Additional clinical problems arise with prolonged cholestasis. Steatorrhea results from impaired bile acid secretion and gives rise to fat-soluble vitamin deficiencies, which yield their own sequelae. In particular, vitamin D malabsorption contributes to hepatic osteodystrophy, and vitamin K deficiency to bleeding abnormalities.⁴ In children with chronic cholestasis, vitamin E deficiency may produce a degenerative neurologic syndrome with ataxia, peripheral neuropathy, and ophthalmoplegia; this deficiency also occurs in adults suffering cholestasis, but neurologic symptoms do not develop.^12,23 In addition, xanthelasma or xanthomas may develop from the elevated serum lipid levels.

Many of the laboratory abnormalities found in cholestasis reflect the accumulation of biliary components in the blood. Increased serum concentrations of bilirubin, bile acids, and cholesterol are therefore commonly found. The most generally useful marker of cholestasis is the serum alkaline phosphatase. This enzyme normally resides on the canalicular membrane, but in cholestasis, because of altered hepatocyte polarity, it occurs along the entire plasma membrane. This misplaced enzyme is then liberated into the blood as retained bile acids partially solubilize the membranes.¹³ Although not specific, alkaline phosphatase elevations of more than three- or fourfold strongly suggest cholestasis, particularly when accompanied by relatively minor increases in transaminase levels. Other enzymes -- gamma-glutamyl transpeptidase, 5'-nucleotidase, and leucine aminopeptidase -- parallel the rise in alkaline phosphatase.

Cholestasis is recognized histologically by the accumulation of biliary constituents in liver tissue. This typically implies the presence of yellow-brown bile pigment -- bilirubin and its degradation products -- in microscopic sections.

Although bile pigment is a common and salient feature of cholestasis, it is not an invariable finding. Some chronic and low-grade cholestatic disorders, for instance, lack visible bile pigment and instead show morphologic abnormalities ascribed to the retention of bile acids. The histologic definition of cholestasis must therefore be expanded to include these abnormalities as well. Small quantities of bile pigment may also be leached from tissue specimens during processing and thus be missing from the microscopic sections. Conversely, bile pigment occasionally appears in noncholestatic settings such as hepatic neoplasms or congenital hepatic fibrosis.

Cholestasis can assume several histologic patterns with differing diagnostic and clinical connotations (Table 4-1). The two main patterns, canalicular cholestasis and chronic cholestasis, are general categories, more indicative of the tempo and degree of cholestasis than any exact cause. The other two patterns, ductular cholestasis and ductal cholestasis, usually develop within a background of canalicular cholestasis, but are distinguished because of their narrower clinical settings.

Canalicular Cholestasis

This standard and commonplace variant signifies an active cholestatic process and is found primarily in clinically acute disease. At times, however, chronic liver disease may also exhibit canalicular cholestasis, particularly when some active cholestatic event, such as severe hepatocyte failure or sepsis, intercedes.

The hallmark of canalicular cholestasis is the canalicular bile plug, an inspissated mass of biliary material situated within a bile canaliculus (Figure 4-2). Of various yellow to green to brown hues, bile plugs follow the canalicular network and thus display circular, linear, or branching profiles depending on the plane of microscopic sectioning. These plugs represent complex accretions of bilirubin, bile acids, lipids, and plasma membrane fragments and exhibit variegated amorphous, lamellar, granular, and crystalline configurations upon ultrastructural examination.⁴³

Bile plugs are primarily located in the centrilobular region, but they spread centrifugally as cholestasis persists, in severe cases, even affecting the periportal zone. The reason for this preference is uncertain, but it probably reflects the regional differences among hepatocytes across the lobule. Sitting at the headwaters of bile flow, the centrilobular liver cells have a greater metabolic vulnerability, receive a lower oxygen tension, and contribute less to bile flow than periportal hepatocytes, all factors that would predispose to centrilobular bile stagnation.⁵

Bile pigment also collects within hepatocytes and, after phagocytosis, in Kupffer cells. This intracellular accumulation may be confused with other yellow-brown cytoplasmic pigments, particularly lipofuscin and hemosiderin, but can be easily distinguished by its vivid green appearance with van Gieson or Hall stains. These stains are rarely necessary, however, since intracellular bile pigment in canalicular cholestasis is almost always accompanied by bile plugs, which are a more obvious -- and therefore more reliable -- diagnostic clue.

