Intravenous thrombolytic therapy and DWI/PWI mismatch development
Diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) are MR techniques increasingly used in acute stroke. The aim of this study was to evaluate the DWI/PWI mismatch volumes in acute stroke patients before and after intravenous thrombolytic therapy. METHODS: Seven patients with ischemic stroke were treated with intravenous recombinant tissue plasminogen activator (rtPA) and imaged with DWI, PWI, MRA, and conventional MRI within 3 hours of symptom onset and on day 1 and 7. Clinical scores (National Institutes of Health Stroke Scale [NIHSS] and Barthel Index) were assessed on each time point. The perfusion deficit was defined using a threshold function measuring the volumes of regions with “time-to-peak” (TTP) delays of 2–4s, 4–6s, 6–8s and above 8 s; these volumes were compared with the DWI lesion volumes, infarct progression and final infarct size. RESULTS: In all patients (n=7) the DWI lesion (< 3 hrs) was significantly smaller (45%) as compared to the PWI lesion volume. The mismatch area decreased from day 0 (113 ml) to day 7 (3 ml) in all patients except for two. Mean NIHSS in these two patients improved by 5 and 2 points, while the other patients improved by a mean of 12 points from day 0 to day 7. The DWI lesion volume - measured by manually outlining the lesion - increased from a mean of 78 ml (day 0) to 136 ml (day 7) measured on T2-weighted imaging. Contributing 31% to the PWI lesion on day 0, TTP delay interval of 2–4 s was found to increase to 47% by day 7 while the region with severely delayed perfusion (> 8 s) underwent a decrease of 13%. Overall the perfusion deficit on day 7 showed a reduction by 27%. The infarct volume measured by manually outlining the DWI-lesion on day 0 increased from a mean of 78 ml to 136 ml on day 7 measured on T2-weighted imaging. CONCLUSIONS: 1.) Intravenous thrombolytic therapy in selected patients with a severe PWI/DWI mismatch is associated with lesion enlargement taking in account that not all of the “tissue at risk” will be safed by thrombolytic therapy. 2.) Temporal development of the PWI/DWI mismatch serves as a parameter of the therapeutic efficacy of thrombolysis.