23 Blood Supply of the Central Nervous System

Blood Supply of CNS Part 1 (Cerebrovascular Circulation)

Presented by Thomas J Perrault Jr. PhD at Atrium Health, Wake Forest University School of Medicine

Objectives

  • Describe types of stroke, hematoma and hemorrhage, causes, and diagnosis.

  • Identify blood supply of the spinal cord.

  • List the major branches of the vertebral and internal carotid arteries and indicate the regions/structures that each artery supplies.

  • Identify and describe the anterior (internal carotid system) and posterior (vertebrobasilar system) arterial circulation of the brain and their anastomoses at the circle of Willis.

  • Identify the course, distribution, and functional area supplied for each of the three cerebral arteries. Identify the blood supply to the cerebellum, medulla, pons, and midbrain.

  • After identifying blood supply of the CNS, account for the neural deficits seen with major types of CVA in these areas.

Part 1: Cerebrovascular Accidents (CVA)

  • CVA is defined as an interruption to blood supply to the brain.

  • Anastomosis: Refers to connections between blood vessels that create redundancies or collaterals.

Two Kinds of Stroke

  1. Ischemic Stroke:

    • Occurs when a vessel is blocked by a clot.

    • Clots can either develop in place (thrombosis) or move from another location to lodge in an artery (embolism).

    • This blockage causes a loss of oxygen and glucose to the affected brain tissue, leading to infarction.

  2. Hemorrhagic Stroke:

    • Results from the rupture of a blood vessel.

    • Often associated with a weak spot in an artery, such as an aneurysm (Auer RN, 2002).

Ischemic Stroke Details

Thrombosis

  • Blockage leads to decreased blood flow.

Embolism

  • Embolus travels down the blood vessel, potentially lodging in a smaller vessel and blocking blood flow.

  • Atherosclerosis Stages:

    • Plaque formation and growth in arteries, leading to narrowed artery blocked by a blood clot.

Causes of Stroke

  • Hemorrhagic Stroke (17%):

    • Intracerebral hemorrhage (10%).

    • Subarachnoid hemorrhage (7%).

  • Ischemic Stroke (83%):

    • Large-vessel thrombosis (31%).

    • Small-vessel thrombosis (20%).

    • Embolic (32%).

Breakdown of Types:

  • Intracerebral hemorrhage

  • Subarachnoid hemorrhage

  • Ischemic large-vessel thrombosis

  • Ischemic small-vessel thrombosis

  • Embolic

Other Types of Strokes

  1. Lacunar Strokes:

    • Ischemic strokes targeting deep branches of anterior or posterior circulation.

    • Often linked to hypertension and diabetes mellitus.

    • Clinical presentations include:

      • Limb hemiparalysis or paresis

      • Ataxic gait

      • Somatosensory loss (Lack of cortical signs like Broca's, Wernicke's, or visual deficits).

    • MRI imaging can show multiple lacunar infarcts in bilateral periventricular white matter.

  2. Watershed Infarction:

    • Ischemia occurring in the border zones between two adjacent arterial territories or between deep and superficial territories of the middle cerebral arteries (two non-anastomosing arterial systems).

Common Hemorrhages

  1. Epidural Hematoma:

    • Characterized as rapidly expanding with arterial blood.

    • Often caused by a torn middle meningeal artery following a skull fracture.

    • Results in dura being pushed away by hematoma.

  2. Subdural Hematoma:

    • Slowly expanding with venous blood.

    • Injury is often from laceration of superior cerebral (bridging) veins during sudden head deceleration; does not cross the dural attachment at the falx cerebri.

    • More common than epidural hematomas.

Comparative Analysis:

  • Epidural Hematoma: Rapid expansion; arterial source; may have lucid interval post-injury.

  • Subdural Hematoma: Slower expansion; venous source; common in patients with head trauma or chronic conditions.

Extreme Details on Dural Hematomas

  • Subdural Hematoma (SDH):

    • Usually results from a laceration of the superior cerebral (bridging) veins; often triggered by head trauma.

    • SDH extends over the hemispheres into the interhemispheric fissure and does not cross the dural attachment of the falx cerebri.

