ARTICLE IN BRIEF
Investigators report that when FLAIR is negative and diffusion-weighted imaging (DWI) is positive, there is a high likelihood that stroke onset has occurred within three hours of testing. When FLAIR is positive and DWI is negative, the stroke most likely occurred more than six hours previously.
SAN DIEGO—The onset of acute ischemic stroke can be accurately estimated through the use of fluid-attenuated inversion recovery (FLAIR), a new application of a standard MRI format, Japanese investigators reported here at the International Stroke Conference, sponsored by the American Stroke Association in February.
With FLAIR, MRI shows a focal hyperintense signal and the signal gains intensity over time. When FLAIR is negative and diffusion-weighted imaging (DWI) is positive, there is a high likelihood that stroke onset has occurred within three hours of testing. When FLAIR is positive and DWI is negative, the stroke most likely occurred more than six hours previously, Junya Aoki, MD, of the department of stroke medicine at the Kawasaki Medical School in Kurashiki, Okayama in Japan, reported.
Figure. DR. JUNYA AO...Image Tools
Since the thrombolytic, tissue plasminogen activator (tPA), is approved for use within three hours of symptom-onset, determining stroke onset is critical, he pointed out.
STUDY PROTOCOLS, FINDINGS
Dr. Aoki and colleagues combined FLAIR and DWI to estimate onset in 336 consecutive patients enrolled between April 2003 and July 2008 with a clearly defined onset of symptoms of less than 24 hours duration.
Patients were divided into three groups: symptom onset before three hours; symptom onset between three and six hours; and those arriving from six to 24 hours after onset. All patients had had DWI and FLAIR MRI. Dr. Aoki's team measured the time to DWI- and FLAIR-positivity.
Sixty studies showed small-vessel disease (15 percent); 33, large-vessel disease (9 percent);155, cardioembolic disease (40 percent); and “other” or “undetermined” cause of stroke in 141 studies (36 percent).
Eighty-six percent of 162 MRIs before 3.0 hours of onset were DWI-positive, as were 95 percent of 109 studies between three and six hours of symptom onset, and almost all of 118 studies at six to 24 hours of symptom onset (p<0.01).
FLAIR-positivity was present in 23 of 162 MRIs (14 percent) at 0 to three hours of onset; 50 of 109 MRI (46 percent) at three to six hours; and 104 of 118 MRI (88 percent) were FLAIR-positive between six to 24 hours of onset (p<0.01).
When FLAIR findings were negative, either with or without DWI-positivity, the probability of onset to image time within 0 to three hours was 66 percent, occurring in 139 of 212 MRIs, and FLAIR was negative at 0 and six hours of onset in 93 percent (of 212 MRIs).
Moreover, 93 percent of patients who were FLAIR-negative had large infarcts (greater than 15 mm in size) in the supratentorial region and symptoms that were less than 1.5 hours in duration.
“This is just a new way to look at MRI findings,” Dr. Aoki commented. “If the technique is confirmed in larger studies, it can tell us just how far along the ischemic scale the stroke is.”
Conference moderator Arthur Pancioli, MD, professor and vice chairman of emergency medicine at the University of Cincinnati, cautioned that the technique “is not ready for prime-time yet, but the DWI mismatch may push treatment decision in a direction. It doesn't give you a ‘yes’ or a ‘no’ [for thrombolytic therapy], and it shouldn't be used in isolation, but it does suggest a treatment approach.”
Ralph L. Sacco, MD, professor of neurology and chairman of the department of neurology at the University of Miami Miller School of Medicine, said: “If we could use imaging to more precisely time the onset of ischemic stroke, thrombolytic therapy might be used in more patients who are in fact eligible.”
DWI positivity occurs almost right away and provides a great acute picture of ischemia, with 86 percent positive between 0 to 3 hours of onset, Dr. Sacco said. FLAIR positivity takes longer to show up on imaging, it lags behind, such that only 14 percent are positive before three hours and 40 percent are FLAIR-positive in three to six hours after symptom-onset.
Dr. Sacco pointed out that “25- to 30-percent of strokes occur either on or before awakening, making it difficult to assess symptom duration. In addition, aphasia makes getting an accurate history and assessment possible. While I wouldn't use this technique by itself to assess stroke onset, anything we can do to pinpoint onset helps with management.”