Cytotoxic edema is responsible for raised intracranial pressure in fulminant hepatic failure: in vivo demonstration using diffusion-weighted MRI in human subjects

Critical care management of acute liver failure

The management of acute liver failure (ALF) in modern hepatology intensive care units (ICU) has improved patient outcomes. Critical care management of hepatic encephalopathy, cerebral edema, fluid and electrolytes; prevention of infections and organ support are central to improved outcomes of ALF. In particular, the pathogenesis of encephalopathy is multifactorial, with ammonia, elevated intra-cranial pressure and systemic inflammation playing a central role. Although ALF remains associated with high mortality, the availability of supportive care, including organ failure support such as plasma exchange, timely mechanical ventilation or continuous renal replacement therapy, either conservatively manages patients with ALF or offers bridging therapy until liver transplantation. Thus, appropriate critical care management has improved the likelihood of patient recovery in ALF. ICU care interventions such as monitoring of cerebral edema, fluid status assessment and interventions for sepsis prevention, nutritional support and management of electrolytes can salvage a substantial proportion of patients. In this review, we discuss the key aspects of critical care management of ALF.

The Glymphatic System May Play a Vital Role in the Pathogenesis of Hepatic Encephalopathy: A Narrative Review

Hepatic encephalopathy (HE) is a neurological complication of liver disease resulting in cognitive, psychiatric, and motor symptoms. Although hyperammonemia is a key factor in the pathogenesis of HE, several other factors have recently been discovered. Among these, the impairment of a highly organized perivascular network known as the glymphatic pathway seems to be involved in the progression of some neurological complications due to the accumulation of misfolded proteins and waste substances in the brain interstitial fluids (ISF). The glymphatic system plays an important role in the clearance of brain metabolic derivatives and prevents aggregation of neurotoxic agents in the brain ISF. Impairment of it will result in aggravated accumulation of neurotoxic agents in the brain ISF. This could also be the case in patients with liver failure complicated by HE. Indeed, accumulation of some metabolic by-products and agents such as ammonia, glutamine, glutamate, and aromatic amino acids has been reported in the human brain ISF using microdialysis technique is attributed to worsening of HE and correlates with brain edema. Furthermore, it has been reported that the glymphatic system is impaired in the olfactory bulb, prefrontal cortex, and hippocampus in an experimental model of HE. In this review, we discuss different factors that may affect the function of the glymphatic pathways and how these changes may be involved in HE.

Advances in medical management of acute liver failure in children: promoting native liver survival

Paediatric acute liver failure (PALF) is defined as a biochemical evidence of acute liver injury in a child with no previous history of chronic liver disease characterised by an international normalised ratio (INR) of 1·5 or more unresponsive to vitamin K with encephalopathy, or INR of 2·0 or more with or without encephalopathy. PALF can rapidly progress to multiorgan dysfunction or failure. Although the transplant era has substantially changed the outlook for these patients, transplantation itself is not without risks, including those associated with life-long immunosuppression. Consequently, there has been an increased focus on improving medical management to prioritise bridging of patients to native liver survival, which is possible due to improved understanding of the underlying pathophysiology of multiorgan involvement in PALF. In this Review, we discuss recent advances in the medical management of PALF with an aim of reducing the need for liver transplantation. The Review will focus on the non-specific immune-mediated inflammatory response, extracorporeal support devices, neuromonitoring and neuroprotection, and emerging cellular and novel future therapeutic options.

Neurological monitoring and sedation protocols in the Liver Intensive Care Unit

Patients with liver disease often have alteration of neurological status which requires admission to an intensive care unit. Patients with acute liver failure (ALF), acute-on-chronic liver failure (ACLF) and rarely cirrhosis are at risk of cerebral edema. These patients require prompt assessment of neurological status including assessment of intra-cranial pressure (ICP) and monitoring metabolic parameters like arterial/venous ammonia levels, serum creatinine and serum electrolytes so that timely specific therapy for raised ICP can be instituted to prevent permanent neurological dysfunction. The overall aims of neuromonitoring and sedation protocols in a liver intensive care unit are to identify the level of multifactorial metabolic encephalopathy, individualize sedation and analgesia requirements for patients on mechanical ventilation, institute specific therapy to correct the neurological insult in ALF and ACLF, provide clear physiological data for guided therapy of drugs like muscle relaxants, antiepileptics, and cerebral edema reducing agents, and assist with overall prognostication. In this review article we will outline the clinical scenarios related to liver disease requiring intensive care and neuromonitoring, current techniques of neurological assessment, sedation protocols and point of care tests which enable the treating physician and intensivist guide therapy for raised ICP.

Laboratory Abnormalities of Hepatic Encephalopathy

Currently, there is no gold standard serologic or imaging modality to detect hepatic encephalopathy (HE). It is a clinical diagnosis gathered from the history and physical. Imaging is nonspecific; however, PET and MRI have shown areas of utility, but are not widely available, cost-efficient, or necessary for diagnosis. Electroencephalogram has shown promise as it can be used in conjunction with the Portal Systemic Hepatic Encephalopathy Score test to diagnose minimal HE. Further research on these techniques would need to be performed to identify strict criteria and cutoffs for diagnosing HE as well as associated sensitivities and specificities.

Brain Integrity Changes Underlying Cognitive and Functional Recovery Postliver Transplant Continue to Evolve Over 1 Year

BACKGROUND

There is evidence of brain recovery on brain magnetic resonance imaging (MRI) early postliver transplant (LT), but the longer-term impact is unclear. The aim of this study was to determine the change in brain MRI parameters, cognition, and health-related quality of life (HRQOL) between 6 and 12 months post-LT.

METHODS

Listed cirrhotics underwent cognitive, HRQOL and brain MRI pre-LT, 6 months (post-LT1), and 1-year (post-LT2) post-LT. Assessment of MRI changes between visits was performed for ammonia-associated metabolite changes using magnetic resonance spectroscopy, white matter changes using tract-based spatial statistics analysis on diffusion tensor imaging data and grey matter changes using voxel-based morphometry analysis on 3D high resolution T1-weighted images.

