Evaluation of mannitol effect in patients with acute hepatic failure and acute-on-chronic liver failure using conventional MRI, diffusion tensor imaging and in-vivo proton MR spectroscopy

Diffusion-weighted arterial spin labeling MRI to investigate mannitol-induced blood brain barrier disruption

PURPOSE

Diffusion-weighted arterial spin labeling (DW-ASL) MRI has been proposed to determine the rate of water exchange (Kw) across the blood brain barrier (BBB). This study aims to further evaluate Kw MRI by comparing it with standard dynamic contrast-enhanced (DCE) MRI and histology in association with mannitol-induced disruption of the BBB.

METHODS

DW-ASL was measured using a multiple b-value MRI protocol in normal rats at three post-labeling delays (N = 19), before and after intra-carotid injection of mannitol to disrupt BBB in one hemisphere (N = 13). An approach using only two b-values to detect mannitol-induced changes was also tested. DCE MRI and Evans blue histology were performed on the same animals. Quantitative analysis and pixel-by-pixel correlation were performed amongst Kw, DCE MRI and Evans blue histology.

RESULTS

Kw in the grey matter in the normal rat brain was 252 ± 38 min-1 (±standard error of the mean). The two b-value approach provided reasonable approximation of multiple-b DW-ASL parameters, reducing acquisition time. Kw is sensitive to mannitol-induced changes in BBB permeability and was reduced to 89 ± 17 min-1 in the affected hemisphere compared to 191 ± 22 min-1 in the unaffected hemisphere (P < 0.05). Regions with abnormality in Kw maps were in general agreement with DCE and Evans blue maps, although there are some distinct differences in location and the change in values.

CONCLUSION

Kw is sensitive to mannitol-induced changes in the BBB, with BBB disruption confirmed by DCE MRI and Evans blue histology.

Guidelines for the Acute Treatment of Cerebral Edema in Neurocritical Care Patients

BACKGROUND

Acute treatment of cerebral edema and elevated intracranial pressure is a common issue in patients with neurological injury. Practical recommendations regarding selection and monitoring of therapies for initial management of cerebral edema for optimal efficacy and safety are generally lacking. This guideline evaluates the role of hyperosmolar agents (mannitol, HTS), corticosteroids, and selected non-pharmacologic therapies in the acute treatment of cerebral edema. Clinicians must be able to select appropriate therapies for initial cerebral edema management based on available evidence while balancing efficacy and safety.

METHODS

The Neurocritical Care Society recruited experts in neurocritical care, nursing, and pharmacy to create a panel in 2017. The group generated 16 clinical questions related to initial management of cerebral edema in various neurological insults using the PICO format. A research librarian executed a comprehensive literature search through July 2018. The panel screened the identified articles for inclusion related to each specific PICO question and abstracted necessary information for pertinent publications. The panel used GRADE methodology to categorize the quality of evidence as high, moderate, low, or very low based on their confidence that the findings of each publication approximate the true effect of the therapy.

RESULTS

The panel generated recommendations regarding initial management of cerebral edema in neurocritical care patients with subarachnoid hemorrhage, traumatic brain injury, acute ischemic stroke, intracerebral hemorrhage, bacterial meningitis, and hepatic encephalopathy.

CONCLUSION

The available evidence suggests hyperosmolar therapy may be helpful in reducing ICP elevations or cerebral edema in patients with SAH, TBI, AIS, ICH, and HE, although neurological outcomes do not appear to be affected. Corticosteroids appear to be helpful in reducing cerebral edema in patients with bacterial meningitis, but not ICH. Differences in therapeutic response and safety may exist between HTS and mannitol. The use of these agents in these critical clinical situations merits close monitoring for adverse effects. There is a dire need for high-quality research to better inform clinicians of the best options for individualized care of patients with cerebral edema.

Hyperammonemia: What Urea-lly Need to Know: Case Report of Severe Noncirrhotic Hyperammonemic Encephalopathy and Review of the Literature

Purpose. A 66-year-old man who presented with coma was found to have isolated severe hyperammonemia and diagnosed with a late-onset urea-cycle disorder. He was treated successfully and had full recovery. Methods. We report a novel case of noncirrhotic hyperammonemia and review the literature on this topic. Selected literature for review included English-language articles concerning hyperammonemia using the search terms “hyperammonemic encephalopathy”, “non-cirrhotic encephalopathy”, “hepatic encephalopathy”, “urea-cycle disorders”, “ornithine transcarbamylase (OTC) deficiency”, and “fulminant hepatic failure”. Results. A unique case of isolated hyperammonemia diagnosed as late-onset OTC deficiency is presented. Existing evidence about hyperammonemia is organized to address pathophysiology, clinical presentation, diagnosis, and treatment. The case report is discussed in context of the reviewed literature. Conclusion. Late-onset OTC deficiency presenting with severe hyperammonemic encephalopathy and extensive imaging correlate can be fully reversible if recognized promptly and treated aggressively.

Cerebral oedema is rare in acute-on-chronic liver failure patients presenting with high-grade hepatic encephalopathy

BACKGROUND & AIMS

Acute-on-chronic liver failure (ACLF) has a rapidly progressive disease course associated with significant mortality. The prevalence of clinically significant cerebral oedema in ACLF is unknown.

