Use of the diffusion-weighted magnetic resonance imaging for early diagnosis of herpes simplex encephalitis in the ED: a case report

Apparent Diffusion Coefficient analysis of encephalitis: A comparative study with topographic evaluation and conventional MRI findings

Objective:

Our purpose was to reveal the efficiency of diffusion weighted imaging (DWI) in the diagnosis of encephalitis, and to determine the relation between the apparent diffusion coefficient (ADC) values, the onset of the clinical symptoms, and the lesion extent.

Methods:

Conventional magnetic resonance imaging (MRI) was performed in 17 patients with encephalitis diagnosed on the basis of laboratory, clinical and radiologic findings during 2009 and 2015. Based on the duration between the onset of the symptoms and the brain MRI findings, the patients were divided into three groups. ADC values of the encephalitis lesion, the lesions’ topographic analysis score, deep gray matter involvement, patients’ clinical situation and the duration of the arrival to the clinic was examined.

Results:

Mean ADC values were 0,988±0,335 x10^-3 mm²/s in group I (0-2 days), 1,045±0,347 x10^-3 mm²/s in Group-II (3-7 days), 1,451±0,225 x10^-3 mm²/s in Group-III (8 days and over). The relation between the ADC values and the duration of the arrival, topographic analysis score, the relation between the patients’ clinical situation and the deep gray matter involvement were found to be statistically significant. The deep gray matter involvement was demonstrated more clearly by FLAIR images when compared with DWI.

Conclusion:

Conventional MRI sequences may be insufficient in showing the encephalitis lesion. DWI must be added to the imaging modalities immediately in the cases suspected of having encephalitis.

DWI and FLAIR imaging in herpes simplex encephalitis: a comparative and topographical analysis

DWI has been described in some reports to be superior to FLAIR in early stage herpes simple virus encephalitis (HSE). Few data exist on detailed topographical MRI analysis in HSE. Our aim was to study DWI and FLAIR, and analyse topographically these sequences in non-neonatal HSE patients with MRI performed within 60 days. Eleven HSE patients were analysed retrospectively. For topographical analysis, we developed a radiological 50-point score (25 points for each hemisphere, with each point corresponding to a brain area). In patients with MRI performed within 2 weeks (n = 9), DWI detected 11% more areas involved than FLAIR. Thalamic involvement was frequent (67%) in the early phase on FLAIR, being the only brain substructure better visualized on FLAIR than on DWI. In areas involved on both sequences, DWI showed more extensive (especially cortical) abnormalities in 14% of the areas. In patients with late MRI (n = 2), FLAIR was superior to DWI (with essentially white matter involvement). From the mesial temporal area, brain signal changes followed a centripetal (i.e. towards anterior, posterior, and superior parts of the brain) gradient. The cut-off score before involving the contralateral hemisphere was 8-9/25 in the initially involved hemisphere. DWI is slightly superior to FLAIR in acute-subacute HSE, except for the thalamus with FLAIR signal changes more frequently seen than earlier reported. Knowledge of typical topographical MRI involvement can help to differentiate from other conditions mimicking HSE.

Diffusion-weighted imaging and apparent diffusion coefficient evaluation of herpes simplex encephalitis and Japanese encephalitis

PURPOSE

The aim of the study was to evaluate (a) the role of diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) values in differentiating necrotising herpes simplex encephalitis (HSE) and non-necrotising Japanese encephalitis (JE) and (b) to correlate the ADC values with the duration of illness.

MATERIALS AND METHODS

Forty-five confirmed cases of encephalitis (38 patients with JE and 7 patients with HSE) underwent MR imaging. IgM antibody capture enzyme-linked immunosorbent assay (IgM MAC-ELISA) and polymerase chain reaction (PCR) tests were performed in cerebral spinal fluid (CSF) sample to confirm the diagnosis of JE and HSE respectively. MRI findings were recorded in terms of site of involvement, extent of lesions, visibility of each lesion on T2W, DWI and FLAIR sequences and ADC calculations. To observe the changes in ADC with duration of illness, patients with JE and HSE were regrouped on the basis of time since clinical presentation. Mean of the ADC value in each patient was noted and subjected for statistical analysis.

RESULTS

In HSE lesions there was a significant restricted diffusion with low average ADC values observed in acute stage and facilitated diffusion with high average ADC values observed in chronic stage. Whereas JE lesions did not show restricted diffusion and significant low ADC values in acute stage, though facilitated diffusion and high ADC values were observed in chronic stage.

CONCLUSION

The diffusion abnormality and conspicuity of lesions on DWI may be different in various acute encephalitis (HSE and JE). The ADC values are different in the acute stages of HSE and JE reflecting the difference in the degree of diffusability of water molecule. These observations may suggest that there may be an abundance of cytotoxic oedema in HSE and paucity of cytotoxic oedema in JE, in acute stage.