Cirrhosis and portal hypertension: Pathologic aspects

Overview

Cirrhosis, the final stage of untreated chronic liver disease (see Chapter 7 ), is primarily attributable to alcohol abuse, viral hepatitis C (see Chapter 68 ), and, increasingly, nonalcoholic steatohepatitis (NASH; see Chapter 69 ) in the United States (US). The true prevalence of cirrhosis is unknown because in early, developing stages, the condition may be asymptomatic. Nevertheless, cirrhosis is the 11th most common cause of death in adults in the US and accounts for up to 41,743 deaths per year in adults.

In autopsy series, cirrhosis is documented in 5% to 10% of cases, but autopsy subjects may not be representative of the general population. Currently, clinicians and pathologists alike consider cirrhosis as a process with many stages, rather than a single entity; in this conceptual framework, only the final end stage requires transplant as definitive treatment, whereas the preceding stages can be managed with more aggressive preventative medical therapies.

The cirrhotic liver functions markedly less efficiently than normal liver, but it is the aberration of the portal blood flow with resultant portal hypertension that causes the most significant complications of cirrhosis. In addition, cirrhosis itself is a major predisposing condition to hepatocellular carcinoma (HCC; see Chapter 89 ) and is increasingly recognized as a predisposing condition for intrahepatic cholangiocarcinoma (iCCA; see Chapter 50 ) and other primary liver carcinomas of mixed hepatocellular-biliary phenotypes. This predisposition to malignancy is likely because of the inflammatory microenvironment, as well as the recognized plasticity of cell types within the liver. However, the cirrhotic liver is considered to be resistant to metastases from extrahepatic tumors.

Interestingly, portal hypertension may occur in the absence of significant matrix deposition and the structural alterations of cirrhosis, a condition referred to as noncirrhotic portal hypertension (see Chapter 74). The underlying conditions associated with noncirrhotic portal hypertension may be idiopathic but are broadly subdivided into prehepatic, intrahepatic, or posthepatic in terms of clinical presentation and for management considerations . This chapter focuses on the histopathologic features of cirrhosis and noncirrhotic portal hypertension.

Pathogenesis and reversibility of cirrhosis

The transformation of normal hepatic architecture through fibrosis (aberrant matrix deposition) to cirrhosis results from progressive deposition of mixed connective tissue in regions of “extinct” parenchyma, angiogenesis, and vascular remodeling, regardless of the underlying etiology. Fibrogenesis is a dynamic, complex, and highly regulated process, triggered by liver parenchymal injury and mediated by the interplay of cellular necrosis and apoptosis on one hand (see Chapter 7 ) and inflammatory cascades that include immune cells (see Chapter 10 ), cytokines, and chemokines (see Chapter 11 ) on the other hand, which result in activation of specific matrix-producing cells. ^, These cells are resident hepatic stellate cells and portal myofibroblasts. During fibrogenesis, prevention of matrix degradation by metalloproteinases is orchestrated by the release of potent tissue metalloproteinase inhibitors; apoptosis of fibrogenic hepatic stellate cells is also inhibited ( Figs. 74.1 and 74.2 ). Scar formation is the consequence of an imbalance favoring collagen synthesis and deposition versus degradation and resorption (see Chapter 7 ). In addition, basement membrane components and connective tissue formed by activated hepatic stellate cells along the hepatic plates results in “capillarization” of the sinusoids, a process that virtually excludes the exchange of molecules (such as albumin and clotting proteins) between hepatocytes and sinusoidal blood. Sinusoidal endothelial fenestrations are closed in capillarization.

