Published Online
on September 8, 2005

A more recent version of this article appeared on October 1, 2005

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Submitted on August 12, 2004
Revised on November 8, 2004
Accepted on November 16, 2004

The Existence and Evolution of Diffusion-Perfusion Mismatched Tissue in White and Gray Matter After Acute Stroke

Masatoshi Koga MD, PhD; David C. Reutens MD, FRACP; Peter Wright FRACP; Thanh Phan FRACP; Romesh Markus MBBS; Bruno Pedreira MD; Greg Fitt FRCR; Indra Lim BSc; and Geoffrey A. Donnan MD, FRACP^*

From the National Stroke Research Institute (M.K., D.C.R., P.W., T.P., R.M., B.P., I.L., G.A.D.) and the Department of Medicine (D.C.R., G.A.D.), University of Melbourne, Melbourne, Australia; and the Department of Radiology (G.F.), Austin Health, Melbourne, Australia.

^* To whom correspondence should be addressed. E-mail: gdonnan{at}unimelb.edu.au.

Background and Purpose--Although white matter is a potential target of acute stroke therapy, there is uncertainty about its relative resistance to ischemia and whether it is capable of mounting a penumbral response. To explore these issues further, we examined the differential effects of ischemia on gray and white matter using magnetic resonance (MR) perfusion-diffusion mismatch after acute stroke.

Methods--MR imaging studies were performed within 12 hours in patients with initial hemispheric ischemic stroke. "At-risk" tissue was defined as tissue with abnormal diffusion-weighted imaging/perfusion-weight imaging or infarction on follow-up image. Tissue was segmented using a probabilistic atlas generated from age-matched controls. The proportions of "at-risk" tissue, which was penumbral at the time of imaging, were compared between gray and white matter.

Results--Thirty-two patients had diffusion-perfusion mismatched penumbral tissue present in both gray and white matter compartments. Although the absolute mismatch volumes were greater in gray (median 42 cm³, interquartile range 18 to 70 cm³) than in white matter (39 cm³, 17 to 49 cm³; P<0.001), the proportion of "at-risk" tissue, which was penumbral at the time of imaging (median 3.7 hours, range 1.5 to 9.9 hours) was greater in white (69%, 49% to 86%) than gray matter (62%, 52% to 75%; P=0.026). However, the proportions spontaneously salvaged by 3 months were similar in both compartments.

Conclusions--These findings are consistent with white matter being able to mount an ischemic penumbral response in humans and being more resistant to cerebral ischemia than gray matter. They also raise the possibility that the therapeutic window is longer for white matter and may require alternative therapeutic strategies.

Key words: cerebral ischemia • diffusion-weighted imaging • perfusion-weighted imaging • white matter

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