Remission of diffusion lesions in acute stroke magnetic resonance imaging

Purpose: The mismatch concept in stroke magnetic resonance (MR) is based on the assumption that diffusion weighted imaging (DWI) indicates infarct core representing irreversibly damaged tissue. However, this thesis has not been proven yet in a large patient cohort. On the other hand, some publications report cases with possible remission of lesions at DWI. Thus, the aim of this study was to analyze temporal evolution of restricted diffusion at follow up MR imaging and analyze clinical and imaging features of cases with remission of DWI lesions. Methods and Materials: 176 consecutive stroke patients (within 12 months) demonstrating restricted diffusion at initial MR examination were evaluated. Extension of diffusion restriction was judged both on initial MR as well as on follow-up after 24 hours. Changes in lesion extension were assessed by two experienced neuroradiologists in consensus. Results: Extension of lesions with restricted diffusion at follow up MR was identical to the initial scan in 104/176 patients (59.1%) and increased in 66/176 (37.5%). The lesion size was decreased (meaning partial remission of the lesion) in 6/176 (3.4%); none of the lesions showed complete remission. All six patients with partial remission of DWI lesions underwent early i.v. thrombolysis and demonstrated excellent clinical outcome. In one case out of the six cases with remission of DWI lesions, the DWI lesions demonstrated a re-increase in size after the first follow up examination, seen at late follow-up. Conclusion: Our findings prove the existing assumption that diffusion restriction represents the infarct core, which may remain unchanged or increase in volume over time, indicating an accuracy of almost 97%. Partial resolution of DWI lesions is extremely rare and usually associated with early i.v. thrombolysis and favourable clinical outcome.