    • More prevalent than epidural hematomas.

  • Epidural Hematoma:

    • Primarily results from rupture of the middle meningeal artery, supplying most of the dura.

    • Typically, a classic “lucid interval” is observed in about 50% of cases; does not spread past cranial sutures.

Brain Herniation

  1. Mass Effect:

    • Refers to the displacement of intracranial structures due to tumors, hemorrhage, edema, or other masses.

  2. Herniation:

    • Occurs when the mass effect becomes severe enough to push intracranial structures from one compartment to another.

    • Types include:

      • Transtentorial Herniation

      • Central Herniation

      • Subfalcine Herniation.

Clinical Presentation:

  • Pressure on abducens nerve may lead to lateral rectus palsy.

  • Severe compression can cause coma and CN III palsy.

  • Herniation of the cingulate gyrus under the falx cerebri may occlude the anterior cerebral artery (ACA).

Stroke Review

  • Recall strategies for understanding strokes:

    • Two primary types of stroke: Ischemic and Hemorrhagic.

    • Ischemia: due to embolism or thrombosis.

    • Hemorrhage: primarily from aneurysm.

    • Types include Lacunar and Watershed Infarcts, along with distinctions of Dural Hematomas.

    • Discussion around Herniations and Mass Effects.

Part 2: Blood Supply to the Spinal Cord

Overview of the Spinal Cord Anatomy

  • The spinal cord receives blood supply primarily from:

    • Anterior spinal arteries

    • Posterior spinal arteries

Ratio of Blood Supply

  • Approximately 1/3 (Posterior Spinal) vs 2/3 (Anterior Spinal) blood supply.

Blood Supply of the Spinal Cord

  • Anterior and posterior spinal arteries:

    • Includes radicular arteries (superficial) and spinal medullary arteries (deep).

    • Notable structure: Artery of Adamkiewicz that supplies lower segments of the spinal cord.

Spinal Arteries Overview

  • Three Main Spinal Arteries:

    1. Anterior Spinal Artery (2/3):

    • Originates from vertebral arteries at the foramen magnum.

    1. Posterior Spinal Arteries (1/3):

    • Typically originate from PICA in most individuals, vertebral artery in a minority.

Detailed Analysis of Spinal Blood Supply

  • Spinal Blood Supply Review:

    • Consists of:

    • Anterior Spinal Artery (1)

    • Posterior Spinal Arteries (2)

    • Radicular Arteries (Superficial)

    • Spinal Medullary Arteries (Deep)

    • Important Anastomosis: The Artery of Adamkiewicz is the primary supply to the anterior spinal artery below the thoracic region of the spinal cord.

Part 3: Cerebral Blood Supply

Overview of CNS Circulation

  • Blood supply to the brain is primarily through:

    • Internal carotid system (anterior circulation)

    • Vertebrobasilar system (posterior circulation)

Major Sources of Blood Supply to the Brain

  • Internal Carotid System:

    • Major branches supply the lateral and medial surfaces of the cerebral cortex and perforating arteries to deep cerebral nuclei.

  • Vertebrobasilar System:

    • Supplies areas such as the brainstem, cerebellum, occipital cortex, and regions of the spinal cord.

    • The Circle of Willis facilitates communication between anterior and posterior circulation.

Pathways of Blood to the Brain

  • Pathway of Internal Carotid Artery:

    • From Aorta → Aortic Arch → Common Carotid → Internal Carotid (Left/Right).

  • Pathway of Vertebral Artery:

    • From Aorta → Aortic Arch → Subclavian Artery → Vertebral Artery (Left/Right).

Circle of Willis

Vessels Involved

  • Comprised of:

    • Internal carotid arteries

    • Anterior cerebral arteries

    • Anterior communicating artery (Acom)

    • Posterior communicating arteries (Pcom)

    • Posterior cerebral artery

    • Basilar artery

Anatomic Functionality

  • Anastomosis: Connections ensure collateral circulation.

Direction of Blood Flow in Circle of Willis

  • Detailed observations of flow direction showcase relationships among the internal carotid, anterior cerebral and posterior cerebral arteries across both hemispheres.

