DWI Reversal Is Associated with Small Infarct Volume in Patients with TIA and Minor Stroke

BACKGROUND AND PURPOSE:More than half of patients with TIA/minor stroke have ischemic lesions on early DWI, which represent irreversibly damaged tissue. The presence and volume of DWI lesions predict early deterioration in this population. We aimed to study the rate and implications of DWI reversal in patients with TIA/minor stroke.MATERIALS AND METHODS:Patients with TIA/minor stroke were prospectively enrolled and imaged within 24 hours of onset. Patients were followed for 3 months with repeat MR imaging either at day 30 or 90. Baseline DWI/PWI and follow-up FLAIR final infarct volumes were measured.RESULTS:Of 418 patients included, 55.5% had DWI and 37% had PWI (time-to-peak of the impulse response ≥2 seconds'' delay) lesions at baseline. The median time from symptom onset to baseline and follow-up imaging was 13.4 (interquartile range, 12.7) and 78.73 hours (interquartile range, 60.2), respectively. DWI reversal occurred in 5.7% of patients. The median DWI lesion volume was significantly smaller in those with reversal (0.26 mL, interquartile range = 0.58 mL) compared with those without (1.29 mL, interquartile range = 3.6 mL, P = .002); 72.7% of DWI reversal occurred in cortically based lesions. Concurrent tissue hypoperfusion (time-to-peak of the impulse response ≥2 seconds) was seen in 36.4% of those with DWI reversal versus 62.4% without (P = .08). DWI reversal occurred in 3.3% of patients with penumbral patterns (time-to-peak of the impulse response ≥6 seconds − DWI) > 0 and in 6.8% of those without penumbral patterns (P = .3). The severity of hypoperfusion, defined as greater prolongation of time-to-peak of the impulse response (≥2, ≥4, ≥6, ≥8 seconds), did not affect the likelihood of DWI reversal (linear trend, P = .147). No patient with DWI reversal had an mRS score of ≥2 at 90 days versus 18.2% of those without reversal (P = .02).CONCLUSIONS:DWI reversal is uncommon in patients with TIA/minor stroke and is more likely to occur in those with smaller baseline lesions. DWI reversal should not have a significant effect on the accuracy of penumbra definition.

Multiple studies have shown that more than half of patients with TIA/minor stroke have evidence of acute ischemic tissue injury on early DWI.^1–3 The presence and the volume of DWI lesions carry a negative prognostic value in this population.^4–6 The DWI-restricted lesions are thought to represent the irreversibly damaged ischemic core.⁷ This premise was recently brought into question by studies suggesting a high rate of DWI lesion reversal in patients with stroke who had undergone thrombolytic therapy.^8,9 A recent systematic review of the published literature on DWI hyperintense tissue outcome reported variable rates of DWI reversal (0%–83%), with a mean reversal rate of 24% in patients with ischemic stroke.¹⁰ In most patients, the size of the acute infarct correlated with both the final infarct volume on follow-up T2/FLAIR imaging and the clinical outcome.^11,12 Most previous work on DWI reversal has been undertaken in patients with moderate-to-severe strokes. Patients with TIA or minor stroke have smaller volumes of ischemia and potentially may have a higher likelihood of reversal. Previous imaging studies have reported reversal of the DWI signal in patients with TIA, but these were relatively small series, without scheduled follow-up imaging and DWI reversal was not studied systematically.^13–15Potentially salvageable tissue known as the “ischemic penumbra” represents viable tissue at risk of infarct that has not yet infarcted.¹⁶ Various methods are used to define the ischemic penumbra on MR imaging, including the mismatch between perfusion and diffusion¹⁷ or clinical-diffusion mismatch.¹⁸ All of these definitions rely on DWI lesions representing irreversibly damaged ischemic core.DWI reversibility, therefore, has implications in both accurate assessment of ischemic core and penumbra and outcome prediction.We, therefore, aimed to determine the rate and characteristics of DWI reversal in 2 large prospective imaging cohorts of patients with TIA/minor stroke. We studied the correlation among the DWI lesion volume, lesion location, concurrent baseline hypoperfusion on perfusion-weighted imaging, the severity of the perfusion deficit, and the reversal of DWI signal on follow-up FLAIR/T2 imaging in this population.