Abstract Introduction Posterior reversible encephalopathy syndrome (PRES) is characterized by vasogenic edema, typically in posterior brain regions, often linked to acute hypertension, eclampsia, or immunosuppressive therapy. Rarely, PRES may occur without these triggers, such as after iodinated contrast exposure during neuroendovascular interventions. The pathophysiology involves endothelial dysfunction, transient blood-brain barrier disruption, and impaired cerebrovascular autoregulation. PRES without hypertension or vascular occlusion is exceptionally uncommon and may mimic acute ischemia. This report highlights a localized, atypical PRES following endovascular middle cerebral artery (MCA) aneurysm repair, where perfusion CT enabled early diagnosis. Case Description A 71-year-old woman underwent elective Y-stent-assisted coil embolization for an unruptured wide-neck right MCA bifurcation aneurysm. The procedure achieved complete occlusion with preserved flow. Hours later, she developed somnolence, left hemiparesis, gaze deviation, and a generalized tonic-clonic seizure. Emergent CT and perfusion imaging revealed focal cortical edema in the right frontoparietal cortex with mild time-to-peak (TTP) prolongation, preserved cerebral blood volume (CBV), and near-normal cerebral blood flow (CBF)—a perfusion mismatch pattern consistent with vasogenic rather than ischemic hypoperfusion. Digital subtraction angiography confirmed patent vessels and absence of stent thrombosis. Blood pressure remained normal throughout. Conservative management with hemodynamic control, antiseizure medication, and supportive care led to complete recovery. Follow-up imaging showed full resolution of edema and normalized perfusion, confirming atypical PRES related to the endovascular procedure. Discussion PRES following neuroendovascular treatment is exceedingly rare, particularly without hypertension or vessel occlusion. In this context, transient endothelial injury and blood-brain barrier disruption from iodinated contrast may trigger focal vasogenic edema. The characteristic perfusion pattern—prolonged TTP with preserved CBV and CBF—reflects transient microcirculatory dysfunction and compartmentalized intracranial pressure elevation rather than ischemia. Recognition of this imaging signature is crucial to avoid misdiagnosis as acute stroke and prevent unnecessary interventions. The patient’s full recovery emphasizes the reversibility of this phenomenon with conservative therapy once identified. Conclusion This case illustrates that PRES can arise as an uncommon, normotensive complication of endovascular aneurysm repair. Perfusion CT was instrumental in differentiating vasogenic from ischemic pathology through the pattern of prolonged TTP with preserved CBV and CBF. Early recognition allowed appropriate conservative management and complete neurological recovery. This abstract is funded by: N/A
J A Carrizosa (2026) studied this question.