inexorable consequence of ongoing hepatic injury. HSCs are located in the perisinusoidal space of Disse

(Fig. 59-2).16 In the normal liver, these cells are quiescent and are primarily responsible for the storage

of vitamin A.17 Injured hepatocytes release soluble factors that activate HSCs to differentiate into

myofibroblastic HSCs, as evidenced by cellular enlargement and proliferation, an increase in rough

endoplasmic reticulum, loss of vitamin A droplets, expression of actin filaments, and increased

expression of “fibril-forming” collagen types I, III, and V.18 They also express components of the

extracellular matrix, including heparan sulfate, dermatan, chondroitin sulfate,19 laminin,20 and

fibronectin.21 Kupffer cells secrete TGF-β1, which appears to be critical for the activation of HSCs.5,22

Both TGF-β and PDGF have been shown to enhance proliferation and fibrogenesis in animal models,5,7,23

with TGF-β being the primary stimulator of collagen synthesis and fibrosis. Further evidence implicating

TGF-β in the production of hepatic fibrosis is the observation that levels of TGF-β are reduced by

therapy with interferon-α in patients who are positive for hepatitis C. This reduction has been

correlated with a regression of hepatic fibrosis.24

CLASSIFICATION

Table 59-1 Classification of Cirrhosis

In addition to the well-characterized effects of TGF-β1 and PDGF on activating HSCs, more recent

research has demonstrated the central role of Hedgehog (Hh) in activation of HSCs and promotion of

fibrosis.25 Hh is a molecule involved in signaling pathways that help determine cell fate during

embryogenesis. The Hh ligand binds to its cell surface receptor patched. Binding of Hh to patched

releases another effector, named smoothened, from a chronic state of inactivation. Activation of

smoothened leads to downstream activation of a number of proteins involved in nuclear transcription,

thereby leading to changes in cell fate and differentiation.25 In the liver, the two primary forms of Hh

are Sonic Hedgehog (SHh) and Indian Hedgehog (IHh), which are expressed by hepatocytes, bile duct

cells, and HSCs. In the healthy liver, quiescent HSCs and endothelial cells keep Hh inactive by

production of inhibitory proteins. When the liver is injured, however, numerous cell types including

hepatocytes, cholangiocytes, HSCs, progenitor cells, lymphocytes, duct cells, and endothelial cells

produce elevated levels of Hh under the influence of cytokines such as PDGF and TGF-β.25–30 Activation

of the Hh pathway tends to be self-sustaining and resistant to negative feedback as long as the injury

process continues.31 It is this surge in Hh levels within the local hepatic milieu that signals quiescent

HSCs to activate. The critical role of Hh signaling in HSC activation and fibrogenesis was recently

demonstrated by Michelotti et al.,32 who showed that deletion of the Hh intermediary smoothened was

sufficient to inhibit both HSC activation and fibrosis formation.

1495

Figure 59-2. Matrix and cellular alterations in hepatic fibrosis. A: In normal liver, a modest amount of low-density matrix is

present in the subendothelial space of Disse. B: In the fibrotic liver, the accumulation of fibril-forming matrix in this region leads

to “capillarization” of the sinusoid and functional changes in all neighboring cell types.

Another interesting concept that has been gaining increasing recognition is the role of the gut

microflora in the development of cirrhosis. Alcoholics, for example, are known to have a greater

susceptibility to small intestinal bacterial overgrowth along with alterations in their gut microflora. This

bacterial overgrowth and dysbiosis lead to increased levels of LPS, which reach the liver to stimulate

Kupffer cells to produce proinflammatory cytokines. The end result is the generation of mitochondrial

damage, reactive oxygen species, and ongoing hepatic inflammation.33–35 A similar role for alterations

in gut microflora has been demonstrated in nonalcoholic fatty liver disease (NAFLD).36,37

As a result of the activation of stellate cells and a subsequent enhancement in collagen and

extracellular matrix synthesis, the space of Disse becomes thickened, so that “capillarization” develops

and the normal fenestrated architecture of the sinusoidal endothelium is lost.38 Obliteration of

sinusoidal fenestrations may be the essential component of fibrosis-induced hepatocellular dysfunction

in cirrhosis, preventing the normal flow of nutrients to hepatocytes and increasing vascular resistance.39

In addition, production of endothelin-1, a potent vasoconstrictor, by endothelial or stellate cells can

cause contraction of the myofilaments within the stellate cell, influencing blood flow to injured areas

and contributing to portal hypertension.40 Initially, fibrosis may be reversible if the inciting agents are

removed. With sustained injury, the process of fibrosis becomes irreversible and leads to cirrhosis.

