Introduction

Fluid-Attenuated Inversion Recovery Imaging (FLAIR) vascular hyperintensity (FVH) were considered resulting from hemodynamic changes other than thrombosis and as a marker of slow flow leading absence of flow void in patients with intracranial atherosclerotic stenosis or occlusion. The correlation of FVH and collateral are still in discrepancy in this disease¹. Three dimensional pseudo-continuous arterial spin labeling (3D pCASL) technique including territorial ASL and multiple post labeling delay (PLD) ASL are promising approaches to study collateral circulation². The present study was to investigate the determinants of presence and intensity of FVH sign and thus its indication for collateral circulation by ASL perfusion imaging in patients with unilateral middle cerebral artery atherosclerotic stenosis or occlusion.

Methods

From October 2015 to June 2016, we prospectively enrolled consecutive patients with unilateral middle cerebral artery(MCA) atherosclerotic severe stenosis(70%-99%) or occlusion confirmed by MR angiography (MRA). Demographics of patients including risk factors, time from symptom onset to MRI scanning were recorded. All patients were performed territorial ASL (PLD=2.0s), two PLD (1.5s and 2.5s) 3D pCASL, T2FLAIR (slice thickness = 5mm), MRA and diffusion weighted imaging (DWI) on a 3.0T scanner(GE MR 750, USA). Cerebral blood flow (CBF) maps of TASL and 3D pCASL were post-processed on AW4.5 Workstation (GE Healthcare, China). FVH was defined as a linear or serpentine hyperintense appearance on FLAIR distal to the stenosis or occlusive lesion in line with a typical arterial course. The Intensity of FVH was graded as none, subtle and prominent. Continuous FVH presenting on more than 4 slices or greater than 1/3 downstream territory was considered as prominent and FVH presenting on less than 4 slices and 1/3 downstream territory considered as subtle. Figure 1 showed two examples with prominent (A) and subtle (B) FVH. DWI lesion volume were measured and lesion pattern were assessed based on previous study³. Collateral perfusion proportion were calculated according to a previous study using two PLD 3D pCASL approach⁴, and meanwhile 2.5s CBF Alberta Stroke Programme Early CT Score (ASPECTS) were quantified in accordance to the original study⁵. Degree of leptomeningeal collateral distribution was assessed as ≤ 1/3, 1/3-2/3, and ≥2/3 MCA territory volume by 2.5s ASL-CBF map subtracting 1.5s ASL-CBF map based on our previous study⁶. Leptomeningeal collateral pattern were then assessed by TASL as shown in Figure 2-4. DWI lesion, collateral perfusion proportion, leptomeningeal collateral pattern and demographics were compared between groups with different intensity of FVH using ANOVA or non-parametric and X² test.

Results

We totally enrolled 51 patients(57.15±10.73 years, 13 females) with 7 patients with prominent FVH, 27 patients with subtle FVH and 17 patients without FVH. Clinical materials including gender, risk factors and time from symptom onset to MRI scanning were not significant different between the 3 groups (not shown in Figure 5). In table of Figure 5, it is seen that patients with normal vascular territory distribution and no collateral compensation were most frequently observed in patients without FVH, patients with collateral perfusion less than 1/3 MCA territory were most frequently observed in patients with prominent FVH. Additionally, 2.5s CBF-ASPECTS were significantly lower in patients with prominent FVH and patients with subtle FVH were significantly lower than patients without FVH.

Discussion and Conclusion

In unilateral middle cerebral artery atherosclerotic stenosis or occlusion, collateral recruitment and degree of collateral perfusion distribution may be associated with the presence and intensity of FVH. FVH are more prevalent in patients with poor collateralization. Patients with more prominent FVH may have experienced more severe hypoperfusion, which indicates that the intensity of FVH may be an useful marker of cerebral hymodynamic impairments.

Acknowledgements

No acknowledgement found.