Imaging suspected posterior circulation stroke in the emergency department: a practical modality-based review.

Posterior circulation stroke (PCS) accounts for 20-25% of ischemic strokes and is disproportionately missed at first presentation. This review summarizes brain parenchymal and neurovascular imaging modalities for the evaluation of suspected PCS in the emergency department (ED). We conducted a structured narrative review of established and emerging modalities, describing each modality's technical principles, clinical roles, performance estimates, evidence base, limitations, and real-world application. Searches emphasized ED populations and posterior fossa infarction; society guidelines and meta-analyses were prioritized. Non-contrast CT is insensitive for acute PCS (reported 16-44%) but remains essential for excluding hemorrhage. CT angiography is roughly 80% sensitive for vertebrobasilar occlusion in selected cohorts and ~ 44% sensitive for PCS overall. CT perfusion adds incremental sensitivity (around 70-75%). MRI with diffusion-weighted imaging is ~ 80% sensitive in pooled estimates; high-resolution DWI may approach 90-95% in single-center series. Emerging modalities - dual-energy CT (41-88% sensitive), portable low-field MRI (estimated 69% sensitive), and accelerated or abbreviated MRI (likely 80-95% sensitive) - are at varying stages of adoption. Performance metrics of emerging modalities derive from small, single-center cohorts with probable spectrum bias. Evaluation of the brain parenchyma and vasculature represent distinct clinical questions, for which dedicated imaging may be required. Accurate diagnosis of PCS requires careful selection and, often, a combination of imaging modalities tailored to the clinical question and local resources.