False-negative diffusion-weighted MR findings in acute ischemic stroke

Abstract

Background and purpose: Lesions associated with acute stroke are often missed by diffusion-weighted imaging (DWI), suggesting that the sensitivity of this technique for detecting acute ischemic stroke may not be as high as initially thought. Our aim was to estimate the rate of false-negative DWI studies in patients with persistent neurologic deficit due to an ischemic stroke and to identify which stroke lesions are most likely to be missed by DWI.

Methods: We reviewed MR images obtained within 48 hours after stroke onset in 139 patients admitted for symptoms consistent with ischemic stroke in whom the deficit lasted more than 24 hours. Cases of negative initial DWI findings with an ischemic lesion visible on follow-up MR studies and a final diagnosis of arterial ischemic stroke were analyzed in terms of delay between onset of symptoms and initial DWI (MR latency), size and vascular distribution of the lesions, and relationship to findings in patients with positive initial DWI results.

Results: We found eight cases (5.8%) of false-negative initial DWI studies, of which four were positive on initial fluid-attenuated inversion recovery (FLAIR) imaging. Follow-up FLAIR/DWI showed a hyperintensity matching clinical presentation in all eight patients. The mean size of the lesion was 0.19 +/- 0.16 cm3. False-negative studies occurred more often in cases of stroke in the posterior (19%) than in the anterior (2%) circulation or when DWI was obtained within 24 hours after symptom onset. Of the six false-negative vertebrobasilar stroke lesions, five were located in the brain stem. In all, 31% of patients with vertebrobasilar ischemic stroke had a false-negative initial DWI study during the first 24 hours.

Conclusion: A false-negative DWI study is not uncommon during the first 24 hours of ischemic stroke. Vertebrobasilar stroke should therefore not be ruled out on the basis of early negative DWI, especially when symptoms persist and are suggestive of this diagnosis.

fig 1.

Case 4: 74-year-old man with sudden left paresthesia. A–D, Seven hours after the onset of symptoms, FLAIR image (10002/148/1, TI = 2200) (A) shows multiple diffuse areas of periventricular hyperintensity with a small hyperintensity in the right subthalamic area (arrowhead, A and C), whereas DWI (2825/92.6/1) (B) is considered normal. Forty-eight hours after symptom onset, FLAIR image remains unchanged (C) while DWI shows a clear hyperintensity in the right subthalamic area (D), matching clinical presentation.

fig 2.

Case 6: 61-year-old man with sudden right crural hemiparesis. A–D, Twenty-two hours after onset of symptoms, FLAIR image (10002/148/1, TI = 2200) (A) shows a small cortical hyperintensity in the left paracentral lobule (arrowhead, A and C), whereas DWI (2825/92.6/1) (B) fails to show a stroke lesion. Four days later, the lesion is still visible on FLAIR image (C), and DWI (D) displays a hyperintensity in the paracentral lobule, consistent with a recent stroke lesion and matching clinical presentation.

fig 3.

Case 7: 45-year-old man with sudden onset of vertigo, dysmetria, and somnolence. A–D, On initial MR examination, performed 5.5 hours after onset, MR angiogram (not shown) displayed a partially thrombosed dolichobasilar artery, which was responsible for the mass effect on the brain stem and heterogeneous signal anterior to the pons on FLAIR images. Initial FLAIR image (A) (10002/148/1, TI = 2200) and DWI (B) fail to reveal a stroke lesion. On follow-up MR examination, performed 15 hours after onset, FLAIR image shows a small right-sided brain stem hyperintensity (arrowhead) (C), which is more clearly visible on DWI (D).

fig 4.

Estimation of the probability of false-negative DWI findings by means of a logistic regression. The probability of false-negative DWI findings is plotted against time for stroke lesions located in the anterior (circles) and posterior (crosses) circulation. For vertebrobasilar stroke lesions (crosses), the probability of false-negative DWI findings diminishes when MR latency increases (𝛉 = 0.438, β = 0.127, P = .04). For lesions located in the anterior circulation (circles), this relation is no longer significant