Acute Hyperammonemic Encephalopathy with Features on Diffusion-Weighted Images: Report of Two Cases

Acute hyperammonemic encephalopathy is a rare toxic encephalopathy caused by accumulated plasma ammonia. A few literatures are reported about MRI findings of acute hyperammonemic encephalopathy. It is different from the well-known chronic hepatic encephalopathy. The clinical symptom and MRI findings of acute hyperammonemic encephalopathy can be reversible with proper treatment. Acute hepatic encephalopathy involves the cingulate cortex, diffuse cerebral cortices, insula, bilateral thalami on diffusion-weighted imaging (DWI), and fluid-attenuated inversion-recovery. Acute hepatic encephalopathy might mimic hypoxic-ischemic encephalopathy because of their similar predominant involving sites. We experienced 2 cases of acute hyperammonemic encephalopathy consecutively. They showed restricted diffusion at the cingulate cortex, cerebral cortices, insula, and bilateral dorsomedial thalami on DWI. One patient underwent acute fulminant hepatitis A, the other patient with underlying chronic liver disease had acute liver failure due to hepatotoxicity of tuberculosis medication. In this report, we presented the characteristic features of DWI in acute hyperammonemic encephalopathy. In addition, we reviewed articles on MRI findings of acute hyperammonemic encephalopathy.