Asdaghi N, Hill MD, Coulter JI, Butcher KS, Modi J, Qazi A, et al. Perfusion MR Predicts Outcome in High-Risk Transient Ischemic Attack/Minor Stroke: A Derivation–Validation Study. Stroke. 2013
This group chose to use threshold of Tmax >4 ml as their definition of perfusion delay. This is similar to DEFUSE1 threshold (the DEFUSE authors later concluded that threshold was too sensitive and tended to overcall penumbra, and changed the threshold to Tmax >6 in the DEFUSE2 study). The use of Tmax >4 ml is one possible reason why Asdaghi et al. found final infarct growth of 3.5ml in the validation cohort when they had predicted >10 ml of at risk tissue on the initial acute stroke MRI.
Granted, because this study was based on a registry, we don’t know if the perfusion mismatch found on the initial scan may have led clinicians to change their management for the patient, and thus, potentially salvaging some of that penumbral region.
How does this change management? Well, for one, if a patient has a perfusion delay (at what Tmax threshold is still controversial) then that patient likely warrants close clinical monitoring. Such a patient may need recanalization therapy if a vessel occlusion is present or possibly hypertensive therapy if no occlusion or a distal occlusion is found. Since the initial scans were performed at 24 hours after onset of symptoms, this may suggest that using radiologic criteria for reperfusion therapy makes more sense than an absolute time window.
This study confirms other research that suggests perfusion mismatch portends a higher risk of radiologic and clinical progression.