Cerebral Vasculature Notes

Cerebral Vasculature

Introduction

  • Emilia Clarke's experience with a subarachnoid haemorrhage (haemorrhagic stroke) highlights the real-world impact of cerebrovascular events.

Learning Objectives

  • Draw, annotate, and explain the blood supply to the cerebrum, brainstem, and cerebellum, referencing the Circle of Willis.
  • Differentiate between cerebral vessels based on cortical landmarks.
  • Summarize the main functional cortical areas of the cerebrum supplied by the anterior, middle, and posterior cerebral arteries.
  • Describe the consequences of ischemic or haemorrhagic strokes in different functional areas.

Causes of Stroke

  • Ischemic (blockage): 85%
  • Hemorrhagic (burst): 15%
  • Causes:
    • Aneurysm
    • Hypertension
    • Cytotoxic edema: failure of ion pumps due to inadequate ATP supply.
    • Increase of brain water by 1% = decrease of 2.5 HU (Hounsfield Units).
  • First 6 hours are critical.

Hemispheric Specialization

Right Cerebrum

  • Specialized for non-linguistic functions:
    • Complex pattern recognition.
    • Vision, audition, tactile senses.
    • Sense of space, spatial shapes, direction in space.
    • Intuition.
  • Based on work of Roger Sperry and split-brain experiments.

Left Cerebrum

  • Dominant for control of:
    • Speech, language.
    • Complex voluntary movement.
    • Reading, writing, arithmetic calculations.
  • Observations of Broca and Wernicke in 1860s regarding speech:
    • 90% of right-handed aphasics have a lesion in the left hemisphere.
    • 60% of left-handed aphasics have a lesion in the left hemisphere.

Cardiovascular System and Aorta

Collateral Branches of the Aorta:

  • Brachiocephalic Trunk (BCT)
  • Left Common Carotid artery (LCC)
  • Left Subclavian artery (LSC)
  • Right Common Carotid artery (RCC) (bifurcation from the brachiocephalic trunk)
  • Right Subclavian artery
  • Left Internal Carotid
  • Left External Carotid
  • Left Vertebral artery
  • If an artery name contains “common”, it bifurcates (splits) into “internal” and “external” branches

Common Carotid Artery

  • Left CCA branches directly off the arch of the aorta.
  • Right CCA is a bifurcation from the brachiocephalic trunk.
  • Presence of the carotid body at the point of bifurcation.

Internal Carotid Artery (ICA)

Four Major Parts:

  1. Cervical part (through cervical vertebrae).
  2. Petrous part (through temporal bone).
  3. Cavernous part (in cavernous sinus).
  4. Cerebral part.

Cerebral Part Termination:

  • Anterior cerebral artery (ACA).
  • Middle cerebral artery (MCA).
  • Posterior communicating artery (PCOM).

Collateral Branch:

  • Ophthalmic artery.

Blood Supply:

  • Anterior part of the brain (via cerebral branches) including the frontal, parietal, temporal, and insula lobes.
  • The eye and its appendages.
  • Branches to the forehead, scalp, and nose.

Circle of Willis

Location:

  • Anastomoses around the optic chiasm and infundibulum of the pituitary stalk in the suprasellar cistern.

Function:

  • Communicating pathway that allows equalization of blood flow between the two sides of the brain.
  • Allows anastomotic circulation, should a part of the circulation be occluded.

Structures: Anterior Circulation

  • Left and right internal carotid arteries (ICA).
  • Left and right anterior cerebral arteries (ACA).
  • Single anterior communicating artery (ACOM).
  • Left and right posterior communicating arteries (PCOM).

Structures: Posterior Circulation (Vital for life)

  • Left and right posterior cerebral arteries (PCA).
  • Single basilar artery (tip).

Blood Supply Territories:

  • Anterior circulation.
  • Posterior circulation.

Circle of Willis - Pathology

  • The anastomosis cannot compensate for a sudden occlusion of the main arteries, leading to ischemia.
  • Most common site: intersection of two arteries = weakest point of the arterial walls à dilation.
    • Compresses adjacent structures.
    • Risk of rupture = Subarachnoid Hemorrhage (SAH).

ACA versus MCA Infarcts

  • ACA lesions are rare due to collateral circulation:
    • Left leg weakness, loss of sensation.
    • Grasp reflex + behavioral issues.
  • MCA infarcts are the most common.
    • General regions based on superficial (lateral surface) or deep (internal capsule and basal ganglia):
      • Face and arm motor weakness.
      • Sensory loss.
  • Anterior circulation accounts for 70% of strokes.
  • Most common sites of occlusion of the internal carotid artery are the proximal 2cm of the origin of the artery and intracranially, the carotid siphon.

Posterior Circulation Stroke (25%)

Common Symptoms:

  • Vertigo.
  • Ataxia (imbalance).
  • Unilateral limb weakness.
  • Diplopia (double vision).
  • Headache, nausea, and vomiting.
  • Hyperextension of the neck à cervical artery dissection (15% of strokes in 15-49 year olds).
  • Vertebral arteries supply the posterior circulation.
  • Dysphagia due to pharyngeal weakness, nausea, vomiting and Horner’s Syndrome.

Posterior Circulation Territories

  • Proximal PC Territory: limb weakness and facial palsy.
  • Middle PC Territory: .
  • Distal PC Territory: Decreased appendicular sensory loss, lethargy and visual field defects.

Vasculature Territories

ACA

  • Medial, parietal lobe.
  • Superior cerebrum.
  • Caudate Nucleus, and limb of internal capsule, globus pallidus.

MCA

  • Lateral aspects of cerebrum.
  • Insula, all basal ganglia.
  • Anterior/lateral temporal lobe.
  • Internal capsule

PCA

  • anterior aspects of frontal lobe
  • Medial, parietal lobe.
  • Superior cerebrum.
  • caudate Nucleus, aut limb of internal capsule, globaspallidus

Cortical Homunculus

  • Motor map in precentral gyrus.

  • Sensory map in postcentral gyrus.

  • Illustrates the representation of body parts in the motor and sensory cortices.

  • ACA impact is anterior.

  • MCA impact is superficial.

  • PCA impact is deep.

Functional Cortical Areas of the Brain

  • Frontal lobe: motor functions, executive functions (planning, problem-solving, attention).
  • Parietal lobe: somatosensory processing, spatial awareness.
  • Temporal lobe: auditory processing, memory.
  • Occipital lobe: visual processing.
  • Broca's area: motor aspects of speech.
  • Wernicke's area: comprehension of language.

Applied Anatomy of Stroke

  • Kahoot! used for application

Middle Cerebral Artery

  • MOST common site of stroke.
  • Broca's Aphasia:
    • Difficulty forming complete sentences; leaving out words.
    • Saying something that doesn’t resemble a sentence.
    • Trouble understanding sentences.
  • Wernicke's Aphasia:
    • Say many words that don’t make sense.
    • Use the wrong words.
    • String together a series of meaningless words that sound like a sentence but don’t make sense.