Pathology and pathogenesis of idiopathic portal hypertension with an emphasis on the liver

Idiopathic portal hypertension (IPH) is characterized by a long-standing presinusoidal portal hypertension of unknown etiology in adults. Some unidentified agent(s) affect(s) the intrahepatic small portal veins or portal tracts. Immunological disturbance, thromboembolism, infectious etiology and/or increased fibrogenesis in portal tracts are suspected as being candidates for the primary agent(s). During the long clinical course of IPH, several pathological changes may occur, including subcapsular parenchymal atrophy, atrophy of the liver, portal and parenchymal fibrosis, and portal venous phlebosclerosis and thrombosis. The last-named of these lesions is mostly found in patients with a history of splenectomy. Subcapsular parenchymal and hepatic atrophy may result from a hepatocellular dropout via apoptosis or necrosis because of intrahepatic hemodynamic disturbances, particularly chronic portal venous blood insufficiency. Pericellular fibrosis and thin fibrous septa are also frequently found and associated with activated perisinusoidal cells positive for smooth muscle actin. At the same time, vague nodular hyperplasia of hepatocytes not surrounded by fibrous septa is not infrequently seen. It may resemble nodular regenerative hyperplasia, partial nodular transformation, or focal nodular hyperplasia. However, liver cirrhosis does not occur even at the terminal stage. Taking these findings into consideration, a new staging of IPH with a combination of hepatic parenchymal atrophy and portal venous thrombosis was proposed: non-atrophic liver without subcapsular parenchymal atrophy (stage I), non-atrophic liver with subcapsular parenchymal atrophy (stage II), atrophic liver with subcapsular parenchymal atrophy (stage III), and portal venous occlusive thrombosis (stage IV). IPH livers are likely to progress from stage I to stage III. Stage IV, which occurs relatively late, has a poor prognosis. This staging is applicable to clinical and autopsy cases without any histological data.     

Pathology of the liver in "idiopathic portal hypertension" associated with autoimmune disease. The Ministry of Health and Welfare Disorders of Portal Circulation Research Committee

The histopathology of the liver in idiopathic portal hypertension (IPH) associated with autoimmune disease (15 cases), was examined and compared with that of IPH without autoimmune disease (31 cases). It was found that hepatic histopathology was heterogeneous in the cases with autoimmune disease. That is, the hepatic histopathology in 7 cases was similar to that of classic IPH without autoimmune disease, and the remaining 8 cases disclosed unusual lesions such as focal non-suppurative cholangitis, nodular parenchymal hyperplasia, moderate portal inflammation, and intrahepatic ductopenia. These unusual lesions, which frequently coexisted in the same case, were not typical ones for making other diagnoses such as primary biliary cirrhosis or nodular regenerative hyperplasia of the liver. These findings suggest that unusual histologic lesions in the livers of IPH patients with autoimmune disease may represent an accentuated immunologic reaction inherent in IPH, or that such cases may be an abortive or incomplete form of primary biliary cirrhosis or nodular regenerative hyperplasia of the liver.     

Pathogenesis of portal sclerosis in the liver with idiopathic portal hypertension. Observations of 19 autopsy cases and animal experiments

The pathomorphological changes of intrahepatic portal veins were studied in 19 autopsy cases of idiopathic portal hypertension (IPH), and the pathogenesis of portal sclerosis was discussed by the observations on the human and experimental materials. The degree and morphological appearance of intimal lesions vary from vessel to vessel. Fibro-cellular proliferation of subendothelial tissue and incorporation of organized mural thrombi were suggested as the cause of intimal thickening in the portal veins. Animal experiment showed that injury of portal vein wall was followed by intimal hyperplasia and/or incorporation of mural thrombi, and resulted in portal sclerosis similar to that of IPH liver. The cause of portal phlebosclerosis in IPH can not be explained by passive congestion alone. There might be a certain possibility of direct injurious effect in the vessel wall in the pathogenesis of portal lesions of IPH. The following pathogenesis of portal sclerosis in IPH is postulated: phlebo-sclerotic changes of the portal veins are initiated by injury to the vessel wall due to unknown cause(s) and accelerated by secondary thrombosis and/or mechanical injury due to increased portal pressure.     

