reversal or shrinkage of early ischemic injury demonstrated by diffusion - weighted mri ( dwi ) is clinically uncommon , even after early thrombolytic reperfusion therapy [ 1 , 2 , 3 , 4 , 5 ] . the dwi - defined early ischemic injury physiologically represents an irreversible ischemic core and a potentially reversible surrounding area . recently , we experienced the case of a nearly complete reversal of a hyper - acute large ischemic injury on dwi . a 67-year - old previously healthy woman suddenly developed stupor and left hemiparesis , and arrived at our hospital 45 min after symptom onset . upon presentation , the national institute of heath stroke scale ( nihss ) score was 12 points , and baseline brain ct was perfectly normal . dwi ( single - shot echo - planar , b = 1,000 s / mm , tr = 8,000 ms , te = 80.8 ms , slice thickness = 6 mm ) performed on the 1.5 t mr scanner ( signa 1.5 t ; general electric , usa ) imaged 78 min after onset demonstrated a large high - signal intensity area in the right hemisphere with a dwi - aspects ( albert stroke program early computed tomography score ) of 5 points , and mr angiography ( mra ) showed an occlusion of the right middle cerebral artery trunk ( fig . perfusion mri was not performed . on the apparent diffusion coefficient ( adc ) map , the mean ratio of the adc value of ischemic to unaffected hemispheres was 0.86 ( range 0.780.92 ) within the five dwi - aspects - negative ischemic areas , and the mean adc ratio was 0.99 ( 0.981.00 ) within the remaining five dwi - aspects - positive non - ischemic areas . accordingly , the patient received intravenous thrombolysis with tissue plasminogen activator at a lower dose of 0.6 mg / kg alteplase on the japanese guideline . the state of health of the patient was improved , and the nihss score 24 h later was of 0 points with minor left - sided numbness . the second dwi ( b = 1,000 s / mm , tr = 5,000 ms , te = 55 ms , slice thickness = 5 mm ) performed on the 3 t mr scanner ( achieva 3 t ; phillips , the netherlands ) imaged 30 h later showed a nearly complete reversal of the large high - signal intensity area demonstrated by initial dwi , and there were very small high - signal intensity spots at the cortical surface ( fig . the mean adc ratio was 1.00 ( 0.991.02 ) within the five areas of the initial dwi - aspects - negative ischemic territory and 0.97 ( 0.881.01 ) within the remaining five initial dwi - aspects - positive non - ischemic areas . the systemic work - up including cardiac and hematological profiles revealed the presence of patent foramen ovale and venous thrombus in her leg , suggesting a paradoxical brain embolism as an etiological mechanism for this stroke . the patient received anticoagulation with warfarin for secondary prevention . at 3 months , clinical outcome was a modified rankin scale score of 0 , and only minor final infarction was localized at the cortical surface on the fluid - attenuated inversion recovery ( flair ) image ( tr = 11,000 ms , te = 125 ms , slice thickness = 5 mm ) ( fig . in this patient , after early thrombolytic reperfusion therapy , the initial dwi - defined large hemispheric ischemic injury showed nearly complete reversal on the follow - up dwi , and very small thrombus - fragmented ischemic areas after complete vessel recanalization were localized at the cortical surface of the terminal zone of the initially occluded middle cerebral artery . a limitation of this case study was the subtle low imaging quality of the hyper - acute dwi , due probably to body motion in acute confusion and to the simple acute stroke mri protocol to minimize scan time in the emergency setting . to assess the ischemic injury more accurately , an advanced 3-tesla mr scanner was utilized at the later scans , although a difference of mri scanner between hyper - acute and the later phases may affect the precise comparison of ischemic injury . since a recent study reported that standard 1.5-tesla mr scanner , rather than 3-tesla mr scanner , provided a lower false - positive and false - negative rate for detecting dwi - defined early ischemic injury within 6 h after stroke , hyper - acute dwi imaged on a 1.5-tesla mr scanner might have been an optimal selection as acute stroke mri protocol in this case study . the latest meta - analysis reported that the rate of complete or partial reversal of ischemic dwi lesions was surprisingly high by an average of 24% , varying from 0 to 83% probably due to the variable definition of the dwi reversibility . time of acute dwi scan from stroke onset , as well as time and type of sub - acute to chronic scans such as dwi , t2- or flair image to assess the final infarct area , may affect frequency and size of the dwi reversibility . true reversal of a dwi abnormality , defined by eliminating the false - positive reversal effect , was uncommon at only 7% in patients receiving early intravenous thrombolysis . in this patient , nearly complete reversal of the initial dwi - defined large ischemic injury persisted on the 3-month follow - up flair image . a previous study quantitatively measured severity or depth of ischemic injury by adc values to define the threshold of the infarct process . in the dwi - defined ischemic area , an adc value below 80% of the unaffected area and no reperfusion were the factors of dwi irreversibility , but the exact threshold of the adc value could not be determined . in this patient , an adc decline with an average of 86% in the dwi - defined ischemic area and early successful reperfusion may largely account for complete and sustained reversal , associated with a favorable clinical outcome . in conclusion , hyper - acute large ischemic injury demonstrated by dwi may very rarely represent a nearly perfect reversible area , and it may be a therapeutic target .
reversal of early ischemic injury on diffusion - weighted mri ( dwi ) occurs rarely . in a stroke patient who abruptly developed stupor and left hemiparesis , 
 dwi scanned 78 min after onset demonstrated a large ischemic injury in the right hemisphere with a dwi - aspects ( albert stroke program early computed tomography score ) of 5 points , although baseline brain ct was perfectly normal . 
 mr angiography ( mra ) showed an occlusion of the right middle cerebral artery trunk , and the patient received intravenous thrombolysis 105 min after onset . a second mra 30 h later showed complete vessel recanalization , and dwi demonstrated a perfect reversal of the initial large ischemic injury , associated with very small thrombus - fragmented cortical surface infarctions . 
 outcome at 3 months was a modified rankin scale score of 0 , and the fluid - attenuated inversion recovery image showed only a small final infarction at the cortical surface . 
 hyper - acute dwi - defined large ischemic injury may very rarely represent a nearly perfect reversible area , and it may be a therapeutic target .