INITIAL ADC PREDICTS THE OCCURRENCE AND SEVERITY OF HEMORRHAGIC TRANSFORMATION IN EXPERIMENTAL STROKE
BACKGROUND: We recently reported that early lower ADC values are associated with an increased hemorrhagic transformation (HT) risk in ischemic stroke patients. The ability to predict the individual HT risk could be of considerable importance, particularly among patients candidates for thrombolysis. In this study we analyzed the relationship between initial ADC value and secondary HT in an experimental embolic model. We hypothesized that 1) initial lower ADC values would be found in lesions destined to HT and 2) the degree of the initial ADC decrease could predict the severity of HT. METHODS: Embolic strokes were created in 14 rabbits by injection of heterologous thrombi. Thrombolysis was initiated 1 hour later. DWI was performed at 0.5 h after embolization and repeated at 1.75, 3 and 5 h. We applied ADC histogram analysis to the entire ischemic hemisphere. The severity of ADC reduction was expressed as cumulative percentage of pixels below the cut-off value of 550 X 10-6 mm2/sec. The brains were then histologically examined for HT 6h after embolization. RESULTS: HT was present in 10/14 brains (4 confluent, 6 petechial). As early as 30 min after embolization ADC values were lower in HT destined lesions. There was a significant correlation between ADC reduction and subsequent HT type (r2 = 0.734, p<0.001). The percentage of pixels under the cut-off ADC value was 10 ± 6% in hemispheres without HT, 17. ± 4% in those with petechial HT and 32 ± 6% in those with confluent HT. The number of pixels with severely reduced ADCs progressively increased over time in the confluent HT destined animals, but increased only slightly in the other groups. Further, the confluent HT destined group experienced a rapid ADC increase at 4 h, immediately before hemorrhage. CONCLUSION: We show that initial lower ADC values are associated with an increased risk of secondary HT. Moreover, the degree of ADC reduction correlated with the severity of HT. These findings are evident as early as 30 min after stroke onset. These results suggest that DWI may be helpful in predicting both HT occurrence and severity. This could have substantial implications for the use of MRI in acute stroke management.