Established cirrhosis, traditionally considered an irreversible process, has been shown otherwise from accumulating evidence by pathologists from treatment trials with pretreatment and posttreatment biopsies for viral hepatitis B (HBV), C (HCV), and hereditary hemochromatosis. A study by Poynard and colleagues (2002) that analyzed 3010 patients with chronic HCV in four major clinical trials found reversal of cirrhosis reported in 75 (49%) of 153 patients with baseline cirrhosis. Although Pol et al. (2004) showed reversal of cirrhosis in 7.8% of 64 immunocompetent patients with HCV-related cirrhosis at 4.6-year mean interval, resolution of cirrhosis was shown in 2 patients upon examination of the liver explants at transplantation. Similarly in HBV, Sun and colleagues (2017) recently proposed a novel classification scheme, the “Beijing Classification” to systematically categorize fibrosis progression and regression based on a cohort of 71 HBV-treated subjects in whom cirrhotic regression was noted from 72% (pretreatment) to 52% in post-treatment biopsies. Falize et al. (2006) analyzed 36 hereditary hemochromatosis patients and demonstrated that regression of fibrosis was seen in 69% of those with bridging fibrosis and in 35% of patients with cirrhosis after venesection therapy. Regression of cirrhosis has also been reported in patients with other diseases, including alcoholic liver disease (ALD), autoimmune hepatitis (AIH), and primary biliary cholangitis. One mechanism proposed for repopulation of hepatic parenchyma is via “stem/progenitor” cells derived from the distalmost biliary tree. Recent studies using routine and immunostains have characterized the progression of “liver buds” as they mature into hepatocytes.

The proposed mechanisms for breakdown and remodeling of liver fibrosis include loss of activated stellate cells via apoptosis, decreased expression of matrix metalloproteinase inhibitors, and increased production and activity of metalloproteinases or collagenases (see Chapter 7 ). Currently, the extent to which cirrhosis is truly reversible is the subject of debate, and an important question not often addressed is the extent to which actual parenchymal and vascular architecture can be restored even if scar tissue is resorbed. Considerations include sampling differences or interpretation errors in the studies showing reversibility; these questions rely on comparisons with prior biopsies for convincing answers. Regardless, these discussions have important clinical implications. Finally, Lee and Friedman (2014) have introduced an ongoing discussion that even with viral cure in HCV, a minority of subjects actually do continue with progressive disease (fibrosis) and HCC (see Chapter 89 ).

Role of liver biopsy in advanced liver disease

Investigation of patients with chronic liver disease, and cirrhosis and portal hypertension involves multiple disciplines and clinical tools, including pathology, radiology, clinical chemistry, virology, serologic testing, and, more recently, molecular testing. Liver biopsy evaluation is diminishing while more serum markers and imaging tests gain traction in clinical practice ; however, in cases with unknown clinical diagnoses, liver biopsy can still be considered a primary diagnostic tool, despite the drawback of invasiveness ^, (see Chapter 23 ). In fact, liver biopsy can serve several important purposes, such as establishing or confirming the clinical concern of cirrhosis or alternative explanation for portal hypertension; assessing the possible underlying causes of disease; distinguishing dysplastic nodules from HCC; and providing tissue for chemical, biochemical, molecular, or ultrastructural studies.

To obtain representative liver tissue for most types of analysis in nonfocal disease processes, needle biopsy, rather than wedge biopsy, has proved to be the most useful technique. This procedure can be done percutaneously with or without ultrasound guidance, via the transjugular route when pressure measurements are needed, or during surgical procedures (see Chapters 22 and 87 ). A cutting needle or the Menghini aspiration needle may be used. If cirrhosis is suspected, a cutting needle is the preferred method of biopsy because the result is less likely to be fragmented, as often occurs with an aspiration needle. A continuous piece of tissue of “adequate” size (both length and diameter) is important in avoiding sampling error. Traditionally, it has been recommended that an adequate biopsy specimen should be no smaller than 20 gauge and at least 1.5 cm in length, or it should contain at least five portal tracts. For accurate and reliable grading and staging of chronic viral hepatitis, however, studies have shown that a biopsy specimen of at least 2 cm that contains at least 11 complete portal tracts is needed.

Usually performed during open surgery or laparoscopy, wedge biopsy is discouraged for evaluation of diffuse parenchymal liver diseases, such as cirrhosis, because this technique samples primarily the subcapsular liver parenchyma, which may contain misleading fibrous septa that extend from the capsule deep into the underlying parenchyma and can be easily confused or overinterpreted as fibrosis ( Fig. 74.3 ). A wedge biopsy is most suitable for evaluation of visible focal lesions present on or immediately below the capsule. Even during open surgery, a needle biopsy to sample deep liver parenchyma is preferable for evaluation of diffuse disease.

