Early time course of FLAIR signal intensity differs between acute ischemic stroke patients with and without hyperintense acute reperfusion marker.

BACKGROUND: In animal models of stroke, the time course of blood-brain barrier (BBB) disruptions has been elaborately studied. In human patients, leakage of gadolinium into cerebrospinal fluid (CSF) space, visualized on MRI fluid attenuated inversion recovery (FLAIR) images, is considered a sign of BBB disruptions. It was termed 'hyperintense acute reperfusion marker' (HARM) and was associated with hemorrhages. However, the time course of the leakage is unknown and difficult to study in human patients. Also, the association of HARM with signal intensities and enhancement in the parenchyma on FLAIR images has not been thoroughly researched.
METHODS: We analyzed imaging data of acute ischemic stroke patients who underwent repetitive MRI examinations within the first 36 h after the time of symptom onset. HARM was evaluated on FLAIR images. Regions of interest (ROI) of the hyperintensities on diffusion-weighted imaging (DWI) were determined for each time point and mirrored to the contralateral side. The ROI were furthermore corrected for CSF-filled space, using apparent diffusion coefficient (ADC) images. The corrected ROI were used to determine mean signal intensities of the lesions relative to the contralateral side on FLAIR, ADC and B0 images for each time point.
RESULTS: The 18 included patients (5 females; median age: 69 years; median NIHSS score: 5) received 3-5 MRI examinations on the first day and 1-2 examinations on day 2 after stroke. Eight of the patients (44.4%) showed HARM on at least 1 examination. In 6 of these patients, HARM was already seen at the second examination, at the earliest 3.5 h after symptom onset. The HARM-positive patients had higher relative signal intensities (rSI) on FLAIR images in the parenchyma corresponding to the DWI-positive tissue compared with the HARM-negative patients. This difference between groups was statistically significant for the 2nd and 3rd examination (medians of 4.31 and 6.37 h from symptom onset, p < 0.001 and p = 0.005, respectively). No significant difference in rSI between groups was seen for ADC or B0 images.
CONCLUSION: HARM does not only represent a contrast medium leakage from the pial system into the CSF space. It is accompanied by a markedly increased rSI in the early ischemic lesion on FLAIR images, which is likely due to parenchymal enhancement. The lack of differences on B0 images excludes a pure T2 effect.