Pathology of the Liver in "Idiopathic Portal Hypertension" Associated with Autoimmune Disease

The histopathology of the liver in idiopathic portal hypertension (IPH) associated with autoimmune disease (15 cases), was examined and compared with that of IPH without autoimmune disease (31 cases). It was found that hepatic histopathology was heterogeneous in the cases with autoimmune disease. That is, the hepatic histopathology in 7 cases was similar to that of classic IPH without autoimmune disease, and the remaining 8 cases disclosed unusual lesions such as focal non suppurative cholangitis, nodular parenchymal hyperplasia, moderate portal inflammation, and intrahepatic ductopenia. These unusual lesions, which frequently coexisted in the same case, were not typical ones for making other diagnoses such as primary biliary cirrhosis or nodular regenerative hyperplasia of the liver. These findings suggest that unusual histologic lesions in the livers of IPH patients with autoimmune disease may represent an accentuated immunologic reaction inherent in IPH, or that such cases may be an abortive or incomplete form of primary biliary cirrhosis or nodular regenerative hyperplasia of the liver. Acta Pathol Jpn 39: 586-592, 1989.     

Portal vein or hepatic vein? A curious aberrant vasculature in the liver with idiopathic portal hypertension

The existence of aberrant vasculatures has been described as one of the characteristic findings in the liver with idiopathic portal hypertension (IPH). In this paper, the morphological features and the genesis of aberrant vasculatures were studied on the basis of autopsy and biopsy materials of IPH and animal experiments. Aberrant vasculatures in IPH livers are characterized as thin-walled vessels located mainly adjacent to the portal tracts and at times in the hepatic lobules. Although some of them are morphologically very similar to hepatic vein branches, they are portal in nature. These aberrant vessels develop in order to compensate for portal circulatory insufficiency due to obliteration of portal vein branches, and play an important role in maintaining an adequate blood supply to the parenchyma. It is predicted that decrease of these intrahepatic collateral vessels is responsible for or related to parenchymal atrophy and deterioration of liver function in the advanced stage of this disease. We regard these vasculatures as characteristic of the intrahepatic portal venous obstruction, particularly with portal hypertension accompanied by increased portal blood flow.     

HLA-DR expression on the microvasculature of portal tracts in idiopathic portal hypertension. Immunohistochemical characteristics and relation to portal phlebosclerosis

We recently reported that HLA-DR antigen was expressed on the microvasculature of portal tracts more frequently in idiopathic portal hypertension (IPH) than in normal livers or in other hepatic diseases, and that this HLA-DR expression may be involved in the development of the portal venopathy characteristic of IPH. The present study was performed to evaluate the relationship between the HLA-DR expression and portal tract lesions, as well as to investigate the immunohistochemical characteristics of the HLA-DR-positive microvasculature using liver wedge biopsy specimens obtained from 32 patients with IPH. According to the degree of phlebosclerosis of the portal veins, the portal tracts were divided into three groups: mild, moderate, and severe. The microvasculature in portal tracts was positive for HLA-DR in 21 (66%) of the 32 specimens and in 133 (44%) of 302 portal tracts. In the 21 specimens, there was no significant difference in the prevalence of HLA-DR-positive microvasculature among the three groups: it occurred in 57 (66%) of 86 portal tracts in the mild group, 53 (61%) of 87 portal tracts in the moderate group, and 23 (49%) of 47 portal tracts in the severe group. The HLA-DR-positive microvasculature was positive for type IV collagen and receptors of Ulex europaeus lectin I, suggesting that HLA-DR-positive microvessels are blood vessels. These findings suggest that HLA-DR antigen is already expressed on portal microvessels in the incipient stage of IPH, and that HLA-DR expression persists during the progression of portal phlebosclerosis. The HLA-DR expression may be an initiating factor leading to immunologic assault on portal microvessels in IPH.     

