Blood Supply of the Brain

• Gray's Anatomy for Students, p. 1016
• Neuroanatomy through Clinical Cases 3rd Edition, p. 70

Arterial Supply - Overview

1. Anterior (Carotid) Circulation

Internal Carotid Artery (ICA)

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

Middle Cerebral Artery (MCA)

• The largest branch of the ICA
• Travels through the lateral (Sylvian) fissure
• Supplies the entire lateral surface of the cerebral hemisphere - including the lateral frontal, parietal, and temporal lobes
• Gives off lenticulostriate arteries that supply the basal ganglia and internal capsule (deep perforating branches)
• MCA territory infarction causes contralateral hemiplegia, hemisensory loss, and aphasia (dominant side)

Anterior Cerebral Artery (ACA)

• Courses anteriorly and medially
• The two ACAs are connected by the anterior communicating artery (AComm)
• Supplies the medial surface of the frontal and parietal lobes (including the leg area of the motor cortex)
• ACA stroke characteristically causes contralateral leg weakness
• The recurrent artery of Heubner (a branch of ACA) supplies the head of the caudate nucleus and anterior limb of the internal capsule

2. Posterior (Vertebrobasilar) Circulation

Vertebral Arteries

• Each arises from the first part of the subclavian artery in the lower neck
• Pass superiorly through the foramina transversaria of the upper six cervical vertebrae
• Enter the cranial cavity through the foramen magnum
• Each gives off a small meningeal branch on entry
• Before joining, each gives off:
  • Posterior inferior cerebellar artery (PICA) - supplies the posterior and inferior cerebellum and the lateral medulla
  • Posterior spinal artery - descends on the posterior spinal cord (can also arise from PICA)
  • Contribution to the anterior spinal artery (the two contributions join to form a single midline vessel)
• The two vertebral arteries fuse at the lower border of the pons to form the basilar artery

Basilar Artery

• Travels rostrally along the anterior surface of the pons
• Gives off (caudal to rostral):
  • Anterior inferior cerebellar arteries (AICA) - supply the anterior inferior cerebellum and the pons/inner ear via the labyrinthine artery
  • Pontine arteries - multiple small perforating branches to the pons
  • Superior cerebellar arteries (SCA) - supply the superior cerebellum and dorsal pons/midbrain
• Terminates at the level of the midbrain by bifurcating into the two posterior cerebral arteries (PCA)

Posterior Cerebral Artery (PCA)

• Connected to the ICA via the posterior communicating artery
• Supplies the medial occipital lobe (primary visual cortex), the inferior temporal lobe, the thalamus (via thalamogeniculate and thalamoperforating branches), and the midbrain
• PCA infarction causes contralateral homonymous hemianopia (with macular sparing)

3. Circle of Willis (Cerebral Arterial Circle)

4. Cortical Territory Map

• Goldman-Cecil Medicine, p. 1932; Gray's Anatomy for Students, p. 1019

5. Venous Drainage

Superficial System

• Cortical veins drain into the superior sagittal sinus (runs along the superior border of the falx cerebri)
• The cavernous sinus (on either side of the sella turcica) receives blood from the face/orbit and drains via:
  • Superior petrosal sinus → transverse sinus
  • Inferior petrosal sinus → internal jugular vein
• Important anastomotic veins:
  • Vein of Trolard (superior anastomotic vein) - drains into the superior sagittal sinus
  • Vein of Labbe (inferior anastomotic vein) - drains into the transverse sinus
  • Superficial middle cerebral vein - drains into the cavernous sinus

Deep System

• Deep white matter and basal ganglia drain via internal cerebral veins and basal veins of Rosenthal
• These join to form the great cerebral vein of Galen
• Vein of Galen joins the inferior sagittal sinus to form the straight sinus (sinus rectus)

Final Pathway

Superior sagittal sinus ──┐
Straight sinus            ├──→ Confluence of sinuses (Torcular Herophili)
Occipital sinus           ┘
        ↓
Transverse sinuses → Sigmoid sinuses → Internal jugular veins

6. Clinical Correlates

• Gray's Anatomy for Students, p. 1020-1021; Neuroanatomy through Clinical Cases 3rd Edition, p. 70-71; Color Atlas of Human Anatomy, p. 392