Growing attention has been given to approaches that might disconnect hepatic injury from the

inexorable path of fibrosis.41

Among the most promising agents currently receiving the greatest attention in the treatment of

fibrosis are the antioxidants.4 The combination of N-acetylcysteine and metformin taken for 12 months

has demonstrated reduction of fibrosis severity in patients with nonalcoholic steatohepatitis (NASH).42

The glutathione donor S-adenosylmethionine (SAMe) has demonstrated improved mortality in alcoholic

cirrhosis, and vitamin E has been shown to improve hepatic fibrosis in the setting of NAFLD.4 While the

results of studies utilizing these agents have had mixed results, ongoing investigations should establish

their role in the treatment of fibrosis. Other studies have focused on utilization of inducible pluripotent

stem cells and embryonic stem cells to replenish functional hepatocytes and restore liver function.

Mesenchymal stem cells have been studied for their ability to reduce the profibrotic and

proinflammatory milieus in the setting of hepatic damage. While these studies are in early stages, their

potential is exciting.43,44

Classification Systems

Morphology

In 1977, the World Health Organization divided cirrhosis into three categories based on the

morphologic characteristics of hepatic nodules (Fig. 59-3).45

1496

Micronodular Pattern. Nodules are almost always less than 3 mm in diameter, are relatively uniform

in size, are regularly distributed throughout the liver, and rarely contain portal tracts or efferent veins.

Micronodular livers are usually of normal size or are mildly enlarged, and the fibrous septa vary in

thickness. These changes reflect relatively early disease and are characteristic of a wide range of disease

processes, including alcoholism, biliary obstruction, venous outflow obstruction, hemochromatosis, and

Indian childhood cirrhosis.

Macronodular Pattern. In this category, nodules vary considerably in size and are larger than 3 mm in

diameter, with some nodules measuring several centimeters. Portal structures and efferent veins are

present but display architectural distortion. These livers are usually coarsely scarred with variably thick

and thin septa and may be either normal or reduced in size. Two separate subcategories are recognized

based on the nature of the fibrous septa. In the first category, characteristic of “posthepatitis” pathology

and found in Wilson disease, fine, sometimes incomplete septa link portal tracts; these are difficult to

see on gross inspection of the liver. The second is characteristic of “postnecrotic” disease, commonly

found in patients with viral hepatitis, and is characterized by coarse, thick septa that are readily

apparent on gross examination. Because of the relatively large size of the nodules relative to the size of

biopsy specimens, diagnosis by biopsy may be difficult in macronodular cirrhosis.

Figure 59-3. A: Small, shrunken liver and a fairly regular pattern of nodularity. This appearance is rather typical of end-stage

cirrhosis, regardless of the cause. B: Photomicrograph of cirrhotic liver tissue, showing irregular nodules of regenerating

hepatocytes surrounded by scar. Trichrome stain. (From Stal P, Broome U, Scheynius A, et al. Kupffer cell iron overload induces

intercellular adhesion molecule-1 expression on hepatocytes in genetic hemochromatosis. Hepatology 1995;21:1308–1316.)

Mixed Pattern. This description is applied to livers in which both micronodules and macronodules are

present in approximately equal proportions.

Etiology

Another commonly used method for classifying cirrhosis is by etiology. The causes of cirrhosis and the

morphologic and histologic characteristics of the liver, however, overlap significantly. Oxidative stress

leading to chronic injury and inflammation appears to be a common theme of these disorders, which

leads to both scar formation and an increased risk of liver cancer.

Alcohol. The relationship between alcohol and liver disease has been well established. In 1849,

Rokitansky, referring to the association of alcohol intake and liver disease, coined the term Laennec

cirrhosis.46 Consumption of at least 30 g of alcohol per day in women and 50 g of alcohol per day in men

over at least 5 years is considered to the minimum threshold alcohol intake for cirrhosis to develop.47

More than 50% of alcoholics with cirrhosis and two-thirds of patients with alcoholic hepatitis and

cirrhosis die within 4 years of diagnosis.48 Alcoholic cirrhosis is the second leading indication for liver

transplantation overall, accounting for 40% of liver transplants in Europe and 25% in the United

States.49–51 Cirrhosis, however, develops in only 10% to 30% of heavy drinkers.52 The reasons why

cirrhosis develops in some alcoholics but not in others are not clear and may depend on a variety of

factors, such as genetic predisposition, nutritional effects, concomitant drug use, and viral infection.