RESULTS

Forty-five patients were included, of which 23 were tested at all visits. Cognitive and HRQOL scores improved between all visits compared with pre-LT values. This trend continued on magnetic resonance spectroscopy with reduced glutamine + glutamate and higher myoinositol, choline between pre-LT/post-LT1 but lower degrees of improvement between post-LT1/post-LT2. On diffusion tensor imaging, mean diffusivity, linear diffusivity and mode of anisotropy continued to increase in the posterior internal capsule at both post-LT visits. On voxel-based morphometry, a continued increase was seen in basal ganglia grey matter between both post-LT visits was seen.

CONCLUSIONS

HRQOL and cognition continue to improve compared with pre-LT values up to 1 year post-LT, although the rate of improvement slows down after 6 months. Grey matter increase is steady over time at 1 year although changes in ammonia-related metabolites and white matter integrity improve at a slower pace at 1 year post-LT.

Lysophosphatidic acid receptor, LPA6, regulates endothelial blood-brain barrier function: Implication for hepatic encephalopathy

Cerebral edema is a life-threatening neurological condition characterized by brain swelling due to the accumulation of excess fluid both intracellularly and extracellularly. Fulminant hepatic failure (FHF) develops cerebral edema by disrupting blood-brain barrier (BBB). However, the mechanisms by which mediator induces brain edema in FHF remain to be elucidated. Here, we assessed a linkage between brain edema and lysophosphatidic acid (LPA) signaling by utilizing an animal model of FHF and in vitro BBB model. Azoxymethane-treated mice developed FHF and hepatic encephalopathy, associated with higher autotaxin (ATX) activities in serum than controls. Using in vitro BBB model, LPA disrupted the structural integrity of tight junction proteins including claudin-5, occludin, and ZO-1. Furthermore, LPA decreased transendothelial electrical resistances in in vitro BBB model, and induced cell contraction in brain endothelial monolayer cultures, both being inhibited by a Rho-associated protein kinase inhibitor, Y-27632. The brain capillary endothelial cells predominantly expressed LPA₆ mRNA, whose knockdown blocked the LPA-induced endothelial cell contraction. Taken together, the up-regulation of serum ATX in hepatic encephalopathy may activate the LPA-LPA₆-G_12/13-Rho pathway in brain capillary endothelial cells, leading to enhancement of BBB permeability and brain edema.

Intensive Care Management of Pediatric Acute Liver Failure

Pediatric acute liver failure is rare but life-threatening illness that occurs in children without preexisting liver disease. The rarity of the disease, along with its severity and heterogeneity, presents unique clinical challenges to the physicians providing care for pediatric patients with acute liver failure. In this review, practical clinical approaches to the care of critically ill children with acute liver failure are discussed with an organ system-specific approach. The underlying pathophysiological processes, major areas of uncertainty, and approaches to the critical care management of pediatric acute liver failure are also reviewed.

Nitrosative Stress-Induced Disruption of Baroreflex Neural Circuits in a Rat Model of Hepatic Encephalopathy: A DTI Study

The onset of hepatic encephalopathy (HE) in liver failure is associated with high mortality; the underlying mechanism is undecided. Here we report that in an acute liver failure model employing intraperitoneal administration of thioacetamide in Sprague-Dawley rats, diffusion weighted imaging revealed a progressive reduction in apparent diffusion coefficient in the brain stem. Diffusion tensor imaging further showed that the connectivity between nucleus tractus solitarii (NTS), the terminal site of baroreceptor afferents in brain stem and rostral ventrolateral medulla (RVLM), the origin of sympathetic innervation of blood vessels, was progressively disrupted until its disappearance, coincidental with the irreversible cessation of baroreflex-mediated sympathetic vasomotor tone signifying clinically the occurrence of brain death. In addition, superoxide, nitric oxide, peroxynitrite and ammonia levels in the NTS or RVLM were elevated, alongside swelling of astroctytes. A scavenger of peroxynitrite, but not an antioxidant, delivered intracisternally reversed all these events. We conclude that nitrosative stress because of augmented peroxynitrite related to accumulation of ammonia and swelling of astrocytes in the NTS or RVLM, leading to cytotoxic edema in the brain stem and severance of the NTS-RVLM connectivity, underpins the defunct baroreflex-mediated sympathetic vasomotor tone that accounts for the high mortality associated with HE.

Resting-state functional MR imaging shed insights into the brain of diabetes

Diabetes mellitus is a common metabolic disease which is associated with increasing risk for multiple cognitive declines. Alterations in brain functional connectivity are believed to be the mechanisms underlying the cognitive function impairments. During the past decade, resting-state functional magnetic resonance imaging (rs-fMRI) has been developed as a major tool to study brain functional connectivity in vivo. This paper briefly reviews the diabetes-associated cognitive impairment, analysis algorithms and clinical applications of rs-fMRI. We also provide future perspectives of rs-fMRI in diabetes.

Hepatic encephalopathy in acute-on-chronic liver failure

The presence of hepatic encephalopathy (HE) within 4 weeks is part of the criteria for defining acute-on-chronic liver failure (ACLF). The pathophysiology of HE is complex, and hyperammonemia and cerebral hemodynamic dysfunction appear to be central in the pathogenesis of encephalopathy. Recent data also suggest that inflammatory mediators may have a significant role in modulating the cerebral effect of ammonia. Multiple prospective and retrospective studies have shown that hepatic encephalopathy in ACLF patients is associated with higher mortality, especially in those with grade III-IV encephalopathy, similar to that of acute liver failure (ALF). Although significant cerebral edema detected by CT in ACLF patients appeared to be less common, specialized MRI imaging was able to detect cerebral edema even in low grade HE. Ammonia-focused therapy constitutes the basis of current therapy, as in the treatment of ALF. Emerging treatment strategies focusing on modulating the gut-liver-circulation-brain axis are discussed.

Magnetic resonance imaging and spectroscopy in hepatic encephalopathy

Hepatic encephalopathy is a brain alteration associated to liver failure that produces cognitive impairments at long term. Neuroimaging are non-invasive methods for the study of the brain by means of spectroscopy and imaging techniques. These technologies give huge information about cerebral metabolism and water distribution to explore brain pathways involved in the pathogenesis of hepatic encephalopathy. Furthermore, new magnetic resonance implementations such as voxel-based morphometry or resting-state functional magnetic resonance imaging allow studying brain atrophy and neuronal connectivity of the cerebral network involved in the neurocognitive impairments observed in the patients. The development of magnetic resonance technology will generate handy tools for the brain study of liver failure to elucidate the time-course of the pathology and thus to obtain an early diagnosis of cerebral complications.