Prompt fixation of the liver biopsy specimen in buffered formalin is vital to high-quality histology. Many special stains and analyses, such as iron or copper quantitation, and molecular and genomic analyses can be performed on formalin-fixed, paraffin-embedded (FFPE) tissue. If an unusual metabolic disorder is suspected and electron microscopic examination is expected, prebiopsy discussion with the pathologist is useful so that additional fresh tissue can be fixed in glutaraldehyde. For final interpretation of any liver tissue, sufficient clinical information is necessary.

The safety of liver biopsy depends on operator experience as well as the underlying condition of the liver, as noted in a large study. The most serious complications are rare and include bleeding (0.6%–0.7%), and death (0.2%). Extrahepatic or intrahepatic tumor seeding from biopsy and/or ablation of tumor is a dreaded but rare complication.

Morphologic findings in cirrhosis

Grossly, the liver with established cirrhosis exhibits a nodular appearance that diffusely involves the entire liver ( Fig. 74.4 ). The cirrhotic liver is firm and may be enlarged or shrunken. The parenchyma may be tan, yellow (when fatty), or dark green when there is bile stasis. The nodules’ sizes may be a clue to the underlying disease: “micronodular” cirrhosis, in which nodules are <3 mm is prototypic of ALD. Mixed micromacronodular cirrhosis is the most common. Large, bulging nodules that are notably discolored from background are worrisome for malignancy, particularly HCC.

Microscopically, the liver parenchyma is divided by interconnecting, variable-sized fibrous septa that contain profiles of lymphatic and vascular lumina, as well as epithelial-lined ductular structures and diverse inflammatory cell types; the septa divide the parenchyma into the nodules that typically no longer retain an identifiable terminal hepatic venule. However, identifiable portal tracts may be found within the septa. Some “hints” of the preceding liver disease may be retained in or near the portal tracts: lymphoid aggregates in HCV or HBV, granulomatous cholangitis in primary biliary cholangitis (PBC), complete absence or replacement of ducts by scar in primary sclerosing cholangitis (PSC). The normal portal-central relationship is lost; the exception to this remodeling is biliary cirrhosis, in which the terminal hepatic venule may retain its central location. The hepatocytes within the nodules may appear morphologically normal, may be undergoing active injury from the disease process, or may show evidence of regeneration. The latter may be characterized by thickened cell plates with as many as two cells across; anisonucleosis; large-cell change with maintenance of nuclear/cytoplasmic (N/C) ratio; or small, crowded cells with increased N/C ratios. The reticulin stain is useful to show cord thickening.

Along the edges of septa, there are recognizable biliary structures admixed with connective tissue and inflammation. This process of epithelial-mesenchymal-inflammatory interaction at the interface with damaged hepatocytes is referred to as the ductular reaction , a prototypic response that occurs in all forms of chronic liver disease, albeit with differing appearance depending on the exact disease process. The epithelial component within this rim is progressively attenuated and ultimately lost concurrently with neoplastic progression of the intranodular hepatocytes from cirrhosis to dysplastic nodule to encapsulated HCC. This can be appreciated by immunohistochemical staining with antibodies to biliary keratins 7 or 19.

Biliary cirrhosis is caused by disorders such as PBC, PSC or secondary sclerosing cholangitis, and biliary atresia. This type of cirrhosis exhibits unique morphologic features appreciated microscopically and characterized by a highly irregular “jigsaw puzzle” or “geographic” nodular pattern ( Fig. 74.5 ). As noted, the terminal hepatic venule may be retained, and loss or effacement of native bile ducts by either lymphoid aggregates or scar tissue may be evident. Ductular reaction (proliferation) may be more pronounced than in other types of cirrhosis. A characteristic clue to biliary cirrhosis is the constellation of findings in periseptal hepatocytes referred to as cholate stasis (chronic cholestasis). These findings include periseptal hepatocyte swelling/ballooning, Mallory-Denk bodies (Mallory’s hyaline), and granules of copper deposition. In addition, foam cell aggregates may be seen in the sinusoids of the nodules. Some investigators have attributed abundant large-cell change to chronic cholestasis. Another subtle histologic clue to biliary cirrhosis is the presence of nodular regenerative hyperplasia within the regenerative nodules.

