Blood Supply of the Brain

1. Anterior Circulation - Internal Carotid Arteries (ICA)

• Each ICA arises as a terminal branch of the common carotid artery in the neck
• Ascends to the skull base and enters via the carotid canal
• On entering the cranial cavity, each ICA gives off four main branches:
  1. Ophthalmic artery - supplies the orbit and eye
  2. Posterior communicating artery (PComm) - connects ICA to the posterior cerebral artery, completing the circle of Willis
  3. Middle cerebral artery (MCA) - the largest branch
  4. Anterior cerebral artery (ACA)

2. Posterior Circulation - Vertebral Arteries

• Each vertebral artery arises from the first part of the subclavian artery in the lower neck
• Ascends through the foramina transversaria of the upper six cervical vertebrae
• Enters the skull through the foramen magnum

1. Small meningeal branch
2. Posterior inferior cerebellar artery (PICA) - supplies posterior/inferior cerebellum and lateral medulla
3. Posterior spinal artery - descends along posterior spinal cord
4. Contribution to the anterior spinal artery (formed by union of branches from both vertebral arteries)

• Formed by the union of both vertebral arteries just inferior to the pons
• Travels rostrally along the anterior surface of the pons
• Branches (caudal to rostral):
  1. Anterior inferior cerebellar arteries (AICA)
  2. Pontine arteries (several small branches to pons)
  3. Superior cerebellar arteries (SCA)
• Terminates by bifurcating into the two posterior cerebral arteries (PCA)

3. Circle of Willis (Cerebral Arterial Circle)

4. Regional Blood Supply of the Cerebral Hemispheres

5. Venous Drainage

Clinical Correlates

• MCA stroke (most common): contralateral hemiparesis/hemisensory loss (face and arm > leg), aphasia (dominant hemisphere), hemineglect (non-dominant)
• ACA stroke: contralateral leg weakness > arm; personality changes (frontal lobe)
• PCA stroke: contralateral homonymous hemianopia, thalamic pain syndrome
• Vertebrobasilar stroke: diplopia, dysphagia, ataxia, ipsilateral facial + contralateral limb sensory loss (lateral medullary/Wallenberg syndrome from PICA)
• Berry aneurysms arise most commonly at branching points of the Circle of Willis - classically at the anterior communicating artery, posterior communicating artery, MCA bifurcation, and basilar tip
• Watershed infarcts occur at the border zones between ACA/MCA and MCA/PCA territories during hypoperfusion states

Brain Hemorrhages

Classification Overview

1. Extradural (Epidural) Hematoma (EDH)

• Blow to the head with brief loss of consciousness
• Lucid interval (hours) - the patient regains consciousness
• Then rapid drowsiness, deterioration, and coma
• Contralateral hemiplegia + ipsilateral dilated pupil (uncal herniation from CN III compression)

2. Subdural Hematoma (SDH)

• Elderly (brain atrophy stretches the bridging veins and creates more movement space)
• Infants (thin-walled bridging veins; shaken baby syndrome)
• Alcoholics (brain atrophy + coagulopathy)
• Patients on anticoagulation

• Acute SDH (< 3 days): Rapid hematoma development, brainstem compression, high mortality. Blood is from bridging veins, cortical arteries, or cerebral lacerations.
• Subacute SDH (3 days to 3 weeks): Symptoms develop gradually; clot contains dark fluid with peripheral membrane formation.
• Chronic SDH (> 3 weeks): Often from trivial trauma; insidious personality change or altered consciousness. The hematoma liquefies; fibroblasts grow in from the dura forming a membrane. Thin-walled vessels in the granulation tissue can rebleed, creating "acute on chronic" SDH.

1. Lysis of clot (~1 week)
2. Fibroblast ingrowth from dura (2 weeks)
3. Early hyalinized connective tissue (1-3 months)
4. Final "subdural membrane" or rebleeding from fragile granulation vessels

3. Subarachnoid Hemorrhage (SAH)

• Anterior communicating artery (AComm) - most common
• Posterior communicating artery (PComm) - causes CN III palsy when expanding
• Middle cerebral artery bifurcation
• Basilar artery tip
• Posterior cerebral artery origin

• Sudden "thunderclap headache" - worst headache of life
• Neck stiffness (meningism from blood in CSF)
• Photophobia, nausea/vomiting
• Loss of consciousness at onset (ICP spikes to near arterial pressure)
• New-onset anisocoria = posterior communicating artery aneurysm until proven otherwise

• Rebleeding (highest risk 24-48 hrs) - 50% mortality if re-rupture causes coma
• Vasospasm (days 4-14) - causes delayed cerebral ischemia; treated with nimodipine
• Hydrocephalus - blood in CSF obstructs arachnoid granulations
• Hyponatremia (cerebral salt wasting)

4. Intracerebral Hemorrhage (ICH) / Intraparenchymal Hemorrhage

• Putamen/basal ganglia (most common - 35-50%) - lenticulostriate arteries
• Thalamus - thalamic perforators
• Pons - basilar perforating arteries (pinpoint pupils, quadriplegia)
• Cerebellum - superior cerebellar artery branches (headache, ataxia, vomiting)
• Lobar - often CAA in elderly

• Reverse coagulopathy (e.g., vitamin K + FFP for warfarin)
• Lower SBP to 140 mmHg if SBP 150-220 mmHg
• Control blood sugar (avoid hypo- and hyperglycemia)
• Treat seizures with antiepileptics
• ICP management: HOB elevation 30°, hyperosmolar therapy, intubation/sedation
• Cerebellar hematoma > 3 cm or causing hydrocephalus: surgical evacuation

Quick Comparison at a Glance

Brain Hemorrhages - Summary

1. Extradural (Epidural) Hematoma

• Vessel: Middle meningeal artery (arterial)
• Shape on CT: Biconvex/lenticular, does NOT cross suture lines
• Classic sign: Lucid interval after head trauma, then rapid deterioration
• Cause: Pterion fracture

2. Subdural Hematoma

• Vessel: Bridging veins (venous)
• Shape on CT: Crescent-shaped, DOES cross suture lines
• Classic sign: Trivial trauma in elderly; insidious onset
• Types: Acute (<3 days), Subacute (3 days-3 weeks), Chronic (>3 weeks)

3. Subarachnoid Hemorrhage

• Vessel: Berry aneurysm at Circle of Willis branches
• CT: Blood in basal cisterns
• Classic sign: "Worst headache of life" (thunderclap)
• Complications: Vasospasm, rebleeding, hydrocephalus

4. Intracerebral (Intraparenchymal) Hemorrhage

• Vessel: Perforating arteries (hypertensive Charcot-Bouchard microaneurysms)
• CT: Round hyperdense lesion with surrounding edema
• Common sites: Putamen, thalamus, pons, cerebellum
• Main cause: Hypertension; also cerebral amyloid angiopathy (CAA) in elderly

Subarachnoid Hemorrhage

Summary - CT Appearance at a Glance