MRI Versus CT for Detection of Acute Vascular Lesions in Patients Presenting With Stroke Symptoms
Graeme J. Hankey MD, FRCP, FRACP Section Editor:
We compared the accuracy of diffusion-weighted MRI (DWI) and CT for the early diagnosis of ischemic stroke, and we estimated the accuracy of MRI for the early diagnosis of hemorrhagic stroke.
We searched index records that appeared in MEDLINE and EMBASE (January 1995 to March 2009). We hand searched the proceedings of the International Stroke Conference and the European Stroke Conference (1995 to 2004). We also searched websites of relevant professional bodies and bibliographies of relevant studies for additional references.
We selected studies that either compared DWI and CT in the same patients for detection of ischemic stroke or examined the utility of MRI for detection of hemorrhagic stroke, had imaging performed within 12 hours of stroke onset, and presented sufficient data to allow construction of 2×2 contingency tables.
Data Collection and Analysis
Four authors independently assessed the methodological quality of each included study using the QUality Assessment of Diagnostic Accuracy Studies (QUADAS) tool.
Three authors independently extracted data on study characteristics and measures of accuracy. We assessed data on ischemic stroke using random-effects and fixed-effect meta-analyses.
Eight studies with a total of 308 participants met our inclusion criteria. Seven studies contributed to the assessment of ischemic stroke and 2 studies to the assessment of hemorrhagic stroke. The clinical spectrum of patients was relatively narrow in all studies, sample sizes were small, there was substantial incorporation bias, and blinding procedures were often incomplete. The Figure shows the forest plots of the sensitivity and specificity estimates for DWI and CT for the 7 studies that assessed patients with ischemic stroke. Among the patients subsequently confirmed to have acute ischemic stroke (161 of 226), the summary estimates for DWI were: sensitivity 0.99 (95% CI, 0.23 to 1.00) and specificity 0.92 (95% CI, 0.83 to 0.97). The summary estimates for CT were: sensitivity 0.39 (95% CI, 0.16 to 0.69) and specificity 1.00 (95% CI, 0.94 to 1.00). The 2 studies on hemorrhagic stroke reported high estimates for diffusion-weighted and gradient-echo sequences but had inconsistent reference standards. We did not calculate overall estimates for these 2 studies. We were not able to assess practicality or cost-effectiveness.
We identified only a limited number of relevant studies. The overall methodological quality of these studies was poor. Our results suggest that DWI is more sensitive than CT, but not more specific, for the early detection of ischemic stroke in highly selected patient populations. The apparently better estimates of diagnostic accuracy of MRI than CT were obtained from patients with a high pretest probability of stroke and therefore may not apply when MRI is used in the broad range of unselected patients presenting with suspected acute stroke usually seen in routine clinical practice. Our data do not allow any comments to be made on the merits of MRI for the early detection of hemorrhagic stroke.
Applicability of Findings to Clinical Practice
There is some evidence that MRI is more accurate than CT for the detection of mild ischemic strokes. However, the use of MRI in the management of acute patients needs to take into consideration practicality and cost-effectiveness. In many countries, CT is quicker to perform, inexpensive, applicable to a higher proportion of acutely ill stroke patients, and more readily available in most emergency care settings. On the other hand, MRI is not immediately available in many hospitals and is more expensive, contraindicated for patients who are medically unstable or have pacemakers or metal implants, and can be unpleasant or difficult to tolerate, especially for patients with more severe strokes.
Further well-designed studies without methodological biases, in more representative patient samples, which assess practicality and costs are now needed to determine which patients should undergo MRI and which should undergo CT in suspected acute stroke. In particular, additional studies are needed to provide clear evidence that MRI can be used as the imaging modality of first choice for patients with suspected acute stroke in routine practice, and that patients without evidence of acute intracerebral hemorrhage on MRI really do not have acute intracranial bleeding (and hence can be safely considered for thrombolytic treatments).
Note: The full-text review is available in The Cochrane Library: Brazzelli M, Sandercock PAG, Chappell FM, Celani MG, Righetti E, Arestis N, Wardlaw JM, Deeks JJ. Magnetic resonance imaging versus computed tomography for detection of acute vascular lesions in patients presenting with stroke symptoms. Cochrane Database of Systematic Reviews 2009, Issue 4.
Sources of Funding
The Chief Scientist Office of the Scottish Government Health Directorates supports M.B. and F.M.C. with a research fellowship. J.M.W. is partly supported by the Scottish Funding Council and Chief Scientist Office through the SINAPSE collaboration (Scottish Imaging Network: A Platform for Scientific Excellence; www.sinapse.ac.uk).
- Received September 23, 2009.
- Accepted September 28, 2009.