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

(ACA, blue region)

.

  • Contralateral hemiplegia (lower limbs affected more severely)
  • Minimal hemisensory loss (lower limbs affected more severely)
  • Dysarthria
  • Aphasia
  • Abulia (lack of motivation)
  • Limb apraxia
  • Urinary incontinence

Middle cerebral artery

(MCA, red region)

Anterior choroidal artery

  • Triad of:
    • Hemiparesis or hemiplegia (including dysarthria)
    • Hemisensory loss
    • Homonymous hemianopsia (with sparing of the horizontal median visual field)

Posterior circulation

Branch of the basilar artery

Posterior cerebral artery

(PCA, green region)

  • Posteroinferior cortex
    • Occipital lobes
    • Posteromedial aspect of the temporal lobes
    • Thalamus
  • Several branches to the cortical lobes and choroid plexus

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
  • Becomes the right transverse sinus
  • 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
  • Can become the left transverse sinus (variant)
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

(paired)

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

Transverse sinus

(paired)

Inferior petrosal sinus

(paired)

Sigmoid sinus

(paired)

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

Sphenoparietal sinus

(paired)

  • Located anteriorly
  • Drains into the cavernous sinus

Cavernous sinus

(paired)

Basilar venous plexus

(paired)

  • 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!

References:[1][2]

Physiology

  • Cerebral perfusion is modulated by the partial pressure of carbon dioxide (pCO2)
    • Increased pCO2vasodilation → increased cerebral blood flow
    • Decreased pCO2vasoconstriction → decreased cerebral blood flow
  • Therapeutic hyperventilation reduces pCO2 → decreases cerebral blood flow → lower intracranial pressure (e.g., used in acute cerebral edema)
  • Cerebral perfusion pressure (CPP) = mean arterial pressure (MAP) - intracranial pressure (ICP)
    • Decreased blood pressure or increased ICP → decreased cerebral perfusion
    • CPP of 0 indicates no brain perfusion (brain death)
    • Hypoxemia increases CPP if pO2 < 50 mm Hg
    • CPP linearly increases with pCO2 until pCO2 > 90 mm Hg

References:[3]

Clinical significance

last updated 11/22/2018
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