In addition to the bile plugs, canalicular cholestasis entails several forms of hepatocyte injury. In early or mild cholestasis, the hepatocytes become enlarged and swollen, sometimes with finely granular cytoplasm, and scattered binucleate cells and mitotic figures are seen (Figure 4-3). As the injury progresses, the hepatocytes gain a pale, lucent appearance, their cytoplasm appearing as thin, and sometimes bile-stained, strands arranged in a net-like web (Figure 4-4). This cytoplasmic reticulation, probably the result of retained bile acids, has inspired an apt avian metaphor, so traditionally this type of liver cell injury is known as feathery degeneration.^29,66 Feathery degeneration represents the classic morphologic expression of cholestatic-induced hepatocyte injury. The same basic appearance is seen in both canalicular and chronic cholestasis, although to various extents and in different histologic contexts. This form of liver cell injury should be distinguished conceptually from the hepatocyte damage that occurs in acute hepatitis, so-called ballooning degeneration. It is characterized by granular swelling of the cell in contrast to the clear, vacuolated cytoplasm seen with feathery degeneration. Obviously these are subtle histologic discriminations, and the distinction between cholestatic and hepatitic injuries is better established by the overall setting: canalicular bile plugs (and associated changes) versus diffuse lobular inflammation and hepatocyte damage.

At first feathery degeneration affects only single scattered hepatocytes, but with continuing cholestasis, small groups of adjoining cells are involved. In severe cholestasis, these clusters may undergo necrosis, yielding the (inaccurately named) bile infarct (Figure 4-5). These demarcated pale foci are formed of indistinct hepatocyte remnants with pyknotic nuclei and bubbly cytoplasm. Escaped bile may be prominent, and fibrin deposits sometimes present. With time, the bile fades and the lesion is gradually replaced by foamy macrophages. Although small bile infarcts may occur in any intense canalicular cholestasis, large lesions, especially around portal tracts, suggest biliary obstruction.

With prolonged cholestasis of any cause, the hepatocytes can organize into cholestatic rosettes -- distinctive gland-like arrangements also known as pseudoglands or tubules (Figure 4-6).^5,29 Rosettes are formed when three or more hepatocytes share a single dilated canaliculus. The lumen frequently contains a bile plug or bile-stained debris, but it may also be empty. The encircling hepatocytes often display feathery degeneration and, moreover, express cytokeratins usually restricted to bile duct epithelium. This implies that these liver cells have undergone biliary metaplasia, possibly a general hepatocellular response to any protracted cholestasis.^41,49

Hepatocyte injury and necrosis subsequently provoke an inflammatory response. A minor scattering of lymphocytes and rare neutrophils collect in the affected lobular zone. Kupffer cells become large and prominent, often with PAS-positive pigment derived from phagocytosis of bile and cellular debris (Figure 4-7). These hypertrophied Kupffer cells can linger for weeks after the initiating event; they thereby serve as markers of prior hepatocellular damage. In long-standing cholestasis, the Kupffer cells may also amass excessive lipid material and develop a foamy xanthomatous appearance. The inflammatory reaction seen in canalicular cholestasis should be distinguished from the primary lobular inflammation seen in acute hepatitis; in cholestasis, the inflammation is focal and principally restricted to areas with bile plugs, rather than more diffusely dispersed across the lobule as in acute hepatitis.

