Brain metabolism in patients with hepatic encephalopathy studied by PET and MR

•Cerebral oxygen uptake and blood flow are reduced to 2/3 in cirrhotics with overt HE.•These two measures are not changed in cirrhotic patients with minimal HE or no HE.•Cerebral ammonia metabolism is enhanced due to increased blood ammonia in patients.•Cerebral ammonia kinetics is not affected by hyperammonemia.•MR demonstrates low-grade cerebral white matter oedema in cirrhotics with HE.

We review PET- and MR studies on hepatic encephalopathy (HE) metabolism in human subjects from the point of views of methods, methodological assumptions and use in studies of cirrhotic patients with clinically overt HE, cirrhotic patients with minimal HE, cirrhotic patients with no history of HE and healthy subjects. Key results are: (1) Cerebral oxygen uptake and blood flow are reduced to 2/3 in cirrhotic patients with clinically overt HE but not in cirrhotic patients with minimal HE or no HE compared to healthy subjects. (2) Cerebral ammonia metabolism is enhanced due to increased blood ammonia in cirrhotic patients but the kinetics of cerebral ammonia uptake and metabolism is not affected by hyperammonemia. (3) Recent advantages in MR demonstrate low-grade cerebral oedema not only in astrocytes but also in the white matter in cirrhotic patients with HE.