Statistical Analysis of the Apparent Diffusion Coefficient in Patients with Clinically Mild Encephalitis/Encephalopathy with a Reversible Splenial Lesion Indicates That the Pathology Extends Well beyond the Visible Lesions

PURPOSE: To investigate whether the genu of the corpus callosum is involved in patients with clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) type I. METHODS: Twenty-three cases of clinically confirmed MERS I were analyzed retrospectively, and MRI features of the lesion were observed. The apparent diffusion coefficient (ADC) values of the same region of interests in lesions at the splenium and genu of the corpus callosum were measured before and after treatment (i.e., four groups), and the average ADC values were calculated. Paired t-tests were used to compare the ADC values of lesions in the splenium and genu before and after treatment. Independent sample t-tests were used to compare the values in the splenium and genu after treatment. RESULTS: The mean ADC values of the splenium before and after treatment were 0.448 ± 0.124 and 0.790 ± 0.070 × 10(−3) mm(2)/s, respectively, showing significant difference (P < 0.01). The mean ADC values in the genu before and after treatment were 0.783 ± 0.067 and 0.829 ± 0.070 × 10(−3) mm(2)/s, respectively, also showing significant difference (P < 0.01). There was no significant difference in the ADC values between the splenium and genu after treatment (P > 0.05). CONCLUSION: The genu showed a slight restriction in diffusion in the acute stage of type I MERS. After treatment, this diffusion restriction diminished as it typically does in the splenium. Our results indicate that the pathology in MERS extends well beyond the visible lesions.