Brain magnetic resonance in hepatic encephalopathy

The term hepatic encephalopathy (HE) covers a wide spectrum of neuropsychiatric abnormalities caused by portal-systemic shunting. The diagnosis requires demonstration of liver dysfunction or portal-systemic shunts and exclusion of other neurologic disorders. Most patients with this condition have liver dysfunction caused by cirrhosis, but it also occurs in patients with acute liver failure and less commonly, in patients with portal-systemic shunts that are not associated with hepatocellular disease. Various magnetic resonance (MR) techniques have improved our knowledge about the pathophysiology of HE. Proton MR spectroscopy and T1-weighted imaging can detect and quantify accumulations of brain products that are normally metabolized or eliminated such as glutamine and manganese. Other MR techniques such as T2-weighted and diffusion-weighted imaging can identify white matter abnormalities resulting from disturbances in cell volume homeostasis secondary to brain hyperammonemia. Partial or complete recovery of these abnormalities has been observed with normalization of liver function or after successful liver transplantation. MR studies have undoubtedly improved our understanding of the mechanisms involved in the pathogenesis of HE, and some findings can be considered biomarkers for monitoring the effects of therapeutic measures focused on correcting this condition.

Magnetic resonance of the brain in chronic and acute liver failure

Brain alterations such as hepatic encephalopathy or brain edema are usually associated with liver failure. The mechanisms that lead to the generation of edema seem to be different depending on the course of liver failure (acute, chronic or acute-on-chronic liver failure). Several neuroimaging methods allow a non-invasive assessment of brain alterations in liver failure. Magnetic resonance has gained more interest due to the ability of giving information about cerebral metabolism using spectroscopy, water distribution by diffusion methods or neuronal connectivity by means of resting state magnetic resonance. These techniques have been applied to experimental models and patients with liver failure to elucidate cerebral pathways involved in the pathogenesis of hepatic encephalopathy. In the future, the development of new magnetic resonance implementations will generate handy tools for the study of the brain and get better understanding of the mechanisms that take place in liver failure. This could be useful for the early diagnosis, as well as for the design of new treatments for cerebral complications of liver failure.

Brain edema in acute liver failure: mechanisms and concepts

Brain edema and associated increase in intracranial pressure continue to be lethal complications of acute liver failure (ALF). Abundant evidence suggests that the edema in ALF is largely cytotoxic brought about by swelling of astrocytes. Elevated blood and brain ammonia levels have been strongly implicated in the development of the brain edema. Additionally, inflammation and sepsis have been shown to contribute to the astrocyte swelling/brain edema in the setting of ALF. We posit that ammonia initiates a number of signaling events, including oxidative/nitrative stress (ONS), the mitochondrial permeability transition (mPT), activation of the transcription factor (NF-κB) and signaling kinases, all of which have been shown to contribute to the mechanism of astrocyte swelling. All of these factors also impact ion-transporters, including Na(+), K(+), Cl(-) cotransporter and the sulfonylurea receptor 1, as well as the water channel protein aquaporin-4 resulting in a perturbation of cellular ion and water homeostasis, ultimately resulting in astrocyte swelling/brain edema. All of these events are also potentiated by inflammation. This article reviews contemporary knowledge regarding mechanisms of astrocyte swelling/brain edema formation which hopefully will facilitate the identification of therapeutic targets capable of mitigating the brain edema associated with ALF.

EEG abnormalities are associated with increased risk of transplant or poor outcome in children with acute liver failure

OBJECTIVES

There are limited data on the incidence of seizures and utility of brain imaging and electroencephalogram (EEG) to predict outcome of children with acute liver failure (ALF). We investigated the association between hepatic encephalopathy (HE) scores, abnormal EEG or neuroimaging, and short-term outcome.

METHODS

Single-center retrospective observational study of infants and children with ALF who underwent continuous EEG monitoring and brain imaging within 24 hours of admission to the intensive care unit (ICU).

RESULTS

A total of 19 patients with ALF with a mean age of 6.8 ± 1.5 years were evaluated. The majority of cases (74%) were indeterminate. Of the total, 10 patients (53%) survived to discharge without liver transplant (LT), 5 (26%) received LT, and 4 (21%) died without LT. Seizures occurred in only 2 cases (19%). Patients who had an abnormal EEG on admission (n = 7) were significantly more likely to die or require LT (P < 0.05, Fisher exact test). Patients with either an admission HE score ≤ 2, or liver injury unit score <222, combined with a normal or mildly abnormal EEG were more likely to survive without LT. Neuroimaging was normal in the majority of cases (87%) and was not associated with outcome.

CONCLUSIONS

Children with a moderate or severe abnormality of EEG background on admission were significantly more likely to require LT or to die. Children with an HE score ≤ 2, and a normal or only mildly abnormal EEG, were significantly more likely to survive without needing LT. These findings are an initial step toward distinguishing patients with ALF who may recover spontaneously from those who will require LT.

Increased toll-like receptor 4 in cerebral endothelial cells contributes to the astrocyte swelling and brain edema in acute hepatic encephalopathy

Astrocyte swelling and the subsequent increase in intracranial pressure and brain herniation are major clinical consequences in patients with acute hepatic encephalopathy. We recently reported that conditioned media from brain endothelial cells (ECs) exposed to ammonia, a mixture of cytokines (CKs) or lipopolysaccharide (LPS), when added to astrocytes caused cell swelling. In this study, we investigated the possibility that ammonia and inflammatory agents activate the toll-like receptor 4 (TLR4) in ECs, resulting in the release of factors that ultimately cause astrocyte swelling. We found a significant increase in TLR4 protein expression when ECs were exposed to ammonia, CKs or LPS alone, while exposure of ECs to a combination of these agents potentiate such effects. In addition, astrocytes exposed to conditioned media from TLR4-silenced ECs that were treated with ammonia, CKs or LPS, resulted in a significant reduction in astrocyte swelling. TLR4 protein up-regulation was also detected in rat brain ECs after treatment with the liver toxin thioacetamide, and that thioacetamide-treated TLR4 knock-out mice exhibited a reduction in brain edema. These studies strongly suggest that ECs significantly contribute to the astrocyte swelling/brain edema in acute hepatic encephalopathy, likely as a consequence of increased TLR4 protein expression by blood-borne noxious agents.

