Rizwan Kalani, MD

Simonsen CZ, Madsen MH, Schmitz ML, Mikkelsen IK, Fisher M, and Andersen G. Sensitivity of Diffusion- and Perfusion-Weighted Imaging for Diagnosing Acute Ischemic Stroke Is 97.5%. Stroke. 2014

Diffusion-weighted imaging (DWI) can sometimes be negative in the setting of acute stroke. This is most notably seen with small infarct size, early timing of scan, and brainstem location. In this study, Simonsen et al retrospectively evaluated DWI magnetic resonance imaging (MRI) and the contribution of perfusion-weighted imaging (PWI) for diagnosing ischemic stroke from a database of intravenous tissue plasminogen activator (IV-TPA) treated patients.

At the center where this study was conducted, MRI (including DWI & PWI) was performed as the initial preferred imaging modality prior to acute stroke thrombolysis. Patients received IV-TPA according to standard guidelines. DWI and PWI lesion evaluation was done by a neuroradiologist and neurologist blinded to final diagnosis. Patient follow-up at 90 days established functional outcomes (modified Rankin scale [mRS]) and etiologic subtype (per TOAST criteria).

569 IV-TPA treated patients were included from 2004-2010 for this study. Four of them ended up having stroke mimics based on clinical and imaging follow-up. Of the 565 patients with clinically diagnosed stroke, 518 had a DWI positive lesion. The sensitivity of DWI for ischemic stroke was 92% with specificity of 75% and positive predictive value of 99.8%. 47 patients had MRIs that were DWI negative, 43 of which had PWI completed. Hypoperfusion in the location corresponding to symptoms was seen in 33. In effect, the combination of DWI and PWI increased sensitivity for detection of hyperacute stroke to 97.5%. DWI negative MRI was associated with less severe stroke (NIHSS 4 vs 7, p=0.0008), improved outcome (80.9% vs 61.8% with mRS 0-1), posterior circulation location (34.9% vs 15.3%, p=0.0019), higher prevalence of small vessel disease (36.2% vs 18.0%, p=0.0047), and longer time from symptom onset to imaging (120 min vs 109 min, p=0.047).

Consistent with prior studies, this manuscript re-demonstrates the high sensitivity of DWI for acute infarct. The addition of PWI can improve the sensitivity further. The authors argue that visualizing the lesion on MRI can assist in decision making about IV-TPA. Furthermore, they suggest that PWI may be of diagnostic utility in DWI negative patients with suspected ischemic stroke who are outside of the acute treatment window (or as part of research study).

Completing MRI prior to thrombolytic treatment decision making is not universal practice. With accumulating evidence supporting earlier IV-TPA administration improving patient outcomes as well as relative safety of thrombolysis demonstrated in stroke mimics, a role for MRI prior to acute stroke treatment is likely to be limited. Results from DEFUSE, EPIPHET, and MR-RESCUE have shown that perfusion imaging does not clearly assist with patient selection for IV-TPA or endovascular treatment.

With continual improvement in PWI techniques, ongoing and future studies will have to further define its role in etiologic diagnosis, management, prognostication, and clinical outcomes after stroke.