A comparative histological and morphometric study of vascular changes in idiopathic portal hypertension and alcoholic fibrosis/cirrhosis

AIM: To examine the pathological changes of hepatic arteries in idiopathic portal hypertension (IPH) which is characterized by the obliteration of the intrahepatic portal vein branches and presinusoidal portal hypertension. METHODS AND RESULTS: Liver specimens (biopsied or surgically resected) from 20 patients with IPH, 20 patients with alcoholic fibrosis/cirrhosis (AF/C) and 20 histologically normal livers were used. The vascular lumina of arterial and venous vessels in portal tracts were morphometrically evaluated by an image analysis system. The ratio of portal venous luminal area to portal tract area (portal venous index) of IPH and that of AF/C were significantly reduced compared with normal liver. The portal venous index for IPH was significantly lower than that for AF/C. The ratio of hepatic arterial luminal area to portal tract area for AF/C was significantly higher than that in normal liver; however, that for IPH was similar to normal. The peribiliary vascular plexus was increased in AF/C but not in IPH. In AF/C, the number of mast cells and macrophages known to be the source of angiogenic substances was significantly increased in the portal tract compared with normal liver, while in IPH it was not increased. CONCLUSIONS: In AF/C, a reduction in portal venous lumen was associated with an increase of hepatic arterial lumen and of angiogenesis-related cells in portal tracts. However, such compensatory arterial changes were not evident in IPH, and this compensatory failure may be a feature of IPH.     

Segmentation and reconstruction of hepatic veins and intrahepatic portal vein based on the coronal sectional anatomic dataset

Three-dimensional (3D) reconstruction of intrahepatic vessels is very useful in visualizing the complex anatomy of hepatic veins and intrahepatic portal vein. It also provides a 3D anatomic basis for diagnostic imaging and surgical operation on the liver. In the present study, we built a 3D digitized model of hepatic veins and intrahepatic portal vein based on the coronal sectional anatomic dataset of the liver. The dataset was obtained using the digital freezing milling technique. The pre-reconstructed structures were identified and extracted, and then were segmented by the method of manual intervention. The digitized model of hepatic veins and intrahepatic portal vein was established using 3D medical visualization software. This model facilitated a continuous and dynamic displaying of the hepatic veins and intrahepatic portal vein at different orientations, which demonstrated the complicated relationship of adjacent hepatic veins and intrahepatic portal vein realistically in the 3D space. This study indicated that high-quality 2D images, precise data segmentation, and suitable 3D reconstruction methods ensured the reality and accuracy of the digital visualized model of hepatic veins and intrahepatic portal vein.     

基于肝内肝门静脉解剖的肝脏右前叶分段新概念

目的根据肝内肝门静脉的走形分布,提出肝脏分段的新概念,为影像学和肝脏外科提供资料。方法采用60例正常的活体肝移植供肝影像资料,研究右前叶肝内肝门静脉的走形和分布以及肝静脉及其属支的回流范围,10例Mevis三维软件重建图像,探讨两者之间的关系。结果 Couinaud分段中的Ⅷ段门脉支可大致分为腹侧支和背侧支,最多可达4支;约90%的背侧支越过肝右静脉分布到Couinaud分段中的VII段。V段的门脉分支大多来自右前叶或Ⅷ段门脉的腹侧支。因此,可将右前叶分为腹侧段:Couinaud分段中的Ⅷ段的腹侧段(S8v)和V段(S5)背侧段:Couinaud分段中的Ⅷ段的背侧段(S8d)两个部分。结论新的划分方法不仅有利于肝内病变的精确定位,而且便于肝脏外科实施新的、更安全的术式。     

Microvasculature in the small portal tracts in idiopathic portal hypertension

Summary The morphology of the microvasculature in the small portal tracts was examined in normal livers, idiopathic portal hypertension (IPH) and other hepatic diseases. The microvasculature examined was arbitrary divided into two groups: that near the limiting plate and that within portal tracts, particularly around bile ducts. Based on comparisons of histology, immunohistochemistry and vascular casts, it is suggested that the former corresponded to inlet venules and the latter to distributing portal veins and peribiliary capillary plexus. Both of these microvasculatures were positive forUlex europaeus lectin I, and (infrequently and weakly) for factor VIII-related antigen. Morphometry disclosed that inlet venules were reduced in number in IPH compared with normal livers and that distributing portal veins, peribiliary capillary plexus and inlet venules were increased in extrahepatic portal obstruction, chronic active hepatitis and extrahepatic obstructive cholestasis. We believe that the change in the microvasculature reflects abnormal microcirculation in the small portal tracts, and that the reduction of inlet venules plays an important role in the development of portal hypertension in IPH.     

