Venous Outflow Imaging in Acute Ischemic Stroke: An ASFNR State of Practice

BACKGROUND: Venous outflow (VO) imaging describes the egress limb of the cerebral collateral circulation and has been associated with outcome in acute ischemic stroke; its added value beyond arterial collaterals and perfusion measures remains uncertain. More than a dozen VO measures have been proposed on CT and MR techniques used in acute stroke, spanning three physical signals: venous opacification, venous transit and venous oxygenation. They differ in what they measure, in evidence maturity and in readiness for reporting. METHODS: A writing group reviewed the peer-reviewed studies of cerebral venous drainage measures in acute ischemic stroke. The scope is CT and MRI obtained during routine acute stroke evaluation, excluding measures that require catheter angiography or ultrasound. We describe each measure's acquisition, definition, evidence and technical limitations, and propose a reporting framework based on these features. KEY MESSAGE: VO markers are descriptive prognostic measures, not treatment-selection criteria. The cortical vein opacification score (COVES) has the most mature CTA evidence and may be considered when venous timing is adequate, though meta-analyses support an association rather than a threshold; comprehensive venous outflow (CVO) adds the internal cerebral vein. Prolonged venous transit (PVT) adds a temporal dimension read from perfusion, but remains investigational, as do the composite arterial-venous scores, quantitative venous timing and oxygen extraction fraction mapping. Susceptibility signs index deoxygenation and venous blood volume, not drainage. Reporting should name the technique and describe opacification, transit or oxygenation findings in their own terms. The evidence base is predominantly anterior-circulation large-vessel occlusion imaged before thrombectomy.