Neurologic manifestations of acute liver failure

Fulminant hepatic failure presents with a hepatic encephalopathy and may progress to coma and often brain death from cerebral edema. This natural progression in severe cases contributes to early mortality, but outcome can be good if liver transplantation is appropriately timed and increased intracranial pressure (ICP) is managed. Neurologists and neurosurgeons have become more involved in these very challenging patients and are often asked to rapidly identify patients who are at risk of cerebral edema, to carefully select the patient population who will benefit from invasive ICP monitoring, to judge the correct time to start monitoring, to participate in treatment of cerebral edema, and to manage complications such as intracranial hemorrhage or seizures. This chapter summarizes the current multidisciplinary approach to fulminant hepatic failure and how to best bridge patients to emergency liver transplantation.

Brain edema in acute liver failure: role of neurosteroids

Brain edema is a major neurological complication of acute liver failure (ALF) and swelling of astrocytes (cytotoxic brain edema) is the most prominent neuropathological abnormality in this condition. Elevated brain ammonia level has been strongly implicated as an important factor in the mechanism of astrocyte swelling/brain edema in ALF. Recent studies, however, have suggested the possibility of a vasogenic component in the mechanism in ALF. We therefore examined the effect of ammonia on blood-brain barrier (BBB) integrity in an in vitro co-culture model of the BBB (consisting of primary cultures of rat brain endothelial cells and astrocytes). We found a minor degree of endothelial permeability to dextran fluorescein (16.2%) when the co-culture BBB model was exposed to a pathophysiological concentration of ammonia (5mM). By contrast, lipopolysaccharide (LPS), a molecule well-known to disrupt the BBB, resulted in an 87% increase in permeability. Since increased neurosteroid biosynthesis has been reported to occur in brain in ALF, and since neurosteroids are known to protect against BBB breakdown, we examined whether neurosteroids exerted any protective effect on the slight permeability of the BBB after exposure to ammonia. We found that a nanomolar concentration (10nM) of the neurosteroids allopregnanolone (THP) and tetrahydrodeoxycorticosterone (THDOC) significantly reduced the ammonia-induced increase in BBB permeability (69.13 and 58.64%, respectively). On the other hand, we found a marked disruption of the BBB when the co-culture model was exposed to the hepatotoxin azoxymethane (218.4%), but not with other liver toxins commonly used as models of ALF (thioacetamide and galactosamine, showed a 29.3 and 30.67% increase in permeability, respectively). Additionally, THP and THDOC reduced the effect of TAA and galactosamine on BBB permeability, while no BBB protective effect was observed following treatment with azoxymethane. These findings suggest that ammonia does not cause a significant BBB disruption, and that the BBB is intact in the TAA or galactosamine-induced animal models of ALF, likely due to the protective effect of neurosteroids that are synthesized in brain in the setting of ALF. However, caution should be exercised when using azoxymethane as an experimental model of ALF as it caused a severe breakdown of the BBB, and neurosteriods failed to protect against this breakdown.

Ammonia toxicity to the brain

Hyperammonemia can be caused by various acquired or inherited disorders such as urea cycle defects. The brain is much more susceptible to the deleterious effects of ammonium in childhood than in adulthood. Hyperammonemia provokes irreversible damage to the developing central nervous system: cortical atrophy, ventricular enlargement and demyelination lead to cognitive impairment, seizures and cerebral palsy. The mechanisms leading to these severe brain lesions are still not well understood, but recent studies show that ammonium exposure alters several amino acid pathways and neurotransmitter systems, cerebral energy metabolism, nitric oxide synthesis, oxidative stress and signal transduction pathways. All in all, at the cellular level, these are associated with alterations in neuronal differentiation and patterns of cell death. Recent advances in imaging techniques are increasing our understanding of these processes through detailed in vivo longitudinal analysis of neurobiochemical changes associated with hyperammonemia. Further, several potential neuroprotective strategies have been put forward recently, including the use of NMDA receptor antagonists, nitric oxide inhibitors, creatine, acetyl-L-carnitine, CNTF or inhibitors of MAPKs and glutamine synthetase. Magnetic resonance imaging and spectroscopy will ultimately be a powerful tool to measure the effects of these neuroprotective approaches.

Endothelial-astrocytic interactions in acute liver failure

Brain edema and the subsequent increase in intracranial pressure are major neurological complications of acute liver failure (ALF), and swelling of astrocytes (cytotoxic brain edema) is the most prominent neuropathological abnormality in ALF. Recent studies, however, have suggested the co-existence of cytotoxic and vasogenic mechanisms in the brain edema associated with ALF. This review 1) summarizes the nature of the brain edema in humans and experimental animals with ALF; 2) reviews in vitro studies supporting the presence of cytotoxic brain edema (cell swelling in cultured astrocytes); and 3) documents the role of brain endothelial cells in the development of astrocyte swelling/brain edema in ALF.

Brain edema in acute liver failure and chronic liver disease: similarities and differences

Hepatic encephalopathy (HE) is a complex neuropsychiatric syndrome that typically develops as a result of acute liver failure or chronic liver disease. Brain edema is a common feature associated with HE. In acute liver failure, brain edema contributes to an increase in intracranial pressure, which can fatally lead to brain stem herniation. In chronic liver disease, intracranial hypertension is rarely observed, even though brain edema may be present. This discrepancy in the development of intracranial hypertension in acute liver failure versus chronic liver disease suggests that brain edema plays a different role in relation to the onset of HE. Furthermore, the pathophysiological mechanisms involved in the development of brain edema in acute liver failure and chronic liver disease are dissimilar. This review explores the types of brain edema, the cells, and pathogenic factors involved in its development, while emphasizing the differences in acute liver failure versus chronic liver disease. The implications of brain edema developing as a neuropathological consequence of HE, or as a cause of HE, are also discussed.

