Severe ADC Decreases Do Not Predict Irreversible Tissue Damage In Acute Human Stroke
Animal experiments indicated that the severity of the apparent diffusion coefficient (ADC) decrease might serve as indicator of tissue viability. We followed the temporal and spatial development of ADC values after acute human stroke to test this hypothesis. Methods We enrolled 10 consecutive patients with acute ischemic stroke during the last 4 hours. Multimodal MRI (DWI, PWI, MRA, T2w) was performed within 4 h after symptom onset and at days 1 and 7. NIH-stroke-scale was assessed. The mean ADC value for the not affected hemisphere served as reference for the relative ADC-reduction of <50%, 50–60%, 60–70% and 70–80%. Volume of these regions was determined for each imaging timepoint using a threshold function. In a second approach we transferred the previously obtained ADC-theshold areas of day 0 to day 1 and 7 for detection of ADC-changes to determine ADC-changes in reference to the initial ADC. Results In 4 patients with clear neurological improvement at day 1 we found a mean reduction of the ADC- lesion“-volume to 56%. The ADC-threshold-volume of 70–80% increased by 38.9% and areas below 70% decreased by between 56.7% (<50% ADC) and 23.5% (60–70%). Some areas with severe ADC decreases showed partial pseudo-normalization (lesion in T2w / normal ADC values, n=3) and normalization (normal T2w / normal ADC values, n=1) at day 1 and 7. Patients without change or a minor clinical improvement showed a mean increase of the ADC-lesion size at day 1 by 83.6 %. In these patients volume with ADC<50% increased by 275.7% while 70–80%-threshold-volume decreased to 52.2%. ADC values within the initial ADC-threshold-volumes differed significantly at day 1 (n=7), reflecting a different dynamics dependent on the initial ADC. Conclusion Ischemic tissue with severe ADC decreases may recover completely. However, areas with severe ADC decreases usually transform towards a less severe decrease in patients with good neurological recovery. In patients without clinical improvement the area of severe diffusion impairment spreads to adjacent areas.