Major vascular systems
The brain receives blood via two main vascular territories:
- Carotid (anterior) system. Formed by the right and left internal carotid arteries (a. carotis interna). They branch off from the common carotid arteries at the level of the thyroid cartilage, pass through the neck without branching, and enter the cranial cavity. This system supplies the frontal, parietal, temporal lobes, and subcortical structures.
- Vertebrobasilar (posterior) system. Formed by the vertebral arteries (a. vertebralis), branching from the subclavian arteries. After passing through the cervical vertebrae and foramen magnum, they merge at the base of the brain into a single basilar artery (a. basilaris). This territory supplies the brainstem, cerebellum, and occipital lobes.
Intracranial vascular network and anastomoses
Upon entering the cranial cavity, the arteries form a powerful compensatory system — the cerebral arterial circle (circle of Willis). It connects the carotid and vertebrobasilar territories, as well as the right and left halves of the cerebral circulatory system.
Main cerebral arteries:
- Anterior cerebral artery (a. cerebri anterior): supplies the medial regions of the frontal and parietal lobes.
- Middle cerebral artery (a. cerebri media): supplies the lateral surface of the hemispheres and deep structures (basal ganglia, internal capsule).
- Posterior cerebral artery (a. cerebri posterior): supplies the occipital lobe and mediobasal regions of the temporal lobe.
The anastomotic system is extremely important: it compensates for blood flow deficiency when one of the major arteries is occluded. However, at the level of intracerebral branches, blood flow cessation usually leads to focal ischemia.
Acute cerebrovascular accidents (ACVA)
Decreased blood flow can lead to ACVA. Based on symptom duration, they are classified into:
- Transient ischemic attacks (TIAs) — temporary disturbance, symptoms resolve completely.
- Strokes — persistent neurological deficit.
Strokes are divided into:
- Ischemic (cerebral infarction) (70–85% of cases): caused by atherosclerosis, thrombosis, or embolism (often cardiogenic). Leads to ischemic tissue necrosis.
- Hemorrhagic: bleeding into the brain tissue (intracerebral) or under the meninges (subarachnoid hemorrhage).
Risk factors and pathogenesis of ischemia
Among modifiable risk factors, arterial hypertension, atherosclerosis, diabetes mellitus, atrial fibrillation, smoking, and obesity lead the list.
Intracranial arteries are most commonly affected by atherosclerosis at bifurcation sites and curves. A stenosis is considered hemodynamically significant when the arterial lumen is narrowed by 70–75% or more. Growth and rupture of an atherosclerotic plaque trigger thrombosis (atherothrombosis) or artery-to-artery embolism, occluding downstream vessels.
Briefly: answers to topical questions
Which arteries form the cerebral arterial circle (circle of Willis)?
The cerebral arterial circle (circle of Willis) is formed by the following arteries and their segments (from anterior to posterior):
- Anterior communicating artery (a. communicans anterior);
- Proximal (A1) segment of the anterior cerebral artery (a. cerebri anterior);
- Distal segment of the internal carotid artery (a. carotis interna);
- Posterior communicating artery (a. communicans posterior);
- Proximal (P1) segment of the posterior cerebral artery (a. cerebri posterior);
- Bifurcation of the basilar artery (a. basilaris).
This vascular ring at the base of the brain provides a closed loop of collateral circulation.
What branches does the internal carotid artery give off after entering the cranial cavity?
After entering the cranial cavity, the internal carotid artery gives off the following main branches supplying the brain:
- Middle cerebral artery (a. cerebri media) — gives off striate branches to the basal ganglia and internal capsule;
- Anterior cerebral artery (a. cerebri anterior);
- Anterior choroidal artery (a. choroidea anterior) — participates in supplying deep structures of the temporal lobe;
- Posterior communicating artery (a. communicans posterior) — an anastomosis between the carotid and vertebrobasilar systems;
- Ophthalmic artery (a. ophthalmica).
Which arteries participate in the blood supply to the internal capsule?
The internal capsule receives its blood supply from branches of the carotid system:
- Middle cerebral artery (a. cerebri media) — gives off deep striate (lenticulostriate) branches (rami striati), which supply the internal capsule and subcortical nuclei;
- Anterior choroidal artery (a. choroidea anterior) — participates in supplying deep brain structures, specifically the genu of the internal capsule.
Meanwhile, the thalamogeniculate artery does not participate in the blood supply to the internal capsule, as it supplies the thalamus.
What branches arise from the basilar artery?
The following branches arise from the basilar artery (a. basilaris):
- Posterior cerebral arteries (a. cerebri posterior) — terminal branches formed at the bifurcation of the basilar artery;
- Superior cerebellar artery (a. cerebelli superior);
- Anterior inferior cerebellar artery (a. cerebelli inferior anterior);
- Labyrinthine artery (a. labyrinthi) — may branch from the basilar or anterior inferior cerebellar artery;
- Penetrating branches to the brainstem — include paramedian branches (rami paramediani), as well as short and long circumferential branches (rami circumferentes breves).
Through which anatomical structures do the vertebral arteries pass on their way to the brain?
On its way to the brain, the vertebral artery (a. vertebralis) passes through the following anatomical structures:
- Enters the transverse foramen of the 6th cervical vertebra;
- Ascends upward within the bony canal formed by the transverse foramina;
- Enters the cranial cavity (intradural part), where at the level of the caudal border of the pons it merges with the contralateral artery.
A detailed description of the passage through other structures (e.g., the foramen magnum) is not provided in the available sources.
What else to study on this topic
- Topography and branches of the external carotid artery
- Anatomic variants of the origin of the major vessels from the aortic arch
- Pathogenetic subtypes of ischemic stroke (atherothrombotic, cardioembolic, lacunar)
- Venous drainage system of the brain
- Blood supply to the spinal cord
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