A Case of Hepatic Encephalopathy With Diffuse Brainstem Signal Changes on Magnetic Resonance Imaging.

Signal changes on brain MRI have been reported in hepatic encephalopathy; however, no specific findings have been established. Moreover, cases of hepatic encephalopathy presenting with MRI signal changes confined to the brainstem are rare. A 75-year-old woman was admitted to our hospital with a one-day history of impaired consciousness. Blood tests revealed elevated ammonia and gamma-glutamyl transpeptidase levels, along with positive anti-mitochondrial M2 antibodies. Brain MRI on admission demonstrated diffuse and symmetrical hyperintensity in the midbrain and pons on fluid-attenuated inversion recovery (FLAIR) imaging, with corresponding hyperintensity on diffusion-weighted imaging (DWI) and low values on the apparent diffusion coefficient (ADC) map. No signal abnormalities were observed in the globus pallidus on T1-weighted imaging (T1WI). Whole-body CT revealed an irregular hepatic surface, a blunt liver edge, and splenomegaly, leading to a diagnosis of liver cirrhosis. Primary biliary cholangitis was confirmed based on serological findings. Following the initiation of branched-chain amino acid therapy, the patient's consciousness improved by day 4 after admission, and the brainstem abnormalities on MRI resolved by day 10. She was ultimately diagnosed with hepatic encephalopathy. This case highlights the importance of considering hepatic encephalopathy in the differential diagnosis of diffuse brainstem signal changes on MRI. The observed MRI features, including symmetrical signal changes, hyperintensity on DWI, and reversible imaging findings during the clinical course, support the diagnosis of metabolic encephalopathy. Additionally, the presence of hyperintensity on DWI with low ADC values may reflect an acute clinical course in hepatic encephalopathy. Furthermore, brainstem-limited signal changes on MRI could be associated with a favorable prognosis.