Mild Encephalopathy With Reversible Splenium Lesion in Pediatric Patients: A Case Series.

BACKGROUND: Mild encephalopathy with reversible splenium lesion (MERS) is a clinical-radiologic entity characterized by a reversible lesion in the splenium of the corpus callosum, visible on magnetic resonance imaging (MRI) imaging, predominantly affecting children. Despite the unclear pathogenesis, some etiologies have been identified, with viral infections being the most common cause in children. Moreover, a minority of patients carry a genetic variant in the MYRF gene, which has been associated with reversible myelin vacuolization. METHODS: Here we present 4 cases of pediatric MERS (age 2-10 years) admitted to Niguarda Hospital, Milan, Italy, in a time span of 13 months between December 2023 and January 2025. RESULTS: Three patients exhibited MRI findings consistent with MERS type 1, involving only the splenial corpus callosum. The other one had a more severe clinical presentation, with stroke-like symptoms and a MERS type 2 MRI presentation, involving the white matter as well. In all of them, a viral etiology was identified (rotavirus, influenza A virus, human herpetic virus [HHV6]). CONCLUSIONS: We support the importance of early MRI in acute unexplained encephalopathy and suggest that genetic testing for MYRF variants should be reserved for selected cases with extensive white matter involvement.