Clinically Mild Encephalopathy with a Reversible Splenial Lesion Caused by Influenza B Virus in an Unvaccinated Child

Reversible lesions involved in the splenium of corpus callosum (RESLES) are a rare clinic-radiological condition, whose pathogenesis could be related to infectious events (such as in mild encephalopathy with reversible splenial lesion—MERS), epilepsy or metabolic/electrolyte disorders. MERS is characterized by an acute mild encephalopathy associated with lesions in the splenium of corpus callosum on brain magnetic resonance imaging. Viral infections are commonly associated with this condition and type A influenza is the most common cause. The prognosis is generally favorable with spontaneous resolution of clinical and radiological abnormalities. We report a case report of type B influenza MERS in an 8-year-old unvaccinated girl with complete clinical and radiological recovery.