Hepatic encephalopathy

Hepatic encephalopathy (also known as portosystemic encephalopathy) refers to a spectrum of neuropsychiatric abnormalities occurring in patients with liver dysfunction and portal hypertension. It results from exposure of the brain to excessive amounts of ammonia.

Hepatic encephalopathy is usually considered a transient acute condition, which may, however, be repeated frequently. In contrast, chronic neurological damage due perhaps to repeated episodes of hepatic encephalopathy is usually termed acquired hepatocerebral degeneration. Unfortunately, the term hepatic encephalopathy is sometimes used more loosely to include both acute and chronic changes. This leads to some unnecessary confusion.

For the purposes of this article we use the terms separately and discussion here is limited to acute hepatic encephalopathy.

Acquired hepatocerebral degeneration is discussed separately.

The vast majority of patients have portosystemic shunts in the setting of cirrhosis, either from the development of spontaneous shunting or as a result of transjugular intrahepatic portosystemic shunting (TIPS) 7. The clinical spectrum can rarely manifest in individuals whom have portosystemic bypass without any associated intrinsic hepatocellular disease. Due to this reason is also sometimes referred to with the broader term portosystemic encephalopathy.

The clinical manifestations range widely from chronic episodic subclinical neurological dysfunction, to acute fulminant neurological impairment, coma and death 8.

In the majority of patients, a superimposed precipitating cause rather than worsening of hepatocellular function can be identified (particularly in acute situations). Such precipitants include:

  • infection (most common): 50% 4
  • excessive nitrogen containing intestinal load
  • reduced nitrogen excretion
    • constipation
    • renal failure
  • metabolic or drug interactions
    • hyponatraemia or hypokalaemia (e.g. from diuretics)
    • sedatives

Due to portosystemic shunting, ammonia from the digestive system or from elsewhere, which is usually metabolised by the liver reaches the systemic circulation. Although the exact mechanism of neurotoxicity have not been elucidated, ammonia is taken up by the brain and has been shown to be toxic to both astrocytes and neurons 8.

MRI

MR imaging features of acute hyperammonemia include:

  • T2/FLAIR
    • mild
      • symmetric high signal within the insula (most common), thalamus, and posterior limbs of the internal capsule, and cingulate gyrus 5-7
      • often reversible with therapy 5-6
    • severe
      • diffuse cortical oedema and hyperintensity
      • perirolandic and occipital regions are typically spared
  • DWI
    • similar distribution to T2/FLAIR
    • reverse with appropriate therapy
  • SWI
    • nearly one-half have microhemorrhages of white matter or cortex 9
      • number and presence of microhemorrhages do not affect outcome
  • MR spectroscopy
    • may show an elevated glutamine/glutamate peak coupled with decreased myo-inositol and choline signals on proton MR spectroscopy 1,7

As the vast majority of cases of acute hepatic encephalopathy will be encountered in patients with established and chronic liver disease, chronic findings of acquired hepatocerebral degeneration are also usually present.

Acute hepatic encephalopathy can be rapidly fatal, while chronic hepatic encephalopathy tends to be a more indolent process. Identifying and treating precipitating cause is important, and leads to resolution in up to 80% of patients 4.

Notably, the extent of severity on FLAIR and DWI correlates with the plasma ammonia level 5. More severe cases of diffuse cortical involvement (particularly on DWI) can be reversible, but are more likely to be fatal, indicating the need for prompt therapy to treat the hyperammonemia in acute hepatic encephalopathy 5.


Toxic and metabolic encephalopathies
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Article Information

rID: 21635
Section: Pathology
Synonyms or Alternate Spellings:
  • Hepatic encephalopathy (HE)
  • Portosystemic encephalopathy (PSE)
  • Portosystemic encephalopathy

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