Ken Uchino
Treatment of acute ischemic stroke has focused on patient selection over the past 2 decades. After time from onset to treatment was shown to be the important outcome predictor in intravenous thrombolysis, other predictors of success in reperfusion therapy were investigated, in order improve patient selection beyond the standard timeframe (initially 3 hours for thrombolysis and 6 hours for endovascular therapy). Over the years, tissue at risk has been investigated with dynamic contrast perfusion imaging, clinical-DWI mismatch, FLAIR-DWI mismatch, and CT ASPECTS scoring for patient selection. One constant feature in all these assessments is the volume of core infarct as part of the predictors.
Starting in 2010, we had implemented a protocol of MR imaging (“hyperacute stroke MRI protocol”) for endovascular intervention in acute ischemic stroke. To prevent overwhelming the system with all patients with suspected strokes coming for MRI, we required demonstration of target large artery occlusion on CT angiography before performing the hyperacute MRI protocol. Thus, we are able to have a set of patients with CTA and MRI being performed in close proximity. In clinical research, we don’t always get to design the study we want, but circumstances can produce a useful dataset.
In our study we asked the question, in the early timeframe within 6 hours after stroke onset, is there an indication of growth of core infarct over time? Patients who are imaged early might have small core infarcts, whereas patients imaged at close to 6 hours would have a larger core. We hypothesized that while time may be an important predictor, presence of collaterals would be an important determinant. We found that in patients with proximal intracranial artery occlusions, we did not see that those who were imaged early had smaller core infarcts (DWI volume) on MRI than those who were imaged later. We saw no relationship between time and DWI volume. The main determinant of core infarct was collaterals visualized on standard CT angiography.