Alcoholic liver disease usually begins with a transition of normal architecture to fatty liver and

1497

alcoholic hepatitis, indicated histologically by the presence of megamitochondria, Mallory bodies

(eosinophilic accumulations of intermediate filaments with cytokeratin proteins), inflammation and

necrosis, and ultimately fibrosis (Fig. 59-4). Classically, the morphology of alcoholic cirrhosis is a

micronodular pattern.

2 Although alcohol may directly activate stellate cells to produce collagen independently of

inflammation and necrosis,53 the key mediator in alcohol-induced liver disease is acetaldehyde, the

product of alcohol metabolism by the enzyme alcohol dehydrogenase. Acetaldehyde (ADH) produces

numerous deleterious effects on the liver, including the following: direct activation of stellate cells

54;

inhibition of DNA repair55; depletion of glutathione, which impairs mitochondrial function and the

ability to handle free radical production; damage to microtubules, which causes protein and water

sequestration52; and formation of reduced nicotinamide adenine dinucleotide (NADH), which opposes

gluconeogenesis and inhibits fatty acid oxidation, so that steatosis and hyperlipidemia develop.52 ADH is

most active in the perivenular/centrilobular zone 3 of the hepatic lobule; as a result, relatively high

concentrations of acetaldehyde are found in this area of the liver. In addition, zone 3 is hypoxic because

of its distance from portal venous and hepatic arterial inflow. These two factors are presumably

responsible for the characteristic initial perivenular location of alcohol-induced liver disease.

Figure 59-4. Alcoholic hepatitis. Mallory bodies (arrows) are evident within the swollen, clear cytoplasm of several hepatocytes.

This hyaline material is chemotactic for leukocytes, many of which are seen within the field. Hematoxylin and eosin (H&E) stain

× 470.

Other effects of ADH include induction of lipid peroxidation with subsequent loss of integrity of cell

membranes, which causes the characteristic “ballooning degeneration” of alcohol-induced liver disease.

In addition to its direct hepatic effects, ADH is now known to play a major role in the derangement of

the gut–liver axis which plays a key role in alcohol-induced liver injury.56 In the “leaky gut hypothesis,”

ADH increases the permeability of the intestinal barrier,57 allowing bacterial endotoxin (LPS) access to

the liver via the portal circulation. Excess circulating endotoxin then activates Kupffer cells through

interaction with Toll-like Receptor 4 (TLR4) to set off the inflammatory cascade responsible for the

development of alcoholic liver disease.35 Necrosis and inflammation in the perivenular region activate

the stellate cells in the space of Disse, so that fibrosis develops. With continued ingestion of alcohol and

hepatic injury, expansion of the areas of fibrosis toward the periportal regions leads to bridging fibrosis

and ultimately cirrhosis.

3 Nonalcoholic Fatty Liver Disease/Nonalcoholic Steatohepatitis. As noted earlier, this entity has

become a major health problem in the United States and adds even further to the litany of health

consequences of obesity. NASH, as this disease was previously called, is only one stage in the NAFLD

process.58 NAFLD is now the most common cause of chronic liver disease in the United States, affecting

up to 30% to 46% of the population.59,60 NASH-related cirrhosis is expected to surpass viral hepatitis as

the leading indication for liver transplantation by 2025.25 It is characterized by infiltration of the liver

with fat, with or without inflammation (hepatitis), which shares pathologic features of alcohol-induced

liver injury but occurs in patients who do not abuse alcohol. NAFLD is associated with obesity,

hyperlipidemia, cardiovascular disease, and noninsulin-dependent diabetes, with 90% of NAFLD patients

having at least one of these risk factors and 30% having three or more.61 It now appears that most

patients traditionally diagnosed with cryptogenic cirrhosis have NAFLD.62 In addition to liver injury and

cirrhosis, NAFLD is a major risk factor for primary liver cancer HCC and, in addition to hepatitis virus

infection, accounts for the rapid rise in the incidence of HCC in Western countries.63 More broadly

1498