Abstract T P35: Baseline Diffusion Weighted Imaging Lesion Volume Predicts Disappearance of Infarct on Fluid Attenuated Inverse Recovery Sequences Within 30 Days of TIA/Minor Stroke

Abstract

Introduction: Evidence of infarction on MRI is predictive of early stroke recurrence after TIA/minor stroke. It has recently been reported that diffusion-weighted imaging (DWI) changes are not associated with evidence of infarction on Fluid Attenuated Inverse Recovery (FLAIR) sequences 90 days later in 30% of patients. We completed a serial MRI study to determine the time course of infarct resolution. We tested the hypothesis that acute DWI lesion volume predicts infarct disappearance by 30 days. Methods: Acute TIA/minor stroke patients (NIHSS≤3) were prospectively imaged at baseline, 7 and 30 days after symptom onset. Lesion volumes were measured planimetrically by a blinded rater at each time point on DWI and FLAIR sequences. Mean and relative (to contralateral tissue) Apparent Diffusion Coefficient ((r)ADC) values were also calculated. Results: Acute DWI lesions were found in 94/172 patients. Median time between symptom onset and baseline MRI was 20.9(19.3) h. DWI volume decreased from baseline (1.51 ml (4.36)) at 7 days (1.13 ml (2.96), P =0.001) and at 30 days (0.40 ml (0.97), P <0.0001). DWI lesions at 7 days pseudo-normalized (infarct visible on FLAIR) in 3.4% and resolved without evidence of infarction in 8% of patients. Seventy-seven (82%) patients had persistent lesions on FLAIR at 30 days (FLAIR+). Baseline NIHSS scores were similar between FLAIR+ (1.40±1.21) and FLAIR– patients (1.18±1.19, P =0.64). Baseline rADC was similar in FLAIR+ (0.84(0.17)) and FLAIR– patients (0.89(0.21), P =0.155). Baseline DWI volumes were larger in FLAIR+ (2.08 ml (6.9)) than FLAIR– patients (0.69 ml (0.95), P =0.007). ROC analysis indicated that a baseline DWI volume <2.04 ml predicted absence of FLAIR lesion at 30 days with a specificity of 100% and sensitivity of 50.6%. Good functional outcome (modified Rankin Score ≤2) at 90 days was similar in FLAIR+ (54/62, 87%) and FLAIR– patients (12/12, 100%, P =0.339). Conclusion: Acute DWI lesions are transient and not always associated with visible infarction on FLAIR, even as early as 7 days after symptom onset. Delaying MRI results in a failure to demonstrate evidence of infarction in the majority of patients, particularly those with DWI lesion volumes below 2 ml.