Hepatic arterial buffer response: pathologic evidence in non-cirrhotic human liver with extrahepatic portal vein thrombosis

Enlargement of the hepatic artery is present in dogs with a congenital extrahepatic portosystemic shunt and is independent of shunt insertion into the systemic circulation

The accurate diagnosis of portovascular anomalies has been facilitated by improvements in diagnostic imaging technology. In humans, hepatic arterial blood flow changes in response to the reduction in portal blood flow. The hepatic arterial buffer response characterizes an intrinsic regulatory mechanism in response to reduced portal venous blood flow, which results in hepatic arterial enlargement. At the authors' institution, enlargement of the hepatic artery has been anecdotally observed in a population of dogs with extrahepatic portosystemic shunting, consistent with previous literature that documents variability in hepatic arterial size. In this retrospective, blinded, analytical study, a hepatic artery:aorta (Ha:Ao) ratio was assessed on CT studies from 112 dogs, with (n = 43) and without (n = 69) an extrahepatic congenital portosystemic shunt in order to compare the hepatic artery size independent of body weight between the two populations. A significant increase in the Ha:Ao ratio was documented in dogs with an extrahepatic portosystemic shunt (EHPSS) compared with those dogs with no EHPSS independent of the location of shunt insertion into the systemic circulation (P < .001). Three cases had repeat CT after surgery, and all had Ha:Ao ratio reductions following treatment. The authors propose that this may be an additional imaging feature observed in dogs with an EHPSS.

Evolving Understanding of Noncirrhotic Portal Hypertension

Although cirrhosis is one of the most common causes of portal hypertension, noncirrhotic portal hypertension can result from hemodynamic perturbations occurring in the prehepatic, intrahepatic, and posthepatic circulation. Intrahepatic portal hypertension can be further subclassified relative to the hepatic sinusoids as presinusoidal, sinusoidal, and postsinusoidal. For many of these differential diagnoses, the etiology is known but the cause of idiopathic noncirrhotic portal hypertension, recently included in porto-sinusoidal vascular disease (PSVD), remains poorly understood. Herein, we discuss the diagnostic pathological features of noncirrhotic portal hypertension, with an emphasis on PSVD.

Inside-the-body light delivery system using endovascular therapy-based light illumination technology

Background

Light-based therapies are promising for treating diseases including cancer, hereditary conditions, and protein-related disorders. However, systems, methods, and devices that deliver light deep inside the body are limited. This study aimed to develop an endovascular therapy-based light illumination technology (ET-BLIT), capable of providing deep light irradiation within the body.

Methods

The ET-BLIT system consists of a catheter with a single lumen as a guidewire and diffuser, with a transparent section at the distal end for thermocouple head attachment. The optical light diffuser alters the emission direction laterally, according to the optical fibre's nose-shape angle. If necessary, after delivering the catheter to the target position in the vessel, the diffuser is inserted into the catheter and placed in the transparent section in the direction of the target lesion.

Findings

ET-BLIT was tested in an animal model. The 690-nm near-infrared (NIR) light penetrated the walls of blood vessels to reach the liver and kidneys without causing temperature increase, vessel damage, or blood component alterations. NIR light transmittance from the diffuser to the detector within the organ or vessel was approximately 30% and 65% for the renal and hepatic arteries, respectively.

Interpretation

ET-BLIT can be potentially used in clinical photo-based medicine, as a far-out technology. ET-BLIT uses a familiar method that can access the whole body, as the basic procedure is comparable to that of endovascular therapy in terms of sequence and technique. Therefore, the use of the ET-BLIT system is promising for many light-based therapies that are currently in the research phase.

Funding

Supported by Programme for Developing Next-generation Researchers (Japan Science and Technology Agency); JSPS KAKENHI (18K15923, 21K07217); JST-CREST (JPMJCR19H2); JST-FOREST-Souhatsu (JPMJFR2017); The Uehara Memorial Foundation; Yasuda Memorial Medical Foundation; Mochida Memorial Foundation for Medical and Pharmaceutical Research; Takeda Science Foundation; The Japan Health Foundation; Takahashi Industrial and Economic Research Foundation; AICHI Health Promotion Foundation; and Princess Takamatsu Cancer Research Fund.

