Thin section magnetic resonance diffusion-weighted imaging in the detection of acute infratentorial stroke.

Introduction Magnetic resonance diffusion-weighted imaging (DWI) is the most accurate technique available for demonstrating acute infarction; however, false-negative DWI is higher in the infratentorium due to the limited spatial resolution with conventional 5 mm DWI. The aim of this study was to compare 5 mm DWI with 3 mm DWI in the detection of acute infratentorial infarction. Methods A 3 mm DWI sequence of the infratentorium was incorporated into the conventional MRI stroke protocol for the evaluation of patients with vertebrobasilar stroke-like deficits. The 5 mm and 3 mm DWI sequences were assessed by two neuroradiologists who were blinded to the clinical findings. Sensitivity and specificity analysis was then performed against the final clinical diagnosis. Results The sensitivity for detection of infratentorial infarction was 81.1% for 5 mm DWI and 94.6% for 3 mm DWI and the specificity was 100% for 5 mm DWI and 97.7% for 3-mm DWI. The false-negative rate in detection of infratentorial infarcts was 5.6% for the 5-mm sequence and 1.6% for the 3-mm sequence. The six 5-mm DWI false-negative cases (4.8%) were less than 9 mm in diameter (3–8 mm, average 4.67 mm) and located in the brainstem. This supports the hypothesis that small lesions may not be detected on 5 mm DWI due to partial volume averaging. Conclusion Where there is clinical suspicion of infratentorial infarction, 3 mm DWI of the infratentorium adds sensitivity compared to 5 mm DWI with only a small reduction in specificity.