Chronic Cholestasis

This pattern represents the typical histologic picture seen in chronic cholestatic conditions. It is especially prominent in such progressive biliary diseases as primary biliary cirrhosis and primary sclerosing cholangitis. Several synonyms have been employed for this pattern depending on which of its aspects is being emphasized; these include cholate stasis, precholestasis, pseudoxanthomatous transformation, and biliary piecemeal necrosis.^5,28,36,44

Chronic cholestasis is defined by a distinctive form of hepatocyte injury with an attendent inflammatory and fibrotic response. These changes occur principally at the margins of the portal tracts and, when bridging fibrosis is present, the fibrous septa. Although uniformly distributed around any particular portal tract, they vary in degree from tract to tract. Bile plugs are notably sparse or absent, and this pattern is therefore less obvious than canalicular cholestasis. The histologic clue on low-power examination is a zone of parenchymal pallor running along the periportal and periseptal areas (Figure 4-8).

The hepatocytes that constitute this zone are pale and swollen, sometimes with faint bile staining, and occasionally with a delicate foamy character that mimics lipid-laden macrophages (Figure 4-9). The appearance corresponds to a degree with feathery degeneration as described with canalicular cholestasis, but these cells also display two singular findings: copper accumulation and Mallory bodies. These additional features, together with the periportal or periseptal location, define the hepatocyte injury of chronic cholestasis.

Normally, the liver helps maintain copper homeostasis by disposing of excess dietary copper through the bile.⁴⁶ When bile secretion is disrupted, copper -- like any other biliary component -- accumulates in the liver, although long-standing disruption is usually required for significant copper retention. The retained intracellular copper combines is eventually sequestered within lysosomes in the form of insoluble aggregates of metallolthionein known as copper-associated protein.^38,48 These copper-laden lysosomes can be recognized on hematoxylin-and-eosin stained sections as small, gray-brown granules within the swollen periportal hepatocytes.

Copper accumulation is easily confirmed by a number of histochemical procedures. Rhodanine or rubeanic acid stains, which directly react with copper, may demonstrate diffuse cytoplasmic positivity or, more commonly, coarse granular lysosomal positivity. Alternately, stains for copper-associated protein such as orcein, aldehyde fuchsin, or Victoria blue highlight the lysosomal deposits (Figure 4-10). Because of the insolubility of copper-associated protein, these stains are generally the more reliable and sensitive technique.^34,35,37 Immunohistochemical procedures have also been applied to specifically highlight metallothionein.^30,38

Copper accumulation is a useful histologic marker of chronic cholestasis, but it is not specific.^34,35,37,47 Wilson's disease and Indian childhood cirrhosis are often characterized by prominent staining, as are occasional hepatic neoplasms. Cirrhosis and extensive fibrosis of any cause can also be accompanied by copper deposition; this is usually mild and focal in extent, as contrasted with the marked accumulation usually found when chronic cholestasis evolves to cirrhosis, but exceptions sometimes arise. Copper accumulation is therefore a stronger indicator of chronic cholestasis in precirrhotic biopsies. Neither copper nor copper-associated protein are observed in ordinary adult liver, but both are regularly present in normal fetal and neonatal liver; the finding therefore has little diagnostic significance in children younger than six months.^32,47

Irregular cytoplasmic masses of dense eosinophilic material known as Mallory bodies occasionally adorn the injured hepatocytes.^33,44 Found in only a minority of cases, they are typically sparse in number, but sometimes may be a conspicuous finding (Figure 4-11). Histologically these Mallory bodies are identical to the more familiar inclusions seen in alcoholic hepatitis; the distinction can usually be made by the histologic background.

Mallory bodies are formed from aggregates of altered cytokeratins, and in general terms, they denote a derangement in cytoskeletal organization and expression.³¹ Their significance in chronic cholestasis is unclear, although they contain bile duct cytokeratins and thus may reflect biliary metaplasia of hepatocytes.³⁹

The connective tissue adjacent to the damaged hepatocytes becomes edematous and inflamed with variable numbers of foamy macrophages, lymphocytes, and neutrophils (Figure 4-12). This infiltrate, joined by thin proliferated bile ductules and small spurs of fibrosis, creeps beyond the portal tract into the adjacent parenchyma and irregularly separates the swollen hepatocytes. By its periportal location and assertive nature, this process simulates the piecemeal necrosis of chronic active hepatitis and has therefore been referred to as biliary piecemeal necrosis.^28,44 The two reactions can usually be distinguished by the heterogeneous inflammatory population found in chronic cholestasis: in chronic active hepatitis, the inflammatory component is predominantly lymphocytic and lacks neutrophils or foamy macrophages. Nevertheless, in a given microscopic field, the distinction can be difficult, and demonstrating copper deposition can then be helpful in establishing a diagnosis of chronic cholestasis.