Anatomically- and physiologically-informed computational model of hepatic contrast perfusion for virtual imaging trials

PURPOSE

Virtual (in silico) imaging trials (VITs), involving computerized phantoms and models of the imaging process, provide a modern alternative to clinical imaging trials. VITs are faster, safer, and enable otherwise-impossible investigations. Current phantoms used in VITs are limited in their ability to model functional behavior such as contrast perfusion which is an important determinant of dose and image quality in CT imaging. In our prior work with the XCAT computational phantoms, we determined and modeled inter-organ (organ to organ) intravenous contrast concentration as a function of time from injection. However, intra-organ concentration, heterogeneous distribution within a given organ, was not pursued. We extend our methods in this work to model intra-organ concentration within the XCAT phantom with a specific focus on the liver.

METHODS

Intra-organ contrast perfusion depends on the organ's vessel network. We modeled the intricate vascular structures of the liver, informed by empirical and theoretical observations of anatomy and physiology. The developed vessel generation algorithm modeled a dual-input-single-output vascular network as a series of bifurcating surfaces to optimally deliver flow within the bounding surface of a given XCAT liver. Using this network, contrast perfusion was simulated within voxelized versions of the phantom by using knowledge of the blood velocities in each vascular structure, vessel diameters and length, and the time since the contrast entered the hepatic artery. The utility of the enhanced phantom was demonstrated through a simulation study with the phantom voxelized prior to CT simulation with the relevant liver vasculature prepared to represent blood and iodinated contrast media. The spatial extent of the blood-contrast mixture was compared to clinical data.

RESULTS

The vascular structures of the liver were generated with size and orientation which resulted in minimal energy expenditure required to maintain blood flow. Intravenous contrast was simulated as having known concentration and known total volume in the liver as calibrated from time-concentration curves (TCC). Measurements of simulated CT ROIs were found to agree with clinically-observed values of early arterial phase contrast enhancement of the parenchyma (∼5 HU). Similarly, early enhancement in the hepatic artery was found to agree with average clinical enhancement (180 HU).

CONCLUSIONS

The computational methods presented here furthered the development of the XCAT phantoms allowing for multi-timepoint contrast perfusion simulations, enabling more anthropomorphic virtual clinical trials intended for optimization of current clinical imaging technologies and applications. This article is protected by copyright. All rights reserved.

Hepatic pseudolesions caused by alterations in intrahepatic hemodynamics

Hepatic pseudolesion may occur in contrast-enhanced computed tomography and magnetic resonance imaging due to the unique haemodynamic characteristics of the liver. The concept of hepatic arterial buffer response (HABR) has become mainstream for the understanding of the mechanism of the reciprocal effect between hepatic arterial and portal venous flow. And HABR is thought to be significantly related to the occurrence of the abnormal imaging findings on arterial phase of contrast enhanced images, such as hepatic arterial-portal vein shunt and transient hepatic attenuation difference, which mimic hypervascular tumor and may cause clinical problems. Third inflow to the liver also cause hepatic pseudolesion, and some of the cases may show histopathologic change such as focal hyperplasia, focal fatty liver, and focal sparing of fatty liver, and called pseudotumor. To understand these phenomena might be valuable for interpreting the liver imaging findings.

Synapomorphic features of hepatic and pulmonary vasculatures include comparable purinergic signaling responses in host defense and modulation of inflammation