Preferential differentiation of the bile ducts along the portal vein in the development of mouse liver

Summary The development of bile ducts in the mouse liver was studied histochemically, with special reference to their preferential differentiation around the portal vein. Both portal vein and hepatic vein shared a common origin, the omphalomesenteric vein. In the early development of the liver, haematopoietic cells were predominant around both veins. With the progressive development of intrahepatic bile ducts, the following three steps were observed: cluster formation of type I hepatocytes around the portal vein, formation of primitive bile duct structures and basal lamina, then formation of ducts surrounded by connective tissue structures composed of type I and type III collagens and lectin-binding sites, which were predominant around the portal vein compared to the hepatic vein. These results suggest that the deposition of abundant connective tissue structures around the portal vein is a prerequisite for the cell differentiation and basal lamina formation in the bile duct precursors. A possible mechanism of the aggregation of type I hepatocytes around the portein vein is also discussed.     

Portal and parenchymal alterations of the liver in idiopathic portal hypertension: a histological and immunochemical study

Idiopathic portal hypertension (IPH) is characterized by presinusoidal portal hypertension owing to the intrahepatic, presinusoidal portal venous block, whereas the primary cause and initial vascular lesions(s) remain only speculative. In this study, a total of 97 IPH livers were histopathologically and immunohistochemically examined, placing emphasis on hepatic parenchymal fibrosis and atrophy as well as on portal tract fibrosis. Alcoholic cirrhosis and normal livers were used as controls. When compared with normal livers, the expression of connective tissue growth factor (CTGF) in periductal mononuclear cells was significant. Matrix metalloproteinase (MMP)9-positive mononuclear cells were fewer in number in the portal tract of IPH liver, when compared with alcoholic cirrhosis. These findings suggest a possible pathogenesis of collagen and elastin deposition because of increased CTGF expression and decreased MMP-9 expression in portal tracts of IPH. Sinusoidal dilatation associated with hepatocellular atrophy and apoptosis occurred frequently, but focally in 20% of the IPH cases. These changes were most often found in hyperplastic hepatocellular areas and in the perivenular areas of hepatic lobules. In these areas, pericellular fibrosis and thin fibrous septa were also frequently seen. In these fibrotic areas, there were deposited not only collagen fibers, but also elastic fibers, in which alpha-smooth muscle actin-positive sinusoidal cells, reflecting activated hepatic stellate cells, were frequently detected. It is possible that in IPH cases, continuing portal venous blood insufficiency may be responsible for hepatic parenchymal damage, which may be followed by hepatocellular apoptotic dropout and then by hepatic parenchymal atrophy and fibrosis.     

Venoocclusive disease of the liver and phlebectatic peliosis in the golden hamster exposed to dimethylnitrosamine

The liver of Syrian hamsters was studied after exposure to dimethylnitrosamine (DMN) in drinking water for, respectively, 8, 12 and 16 weeks. One additional group of animals was offered DMN for 8 weeks, but maintained for further 8 weeks after removal of the compound. The changes consisted of a narrowing portal venopathy, probably arising, initially, from toxic pylephlebitis, being followed by widespread subendothelial prolapse of hepatocytes encroaching upon the lumen of terminal hepatic veins, which generally were free of inflammatory fibrosing lesions. The venous lesions were unrelated to malignant processes in the biliary duct system, which occurred after 16 weeks. Dilatation of sinusoids and small venules was associated with the presence of prolapsed hepatocytes around their openings into involved larger veins. At the end of 12 and 16 weeks of continuous ingestion of DMN, but also where the agent was withdrawn already at 8 weeks, phlebectasis and transitional stages in the formation of teleangiactatic type of peliosis were demonstrated, probably resulting from progressively impeded blood flow due to partial occlusion by prolapsed hepatocytes in terminal veins. The mechanism enabling hepatocytes to penetrate the venous wall was not clarified. There was no indication of invasive malignancy. Hepatocyte prolapse appeared more likely to result from some unknown mechanism of benign infiltration, promoted by regenerative stimulation. This may have been initiated by mild persistent ischemia due to the demonstrated portal venopathy. No endothelial hyperplasia was seen at any stage of the experiments thus eliminating the probability of peliosis being a source of vascular neoplasia, which has previously been described following more prolonged exposure to DMN. Certain parallelisms of the experimental results with hepatic vascular lesions in man subjected to drug therapy are discussed.     

