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.