Hemodynamic Insights Into the Asymmetrical Medullary Vein Sign on T2* Imaging in Hyperacute M1 Occlusion

Background In treating acute ischemic stroke (AIS), asymmetrical vein signs (AVS) on blood-oxygen-level-dependent imaging reflect increased deoxyhemoglobin levels due to increased oxygen extraction fraction. Meanwhile, although veins connecting pial and deep venous systems, such as transcerebral veins, are well studied, dynamic observation of these veins remains challenging. This study aimed to elucidate the venous flow of the deep white matter (DWM), focusing on medullary AVS in patients with hyperacute cardioembolic M1 occlusion. Methods This retrospective cross-sectional study involved 50 patients with AIS caused by M1 occlusion who received mechanical thrombectomy at Kameda Medical Center from July 2018 to December 2021. The study investigated medullary AVS and their association with angiographic collateral flow grades and occlusion locations. Welch's t-test was used for continuous variables, while Fisher's exact test was employed for categorical variables. Results A total of 41 patients were eligible for analysis. No significant association was found between medullary AVS and angiographic collateral flow grade (p=1.000); however, a significant association was observed between proximal M1 occlusion and medullary AVS (p=0.006), supporting the hypothesis that medullary AVS is significantly influenced by ischemic conditions in the territory of lenticulostriate arteries. Conclusion Three possible mechanisms for medullary AVS were considered: local ischemia in the DWM, ventriculopetal ischemic venous flow from the pial veins, and ventriculofugal ischemic venous flow from the basal ganglia. The results of the present study and the fact that the DWM is exclusively perfused by the cortical arteries favor the ventriculofugal flow hypothesis as the mechanism of medullary AVS. Although direct observation of the veins in the DWM by cerebral angiography is challenging, it can be deduced indirectly.