Penumbral salvage

Of great relevance to the potential use of multimodal MRI in extending the time window for thrombolysis have been the observations that perfusion-diffusion mismatch was present for up to 24 h after symptom onset (Table 3.2). Whilst the presence and volume of mismatch decreases over time, at least 50% of patients still have significant tissue at risk 24 h after stroke onset (Fig. 3.4). This correlates well with positron emission tomography studies that show penumbral tissue persists up to 48 h after symptom onset, and that spontaneous survival of this tissue results in clinical improvement (Markus et al. 2003 Read et al. 2000). There is mounting evidence that the time window for salvage of the penumbra is well beyond 3 h and multimodal MRI can identify such patients. 

Fig. 3.12. Patient (top) with acute perfusion-diffusion mismatch and an acute blood glucose level of 12.3 mmol/1. Despite major reperfusion, much of the at-risk mismatch tissue progressed to infarction. In contrast, the bottom patient with an acute blood glucose of 5.3 mmol/1 and a large area of mismatch, had major penumbral (mismatch) salvage on follow-up imaging...

Penumbral assessment is critical to identify whether reperfusion can lead to tissue salvage and improved outcome... 

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