Subtype Classification Of Clinically Mild Encephalitis/encephalopathy With A Reversible Splenial Lesion And ADC Value Quantitative Analysis

Objective To explore the possibility and significance of subtypes classification of the Clinically mild encephalitis/encephalopathy with a reversible splenial lesion（MERS）on MRI,and investigate whether the genu of the corpus callosum（GCC）can be involved and recovered in MERS patients.Methods Twenty seven cases with clinically confirmed MERS in nearly 5 years were analyzed retrospectively,and the MRI features of the lesion were observed.The ADC value（total of four groups）of lesions at the splenium of the corpus callosum（SCC）and genu of the corpus callosum（GCC）were measured for the same region of interest（ROI）before and after treatment,and the average value was calculated.The paired sample t-test was used to compare the ADC value of lesions at SCC and GCC before and after treatment.The independent sample t-test was used to compare the difference of average ADC value between SCC and GCC after the first treatment.Results According to the morphology of the lesions,there are three subtypes in type I MERS,such as round shape,olive shape and boomerang shape.The type II MERS lesions involved the entire corpus callosum or adjacent white matter or both,with axial symmetric features.In the 27 patients with MERS,the mean ADC value of the SCC was（0.467±0.157）×10^-3mm²/s and the average ADC value of the GCC was（0.778±0.130）×10^-3mm²/s;the first follow up MR showed that the mean ADC value of the SCC was（0.765±0.131）×10^-3mm²/s,and the average ADC of the GCC was（0.825±0.109）×10^-3mm²/s.The ADC values of SCC before and after treatment were significantly different（t=-9.953,P<0.05）.The ADC values of GCC before and after treatment were significantly different（t=-4.071,P<0.05）.No significant difference of the ADC value was found between SCC and GCC after treatment（t=-1.028,P>0.05）.Conclusion The lesion location and morphology of intracranial lesions in MERS are highly recognizable.TypeⅠMERS can be further classified into three subtypes from MRI images（Ia-circle,Ib-oval,Ic-Boomerang）.Our results suggested that the range of lesions in MERS may be wider than the previous cognition.