsilateral motor and sensory defects involving more than two-thirds of the legs, face, and arms
- Cognitive dysfunction characterized by visual and spatial distortion, dysphasia, dyscalculia or decreased level of consciousness
If all three symptoms are present, then it is likely that a total anterior circulation infarct has occurred. In these cases, cortical and central branches of the middle cerebral artery could have been injured.
Posterior circulation infarction
Posterior circulation infarcts are characterized clinically by the bilateral motor and sensory decline, cerebellar dysfunction, ipsilateral cranial nerve palsy, and disordered conjugate gaze. It is more difficult to isolate the specific vascular lesion associated with the posterior circulation because of the wide anatomical variety.