Mild Encephalitis/Encephalopathy With a Reversible Splenial Lesion of the Corpus Callosum (MERS): A Report of Two Pediatric Cases

Mild encephalitis/encephalopathy with a reversible splenial lesion of the corpus callosum (MERS) is an uncommon clinico-radiological syndrome marked by transient lesions of the splenium, which are typically demonstrated as diffusion-restricted hyperintensities on MRI. It presents with acute neurological symptoms such as seizures, dysarthria, or ataxia, often following viral infections. We report two pediatric cases of MERS observed in the ED. The first was a 23-month-old boy with focal status epilepticus in the setting of acute gastroenteritis. The second was an eight-year-old boy who presented with dysarthria, gait ataxia, and sensorimotor deficits after a febrile viral illness. Brain MRI in both patients showed diffusion-restricted lesions in the splenium of the corpus callosum, with no contrast enhancement. CSF and infectious workups were unremarkable, except for positive respiratory viral PCR in one case. Neurological recovery was rapid and complete in both children. Follow-up MRIs demonstrated full resolution of the lesions. These clinical and radiological patterns confirmed the diagnosis of MERS. These cases highlight the importance of recognizing MERS as a reversible and self-limiting cause of pediatric encephalopathy. Early MRI is crucial for diagnosis, avoiding unnecessary interventions, and guiding supportive management. Awareness of MERS and its typical imaging features is essential for clinicians and radiologists dealing with pediatric neurological presentations.