ATT- A Double Edged Sword?

Antitubercular therapy (ATT) induced hepatotoxicity, although well known to clinicians, is often over looked and underrated. Given the low threshold of starting ATT, especially empirically, the adverse manifestations can take a considerable toll. A variety of associated risk factors compound the morbidity. We throw light on one such a case where ATT was detrimental to the patient and review the literature and possible preventive strategies.

Serial evaluation of children with ALF with advanced MRI, serum proinflammatory cytokines, thiamine, and cognition assessment

OBJECTIVES

This prospective, sequential study was done to understand changes in cerebral edema (CE) on magnetic resonance imaging and magnetic resonance spectroscopy, liver functions, and neurocognitive testing (NCT) in children with acute liver failure (ALF).

METHODS

A total of 11 ALF and 8 healthy controls were evaluated with advanced magnetic resonance (MR) imaging, blood proinflammatory cytokines (PCs), thiamine levels, liver functions, and NCT. Reevaluation was done at 43.5 ± 26.9 days (first follow-up, n = 8) and 157.3 ± 52.3 days (second follow-up, n = 6) after discharge.

RESULTS

At diagnosis, patients with ALF had vasogenic and cytotoxic CE, raised brain glutamine (23.2 ± 3.4 vs. 15.3 ± 2.7), and serum PCs (tumor necrosis factor [TNF]-α 40.1 ± 8.9 vs. 7.2 ± 2.7  pg/mL, interleukin [IL]-6 29.2 ± 14.4 vs. 4.7 ± 1.2  pg/mL). The mammillary bodies (MBs) were smaller, and brain choline (1.9 ± 0.36 vs. 2.6 ± 0.6) and blood thiamine (55.2 ± 6.7 vs. 81.8 ± 10.2  nmol/L) were lower than controls. At first follow-up, the brain glutamine and CE recovered. Brain choline and MBs volume showed improvement and thiamine levels normalized. Significant reduction in TNF-α and IL-6 was seen. The patients performed poorly on NCT, which normalized at second follow-up. Liver biochemistry and thiamine levels were normal and TNF-α and IL-6 showed further reduction at second follow-up.

CONCLUSIONS

Patients with ALF have CE contributed by raised brain glutamine and PCs. MBs are small because of thiamine deficiency and show recovery in follow-up. CE and brain glutamine recover earlier than normalization of NCT and liver functions. Persistence of raised cytokines up to 6 months after insult suggests possible contribution from liver regeneration.

Neuroimaging in acute liver failure

Acute liver failure (ALF) is frequently complicated by the development of brain edema that can lead to intracranial hypertension and severe brain injury. Neuroimaging techniques allow a none-invasive assessment of brain tissue and cerebral hemodynamics by means of transcranial Doppler ultrasonography, magnetic resonance and nuclear imaging with radioligands. These methods have been very helpful to unravel the pathogenesis of this process and have been applied to patients and experimental models. They allow monitoring the outcome of patients with ALF and neurological manifestations. The increase in brain water can be detected by observing changes in brain volume and disturbances in diffusion weighted imaging. Neurometabolic changes are detected by magnetic resonance spectroscopy, which provides a pattern of abnormalities characterized by an increase in glutamine and a decrease in myo-inositol. Disturbances in cerebral blood flow are depicted by SPECT or PET and can be monitored and the bedside by assessing the characteristics of the waveform provided by transcranial Doppler ultrasonography. Neuroimaging methods, which are rapidly evolving, will undoubtedly lead to future diagnostic and therapeutic progress that could be very helpful for patients with ALF.

Acute liver failure: current practice and recent advances

ALF is an important cause of liver-related morbidity and mortality. Advances in the management of ICH and SIRS, and cardiorespiratory, metabolic, and renal support have improved the outlook of such patients. Early transfer to a liver transplant center is essential. Routine use of NAC is recommended for patients with early hepatic encephalopathy, irrespective of the etiology. The role of hypothermia remains to be determined. Liver transplantation plays a critical role, particularly for those with advanced encephalopathy. Several detoxification and BAL support systems have been developed to serve as a bridge to transplantation or to spontaneous recovery. However, such systems lack sufficient reliability and efficacy to be applied routinely in clinical practice. Hepatocyte and stem cell transplantation may provide valuable adjunctive therapy in the future.

Magnetic resonance quantification of water and metabolites in the brain of cirrhotics following induced hyperammonaemia

BACKGROUND & AIMS

Hepatic encephalopathy (HE) is now thought to be caused by cerebral oedema although the precise pathogenesis is uncertain. We hypothesised that if ammonia is a key factor, induced hyperammonaemia would lead to transient changes in brain water distribution and metabolite concentration, detectable by diffusion tensor imaging (DTI) and magnetic resonance spectroscopy (MRS).

METHODS

Thirteen cirrhotic patients being evaluated for liver transplantation were challenged with 54 g of equal parts of threonine, serine, and glycine. Conventional magnetic resonance imaging was performed to exclude structural lesions and localise regions of interest. DTI was used to generate white matter apparent diffusion coefficient (ADC) maps and proton MRS to measure brain metabolite concentrations before and after the challenge.

RESULTS

The challenge caused a mean (±SD) rise in blood ammonia of 58 (±41) μmol/L, which was accompanied by a significant 9% increase in ADC (p=0.004). Increased ADC significantly correlated with blood ammonia (r=0.58, p=0.04). The change in ammonia levels also correlated with the increase in glutamine levels (r=0.78, p=0.002). Myo-inositol concentration decreased significantly by 0.7 (±0.7)mMol/L between scans and this correlated with the mean difference in ADC (r=0.59, p<0.04).

CONCLUSIONS

These results show that ammonia can directly drive changes in brain water distribution as a mechanism for cerebral oedema development. Since cerebral astrocytes contain glutamine synthetase, our MRS data suggest intracerebral formation of glutamine from ammonia. The rapid decrease in myo-inositol indicates that this organic osmolyte plays a protective role in HE by release from astrocytes in order to maintain cell volume.