Internal Carotid Artery Overview

Segmentation

  • Divided into C1-C4 segments:

    • C1: Cervical

    • C2: Petrous

    • C3: Cavernous

    • C4: Supraclinoid or cerebral (H. Gibo et al., 1981)

Major Branches of the Internal Carotid Artery

  • Terminal branches of C4:

    • Anterior Cerebral Artery (ACA)

    • Middle Cerebral Artery (MCA)

  • Intermediate branches of C4:

    • Ophthalmic artery

    • Posterior communicating artery

    • Anterior choroidal artery.

Anterior Cerebral Artery (ACA) Specifics

Functional Areas & Supply

  • Branches:

    • Supplies areas such as:

    • Paracentral lobule (hip, lower limb, genital area representation)

    • Frontal lobe cognitive areas

    • Cingulate gyrus and corpus callosum.

  • Significant perforating branches target deep cerebral nuclei and internal capsule.

Clinical Presentation of ACA Stroke

  • Symptoms of ischemic stroke involving ACA typically include:

    • Weakness and sensory loss of the contralateral leg

    • Urinary incontinence

    • Altered mental status or judgment

    • Behavioral and emotional disorders.

Anterior Communicating Artery

  • Anatomy:

    • Connects old and new ACA circulations, often comprises more than one artery per individual.

Comparison of A1 and A2 Occlusions in ACA

  • Distinction in clinical effects arising from A1 occlusion compared to A2 occlusion demonstrates the importance in understanding cerebrovascular dynamics.

Middle Cerebral Artery (MCA) Overview

Functional Areas & Supply

  • Segments of MCA:

    • M1: Proximal

    • M2: Sylvian

    • M3: Distal

  • Supplies:

    • Most of the lateral surface of the cerebral hemispheres, including important functional areas:

    • Primary and secondary motor cortex

    • Sensory cortices including areas like Wernicke's and Broca's.

Signs of Ischemic Stroke Involving MCA

  • Clinical manifestations include:

    • Contralateral weakness of upper limb and face

    • Dysphagia

    • Expressive (non-fluent) aphasia due to damage in Broca's area

    • Receptive (fluent) aphasia related to Wernicke's area

    • Possible partial visual deficits due to white matter involvement.

Lenticulostriate Arteries Overview

  • Medial Lenticulostriate Arteries:

    • Arising from A1 segment of ACA, supplying parts of the globus pallidus and anterior internal capsule.

  • Lateral Lenticulostriate Arteries:

    • Arising from **proximal *MCA*, they supply the lateral segment of the *putamen* and the posterior internal capsule.

    • Notably prone to rupture in patients with uncontrolled hypertension.

Posterior Communicating Artery

Clinical Relevance

  • Serves as a branch of ICA and supplies blood to critical areas such as:

    • Thalamus

    • Optic chiasm

    • Regions of the hypothalamus.

Potential Complications

  • Aneurysms are common in this artery; occurrence leads to significant conditions such as third nerve palsy.

Key Points for Blood Supply

  • Overall Supply: Brain is vascularized by two internal carotid and two vertebral arteries.

  • Vertebral Arteries: Unite to form a basilar artery, which after supplying several critical areas, bifurcates into two posterior cerebral arteries.

  • Internal carotids branch into anterior and middle cerebral arteries, notably forming the Circle of Willis, providing redundancy to blood supply.

Homework Assignments

  • Practice Drawing Circle of Willis (COWS) from memory.

  • Prepare to discuss posterior blood flow in the next class session!

The Circle of Willis

  • Functions as a crucial anastomosis between anterior and posterior blood supplies to the brain.

Anatomical Components Include:

  • Internal Carotid arteries, Middle Cerebral Arteries, Anterior Cerebral Arteries, Posterior Communicating arteries, Basilar artery, and Posterior Cerebral Arteries.

Review Materials

  • Additional slides provided for clarity on concepts; these are intended for supplemental learning.

  • Contact: Thomas.Perrault@wfusm.edu for inquiries.

  • Formative practice problems are accessible through Canvas.