Abstract A026: Posterior circulation Clot Burden Score (pc-CBS) predicts clinical outcome after acute ischemic stroke related to posterior circulation occlusions : An externally validated radiological score

Introduction: Posterior circulation strokes (PCS) account for one-quarter of ischemic strokes and differ from anterior circulation events in presentation, vascular anatomy, and treatment implications. Prognostic tools for PCS are scarce, and existing scores apply mainly to basilar artery occlusion, despite their potential to guide acute treatment and trial design. We aimed to develop and externally validate the Posterior Circulation Clot Burden Score (pc-CBS), a CTA/MRA-based tool to predict 3-month functional outcome across the entire posterior circulation. Methods: This investigator-initiated, retrospective cohort study included 488 consecutive PCS patients with CTA/MRA-confirmed occlusion from the ASTRAL registry (Lausanne, Switzerland) in the derivation/internal validation cohort. External validation used individual-level data from 1,340 patients across 21 stroke centers in 3 continents. Eight arterial segments (extracranial/intracranial vertebral, proximal/mid/distal basilar, P1/P2 posterior cerebral, posterior communicating arteries) were graded as patent or occluded/hairline (