Down-regulation of Kir4.1 in the cerebral cortex of rats with liver failure and in cultured astrocytes treated with glutamine: Implications for astrocytic dysfunction in hepatic encephalopathy

Brain edema in acute hepatic encephalopathy (HE) is due mainly to swelling of astrocytes. Efflux of potassium is implicated in the prevention of glial swelling under hypoosmotic conditions. We investigated whether pathogenic factors of HE, glutamine (Gln) and/or ammonia, induce alterations in the expression of glial potassium channels (Kir4.1, Kir2.1) and Na(+) -K(+) -2Cl(-) cotransporter-1 (NKCC1) in rat cerebral cortex and cultured rat cortical astrocytes and whether these alterations have consequences for potassium efflux and astrocytic swelling. Thioacetamide-induced acute liver failure in rats resulted in significant decreases in the Kir4.1 mRNA and protein contents of cerebral cortex, whereas expression of Kir2.1 and NKCC1 remained unaltered. Incubation of primary cortical astrocytes for 72 hr in the presence of Gln (5 mM), but not of ammonia (5 mM or 10 mM), induced a decrease in the levels of Kir4.1 mRNA and protein. Similarly to incubation with Gln, reduction of Kir4.1 mRNA expression by RNA interference caused swelling of astrocytes as shown by confocal imaging followed by 3D computational analysis. Gln reduced the astrocytic uptake of D-[(3) H]aspartate, but, in contrast to the earlier reported effect of ammonia, this reduction was not accompanied by decreased expression of the astrocytic glutamate transporter GLT-1 mRNA. Both Gln and ammonia decreased hypoosmolarity-induced (86) Rb efflux from the cells, but the effect was more pronounced with Gln. The results indicate that down-regulation of Kir4.1 may mediate distinct aspects of Gln-induced astrocytic dysfunction in HE.

Neuroimaging biomarkers of epileptogenesis

Much progress has been made in the field studying the process of epileptogenesis via neuroimaging techniques. Conventional imaging methods include magnetic resonance imaging with morphometric analysis, magnetic resonance spectroscopy and positron emission tomography. Newer network-based methods such as diffusion tensor imaging and functional magnetic resonance imaging with resting functional connectivity are being developed and applied to clinical use. This review provides a brief summary of the major human and animal studies in both partial and generalized epilepsies that demonstrate the potential of these imaging modalities to serve as biomarkers of epileptogenesis.

Neuroimaging findings in alcohol-related encephalopathies

OBJECTIVE

Our aim was to review the emergent neuroimaging findings of alcohol-related CNS nontraumatic disorders. Alcohol (ethanol) promotes inflammatory processes, increases DNA damage, and creates oxidative stress. In addition, the accompanying thiamine deficiency may lead to Wernicke encephalopathy. Associated changes in serum osmolarity may lead to acute demyelination.

CONCLUSION

Alcohol-related encephalopathies can be life-threatening conditions but can be prevented or treated, if recognized.

Neurogenic diabetes insipidus presenting in a patient with subacute liver failure: a case report

Introduction

To the best of our knowledge, this is the first report in the literature of development of neurogenic diabetes insipidus in a patient with subacute liver failure.

Case presentation

A 25-year-old man presented with subacute liver failure. While awaiting a liver transplant, the patient developed cerebral edema, which resulted in neurogenic diabetes insipidus secondary to cerebral edema. The patient died before the liver transplantation could be carried out.

Conclusion

Neurogenic diabetes insipidus is well recognized in the neurosurgical population as a consequence of cerebral edema and increased intracranial pressure, both of which occur commonly in patients with subacute liver failure.

Brain expression of the water channels aquaporin-1 and -4 in mice with acute liver injury, hyperammonemia and brain edema

Cerebral edema is a feared complication to acute liver failure (ALF), but the pathogenesis is still poorly understood. The water channels Aquaporin-1 (Aqp1) and -4 (Aqp4) has been associated with brain edema formation in several neuropathological conditions, indicating a possible role of Aqp1 and/or Aqp4 in ALF mediated brain edema. We induced acute liver injury and hyperammonemia in mice, to evaluate brain edema formation and the parallel expression of Aqp1 and Aqp4 in ALF. Liver injury and hyperammonemia were induced by +D-galactosamine (GLN) plus lipopolysaccharide (LPS) intraperitoneally and intravenous ammonia-acetate (NH(4)(+)), the GLN+LPS+NH(4)(+) group. The vehicle control group (CONTROL) was treated with NaCl and phosphate-buffered saline. The GLN+LPS+NH(4)(+) group showed significantly elevated p-alanine aminotransferase, p-INR and p-ammonium vs. CONTROL (p < 0.001). Cortical brain water content was significantly elevated in the GLN+LPS+NH(4)(+) group vs. CONTROL, mean (SEM) 80.8(0.3) vs 80.0(0.1) % (p < 0.05). Western blot of membrane enriched cortical brain tissue showed significantly upregulation of Aqp4 in the GLN+LPS+NH(4)(+) group vs. CONTROL, mean AU (SEM) 100775(14820) vs. 58857(6266) (p < 0.05), and stationary levels for Aqp1. Aqp1 and Aqp4 mRNA were stationary. This study indicates that Aqp4, but not Aqp1, may be of importance in the pathogenesis of cortical brain edema in mice with ALF.

Acute hepatic encephalopathy: diffusion-weighted and fluid-attenuated inversion recovery findings, and correlation with plasma ammonia level and clinical outcome

BACKGROUND AND PURPOSE

In acute hepatic encephalopathy, MR imaging abnormalities have been described in the PVWM, thalami, and corticospinal tracts. We sought to determine characteristic regions of involvement on FLAIR and DWI, to evaluate their reversibility, and to correlate MR imaging extent with clinical severity.

MATERIALS AND METHODS

Twenty patients who presented clinically with acute hepatic encephalopathy and MR imaging <21 days after symptom onset were reviewed retrospectively. Two neuroradiologists recorded involved regions on FLAIR and DWI in each, measured ADC values in affected regions and NAWM, and scored the MR imaging severity/extent. The initial severity (West Haven grade), follow-up clinical severity (degree of improvement), and maximal PAL within ±8 days of MR imaging were recorded and correlated with the MR imaging severity.

