There is paucity of studies regarding the utility of various conventional MRI sequences in the diagnosis of viral encephalitis. The present study evaluates the usefulness of various MRI sequences in acute viral encephalitis. 88 consecutive viral encephalitis patients, aged 2-72 years were subjected to clinical evaluation. Consciousness was assessed by Glasgow Coma Scale (GCS). Serum or cerebrospinal fluid (CSF) was analyzed for dengue, Japanese encephalitis (JE), herpes, measles, echo, coxsackie and polio viruses using ELISA or PCR. Cranial MRI was done and T1, T2, FLAIR and DW images were obtained. The MRI changes were correlated with type of encephalitis and duration of illness. All the patients had altered sensorium and 37 had seizures. 22 patients had JE, 9 had dengue, 8 had herpes simplex encephalitis (HSE), 2 had Epstein-Barr virus encephalitis (EBVE) and 47 had non-specific encephalitis. The median duration of MRI study from onset was 10 days. In JE (20/22), HSE (8/8), and EBVE (2/2), MRI abnormalities were more common compared to dengue (2/9) and non-specific (20/47) encephalitis. The MRI abnormalities were more common in FLAIR (57.1%) compared to T2 (52.9%), DWI (38.1%) and T1 (19.3%) sequences. The mean ADC value in JE patients was lower (974.0±110.85×10⁻⁶ mm²/s) than HSE (1024.33±485.76×10⁻⁶ mm²/s). Additional MRI lesions were seen in 12.6% cases on FLAIR sequence. FLAIR and T2 sequences were more sensitive in revealing abnormalities in viral encephalitis.
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