[4] Their diameter has been measured at approximately 300 micrometers,[5] but there is variability between individuals in the size, quantity and location of these vessels, and between either hemisphere within the same subject.

[11] Therapies that attempt to optimize leptomeningeal collateral circulation appear to improve outcomes following acute ischaemic stroke.

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 salvageable.

The authors argued that the presence of such collaterals on imaging should be considered a risk factor for ICH in patients where carotid stenting is otherwise indicated.

[15][16] German physician Otto Heubner first demonstrated their presence in his 1874 work Die luetische Erkrankung Der Hirnaterien.

[6] The concept of the ischaemic penumbra, where brain tissue shows capacity to recover if perfusion is quickly restored, was defined in 1981 by Astrup et al.