Acute Hepatic (or Hyperammonemic) Encephalopathy: Diffuse Cortical Injury and the Significance of Ammonia

Abstract

We read with great interest the description by U-King-Im et al 1 in the February issue of the American Journal of Neuroradiology (AJNR) of 4 patients with "acute hyperammonemic encephalopathy" on diffusion-weighted imaging (DWI). In the September 2010 issue of AJNR, we used a similar term of "acute hepatic encephalopathy" (most of the patients had hyperammonemia), and the terms could perhaps be considered interchangeable (notably, both would result in the acronym AHE). 2 We thank them for describing their findings, which are similar to the cases we described that, in our opinion, lie at the severe end of the spectrum of AHE. Of particular note is that 2 of their 4 patients died. In our study, 3 of 5 patients died; they had a similar distribution on DWI, which we termed "diffuse cortical involvement." U-King-Im et al 1 limited this description to the cingulate and insular gyri, but review of their available images demonstrates the abnormalities to be more extensive than those 2 regions. We do not point this out for the purpose of criticism; rather, we agree that these findings should alert the radiologist to the possibility of AHE. Thus, the combination of these 2 studies would indeed suggest (though preliminarily) that "diffuse cortical involvement" or alternatively "cingulate and insular involvement" may portend a poor outcome, though AHE is potentially reversible with therapy (such as lactulose).They also similarly noted thalamic brain stem involvement in 1 patient, which we noted in most of our 20 patients. Hence, it would be of interest to us whether subtle involvement of the thalami or dorsal brain stem existed on further review of fluid-attenuated inversion recovery (FLAIR) or DWI in these 4 patients or if they may have other patients who may have been eventually excluded from their study or not included due to stringent criteria, for example due to confounding diagnoses with preliminarily negative findings on MR imaging (we have noted that such situations uncommonly occur). Such confirmation of milder cases limited to the thalami, for example, would help solidify our findings that AHE occurs along a spectrum, with multifocal diffuse cortical findings being at the severe end.We proposed the terminology "acute hepatic encephalopathy" rather than "acute hyperammonemic encephalopathy" for several reasons: 1) Although some correlation likely exists, the degree of correlation between serum ammonia levels and AHE severity (the "ammonia hypothesis") is still controversial. 2) Ammonia levels may be mildly elevated in patients with chronic cirrhosis without symptoms of AHE. 3) Severely encephalopathic patients may have normal ammonia levels. 4) Serum ammonia has been shown to be a poor predictor as a single test for the presence of AHE.3,4 More recent evidence suggests rather that there is a synergistic effect between ammonia and various other inflammatory cytokines that results in excess glutamine within astrocytes, leading to osmotic swelling of the astrocytes and the subsequent brain edema as well as other neuro...

Acute Acquired Metabolic Encephalopathy Based on Diffusion MRI

“…Therefore, it is believed that hyperammonemic encephalopathy may be similar to acute hepatic encephalopathy (HE). However, this hypothesis is controversial [ 57 ].…”

Cerebral Blood Flow of the Neonatal Brain after Hypoxic–Ischemic Injury

“…This association between hyperemia and unfavorable clinical outcome is also observed in children and adults. 35 36 37 38…”

“…This association between hyperemia and unfavorable clinical outcome is also observed in children and adults. [35][36][37][38] General clinical findings in perinatal asphyxia include short-and/or long-term manifestations, such as seizures and spastic cerebral palsy, respectively, although other manifestations are possible depending on the location and extent of the ischemic insults. 4 Classical magnetic resonance imaging (MRI) patterns of HIE in infants have been described extensively in the literature.…”