Imaging diagnosis of acute encephalopathy in childhood

Masashi Mizuguchi
Department of Developemental Medical Scences, Graduate School of Medicine, the University of Tokyo

Abstract
　　The pathological substrate of acute encephalopathy is diffuse or widespread, non-inflammatory brain edema. This article reviews the neuroradiologic findings in many syndromes of acute encephalopathy, by classifying them into four major categories according to their pathogenesis.
A. Encephalopathy due to metabolic error : Various metabolic disorders may present with acute encephalopathy. Many of them show diffuse brain atrophy, and some exhibit symmetric lesions of the deep gray matter. Reye syndrome shows diffuse brain edema.
B. Encephalopathy due to cytokine storm : Reye-like syndrome, hemorrhagic shock and encephalopathy (HSE) syndrome show early-onset, vascular edema affecting the whole brain or cerebral cortex. Acute necrotizing encephalopathy (ANE) is characterized by symmetric lesions affecting the thalamus, deep cerebral white matter, brainstem tegmentum and cerebellar medulla.
C. Encephalopathy due to excitotoxicity, such as acute infantile encephalopathy predominantly affecting the frontal lobes (AIEF) and hemiconvulsion-hemiplegia (HH) syndrome, is characterized by late-onset, cellular edema affecting localized areas of the cerebral cortex. These areas show edema and hyperperfusion from the 4th to 7th day of illness, and atrophy and hypoperfusion during the subsequent weeks.
D. Encephalopathy of unknown pathogenesis : Clinically mild encephalitis/ encephalopathy with a transient splenial lesion has recently been described.

Keywords： Reye syndrome, Acute necrotizing encephalopathy,
Acute infantile encephalopathy predominantly affecting the frontal lobes