Cerebrovascular system

Arterial supply

The arterial supply of the brain is provided by the internal carotid arteries and the vertebral arteries, which are derivatives of the branches of the aortic arch

Internal carotid arteries (ICA)

Vertebral arteries


Circle of Willis

Most saccular cerebral aneurysms, also known as berry aneurysms, occur in the anterior circulation of the brain, usually at the junction of the anterior cerebral artery and the anterior communicating artery in the circle of Willis. They are the most common cause of nontraumatic subarachnoid hemorrhage.


Cerebral arterial territories

Artery Arterial territory Main Branches Features of stroke

Anterior circulation

Branches of the internal carotid artery

Anterior cerebral artery



Middle cerebral artery


Anterior choroidal artery

Posterior circulation

Branch of the basilar artery

Posterior cerebral artery


  • Posteroinferior cortex
    • Occipital lobes
    • Posteromedial aspect of the temporal lobes
    • Thalamus


Cerebral watershed areas

  • Description: Areas of the brain located at the junction of two nonanastomosing arterial territories, which is most susceptible to ischemia secondary to prolonged hypotension (watershed infarct).
  • Cortical border zones (external)
    • Frontal cortex and paramedian cortex: Between ACA and MCA territories
    • Occipital cortex: Between MCA and PCA territories
  • Subcortical border zones (internal): adjacent to the lateral ventricles
    • Between the lenticulostriate and MCA (i.e., between the branches of the MCA): most common
    • Between the anterior choroidal and MCA or PCA


Venous drainage

The cerebral hemispheres are drained by superficial and deep cerebral veins, which empty into the dural venous sinuses

Superficial cerebral veins

Superficial veins
Drain the white matter

Bridging vein

Draining venous sinus

Superior cerebral veins

Superior anastomotic vein Superiorsagittal sinus
Middle cerebral veins Inferior anastomotic vein Cavernous sinus
Inferior cerebral veins Cavernous and transverse venous sinuses

Deep cerebral veins

Deep cerebral veins drain the cerebral medulla and drain into the straight sinus.

Dural venous sinuses

Venous sinus Characteristics
Superior sagittal sinus
  • Located at the midline
  • Terminates at the confluence of sinuses
  • Drains blood from cortical veins of the cerebral hemispheres
  • Main location of cerebral fluid return via arachnoid granulations
Inferior sagittal sinus
  • Located at the midline
  • Joined by the great cerebral vein of Galen before draining into the straight sinus
  • Drains blood from the medial surface of the cerebral hemispheres
Straight sinus
  • Located at the midline
  • Terminates at the confluence of sinuses
Occipital sinus
  • Located posteriorly
  • Drains into the confluence of sinuses
Confluence of sinuses
  • Formed by the union of the superior sagittal sinus, straight sinus, and occipital sinus
  • Located posteriorly
  • Drains into left and right transverse sinus

Superior petrosal sinus


  • Located laterally
  • Drains into the transverse sinus
  • Drains blood from the inner ear structures via the labyrinthine vein

Transverse sinus


Inferior petrosal sinus


Sigmoid sinus


  • Located laterally
  • Continuation of transverse sinus that arches downward in an S-shaped groove into the internal jugular vein

Sphenoparietal sinus


  • Located anteriorly
  • Drains into the cavernous sinus

Cavernous sinus


Basilar venous plexus


  • Lies over the basilar part of the occipital bone (the clivus)
  • Connected with the cavernous and petrosal sinuses and the internal vertebral (epidural) venous plexus.

Brain veins run in the subarachnoid space, have no valves to allow bidirectional blood flow, and have no muscular layer in the vessel wall!




Clinical significance