Leptomeningeal collateral circulation

The leptomeningeal collateral circulation (also known as leptomeningeal anastomoses or pial collaterals) is a network of small blood vessels in the brain that connects branches of the middle, anterior and posterior cerebral arteries (MCA, ACA, and PCA). The leptomeningeal collateral circulation (also known as leptomeningeal anastomoses or pial collaterals) is a network of small blood vessels in the brain that connects branches of the middle, anterior and posterior cerebral arteries (MCA, ACA, and PCA). Leptomeningeal collaterals lie within the leptomeninges, the two deep layers of the meninges called the pia mater and the arachnoid mater. Their diameter has been measured at approximately 300 micrometers, but there is variability between individuals in the size, quantity and location of these vessels, and between either hemisphere within the same subject. Inter-territorial end to end anastomoses exist between branches of the ACA and MCA, the PCA and MCA, the ACA and PCA, and the right and left ACAs. Intra-territorial anastamoses connect adjacent arterial branches within the same arterial territory (between two branches of the same MCA, for example). Inter-territorial leptomeningeal anastamoses between the PCA and ACA have been observed between the parieto-occipital branch of the PCA, and the precuneal branch or the posterior pericallosal branch of the ACA. Inter-territoral leptomeningeal anastamoses between the right and left ACAs have been observed between the right and left pericallosal arteries and the right and left callosal marginal arteries. Anastamoses have also been observed between precuneal branches originating from the middle portion of the pericallosal artery, or from the posterior portion of the callosal marginal branch of one side joining the opposite paracentral branch. Leptomeningeal collateral vessels allow limited cerebral blood flow and brain tissue perfusion when normal circulation through the circle of Willis is impaired, through a series of anastomotic connections between cerebral arteries. During an ischaemic stroke, blood flow through a cerebral artery is compromised. This frequently causes substantial injury to the area of the brain supplied by the artery, but not all of this territory is necessarily affected. A post mortem study of MCA strokes demonstrated that the area of brain injury was often smaller than the total area supplied by the MCA. Leptomeningeal collateral vessels from the ACA and PCA appeared to allow for perfusion of some brain tissue to persist, partially compensating for the loss of the major vessel. This compensatory effect is however usually inadequate to maintain a normal blood supply. There is anatomical variation in collateral circulation from person to person, and as we age, collateral vessels decrease in diameter and number. Therapies that attempt to optimize leptomeningeal collateral circulation appear to improve outcomes following acute ischaemic stroke. MRI and CT brain imaging is used to determine the severity of a stroke, and help guide treatment. Fluid attenuated inversion recovery (FLAIR) vascular hyperintensity (FVH) is a radiographic marker seen on brain imaging in acute ischaemic stroke. FVH can be used as a proxy for slow leptomeningeal collateral blood flow, and may help reveal which areas of brain tissue are potentially salvagable.