Ductal Cholestasis

This type of cholestasis is characterized by bile pigment within the interlobular bile ducts (Figure 4-13). It is an uncommon pattern, easily overlooked if the pigment is sparse, but nevertheless noteworthy because it strongly suggests biliary obstruction.^36,66 The ductal epithelial cells are often bile-stained and can appear normal, enlarged and reactive, or, with luminal dilatation, flattened and atrophic. Unfortunately, ductal cholestasis is an infrequent observation in biliary obstruction, so its diagnostic utility is limited. Furthermore, it may be seen, albeit rarely, in the absence of bile duct blockage. Typically this occurs when the ductal epithelium has been severely damaged, as may happen, for instance, in liver transplantation, severe neonatal hepatitis, confluent hepatocellular necrosis, and fatal exertional heatstroke.⁴⁵

Ductular Cholestasis

The key feature of this pattern is the accumulation of bile pigment within proliferated bile ductules found along the perimeter of the portal tracts (Figure 4-14). These ductules are dilated and contain dense inspissated bile; their epithelial cells may be swollen or thinned and almost inapparent. Neutrophils are variably scattered around and within the ductules, and canalicular cholestasis may be present.

This pattern generally signifies sepsis, and affected patients are often severely jaundiced and ill.^27,40,42 Bacterial pneumonia and intraabdominal suppuration are the common settings. The pathogenesis presumably entails interefence with normal ductular secretory and resorptive processes by bacterial endotoxins, although the precise mechanism is uncertain. This pattern has also been noted in other setting including liver transplantation, total parenteral nutrition, and drug-induced toxicity (in particular with the discontinued agent benoxaprofen).^42,101,137 It has also been reported with extensive hepatocellular necrosis and chronic liver disease in terminal stages, but concomitant sepsis is often a confounding feature in these cases. Contrary to one's expectation, ductular cholestasis is not generally a feature of acute biliary obstruction in the absence of superimposed sepsis. (One exception to this rule is biliary atresia in newborns, which may show inspissated bile plugs within ductules.)

Once cholestasis is recognized, the next problem is to determine which of the numerous diagnostic possibilities is responsible. A basic strategy assesses the duration of the cholestatic process and its likely anatomic level, thereby separating cholestatic disease into several general categories, as illustrated in Table 4-2. This classification provides a broad diagnostic framework for discriminating among the various possibilities and narrowing the differential diagnosis.

As a rule, the duration of the cholestasis is gauged by the histologic pattern: canalicular cholestasis is associated with acute cholestatic disease, and chronic cholestasis -- as the name indicates -- with chronic disease. Note that these histologic appearances need not correspond exactly with the clinical chronology. Canalicular cholestasis may arise in long-standing liver disease, often as a terminal complication, and on the other hand, histologically defined chronic cholestasis may present as a clinically acute process.

The anatomic level of the disease is identified, not by the histologic changes of cholestasis, but by the additional morphologic features present. The specific details of these features are presented in the remainder of this chapter and in Chapters 5 and 6, but the level can be generally assessed by noting the distribution of the morphologic process.

Large bile duct conditions are suggested by particular changes in the portal tracts, including prominent ductular proliferation and a neutrophil-rich inflammatory infiltrate. These are secondary alterations, indirectly reflecting the obstruction downstream, and therefore, although characteristic, they are generally not definitive. The diagnosis is instead established by radiographic imaging techniques.

The small bile duct disease are indicated by epithelial damage and inflammation affecting the interlobular and septal bile ducts (Chapter 5). Chronic varieties of the small duct condition are often remarkable because the bile ducts progressively disappear; this is an important observation associated with a small list of diagnostic possibilities. Both large and small ducts can be directly involved in certain diseases -- for instance, primary sclerosing cholangitis and biliary atresia -- and features of both categories can be present.