门静脉的解剖与变异

目的：利用经动脉性门静脉造影CT重建门静脉、肝静脉三维结构，观察生理状态下的门静脉的解剖与变异。方法：150例病人，导管置入于肠系膜上动脉内，注入造影剂后门静脉期和肝静脉期连续扫描肝脏。三维重建门静脉及肝静脉，分析门静脉的解剖与变异。结果：150次成像中门静脉变异25例，12例（8．0％）显示门静脉呈三分叉状，10例（6，7％）门静脉先分出右后支，然后上行分为左支和右前支，1例（0．7％）门静脉左支水平段缺如，门静脉右支缺如2例（1．3％），余下125例（83．3％）显示正常左右门静脉分支。结论：门静脉的三维图像重建及类型分析对术前手术方式的确定有一定的临床意义。     

PORTAL VEIN OR HEPATIC VEIN ?

The existence of aberrant vasculatures has been described as one of the characteristic findings in the liver with idopathic portal hypertension (IPH). In this paper, the morphological features and the genesis of aberrant vasculatures were studied on the basis of autopsy and biopsy materials of IPH and animal experiments. Aberrant vasculatures in IPH livers are characterized as thin-walled vessels located mainly adjacent to the portal tracts and at times in the hepatic lobules. Although some of them are morphologically very similar to hepatic vein branches, they are portal in nature. These aberrant vessels develop in order to compensate for portal circulatory insufficiency due to obliteration of portal vein branches, and play an important role in maintaining an adequate blood supply to the parenchyma. It is predicted that decrease of these intrahepatic collateral vessels is responsible for or related to parenchymal atrophy and deterioration of liver function in the advanced stage of this disease. We regard these vasculatures as characteristic of the intrahepatic portal venous obstruction, particularly with portal hypertension accompanied by increased portal blood flow. ACTA PATHOL. JPN. 35 : 885–897, 1985.     

PATHOGENESIS OF PORTAL SCLEROSIS IN THE LIVER WITH IDIOPATHIC PORTAL HYPERTENSION

The pathomorphological changes of intrahepatic portal veins were studied in 19 autopsy cases of idiopathic portal hypertension (IPH), and the pathogenesis of portal sclerosis was discussed by the observations on the human and experimental materials. The degree and morphological appearance of intimal lesions vary from vessel to vessel. Fibrocellular proliferation of subendothelial tissue and incorporation of organized mural thrombi were suggested as the cause of intimal thickening in the portal veins. Animal experiment showed that injury of portal vein wall was followed by intimal hyperplasia and/ or incorporation of mural thrombi, and resulted in portal sclerosis similar to that of IPH liver. The cause of portal phlebosclerosis in IPH can not be explained by passive congestion alone. There might be a certain possibility of direct injurious effect in the vessel wall in the pathogenesis of portal lesions of IPH. The following pathogensis of portal sclerosis in IPH is postulated: phlebosclerotic changes of the portal veins are initiated by injury to the vessel wall due to unknown cause (s) and accelerated by secondary thrombosis and/ or mechanical injury due to increased portal pressure.TA PATHOL. JPN. 35: 299–314, 1985.     

Partial nodular transformation of liver in an adult with persistent ductus venosus. Review with hypothesis on pathogenesis

Partial nodular transformation of the liver (PNT) is a rare condition of unknown pathogenesis in which nodules composed of hepatocytes replace portions of the parenchyma. There is usually evidence of portal hypertension and portal vein thrombosis. We present a case of PNT in a man with persistent ductus venosus and hypoplasia of the major intrahepatic portal veins but without evidence of portal hypertension or portal vein thrombosis. Portal venules were largely absent between nodules, as documented by morphometry. We suggest the pathogenesis of PNT is similar to that previously proposed for nodular regenerative hyperplasia, that is, atrophy occurs in parenchyma with insufficient blood supply and nodules arise by hyperplasia in areas with adequate supply. Partial nodular transformation and nodular regenerative hyperplasia differ mainly in the cause and distribution of the portal vein obliteration.     

