Diffusion-weighted MRI highly sensitive, specific vs. CT in acute ischemic stroke [Classics Series]

1. Among patients with acute neurologic deficits presenting within six hours of symptoms onset, diffusion-weight magnetic resonance imaging (DWI) was shown to be significantly more sensitive and specific for the diagnosis of ischemic stroke than non-contrast computed tomography (NCCT).

Original Date of Publication: September 2002

Study Rundown: Thrombolysis is a widely accepted method for the management of acute ischemic stroke, with the goal of opening blocked vessels to restore blood flow to at-risk brain tissue. One of the primary requirements for the administration of intravenous thrombolytic drugs is the exclusion of intracranial hemorrhage as an explanation for a patient’s acute neurologic symptoms. NCCT is the method of choice for fast and accurate detection of intracranial bleeding. Its performance in the detection of early acute ischemic stroke, however, is generally poor, with a reported sensitivity of approximately 40-60% within the first six hours from symptom onset. DWI is an attractive alternative magnetic resonance imaging sequence that allows for the high-resolution depiction of areas of reduced blood flow in the brain much earlier than is generally possible with NCCT. In this comparative trial, patients presenting to the emergency department with symptoms concerning for acute ischemic stroke were assigned to undergo both NCCT and DWI in a randomized order. For each patient and for each imaging study, the presence or absence of stroke was determined alongside other parameters to determine the diagnostic utility of both methods. Imaging was obtained a mean of 180 and 189 minutes after symptoms onset, for CT and DWI respectively. The results revealed that DWI is significantly more sensitive and specific than NCCT for the diagnosis of acute ischemic stroke. Additionally, researchers found that interreader reliability differed greatly between the two imaging modalities, with almost perfect agreement when using DWI and only modest agreement when using NCCT, suggesting that DWI is less susceptible to interpretive errors than NCCT. This was the first trial to provide a randomized, head-to-head comparison of the two diagnostic imaging methods for stroke, and it served to significantly strengthen the evidence base in support of DWI that had been built in prior trials.

Click to read the study in Stroke

In-Depth [randomized controlled trial]: In this study, 54 consecutive patients presenting to a single academic medical center emergency department with symptoms concerning for acute ischemic stroke were prospectively enrolled to undergo both NCCT and DWI in a randomized order. Primary inclusion criteria included presentation for evaluation within six hours of symptom onset and a National Institute of Health Stroke Scale (NIHSS) greater than three, with higher values indicating greater stroke severity. All images were read by expert neuroradiologists and stroke neurologists and categorized according to the presence or absence of ischemic stroke, the vascular distribution of the stroke, the stroke subtype (none, lacunar, territorial, or hemodynamic), and other parameters. Readers were blinded to the specific details of each case.

Overall, NCCT demonstrated a sensitivity and specificity of 61% and 65%, respectively, for the diagnosis of acute ischemic stroke, and interreader reliability was moderate. DWI significantly outperformed NCCT, with a sensitivity and specificity of 91% and 95%, respectively, and almost perfect interreader reliability. Notably, no acute lacunar infarcts were visible on NCCT while four were diagnosed using DWI, suggesting that DWI may also be superior for the identification of specific stroke subtypes. All infarcts in this study were within the middle cerebral artery distribution, and the mean NIHSS of enrolled patients was 11 (range 3-27). The mean time from initial evaluation to the receipt of diagnostic imaging was comparable for both modalities (NCCT=180 minutes, DWI=189 minutes).

Image: PD

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