Neurologists say MR, not CT, should be used for stroke, but practical questions arise

The American Academy of Neurology has weighed in heavily on the side of MR as opposed to noncontrast CT for the diagnosis of stroke patients in its newly published practice guidelines. However, the practice may not be feasible in the real world, according to a neuroradiology expert.

The American Academy of Neurology (AAN) issued new practice guidelines in the July 13 edition of its Neurology comparing all the scientific data through 2008 on diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) in acute ischemic stroke. A panel of experts in vascular neurology and radiology found DWI is established as useful and should be considered more useful than noncontrast CT for the diagnosis of acute ischemic stroke within 12 hours of symptom onset (2010;75:177-185).

The AAN guideline did not consider CT perfusion imaging, which is common in stroke settings. The panel couldn’t make a recommendation regarding CT perfusion because the data available so far comes from small case series. Though compelling, they don’t meet the standard of evidence the committee was looking for, said Dr. Steven Warach, coauthor of the recommendations and section chief of stroke diagnostics and therapeutics at the National Institute of Neurological Disorders and Stroke, a part of NIH.

“The routine practice in many hospital emergency departments is still to get a noncontrast CT to rule out stroke for all patients who present with a suspicion of acute ischemic stroke,” Warach said. “Based on the scientific evidence, that routine practice is not justifiable and cannot be considered the highest quality of care.”

A recommendation like this doesn’t take into account the extra cost of staffing for MR coverage 24/7 or the practicalities of treating a patient, said Dr. M.J. Bernadette Stallmeyer, an interventional neuroradiologist at Our Lady of Lourdes Regional Medical Center in Lafayette, LA, and a member of the Society of Interventional Radiology’s Catheter Lysis of Thromboembolic Stroke Course steering committee.

“I was at a big academic center before Our Lady Of Lourdes and, all things being equal, if the patient was in the ER, it was a lot easier to send them 30 feet down the hall for a CT scan than it was to send them to the next building for an MR,” she said.

And with stroke patients, every minute counts, she said. If a patient is getting an MR, the physician has to build in extra transport time and check for contraindications, a minimum 20-minute endeavor.

“Certainly another issue in the real world is many places don’t have more than one MR scanner and if a patient comes in during the day, which is when most stroke patients come in, what do you do? Do you pull your outpatient off the scanner?” Stallmeyer said. “Everyone will tell you, ‘yes.’ But in the real world, the next day you’ll be getting a call from some irate physician complaining their patient got thrown off the scanner for an acute stroke patient.”

The AAN maintains it is likely stroke patients are being deprived of needed thrombolytic therapy because of diagnostic uncertainty in the emergency departments when CT is used for diagnosis.

“We hope that guidelines coming out, such as from the American Heart Association and AAN, will help hospitals make that change,” Warach said. “That’s where this could have the greatest immediate impact.”

The American Heart Association (AHA) agrees with the AAN’s recommendations.

“No one would argue that MRI doesn’t have more diagnostic accuracy than a CT scan and that’s been clear,” said Dr. Ralph Sacco, president of AHA. “The latest studies reviewed in this article do clearly demonstrate the superiority of MRI for picking up a stroke in the earliest phases after symptoms start.”

However there is always the issue of resources. Some community hospitals don’t have an MRI scanner.

“We want to make sure that patients with acute stroke don’t get treatment delays waiting for an MRI,” he said. “If the hospital system is not set up to rapidly do MRIs on acute strokes, CT still has a very important role in the triage for acute stroke when time is of the essence.”

Of course, if a hospital doesn’t have an MRI machine or the patient has a contraindication, there is no choice but to use CT, Warach said. If they have both, though, it’s hard to defend not using MR for stroke based on the scientific data.

Stallmeyer disagrees.

“One of my concerns here is people will look at this study and say, ‘MR is more sensitive,’ and patients will get delayed in treatment,” Stallmeyer said. “Hopefully a lot of hospitals are going to look at this and decide it’s somewhat impractical to implement at their facility.”