Role and Prognostic Implications of Venous Outflow Assessment in Acute Ischemic Stroke

Introduction: The venous outflow profile (VOP) is a crucial yet often overlooked aspect affecting stroke outcomes. It plays a major role in the physiopathology of acute cerebral ischemia, as it accounts for both the upstream arterial collaterals and cerebral microperfusion. This enables it to circumvent the limitations of various arterial collateral evaluation systems, which often fail to consider impaired autoregulation and its impact on cerebral blood flow at the microcirculatory levels. In this narrative review, we will highlight the different parameters and modalities used to assess the VOP in acute ischemia. VO Assessment With Different Modalities: CT parameters include cortical vein opacification score, interhemispheric difference of composite scores of the draining veins classifications on single-phase CT angiography (CTA), as well as the extent and velocity of optimal cortical venous filling on multiphase CTA. Differences in contrast administration and acquisition time render the single-phase CTA parameters less reliable. Perfusion parameters are semiautomated, thus offering greater reproducibility. These include time to peak and prolonged venous transit. Finally, the venous transit time is an MRI parameter. Associations and Prognostic Implications: VOP parameters’ significance lies in their potential to predict tissue fate and, subsequently, clinical outcomes. Recent studies indicate that favorable VOP is independently associated with slower rates of infarct edema progression, smaller infarct volumes, and higher rates of functional independence after 90 days. Moreover, it is considered a predictor of recanalization success and the first-pass effect during mechanical thrombectomy. Conversely, an unfavorable VOP predicts futile recanalization and indicates a higher risk of reperfusion hemorrhage. Our aim is to explore these prognostic implications and their relevance in determining the utility of intracranial intervention.