MRI Better Than CT Scan for Diagnosising Stroke According to New Guidelines
New guideline from the American Academy of Neurology (AAN) state doctors should use a diffusion MRI scan to diagnose stroke instead of a CT scan. The new guideline is published in the July 13, 2010, issue of Neurology.
Stroke is the third leading cause of death and the leading cause of permanent disability in the United States. The majority of strokes are ischemic, caused by lack of blood flow in the brain, usually due to a blockage or a blood clot. The window for treatment to reverse the damage from an ischemic stroke is measured in hours.
CT scans are a specialized kind of X-ray taken of the brain while MRI uses magnets and radio waves that show clearer images of brain tissue. Diffusion MRI measures molecular water motion in the tissue, showing where water diffusion is restricted and therefore brain damage has occurred.
Peter Schellinger, MD and colleagues analyzed the literature from 1966 to January 2008 to address the diagnostic and prognostic value of MRI and CT scans in the diagnosis of strokes.
In one large study, among others, that was reviewed for the guideline, stroke was accurately detected 83% of the time by MRI versus 26% of the time by CT.
The AAN guideline states diffusion MRI should be considered more useful than a CT scan for diagnosing acute ischemic stroke within 12 hours of a person’s first stroke symptom.
The authors noted the sensitivity of MRI for the diagnosis of ischemic stroke in a general sample of patients with possible acute stroke is not perfect. On the basis of Class II and III evidence, baseline DWI volumes probably predict baseline stroke severity in anterior territory stroke (Level B) but possibly do not in vertebrobasilar artery territory stroke (Level C).
Schellinger states studies have proven the importance of using MRI in emergency rooms but says doubts still exist surrounding the use of stroke MRI scans in clinical settings. “This guideline gives doctors clear direction in using MRI first, ultimately helping people get an acute stroke diagnosis and treatment faster. However, one situation in which CT may still be used first is when a person needs an emergency injection of drug therapy (also known as intravenous thrombolytic therapy) to break up blood clots, if MRI is not immediately available, to avoid delays in starting this treatment. MRI can be added later if more information is needed. Otherwise MRI should be used first.”
evidence-based guideline: the role of diffusion and perfusion mri for the diagnosis of acute ischemic stroke: report of the therapeutics and technology assessment subcommittee of the american academy of neurology. - Schellinger, P.D., MD, PhD, Bryan, R.N., MD, PhD, Caplan, L.R., Detre, J.A., Edelman, R.R., Jaigobin, C., Kidwell, C.S., Mohr, J.P., Sloan, M., MD, MS, Sorensen, A.G., Warach, S., MD, PhD.; Neurology July 2010 Volume 75 Issue 2 Pages: 177-185