Relativity of Ischemic Core Volume Estimation.

See related article, p 2368 Mechanical thrombectomy (MT) has become standard of care for patients with acute ischemic stroke because of large vessel occlusion as it reduces disability compared with standard of care treatment within 6 hours of symptom onset. Recent results of the DAWN trial (Diffusion Weighted Imaging [DWI] or Computed Tomography Perfusion [CTP] Assessment with Clinical Mismatch in the Triage of Wake-Up and Late Presenting Strokes Undergoing Neurointervention with Trevo) and the DEFUSE3 trial (Endovascular Therapy Following Imaging Evaluation for Ischemic Stroke) suggest that patients with acute ischemic stroke can benefit from MT even when they are admitted beyond the 6-hour window. These 2 trials identified patients who could benefit from reperfusion using CTP or magnetic resonance perfusion processed with the Rapid software. Current guidelines of the American Heart Association and the American Stroke Association regarding the management of patients with acute ischemic stroke already recommend MT in selected patients with large vessel occlusion in the anterior circulation within 6 to 16 hours of last known well and state that MT is reasonable in selected patients with acute ischemic stroke within 16 to 24 hours of last known well, if they have an anterior circulation large vessel occlusion and meet the DAWN eligibility criteria. Given this, a standardized software approach of CTP and magnetic resonance perfusion postprocessing will likely become increasingly important to select patients for MT, especially beyond the first 6 hours after symptom onset. Hoving et al investigated how reliable CTP data, postprocessed with the Rapid software, could predict follow-up infarct volumes in patients with successful reperfusion, defined as a modified Treatment in Cerebral Infarction (mTICI) grade of 2b-3. They assessed the volumetric and spatial agreement of CTP-estimated ischemic core with 24 hours of follow-up infarct on DWI. Of note, 98% of their cohort, which included individual patient data from the randomized trials of the HERMES collaboration (Highly Effective Reperfusion Evaluated in Multiple Endovascular Stroke Trials) 1,6 and the EXTEND-IA TNK trial (Extending the Time for Thrombolysis in Emergency Neurological Deficits Intra-Arterial Using Intravenous Tenecteplase), was treated within 6 hours after symptom onset. Hoving et al demonstrated a moderate spatial and volumetric agreement of CTP-estimated ischemic core at baseline with follow-up DWI infarct. They found core volumes estimated using a CTP-cerebral blood flow threshold of <30% to be substantially smaller than DWI lesions at 24-hour follow-up. The median volumetric difference between CTP core and DWI infarct was 25.4 mL (interquartile range: 10.0– 63.7 mL). When putting these results into perspective with some previous findings, they contrast the notion that CTP tends to overestimate the ischemic core. Such an overestimation has been observed using both cerebral blood flow–derived and cerebral blood volume–derived infarct core volumes and seems to be most frequent, if CTP is performed early after symptom onset and if reperfusion is rapidly restored. However, in the study by Hoving et al, infarct core overestimation was observed in only 5% of patients and was predominantly located in the white matter. A study analyzing the reliability of CTP to classify infarct core and penumbra in a subset of patients included in the MR CLEAN trial (Multicenter Randomized Clinical Trial of Endovascular Treatment for Acute Ischemic Stroke in the Netherlands) demonstrated a considerable misclassification of core volume (median: 30.4 mL). The total CTP ischemic core volumes in that study were rather large (median: 49.7 mL). This supports the observation of Hoving et al that increased absolute volumetric differences were associated with larger estimated core volumes. CTP may have diagnostic value in patients with small vessel occlusions and can be used to predict clinical outcome. However, the study by Hoving et al and previous findings by others call into question, whether CTP renders an accurate prediction of larger infarct cores and if it should be used to select patients for MT within the first 6 hours after symptom onset. The current thresholds for CTP were established in comparison to DWI volumes and in an era of not-so-fast reperfusion. But even patients with large DWI lesions showed possible benefit in a post hoc analysis of the THRACE trial (Thrombectomie des Artères Cerebrales), especially in the case of an M1 occlusion and ischemia localized in the superficial middle cerebral artery territory. As we are advancing to the era of personalized medicine, additional factors to the absolute ischemic volume should be considered before excluding patients from a highly effective treatment method with a surprisingly low number-needed-to-treat. Ernst et al showed nicely that outcome prediction is affected not only by lesion volume but also by the location of the infarcted area. Additionally, as ultrafast reperfusion with door-to-reperfusion times of ≈60 minutes will be a reality in the near future, The opinions expressed in this article are not necessarily those of the editors or of the American Heart Association. From the Department of Neuroradiology, University Medical Center Goettingen, Germany. Guest Editor for this article was Georgios Tsivgoulis, MD. Correspondence to Marios-Nikos Psychogios, MD, PD, Department of Neuroradiology, University Medical Center Goettingen, RobertKoch-Str. 40, 37075, Goettingen, Germany. Email m.psychogios@med. uni-goettingen.de Relativity of Ischemic Core Volume Estimation