Blood Supply

Blood Supply of the Brain Stroke

  • Stroke: Occurs when an artery leading to or within the brain is either blocked or ruptured, leading to diminished oxygen and nutrients to the brain.

  • Statistics:

    • 5th leading cause of death in the US.

    • 1st leading cause of disability in the US.

  • Types of Stroke:

    • Ischemic/occlusive (most common, 85%): Blockage in an artery.

      • Embolic: Blood clot travels from elsewhere in the body.

      • Thrombotic: Blood clot forms in the arteries.

    • Hemorrhagic: Rupture of an artery (e.g., weakened vessel, aneurysm, arteriovenous malformation).

  • Related Terminology:

    • Infarct: Area of dead cells/necrotic tissue.

    • Ischemia: Restriction in blood supply.

    • Anoxia: Without oxygen.

    • Hypoxia: Decreased oxygen.

    • Lesion: Injury.

    • Carotid Endarterectomy (CEA): Surgical procedure to remove blockage from the internal carotid artery (ICA) to reduce stroke risk.

Introduction to Blood Supply to the Brain

  • The CNS is highly metabolic and requires a constant blood supply for oxygen and nutrients.

  • Consequences of Blood Flow Interruption:

    • Loss of consciousness within 10 seconds of blood supply cessation.

    • Cessation of electrical activity after 20 seconds.

    • Irreversible brain damage typically begins after a few minutes.

Arterial Supply of the Brain

  • The arterial supply comes from two main systems:

    1. Anterior Circulation: From the internal carotid arteries (80% of the brain), supplies most of the cerebral hemispheres except parts of the occipital and inferior temporal lobes.

    2. Posterior Circulation: From the vertebral arteries and basilar artery (20% of the brain), supplies the brain stem, cerebellum, parts of the spinal cord, and some of the cerebral hemispheres.

  • Note: Most arteries are paired (i.e., left and right), unless otherwise specified.

Internal Carotid Artery (ICA) and Its Branches

  • ICA: Arises from the common carotid artery.

  • Branches of the ICA:

    • Ophthalmic artery: Travels with the optic nerve to supply the eye; blockage can cause blindness.

    • Anterior choroidal artery: Supplies optic tract, internal capsule, thalamus, amygdala, hippocampus, choroid plexus in lateral ventricles; a common site of stroke.

    • Posterior communicating artery: Connects ICA to posterior cerebral artery (PCA).

  • Bifurcations of ICA:

    • Anterior cerebral artery (ACA):

      • Supplies medial portions of the frontal and parietal lobes.

      • Symptoms of Occlusion or Hemorrhaging:

        • Contralateral hemiplegia (worse in legs) affecting the primary motor cortex.

        • Contralateral hemiparesthesia (worse in leg) from the primary somatosensory cortex.

        • Cognitive and personality changes from the medial prefrontal cortex and limbic system.

        • Difficulty with movement planning from basal nuclei.

    • Middle cerebral artery (MCA):

      • Supplies most of the lateral surfaces of the brain.

      • Symptoms of Occlusion or Hemorrhaging:

        • Left hemisphere damage can lead to Broca’s or Wernicke’s area issues (aphasia).

        • Right hemisphere damage can lead to perceptual deficits (e.g., left neglect).

        • Contralateral hemiplegia affecting the primary motor cortex (worse in arm, trunk, face).

Vertebral-Basilar System

  • Each Vertebral Artery: Has three branches.

    • Vertebral artery (VA): Supplies portions of the brainstem and cerebellum.

    • Branches:

      • Anterior spinal artery: Supplies anterior 2/3 of the spinal cord.

      • Posterior spinal artery: Supplies posterior 1/3 of the spinal cord.

      • Posterior inferior cerebellar artery (PICA): Supplies posterior portions of the inferior cerebellum and lateral medulla; damage can cause Wallenberg's syndrome (variety of symptoms including dysphagia, vertigo).

  • Basilar Artery (BA): Formed from the joining of the two vertebral arteries.

    • Branches of BA:

      • Anterior inferior cerebellar artery (AICA).

      • Pontine arteries.

      • Superior cerebellar artery.

      • Posterior cerebral artery (PCA): Supplies medial and inferior surfaces of the temporal and occipital lobes.

        • Symptoms of Occlusion:

          • Visual and visual-perceptual impairments from the occipital lobe.

Cerebral Arterial Circle (Circle of Willis)

  • Provides an anastomosis that surrounds the optic chiasm and pituitary gland.

  • Connects internal carotid and vertebral-basilar systems to ensure blood flow to the brain under compromised conditions.

  • Significant anatomical variation exists; less than half of the population has a textbook Circle of Willis.

Venous Drainage of the Brain

  • The brain is drained by:

    • A network of deep and superficial veins.

    • Dural Sinuses: Formed by the separation of dural layers.

    • Right and left Internal Jugular Veins (IJVs).