Derivation and External Validation of the "FORECAST-PC" Prediction Scores

Outcome prediction after endovascular treatment (EVT) for posterior circulation (PC) acute ischemic stroke remains challenging, as current prognostic tools are often limited strictly to basilar artery occlusions or rely heavily on anterior circulation data. The FORECAST-PC study is an investigator-initiated, retrospective, international multicenter cohort study designed to develop and validate comprehensive PC outcome prediction models across key stages of the clinical pathway: Baseline, Pre-EVT, Immediately Post-EVT, and 24-hours Post-EVT. The models are derived from patients across three European centers and externally validated on an unseen cohort from 11 international centers to ensure robustness against geographic domain shifts and variations in clinical workflows. The clinical utility of these models is assessed using Decision Curve Analysis to demonstrate the net benefit of model-guided prognostication over standard clinical assumptions.

Inclusion criteria

• Age > 18 years
• Presentation with acute ischemic stroke (AIS) attributed to a radiologically confirmed posterior circulation occlusion
• Selected for Endovascular Thrombectomy (EVT) according to the treating physician
• Pre-stroke modified Rankin Scale (mRS) 0-3
• EVT initiated or attempted within 24-hours of the last known well (LKW) time
• Includes cases with/without prior intravenous thrombolysis (IVT), mothership, and drip-and-ship pathways

Exclusion criteria

• EVT carried out beyond 24 hours from stroke onset
• EVT performed secondarily after in-hospital worsening or stroke recurrence
• In-hospital strokes (to avoid the confounding influence of prior systemic comorbidities and the acute event that necessitated initial admission)
• Missing primary outcome data
• Inconsistencies between descriptive dependence status and raw pre-stroke mRS
• Stroke cases occurring prior to 2015 (to account for major changes in endovascular treatment techniques)