Sustaining cerebral perfusion in intracranial atherosclerotic stenosis: The roles of antegrade residual flow and leptomeningeal collateral flow

Abstract

We aimed to investigate the roles of antegrade residual flow and leptomeningeal collateral flow in sustaining cerebral perfusion distal to an intracranial atherosclerotic stenosis (ICAS). Patients with apparently normal cerebral perfusion distal to a symptomatic middle cerebral artery (MCA)-M1 stenosis were enrolled. Computational fluid dynamics models were built based on CT angiography to obtain a translesional pressure ratio (PR) to gauge the residual antegrade flow. Leptomeningeal collaterals (LMCs) were scaled on CT angiography. Cerebral perfusion metrics were obtained in CT perfusion maps. Among 83 patients, linear regression analyses revealed that both translesional PR and LMC scale were independently associated with relative ipsilesional mean transit time (rMTT). Subgroup analyses showed that ipsilesional rMTT was significantly associated with translesional PR ( p < 0.001) rather than LMC scale in those with a moderate (50–69%) MCA stenosis, which, however, was only significantly associated with LMC scale ( p = 0.051) in those with a severe (70–99%) stenosis. Antegrade residual flow and leptomeningeal collateral flow have complementary effects in sustaining cerebral perfusion distal to an ICAS, while cerebral perfusion may rely more on the collateral circulation in those with a severe stenosis.

Hemodynamics and stroke risk in intracranial atherosclerotic disease

“…21 A previous study using quantitative MRA to quantify cerebral blood flow in patients with atherosclerotic vertebrobasilar artery stenosis demonstrated the association between reduced cerebral blood flow and increased risk of recurrent stroke. A larger pressure gradient or steeper pressure drop means reduced antegrade flow through the stenotic lesion, which might lead to hypoperfusion and cerebral ischemia when the collateral circulation could not adequately compensate the territorial blood flow.…”

“…[19][20][21] (1) Three-dimensional geometry of the arteries of interest was reconstructed from CTA source images, covering the intracranial ICA, MCA-M1, and ACA-A1 segments for cases with an ICA or MCA-M1 lesion; and VA-V4, BA, and PCA-P1 segments for cases with a VA-V4 or BA lesion. CFD modeling procedures were described in our previous work.…”

“…CFD modeling procedures were described in our previous work. 21 Translesional WSSR was calculated as WSS stenotic − throat /WSS prestenotic ; WSS stenotic-throat was measured at the most severely narrowed cross-section of the diseased intracranial artery, and WSS prestenotic was measured at the proximal normal vessel segment. (2) A mesh was then created on the vessel surface and within the vessel lumen in ANSYS ICEM CFD, with the maximal element sizes of 0.1 for the inlet(s) and outlets and 0.25 for other parts of the mesh, containing 0.5 to 1 million elements in total for each case.…”

“…CFD modeling procedures were described in our previous work. [19][20][21] (1) Three-dimensional geometry of the arteries of interest was reconstructed from CTA source images, covering the intracranial ICA, MCA-M1, and ACA-A1 segments for cases with an ICA or MCA-M1 lesion; and VA-V4, BA, and PCA-P1 segments for cases with a VA-V4 or BA lesion. (2) A mesh was then created on the vessel surface and within the vessel lumen in ANSYS ICEM CFD, with the maximal element sizes of 0.1 for the inlet(s) and outlets and 0.25 for other parts of the mesh, containing 0.5 to 1 million elements in total for each case.…”

“…A smaller translesional PR indicates a larger pressure drop or pressure gradient across the sICAS lesion, which may restrict antegrade perfusion in the relevant area. 21 Translesional WSSR was calculated as WSS stenotic − throat /WSS prestenotic ; WSS stenotic-throat was measured at the most severely narrowed cross-section of the diseased intracranial artery, and WSS prestenotic was measured at the proximal normal vessel segment. A higher WSSR indicates higher WSS across the sICAS lesion.…”