A, Brain MRI at second relapse. Fluid attenuation inversion recovery (FLAIR) and postcontrast T1-weighted axial images show relapse of multiple, large, confluent, and asymmetric areas of abnormal T2 signal with scattered small, patchy enhancing areas. B, T2-weighted MRI. A detailed image of the midbrain shows faint hyperintensity in the PAG matter, which represents demyelination or residual gliosis (arrow).