RESULTS

On FLAIR and DWI respectively, there were abnormalities in the thalami (85%, 70%), PLIC (75%, 80%), PVWM (80%, 85%), and DBS (70%, 35%) and diffuse cortical involvement (30%, 25%). There were relatively strong significant (P < .005) correlations of FLAIR (r = 0.680, P = .001) and DWI severity (r = 0.690, P = .001) with PAL, and of PAL with the clinical outcome (r = 0.691, P = .001). Both FLAIR (r = 0.592, P = .006) and DWI (r = 0.487, P = .029) severity correlated moderately with the clinical outcome but were not significant at the P < .005 level after Bonferroni correction.

CONCLUSIONS

Patients with acute hepatic encephalopathy may exhibit characteristic regions of involvement on FLAIR with DWI findings that can be reversible. The MR imaging extent on FLAIR and DWI strongly correlates with the maximal PAL, and PAL correlates well with the clinical outcome. Diffuse cortical involvement has a higher potential for neurologic sequelae but can be reversible.

Review article: the current management of acute liver failure

BACKGROUND

Acute liver failure is a devastating clinical syndrome with a persistently high mortality rate despite critical care advances. Orthotopic liver transplantation (OLT) is a life-saving treatment in selected cases, but effective use of this limited resource requires accurate prognostication because of surgical risks and the requirement for subsequent life-long immunosuppression.

AIM

To review the aetiology of acute liver failure, discuss the evidence behind critical care management strategies and examine potential treatment alternatives to OLT.

METHODS

Literature review using Ovid, PubMed and recent conference abstracts.

RESULTS

Paracetamol remains the most common aetiology of acute liver failure in developed countries, whereas acute viral aetiologies predominate elsewhere. Cerebral oedema is a major cause of death, and its prevention and prompt recognition are vital components of critical care support, which strives to provide multiorgan support and 'buy time' to permit either organ regeneration or psychological and physical assessment prior to acquisition of a donor organ. Artificial liver support systems do not improve mortality in acute liver failure, whilst most other interventions have limited evidence bases to support their use.

CONCLUSION

Acute liver failure remains a truly challenging condition to manage, and requires early recognition and transfer of patients to specialist centres providing intensive, multidisciplinary input and, in some cases, OLT.

Therapeutic hypothermia for acute liver failure

Cerebral edema is a potentially life-threatening complication of acute liver failure, the syndrome of abrupt loss of liver function in a patient with a previously healthy liver. Although the prevalence of cerebral edema appears to be decreasing, patients with rapidly progressive (hyperacute) liver failure, such as after acetaminophen overdose, remain at highest risk. In severe cases of cerebral edema, intracranial hypertension develops and leads to brain death after brainstem herniation or to anoxic brain injury and permanent neurologic impairment. Intracranial hypertension in patients with acute liver failure often can be temporarily controlled by manipulating body position, increasing the degree of sedation, and increasing blood osmolarity through pharmacologic means. However, these maneuvers often postpone, but do not eliminate, the risk of brainstem herniation unless orthotopic liver transplantation or spontaneous liver regeneration follows in short order. To buy time, the induction of therapeutic hypothermia (core temperature 32 degrees C-35 degrees C) has been shown to effectively bridge patients to transplant. Similar to the experience in patients with cerebral edema after other neurologic insults, hypothermia reduces cerebral edema and intracranial hypertension in patients with acute liver failure by decreasing splanchnic ammonia production, restoring normal regulation of cerebral hemodynamics, and lowering oxidative metabolism within the brain. Hypothermia may also ameliorate the degree of liver injury. Hypothermia has not been adequately studied for its safety and theoretically may increase the risk of infection, cardiac dysrhythmias, and bleeding, all complications independently associated with acute liver failure. Therefore, although an ample body of experimental and human data provides a rationale for the use of therapeutic hypothermia in patients with acute liver failure, multicenter, randomized, controlled clinical trials are needed to confirm that hypothermia secures brain viability and improves survival without causing harm.

Acute toxic leukoencephalopathy: potential for reversibility clinically and on MRI with diffusion-weighted and FLAIR imaging

OBJECTIVE

Toxic leukoencephalopathy may present acutely or subacutely with symmetrically reduced diffusion in the periventricular and supraventricular white matter, hereafter referred to as periventricular white matter. This entity may reverse both on imaging and clinically. However, a gathering together of the heterogeneous causes of this disorder as seen on MRI with diffusion-weighted imaging (DWI) and an analysis of their likelihood to reverse has not yet been performed. Our goals were to gather causes of acute or subacute toxic leukoencephalopathy that can present with reduced diffusion of periventricular white matter in order to promote recognition of this entity, to evaluate whether DWI with apparent diffusion coefficient (ADC) values can predict the extent of chronic FLAIR abnormality (imaging reversibility), and to evaluate whether DWI can predict the clinical outcome (clinical reversibility).

MATERIALS AND METHODS

Two neuroradiologists retrospectively reviewed the MRI examinations of 39 patients with acute symptoms and reduced diffusion of periventricular white matter. The reviewers then scored the extent of abnormality on DWI and FLAIR. ADC ratios of affected white matter versus the unaffected periventricular white matter were obtained. Each patient's clinical records were reviewed to determine the cause and clinical outcome. Histology findings were available in three patients. Correlations were calculated between the initial MRI markers and both the clinical course and the follow-up extent on FLAIR using Spearman's correlation coefficient.

RESULTS

Of the initial 39 patients, seven were excluded because of a nontoxic cause (hypoxic-ischemic encephalopathy [HIE] or congenital genetic disorders) or because of technical errors. In the remaining 32 patients, no correlation was noted between any of the initial MRI markers (percentage of ADC reduction, DWI extent, or FLAIR extent) with the clinical outcome. Three patients had histologic correlation. However, moderate correlation was seen between the extent of abnormality on initial FLAIR and the extent on follow-up FLAIR (r = 0.441, p = 0.047). Of the 13 patients who underwent repeat MRI at 21 days or longer, the reduced diffusion resolved in all but one. Significant differences were noted between ADC values in affected white matter versus unaffected periventricular white matter on initial (p < 0.0001) but not on follow-up MRI (p = 0.13), and in affected white matter on initial versus follow-up (p = 0.0014) in those individuals who underwent repeat imaging on the same magnet (n = 9), confirming resolution of the DWI abnormalities.

