CARLSBAD, Calif. – Time will tell if current practice for stroke diagnosis will change following issuance of a new guideline from the American Academy of Neurology that recommends diffusion weighted MRI for diagnosing acute ischemic stroke in patients presenting within 12 hours of symptom onset.
David S. Liebeskind
“Not a lot of people are using MRI,” Dr. A. Greg Sorensen, a professor in radiology at Harvard Medical School, Boston, and member of the guideline subcommittee, said at the annual meeting of the Society of NeuroInterventional Surgery. An informal poll he conducted at the meeting of about 300 physicians on the front line of stroke treatment indicated that 24% were using diffusion-weighted MR imaging (DWI) for patients who present within 4.5 hours of symptom onset and 38% were using it after 4.5 hours of symptom onset.
The guideline was issued by a panel of neurologists, neuroradiologists, and radiologists who performed a literature search in which they identified relevant abstracts published from 1966 through January 2008 that were related to the diagnostic and prognostic value of DWI and perfusion-weighted imaging (PWI).
The panelists concluded that there was strong (level A) evidence that DWI should be considered superior to non–contrast CT for the diagnosis of acute ischemic stroke in patients presenting within 12 hours of symptom onset, with an estimated sensitivity of 80%-90%. However, there was insufficient evidence to support or refute the value of PWI for acute ischemic stroke diagnosis.
They reported that although non–contrast CT is the current diagnostic standard for acute stroke, it has limited sensitivity, especially in the initial hours (Neurology 2010;75:177-85).
In addition, they found level B evidence to support the use of DWI volume in predicting baseline clinical stroke severity and final lesion volume in anterior-circulation strokes. Baseline PWI volume also was found to be useful in predicting baseline clinical stroke severity, although the evidence for that was weak (level C).
Weak evidence was available to support the use of DWI volume in predicting clinical outcome, as measured by the National Institutes of Health Stroke Scale and Barthel Index for daily functioning, and the panelists determined that baseline DWI was not useful in predicting baseline NIHSS score in posterior-circulation strokes.
“This information is not a revelation. We have known for some time that DWI is superior to non–contrast CT for the diagnosis of ischemic stroke,” commented Dr. Ansaar T. Rai in an interview. He had spoken at the meeting on the use of CT perfusion for acute stroke imaging. “Non–contrast CT of the brain has been around since the early 1970s – it’s an old technology. But this study did not compare DWI/PWI with CT perfusion. I think a more appropriate issue is to identify the best advanced imaging study that can be efficiently used to diagnose acute ischemic stroke and triage stroke patients.
“If treatment for ischemic stroke is going to gain ground from its current dismal state, in which only 1%-2% of strokes are being treated, then stroke treatment must be disseminated widely, not just in big centers,” said Dr. Rai, director of interventional neuroradiology at West Virginia University Health Sciences Center, Morgantown.
He pointed out that CT is three times more available than MRI nationwide. In addition, CT scans are generally available 24 hours a day, 7 days a week in almost every hospital, unlike MRIs which are generally not available after 5 p.m. or require that a technician to be called in, a situation that is expensive and wastes valuable time.
For these reasons, Dr. Rai said he advocates the use of a stroke CT protocol – including a non–contrast CT, CT angiogram, and CT perfusion – as the diagnostic test of choice for suspected acute ischemic stroke. “The whole test takes 30 seconds to perform and within 5 minutes we have the information of exactly where the clot is and what part of the brain is affected.”
He put advanced CT imaging on a par with DWI/PWI for diagnosis of stroke and triaging patients for treatment, especially endovascular therapy. “At our institution, based on our experience, we are going to continue to [use] the ‘stroke CT’ for triage of acute stroke patients.”
At the University of California, Los Angeles, Stroke Center, a major clinical and research center, Dr. David S. Liebeskind, the director of stroke imaging, has state-of-the-art imaging tools readily available. Like Dr. Rai, he agreed with the AAN’s findings that DWI is preferred over non–contrast CT, but also said that the more appropriate comparison would have been DWI/PWI to equivalent CT techniques including perfusion imaging.