Read the inextricable links between the collateral circulation and ischemic stroke in one article!

Ischemic stroke accounts for 60%-80% of all strokes, and its prevention and treatment research has become a global hot spot
.
The clinical presentation and response to treatment in patients with ischaemic stroke vary widely, and one of the key factors is the presence of
collateral circulation.
Currently, the mainstay of treatment for ischaemic stroke is recanalization
.
After cerebral ischemia, the rapid establishment of collateral circulation is essential
for the protection of ischemic tissue and the restoration of neurological function.

Cerebral collateral circulation means that when the supplying artery is severely narrowed or occluded, blood flow can reach the ischemic area through other blood vessels (collateral or newly formed vascular anastomosis), so that the ischemic tissue can be perfused to varying
degrees.

According to the open level, the lateral branch circulation of the brain can be divided into 3 levels:

The primary collateral circulation compensation, or Willis ring, is the most important collateral circulation pathway in the skull, which is a bridge between the main arteries in the skull, so that the left and right cerebral hemispheres and the blood flow of the anterior and posterior circulation communicate with each other
.
Secondary collateral circulation compensation mainly includes the ophthalmic artery and the first-degree leptomeningeal collateral
.
When the compensation of the Willis ring does not meet the blood supply demand, the secondary compensatory pathway comes into play
.
Tertiary collateral circulation compensation, or neovascularization, refers to the supply of blood to neovascularization through angiogenesis and arterigenesis
.
When secondary compensation still cannot meet the blood supply demand, neovascularization becomes the final collateral compensation pathway, and it is also the key and hot spot
in the current research on collateral compensation to guide clinical treatment.

Relationship between collateral circulation and ischemic stroke

Collateral circulation is one of the compensatory mechanisms of cerebral circulation, which can increase the ischemic semi-dark zone blood supply after stroke, and plays an important role
in the prognosis assessment of acute ischemic stroke.
Studies have shown that in the site where ischemia may occur, the collateral circulation of the brain plays an important role
in maintaining the physiological function of brain tissue and tissue perfusion in the pathological state.

In patients with severe internal carotid artery stenosis, good collateral circulation can effectively reduce the risk of
hemispheric stroke and transient ischemic attack if the Willis ring is intact.
When the primary collateral circulation is dysplasia or is still unable to maintain normal perfusion, the secondary collateral circulation provides an additional blood supply, at which time the ability of cerebrovascular autoregulation is impaired, and cerebral perfusion is significantly reduced
.
If the distal blood supply is still not satisfied, the body will use the tertiary collateral, that is, neovascularization
.

In the development of ischemic stroke, the speed of vascular occlusion and the state of cerebral artery development determine the speed and degree of
collateral circulation establishment.
If ischemic stroke has a sudden onset and cannot effectively establish collateral circulation in time, brain function damage is serious; Conversely, the slower the occurrence of arterial occlusion, the more effective collateral circulation can be gradually established, the less damage to brain tissue, and the better
the prognosis.
The establishment of collateral circulation and its compensatory capacity are influenced
by a variety of factors.

Studies have shown that the compensatory capacity of the collateral circulation depends not only on the lumen diameter of the collateral circulation, but also on the pressure gradient at the end of the ACoA/PCoA blood
vessel.
In addition, the establishment of collateral circulation is positively correlated
with the degree of vascular stenosis.
After cerebral artery occlusion, the degree of collateral circulation establishment is related to the integrity of the Willis ring and the number of effective collateral circulation, and the establishment of multiple collateral cycles can significantly reduce the infarct volume
.

The formation process of the lateral branch circulation of the brain and the role of regulators

Animal studies have shown that arterial stenosis or occlusion can lead to hemodynamic changes, and changes in vascular shear and hypoxia are the main triggers of
vascular regeneration.

In the pathological state, there are two main processes for the formation of collateral circulation - angiogenesis and arterigenesis
.
The former refers to the disintegration of the basement membrane of existing vascular endothelial cells caused by ischemia and hypoxia, the activation, migration, proliferation, adhesion and reconnection of endothelial cells, the formation of a lumen like structure, and finally the formation of new blood vessels; The latter refers to the increase in collateral arterial blood flow and intravascular shear due to arterial blockage, resulting in cell proliferation and vascular remodeling, resulting in thicker functional collateral arteries
.

The formation of the lateral branch circulation of the brain is related
to the joint action of endogenous angiotropic factors, vascularendothelial growth factor (VEGF), platelet-derived growth factor family and angiopoietin.
In addition, transforming growth factor, granulocyte-macrophage colony-stimulating factor, hypoxia-inducible factor-1α, and circulating endothelial progenitor cells also play an important role
in the process of vascular regeneration.

The above factors may act on vascular endothelial cells and smooth muscle cells, not only participate in the occurrence of intracranial and extracranial vascular stenosis or occlusion, but also stimulate angiogenesis, and participate in the formation
of abnormal blood vessels on the skull base and cortical surface.

Clinical significance of the establishment of collateral circulation in the brain

In recent years, there has been more and more research on the compensatory effect of cerebral artery stenosis or occlusion of the posterior collateral circulation, and the ultimate purpose of the research is to be used in clinical treatment
.
At present, there are not many
drugs available clinically to promote the establishment of collateral circulation.

Therefore, determining the degree of collateral circulation by angiography can help guide treatment decisions
in patients with acute cerebral ischemia.
However, hyperperfusion of collateral circulation in ischemic areas may increase the risk of intracerebral haemorrhage, particularly in hypertensive patients; At the same time, hemodynamic disturbances after vascular occlusion can lead to the formation
of collateral aneurysm.

epilogue

Collateral circulation is an important factor in
the occurrence and outcome of ischaemic stroke.
Primary collateral compensation is congenital and currently clinically unavailable
.
How to effectively open the secondary collateral circulation and promote tertiary collateral compensation should become an important research direction
of clinical treatment.
Collateral circulation compensation assessment can help individualize treatment regimens
.
Therapies to promote vascular regeneration and collateral establishment have become new targets for ischemic stroke treatment
.