CONCLUSION

Acute toxic leukoencephalopathy with reduced diffusion may be clinically reversible and radiologically reversible on DWI, and may also be reversible, but to a lesser degree, on FLAIR MRI. None of the imaging markers measured in this study appears to correlate with clinical outcome, which underscores the necessity for prompt recognition of this entity. Alerting the clinician to this potentially reversible syndrome can facilitate treatment and removal of the offending agent in the early stages.

Advance in roles of ammonia and cytokines in hepatic encephalopathy

Hyperammonia theory has been thought as a most feasible mechanism of hepatic encephalopathy following liver injury. Astroglial swelling was reckoned as pathological basis of hepatic encephalopathy. Many assumed mechanisms include oxidative stress activation, mitochondrial permeability transition and glutamine theory, by which ammonia acts on astroglial swelling. Cytokins have influence on the development of hepatic encephalopathy. There are mutual effects of both ammonia and cytokines inducing hepatic encephalopathy.

Reversible cytotoxic edema in a cirrhotic patient following TIPS

The authors report the magnetic resonance imaging (MRI) findings in a 52-year-old man with cirrhosis from chronic hepatitis C who developed episodic acute hepatic encephalopathy Type C following placement of transjugular intrahepatic portosystemic shunt (TIPS). Brain MRI revealed hyperintense T2 signal and restricted diffusion distributed through the cerebral cortex. The patient's mentation improved with treatment of his hyperammonemia. Brain MRI performed 5 months later revealed diffuse cerebral atrophy and new areas of hyperintense T2 signal in the cerebral white matter. The cortical signal abnormalities and low apparent diffusion coefficient values on the initial MRI resolved with exception of a mild amount of hyperintense FLAIR signal in the cingulate cortex. Acute hepatic encephalopathy following portosystemic shunting -- either from placement of TIPS or from development of spontaneous shunts -- is a widely recognized complication of portal hypertension and cirrhosis. We report MRI findings of reversible cytotoxic edema in a patient with acute hepatic encephalopathy following placement of TIPS.

Measurement of cytotoxic and interstitial components of cerebral edema in acute hepatic failure by diffusion tensor imaging

PURPOSE

To use diffusion tensor imaging (DTI) metrics for measuring cytotoxic and interstitial components of cerebral edema (CE) in acute hepatic failure (AHF) patients. CE is a major complication in patients with AHF.

MATERIALS AND METHODS

DTI was performed in 20 patients with AHF and 15 controls. Ten patients underwent repeat imaging after recovery from encephalopathy. Various regions of interest (ROIs) were drawn in the white and deep gray matter of the brain for the quantitation of fractional anisotropy (FA), mean diffusivity (MD), spherical isotropy (CS), linear anisotropy (CL), and planar anisotropy (CP) values.

RESULTS

Significantly decreased MD values were observed in most brain ROIs in patients compared to controls. Significantly decreased FA, CL with increased CS values was also observed. In survivors with normal clinical profile after 3 weeks, a significant increase in MD and FA values were associated with decreased CS values in some regions compared to baseline study; however, it was still significantly changed compared to controls.

CONCLUSION

Decreased MD and increased CS associated with decreased FA represent cytotoxic and interstitial components of CE, respectively. Incomplete normalization of these metrics in survivors after 3 weeks clinical recovery may be due to incomplete metabolic recovery.

Voxel-based diffusion tensor magnetic resonance imaging evaluation of low-grade hepatic encephalopathy

PURPOSE

To quantify the changes in brain water diffusivity in hepatic encephalopathy (HE) associated with cirrhosis using diffusion tensor imaging (DTI) and to correlate with neuropsychological (NP) scores.

MATERIALS AND METHODS

DTI was performed in 14 patients with low-grade HE and age/gender-comparable 16 healthy controls. Whole brain mean diffusivity (MD) and fractional anisotropy (FA) maps were calculated, normalized to common space, smoothed, and compared voxel-by-voxel between groups using analysis of covariance with age included as a covariate. The average MD and FA values were also calculated from individual subjects for selected brain regions and correlated with the neuropsychological scores.

RESULTS

Patients with HE showed increased MD in the cortical gray and white matter and the internal capsule. Less extensive brain regions with decreased FA were observed in the bilateral frontal and occipital white matter. MD values from the corpus callosum correlated inversely with several NP scores among HE patients and controls. Positive correlations were observed with FA values and cognitive scores.

CONCLUSION

Voxel-based DTI analysis showed widespread brain regions with increased MD values, indicating enhanced water content and decreased FA in cirrhotic patients with HE. The MD and FA values from selected regions correlated with the NP scores.

Quantification of cerebral edema on diffusion tensor imaging in acute-on-chronic liver failure

Cerebral edema is a major complication of acute liver failure but may also be seen in other forms of liver failure such as acute-on-chronic liver failure (ACLF) and chronic liver failure (CLF). ACLF develops in patients with previously well-compensated chronic liver disease following acute hepatitis A or E superimposed on underlying liver cirrhosis. The aim of this study was to detect the occurrence, and determine the nature, of cerebral edema in patients with the defined subset of ACLF using diffusion tensor imaging (DTI) metrics. Twenty-three patients with ACLF were studied and compared with 15 healthy controls and 15 patients with CLF. DTI metrics including fractional anisotropy (FA), mean diffusivity (MD), linear anisotropy (CL), planar anisotropy (CP), and spherical isotropy (CS) were calculated by selecting regions of interest in the white matter and deep grey matter of the brain. Significantly decreased FA and increased CS were observed in the anterior limb (ALIC) and posterior limb (PLIC) of the internal capsule and frontal white matter (P<0.05) in patients with different grades (1-4) of ACLF when compared with healthy controls. No significant changes in MD and CP were seen in any brain region. However, significantly decreased CL was observed in the PLIC, caudate nuclei and putamen. In patients with CLF, significantly decreased FA with increased CS in the ALIC and PLIC along with significantly increased MD in the ALIC and caudate nuclei were observed. The presence of significantly decreased FA and CL and increased CS along with no significant change in MD and CP suggests the presence of both intracellular and extracellular components of cerebral edema in patients with ACLF.