Recognition of cirrhosis can be straightforward when an adequate biopsy specimen is examined, even on hematoxylin and eosin–stained sections. It may be helpful to use Masson trichrome or another connective tissue stain to highlight the dense perisinusoidal fibrosis of alcoholic hepatitis, nonalcoholic steatohepatitis and cirrhosis. Connective tissue stains are particularly helpful to discern if the broken edges of fragmented needle biopsy specimens are because of a tissue plane, or artefact, as a thin layer of collagen adheres to the curved edge of a cirrhotic nodule ( Fig. 74.6 ).

Another significant clue to cirrhosis is the numerous vascular channels within septa that traverse or course across the core biopsy.

On the other hand, cirrhosis may be difficult to diagnose on needle biopsy specimens; for instance, when a macronodule is sampled or is “incomplete” (incomplete septal cirrhosis), it may create challenges, but morphologic clues exist. In the last case, although the complete spectrum of morphologic features of cirrhosis are not exhibited, the vascular relationships are markedly altered, and ectatic, eccentrically located portal veins parallel to abnormally thin septa may be noted. In addition, some septa may be seen to extend into the parenchyma and end blindly. This type of “incomplete septal cirrhosis” is common in HBV-related liver disease.

Additional stains considered routine by liver pathologists in evaluation of liver biopsies include the iron stain and periodic acid–Schiff stain after diastase digestion (PAS-d). The former is useful in detecting and relaying semiquantification of hepatocellular iron, detecting reticuloendothelial iron, and highlighting intracanalicular bile plugs. PAS-d is useful in detecting the variable-sized periportal eosinophilic “globules” that accumulate in the endoplasmic reticulum when a Z allele is present in subjects with either MZ or ZZ α ₁ -antitrypsin deficiency. PAS-d also is quite helpful in noting bile duct basement membranes, perisinusoidal basement membranes, and PAS-d–laden Kupffer cells and portal and septal macrophages characteristic of recent necroinflammatory activity.

Not all larger nodules detected in cirrhotic livers are malignant. A macroregenerative nodule or large regenerative nodule usually measures 0.5 to 1.5 cm and is rarely 5 cm or more in diameter. It is seen more commonly in macronodular cirrhosis and may be distinct from surrounding cirrhotic nodules on gross examination. Histologically, a macroregenerative nodule may contain portal structures or short fibrovascular septa. The hepatocytes within the nodule are similar to the hepatocytes in smaller cirrhotic nodules but almost always exhibit hyperplastic change, evidenced by thickened plates. The clonal nature of the macroregenerative nodule has been shown, and its malignant potential is low but unquestioned.

A dysplastic nodule is a premalignant lesion that usually measures more than 0.5 cm. Evolution to HCC within months or a few years has been well documented. A high-grade dysplastic nodule exhibits more clear-cut architectural or cytologic atypia, such as bulging or map-like clonal growth; pseudoglandular formation; unpaired arteries; and small-cell change characterized by increased cell density, high N/C cell ratio, and nuclear hyperchromasia. These morphologic changes are insufficient, however, for the diagnosis of HCC because a dysplastic nodule does not invade the surrounding stroma or blood vessels, and it maintains cell plates no more than three cells wide.

Distinguishing a high-grade dysplastic nodule from well-differentiated HCC can be extremely difficult or impossible from a needle biopsy specimen, although it may be less ambiguous when an explant is examined ( Fig. 74.7 ; see Chapter 89 ). Identification of ductular reaction at the periphery aids in positive identification of cirrhosis or dysplastic nodule. ^, Clinical management of patients with cirrhosis and dysplasia in biopsy specimens is challenging.