Intrahepatic distribution of nerves in the rat

The intrahepatic distribution of nerves in the rat was studied using neurohistochemical and electron microscopic methods. Innervation was restricted primarily to vessels in the portal space and hilus. Both adrenergic and cholinergic fibers were observed in the adventitia of hepatic arteries, and to a lesser extent adjacent to portal veins. Some of the cholinergic fibers, however, were not contiguous with the vasculature. Near the hilus many of these fibers were associated with ganglia while peripherally some coursed into the immediately adjacent parenchyma where end bulbs abutted on hepatocytes. Ultrastructurally, scattered small nerves, devoid of neurolemma, were found contiguous with the portal lamina of hepatocytes. Nerve fibers deeper within the lobule were not seen but numerous gap junctions were observed between contiguous hepatocytes. Central and sublobular hepatic veins lacked innervation but adrenergic nerves were demonstrated in the walls of larger hepatic veins. Innervation of the biliary system was sparse. While nerves were interposed between vessels and bile ducts, such nerves tended to be associated more closely with the vasculature.     

POEMS syndrome with idiopathic portal hypertension: Autopsy case and review of the literature

Polyneuropathy, organomegaly, endocrinopathy, M protein, and skin changes (POEMS) syndrome is a rare multi‐system disease. Reported herein is an autopsy case of POEMS syndrome in a subject who developed idiopathic portal hypertension (IPH). The patient was a 38‐year‐old woman who was initially admitted to the Saiseikai Central Hospital because of polyneuropathy and edema. Diagnosis of POEMS syndrome was established on additional symptoms (splenomegaly and papilloedema) and serum M‐protein. Corticosteroid was given for 10 years. The patient was admitted again at the age of 48 years because of gastrointestinal bleeding due to portal hypertension. The patient died of hepatoencephalopathy at 58 years of age. The liver at autopsy demonstrated dense portal fibrosis and obliteration of small portal vein branches, which are characteristic histological findings of IPH. Portal hypertension is a rare symptom in POEMS syndrome. Only three cases of IPH associated with POEMS syndrome (including the present one) have been reported so far. In the previous two reports, liver biopsy failed to determine the cause of portal hypertension. This is the first report on the occurrence of histological findings compatible with IPH in the liver. Although it is not confirmed whether IPH is related to POEMS syndrome, elevated serum cytokines such as vascular endothelial growth factor and coagulation abnormality could have contributed to the development of IPH in the present case.     

Phylogenetic analyses of the hepatic architecture in vertebrates

The mammalian liver has a structural and functional unit called the liver lobule, in the periphery of which the portal triad consisting of the portal vein, bile duct and hepatic artery is developed. This type of hepatic architecture is detectable in many other vertebrates, including amphibians and birds, whereas intrahepatic bile ducts run independently of portal vein distribution in actinopterygians such as the salmon and tilapia. It remains to be clarified how the hepatic architectures are phylogenetically developed among vertebrates. The present study morphologically and immunohistochemically analyzed the hepatic structures of various vertebrates, including as many classes and subclasses as possible, with reference to intrahepatic bile duct distribution. The livers of vertebrates belonging to the Agnatha, Chondrichthyes, Amphibia, Aves, Mammalia, and Actinopterygii before Elopomorpha, had the portal triad‐type architecture. The Anguilliformes livers developed both periportal bile ducts and non‐periportal bile ducts. The Otocephala and Euteleostei livers had independent configuration of bile ducts and portal veins. Pancreatic tissues penetrated the liver parenchyma along portal veins in the Euteleostei. The liver of the lungfish, which shares the same origin with amphibians, did not have the portal triad‐type architecture. Teleostei and lungfish livers had ductular development in the liver parenchyma similar to oval cell proliferation in injured mammalian livers. Euteleostei livers had penetration of significant numbers of independent portal veins from their intestines, suggesting that each liver lobe might receive a different blood supply. The hepatic architectures of the portal triad‐type changed to non‐portal triad‐type architecture along the evolution of the Actinopterygii. The hepatic architecture of the lungfish resembles that of the Actinopterygii after Elopomorpha in intrahepatic biliary configuration, which may be an example of convergent evolution.