Usefulness of various MRI sequences in the diagnosis of viral encephalitis

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.

Graphical abstractThis study highlights the sensitivity of different MRI sequences in revealing brain abnormalities in 88 patients with viral encephalitis. MRI abnormalities were more common in herpes and Japanese encephalitis compared to dengue encephalitis. The MRI abnormalities in FLAIR sequence was 57.1%, T2 52.9%, DWI 38.1% and T1 19.3%. Additional MRI lesions were seen in 12.6% patients on FLAIR sequence. Flair and T2 sequences are more sensitive in revealing abnormality if MRI is done after 48 h of onset of viral encephalitis.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights▶ In a patient with febrile encephalopathy, thalamic and basal ganglia involvement suggest Japanese encephalitis (JE) and frontotemporal involvement herpes simplex encephalitis (HSE). ▶ Cranial MRI is usually abnormal in JE (93%) and HSE (100%) whereas it is normal in dengue. ▶ T2 and FLAIR sequences are more sensitive than other sequences if MRI is done after 48 h.