Critical flicker frequency for quantification of low-grade hepatic encephalopathy

Quantitative T1 mapping of hepatic encephalopathy using magnetic resonance imaging

Changes are shown in the spin-lattice (T1) relaxation time caused by the putative deposition of manganese in various brain regions of hepatic encephalopathy (HE) patients using a novel and fast magnetic resonance imaging (MRI) method for quantitative relaxation time mapping. A new method, T1 mapping with partial inversion recovery (TAPIR), was used to obtain a series of T1-weighted images to produce T1 maps. Imaging of 15 control subjects and 11 patients was performed on a 1.5T MRI scanner. The measurement time per patient with this technique, including adjustments, was approximately 5 minutes. Regions of interest in the globus pallidus, the caudate nucleus, the posterior and anterior limbs of the internal capsule, the putamen, the frontal and occipital white matter, the white matter of the corona radiata, the occipital visual and frontal cortices, and the thalamus were interactively defined in the left hemisphere and analyzed with respect to their T1 values. T1 changes in the brains of HE patients can be determined quantitatively with TAPIR in short, clinically relevant measurement times. Significant correlations between the change in T1 and HE severity have been shown in the globus pallidus, the caudate nucleus, and the posterior limb of the internal capsule. No significant correlation of T1 with grade of HE was found in the putamen, frontal white matter, white matter of the corona radiata, white matter in the occipital lobe, the anterior limb of the internal capsule, visual cortex, thalamus, or frontal cortex. In conclusion, these measurements show that T1 mapping is feasible in short, clinically relevant acquisition times.

Mini-asterixis in hepatic encephalopathy induced by pathologic thalamo-motor-cortical coupling

Recently, it was shown that a slowed motor cortical drive in hepatic encephalopathy (HE) results in mini-asterixis (MA). During forearm elevation, the authors have now investigated the coupling between motor cortex and thalamic activity using magnetoencephalography in six cirrhotic patients with HE and MA and in six control subjects. HE patients showed thalamo-motor-cortical coupling at a significantly lower frequency than the coupling in control subjects. The pathologic motor cortical drive in HE probably results from altered thalamocortical oscillatory coupling.

Portal hypertension

Portal hypertension, the main complication of cirrhosis, is responsible for its most common complications: variceal hemorrhage, ascites, and portosystemic encephalopathy. Portal hypertension is the result of increased intrahepatic resistance and increased portal venous inflow. Vasodilatation (splanchnic and systemic) and the hyperdynamic circulation are hemodynamic abnormalities typical of cirrhosis and portal hypertension. Gastroesophageal varices result almost solely from portal hypertension, although the hyperdynamic circulation contributes to variceal growth and hemorrhage. Ascites results from sinusoidal hypertension and sodium retention, which, in turn, is secondary to vasodilatation and activation of neurohumoral systems. The hepatorenal syndrome represents the result of extreme vasodilatation, with an extreme decrease in effective blood volume that leads to maximal activation of vasoconstrictive systems, renal vasoconstriction, and renal failure. Spontaneous bacterial peritonitis is a potentially lethal infection of ascites that occurs in the absence of a local source of infection. Portosystemic encephalopathy is a consequence of both portal hypertension (shunting of blood through portosystemic collaterals) and hepatic insufficiency that result in the accumulation of neurotoxins in the brain. This review covers the recent advances in the pathophysiology and management of the complications of portal hypertension.

Management of hepatic encephalopathy

Hepatic encephalopathy (HE) is seen as a clinical manifestation of low grade chronic cerebral edema, which is accompanied by alterations in glioneural communication. Different factors such as ammonia, inflammatory cytokines, benzodiazepines and electrolyte imbalances may precipitate or aggravate glia edema, thereby explaining precipitation of HE episodes by a variety of unrelated factors. Recognition and rigorous treatment of these precipitating factors is the most important measure in HE therapy which may be augmented by dietary and medical approaches. Among these approaches, evidence for proven therapeutical efficacy in HE on the basis of placebo-controlled trials is existing only for transplantation, protein restriction, administration of vegetable proteins, ornithine-aspartate, oral branched-chain amino acid treatment as well as lactulose enemas. The efficacy of oral lactulose has not been demonstrated on the basis of placebo-controlled trials.