Abstract
Acute encephalopathy occurs in 500–800 persons/year, and is most common in infants aged 0 to 3 years. Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) is the most common subtype, followed by clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS, 18%), and acute necrotizing encephalopathy (ANE, 3%). Although AESD is sometimes difficult to distinguish from febrile status epilepticus, the usefulness of high b-value diffusion-weighted images, arterial spin labeling (ASL), and MR spectroscopy has been reported. The bright tree appearance, characteristic of AESD, is considered to reflect the proliferation of gemistocytic astrocytes at the corticomedullary junction from the autopsy study. MERS is characterized by reduced reversible diffusion of the corpus callosum and has a good prognosis. It should be noted that acute focal bacterial pyelonephritis is often associated with MERS. WES analysis in patients with familial MERS reveals MYRF gene mutation, suggesting that the myelin sheath edema may be an underlying pathogenetic factor. Autoimmune GFAP astrocytopathy is characterized by symmetric lesions in the posterior thalamus and linear lesions in the lateral ventricles or corpus callosum.
