Kara Jo Swafford, MD
The ischemic penumbra represents hypo-perfused tissue at risk of infarction if cerebral blood flow is not restored and may persist for hours after onset of ischemia. Progression from penumbra to infarction may be delayed due to the presence of collateral circulation. The 2018 American Heart Association acute ischemic stroke guidelines, in part based on the results of the DAWN and DEFUSE 3 trials, support the use of perfusion imaging for identifying patients with potentially salvageable tissue to help in selecting appropriate candidates for mechanical thrombectomy. Limited data exists on penumbra characteristics in patients with untreated acute ischemic stroke compared to those receiving reperfusion therapy within a delayed time window (i.e., up to 24 hours after stroke onset). Vagal et al designed a multicenter retrospective cross-sectional study to investigate how time from stroke onset may affect penumbral salvage and infarct growth in untreated acute ischemic stroke patients within the first 24 hours, including the role of collaterals.
Analyzing data from 94 patients, their study suggests collateral cerebral blood flow is important in the natural evolution of ischemic injury, regardless of the timing of penumbra assessment. Greater collateral circulation was associated with greater penumbral salvage and less infarct growth within the first 24 hours. Time of stroke onset was not associated with either penumbral salvage or infarct growth. Although patients with spontaneous recanalization had greater penumbral salvage and lower infarct growth, the difference was not statistically significant.
Strengths of this study include investigating the natural history of stroke evolution in untreated acute ischemic stroke patients within 24 hours of symptom onset. Limitations include its retrospective, cross-sectional design, potential for case selection bias, small sample size and lack of correction for factors influencing infarct growth such as hyperglycemia and blood pressure.