METHODS

We aimed to describe the prevalence of cerebral oedema in a cohort of ACLF adult (>18 years). We identified patients admitted to a single, specialist intensive care unit between January 2005 and January 2011 with high-grade hepatic encephalopathy (≥3) and a clinical picture of either ACLF or chronic liver disease (CLD). Patients who had undergone cranial CT imaging were identified and their imaging reviewed. The ACLF and CLD groups were compared.

RESULTS

One thousand and eight patients with CLD were admitted. One hundred and seventy-three patients (110 male) underwent neuroimaging. Eighty-one (48 male) fulfilled criteria for ACLF. Variceal bleeding (30%) and sepsis (31%) were the most frequent precipitants of ACLF. Of those with neuroimaging from the total cohort, 30% of CT scans were normal, 30% demonstrated increased cerebral atrophy for age, 17% small vessel disease and 16% intracranial haemorrhage (ICH). Cerebral oedema was seen in three patients with ACLF only. An increased prevalence of ICH was observed in the ACLF group (23% vs. 9%, P = 0.008).

CONCLUSION

The prevalence of clinically relevant cerebral oedema was low (4%) but fatal. Death was attributable to tonsillar herniation. An increased prevalence of ICH was seen in ACLF patients and remains an important differential.

Thiamine deficiency related microstructural brain changes in acute and acute-on-chronic liver failure of non-alcoholic etiology

BACKGROUND & AIMS

Mammillary body atrophy in alcoholic liver disease usually indicates thiamine deficiency. The purpose of this study was to explore the relationship among blood thiamine, mammillary bodies, major fiber bundle fractional anisotropy, and volume changes with diffusion tensor tractography in patients with acute and acute-on-chronic liver failure of non-alcoholic etiology.

METHODS

Blood thiamine, mammillary bodies, fiber bundle fractional anisotropy and volume of major fiber tracts were quantified from acute and acute-on-chronic liver failure patients and compared with healthy controls. In 7 acute liver failure patients, follow-up study was done after clinical recovery at 5 weeks.

RESULTS

Blood thiamine, mammillary bodies and fornix volume, and fornix fiber bundle fractional anisotropy were significantly decreased as compared to controls. Blood thiamine showed significant positive correlation with mammillary bodies' volume only. On follow-up study, acute liver failure patients showed significant reversibility only in blood thiamine level and mammillary bodies' volume.

CONCLUSIONS

Mammillary bodies' volume changes are primarily a consequence of thiamine deficiency, which may secondarily result in microstructural changes in the fornix. These observable changes are known to be specific and may be reversible with restoration of blood thiamine level. These imaging changes may be used as imaging biomarker of thiamine deficiency in these patients in future.

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.

Pathogenesis and diagnosis of hepatic encephalopathy

Hepatic encephalopathy (HE) is a common and potentially devastating neuropsychiatric complication of acute liver failure and cirrhosis. Even in its mildest form, minimal HE (MHE), the syndrome significantly impacts daily living and heralds progression to overt HE. There is maturity in the scientific understanding of the cellular processes that lead to functional and structural abnormalities in astrocytes. Hyperammonemia and subsequent cell swelling is a key pathophysiological abnormality, but this aspect alone is insufficient to fully explain the complex neurotransmitter abnormalities that may be observable using sophisticated imaging techniques. Inflammatory cytokines, reactive oxygen species activation and the role of neurosteroids on neurotransmitter binding sites are emerging pathological lines of inquiry that have yielded important new information on the processes underlying HE and offer promise of future therapeutic targets. Overt HE remains a clinical diagnosis and the neurophysiological and imaging modalities used in research studies have not transferred successfully to the clinical situation. MHE is best characterized by psychometric evaluation, but these tests can be lengthy to perform and require specific expertise to interpret. Simpler computer-based tests are now available and perhaps offer an opportunity to screen, diagnose and monitor MHE in a clinical scenario, although large-scale studies comparing the different techniques have not been undertaken. There is a discrepancy between the depth of understanding of the pathophysiology of HE and the translation of this understanding to a simple, easily understood diagnostic and longitudinal marker of disease. This is a present area of focus for the management of HE.

The role of magnetic resonance imaging and spectroscopy in hepatic encephalopathy

Hepatic encephalopathy (HE) is a diverse manifestation of acute and chronic liver failure, ranging from cognitive impairment, only detectable on psychometric evaluation through to confusion, coma and death from cerebral oedema. While there is widespread acceptance of its importance, there is little consensus on how best to diagnose and monitor HE. Clinical descriptions, psychometric testing, electroencephalography and magnetic resonance (MR) imaging (and lately, MR spectroscopy) have all been proposed. MR techniques, in contrast to other modalities, have the benefit of objectivity and of being able to interrogate the brain directly with respect to changes in brain size, function and the metabolic disturbances thought to underlie HE, particularly in the context of astrocyte swelling. Modern clinical MRI scanners with multinuclear MR spectroscopy capabilities and brain mapping software can demonstrate structural and functional cellular changes using volumetric MRI, magnetization transfer MRI, diffusion-weighting MRI, functional MRI with oxygenation measurements and in vivo and in vitro (1)H and (31)P MR spectroscopy. This review describes the relative merits of these techniques and provides guidance on the directions for future research and translation into clinical practice.