Transient Splenial Lesion of the Corpus Callosum in Clinically Mild Influenza-Associated Encephalitis/Encephalopathy

Patient 1 (21 years old) with IAEE and sudden onset of facial numbness and left upper monoparesis on day 5. A, Axial T2-weighted image shows a hyperintense well-defined and circumscribed splenial lesion (arrowheads). B, Axial T2-weighted image through the supraventricular region shows patchy high signal intensity of deep white matter lesions (arrows). C and D, Splenial (arrowheads) and deep white matter (arrows) lesions have higher signal intensity on isotropic DWI than those on T2-weighted images. E and F, ADC map images reveal significant restricted diffusion with reduced ADC values obtained from 3 regions of interest of splenial and white matter lesions (0.42 ± 10⁻³ mm²/s, 0.47 ± 10⁻³ mm²/s, and 0.51 ± 10⁻³ mm²/s). G and H, Follow-up isotropic DWI on day 11 shows the reversal of diffusion restriction in both splenial and white matter lesions.