ADD-ONS / ANATOMY
Collateral cerebral circulation
Created 01/03/2022, last revision 18/05/2023
- collateral cerebral circulation refers to the network of vascular channels that stabilize cerebral blood flow if the main vessel is stenosed or occluded
- arterial insufficiency may be caused by thromboembolism, hemodynamic compromise, or a combination of these factors
- reduced anterograde flow changes pressure gradients, and this leads to the opening of the collaterals
- the quality of the collateral circulation significantly influences the severity and extent of cerebral infarction
- well-developed and functional collaterals can temporarily replace the function of the occluded artery, and thus considerably improve the patient’s prognosis
Classification
Functional
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Anatomic
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Circle of Willis
- intracranially, the basal arteries are interconnected to form the arterial circle of Willis
- it is a heptagon consisting of the following:
- left and right ICA
- left and right A1 segments connected by an unpaired AComA
- left and right P1 segments
- left and right PComA (connecting ICA and P1 segment on each side)
- PCOM originates at the anterior perforating substance and runs back through the interpeduncular cistern
- basilar artery tip
- branches of the circle of Willis also supply the optic chiasm and tracts, infundibulum, hypothalamus, and other structures at the base of the brain
- medial lenticulostriate arteries (segment A1)
- perforating branches (from the AComA)
- thalamoperforating and thalamogeniculate arteries (from the basilar tip, proximal PCA, and PComA)
- the circle of Willis allows redirection of the blood flow between both sides of the brain and between the vertebrobasilar and the internal carotid artery systems
- a complete circle is present in < 30% of patients; individual anatomical variants are common
- different diameter of the vessels on the right and left side
- predominance of carotid or vertebral blood flow
- significant asymmetry of the whole circuit
- absence/hypoplasia of one of the arteries
- AComA is absent in 1% of cases
- the proximal segment of the ACA is absent in approximately 10%
- PComA is absent or hypoplastic in 30% of cases
Leptomeningeal anastomoses (LMAs)
- LMAs are pial arteries that connect branches of two major cerebral arteries supplying two distinct cortical territories
- these are most commonly end-to-end anastomoses between the ACA-MCA, ACA-PCA, and MCA-PCA; there are also anastomoses between both ACAs
- occlusion of a cerebral artery leads to hypoperfusion in the corresponding vascular territory, creating a pressure gradient between the vessels of the unaffected area and the territory of the stenotic/occluded artery, resulting in the retrograde filling of the affected area
Factors affecting LMAs functionality
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Assessment of collateral circulation
Neurosonology
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STEAL PHENOMENON IN PATIENT WITH RIGHT SUBCLAVIAN ARTERY STENOSIS