Hepatosplanchnic and pulmonary vasculatures constitute synapomorphic, highly comparable networks integrated with the external environment. Given functionality related to obligatory requirements of "feeding and breathing," these organs are subject to constant environmental challenges entailing infectious risk, antigenic and xenobiotic exposures. Host responses to these stimuli need to be both protective and tightly regulated. These functions are facilitated by dualistic, high-low pressure blood supply of the liver and lungs, as well as tolerogenic characteristics of resident immune cells and signaling pathways. Dysregulation in hepatosplanchnic and pulmonary blood flow, immune responses, and microbiome implicate common pathogenic mechanisms across these vascular networks. Hepatosplanchnic diseases, such as cirrhosis and portal hypertension, often impact lungs and perturb pulmonary circulation and oxygenation. The reverse situation is also noted with lung disease resulting in hepatic dysfunction. Others, and we, have described common features of dysregulated cell signaling during liver and lung inflammation involving extracellular purines (e.g., ATP, ADP), either generated exogenously or endogenously. These metabokines serve as danger signals, when released by bacteria or during cellular stress and cause proinflammatory and prothrombotic signals in the gut/liver-lung vasculature. Dampening of these danger signals and organ protection largely depends upon activities of vascular and immune cell-expressed ectonucleotidases (CD39 and CD73), which convert ATP and ADP into anti-inflammatory adenosine. However, in many inflammatory disorders involving gut, liver, and lung, these protective mechanisms are compromised, causing perpetuation of tissue injury. We propose that interventions that specifically target aberrant purinergic signaling might prevent and/or ameliorate inflammatory disorders of the gut/liver and lung axis.

Endovascular management of ruptured left gastric artery pseudoaneurysm giving rise to replaced left hepatic artery following radical cystectomy: A case report

Visceral artery pseudoaneurysms are rare and potentially fatal unless recognized and treated immediately. Here we present to our mind the first documented case of a ruptured pseudoaneurysm involving the left gastric artery giving rise to Michels' Type II replaced left hepatic artery. An 84-year-old female presented with an acute rupture of such an aneurysm post radical cystectomy. CT Angiogram prior to intervention was key for appropriate catheter selection. Endovascular embolization proved effective, and the patient recovered unremarkably. The case report includes a brief discussion regarding the investigation and management of such ruptures, as well as the rarity of the variant anatomy described.

Two cases of benign hepatic nodules caused by sinusoidal dilatation with different hemodynamics

We describe two cases of benign nodules caused by sinusoidal dilatation with different hemodynamic statuses. Case 1 was a 50-year-old woman with a 1-cm nodule that showed a low density in the arterial phase of computed tomography. Pathologically, there were no atypical cells with sinusoidal dilatation, and immunostaining was negative for CD34. We speculated that sinusoidal dilatation was caused by congestion due to loss of frequency of the central vein. In contrast, case 2 was a 50-year-old woman with a 1.5-cm nodule that was highly stained in the arterial phase of computed tomography. Although she had a sinusoidal dilatation similar to that in case 1, immunostaining was positive for CD34. Sinusoidal dilatation was thought to be caused by hyperperfusion of arterial blood. Moreover, CD34 may be potentially useful for the differentiation of the hemodynamic status.

Anatomically based simulation of hepatic perfusion in the human liver

Liver structures of a healthy subject are digitised and segmented from computed tomography (CT) images, and hepatic perfusion is modelled in the hepatic artery and portal vein of the healthy subject with structured tree-based outflow boundary conditions. This self-similar structured tree is widely used in the literature, eg, blood flow simulation in larger systemic arteries and cerebral circulation, and is used in this study to model the effect of the smaller hepatic arteries and arterioles, as well as the smaller hepatic portal veins and portal venules. Physiologically reasonable results are obtained. Since the structured tree terminates at the size of the microvasculature system in liver lobules, the structured tree boundary condition will enable the proposed organ-level model of hepatic arterial flow to be easily connected to tissue-level models of liver lobules. Blood flow in the hepatic vein is also modelled in this subject with three-element Windkessel model as outflow boundary conditions. The benefit of integrating the perfusion in all hepatic vascular vessels is that it helps us analyse some complicated clinical phenomenon more efficiently, eg, one possible application is to obtain the portal pressure gradient (PPG) to help examine the reliability of hepatic venous pressure gradient (HVPG) as an indirect measure of portal pressure. Moreover, since four to six generations of hepatic vessels, which are sufficient for liver classification analysis, were employed in the model, this study is setting the computational foundation of a potentially handy surgical tool.