The hepatocellular cholestatic disorders are a diverse group in which pathologic alterations center on the hepatic lobules. Included are both primary cholestatic conditions, where the histologic changes can be ascribed solely to cholestasis, and secondary cholestatic disorders, in which other background features are also present. Briefly addressed later in this chapter, the secondary conditions are considered in detail elsewhere.

This approach provides a first-step towards appraising and categorizing cholestatic liver biopsies. A differential diagnosis can be then be constructed and specific diagnostic clues can be pursued. As always, attention to the clinical history and ancillary data is essential.

Biliary obstruction is defined as the mechanical blockage of the extrahepatic or large intrahepatic bile ducts. This occlusion not only hinders bile flow and produces cholestasis but it also may lead to bacterial cholangitis and sepsis, and, when persistent, can result in cirrhosis and its attendant sequelae. Biliary obstruction is largely a clinical and radiographic diagnosis, and liver biopsy is seldom a necessary procedure. The histologic features of obstruction are nevertheless important to recognize; clinical features or diagnostic studies may be equivocal or misleading -- especially with early or low-grade obstruction -- and a liver biopsy may be the sole indicator of biliary disease.

An impressive list of diseases can give rise to biliary obstruction (Table 4-3). Many of these are rare causes, occurring only with case-report frequency, and most instances of obstruction result from gallstones, masses (primarily neoplasms), or strictures.

Gallstones cause biliary obstruction by lodging in the common bile duct, usually at its distal end, and blocking the lumen in an intermittent, ball-valve fashion. The majority of these common duct stones are cholesterol or black pigment stones that have originated in the gallbladder and then migrated into the duct.^54,74,89 A notable proportion, however, are brown pigment stones that have likely formed directly within the common bile duct.^54,91 These stones, distinguished by their dull yellow-brown, earthy appearance, usually occur in a background of biliary stasis and infection; hence they may be associated with biliary strictures, sclerosing cholangitis, and congenital bile duct abnormalities, and also account for most of the common duct stones that recur after cholecystectomy.^59,74,87 In the Far East, where they are much more prevalent than in the West, brown pigment stones may involve the intrahepatic bile ducts (hepatolithiasis) and represent a component of recurrent pyogenic cholangitis (Chapter 5).

At times, stones still within the gallbladder can produce biliary obstruction (Mirizzi syndrome). This occurs when the stone impacts in the gallbladder neck or cystic duct and produces an inflammatory reaction that compresses the adjacent common hepatic duct.⁶²

All manner of neoplasms and tumor-like masses can obstruct bile ducts. Prominent offenders, of course, are carcinomas of the bile ducts, the gallbladder, and the periampullary region, including the pancreas, duodenum, and ampulla of Vater.⁷⁰ The rare benign tumors of these sites act similarly. Even hepatocellular carcinomas may present with biliary obstruction by invading bile ducts and clogging them with tumor, necrotic debris, or blood clot.^80,93

Metastatic tumors can also cause obstruction. This typically results from involvement of lymph nodes in the porta hepatis or the pancreaticoduodenal chain, but some cancers metastasize directly to the duct wall or periductal connective tissues.^65,88,99 The primary cancers commonly responsible are carcinomas of the stomach, colon, breast, and lung, lymphomas, and melanoma.^70,86,90

Other large or strategically situated hepatic masses can encroach on major intrahepatic ducts and cause focal biliary obstruction. Metastatic tumors are the most common examples, but other expansile space-occupying lesions -- primary hepatic neoplasms, cysts, and abscesses -- may do likewise.^{50,58,60,79,94} Because these masses block local vasculature as well as bile ducts, the neighboring liver often shows sinusoidal dilatation in addition to the portal tract changes of biliary obstruction. This combination of findings in a biopsy specimen can therefore alert the pathologist to a nearby unsampled mass such as a missed metastatic focus.⁶⁷

Benign biliary strictures develop when injury to the ductal wall yields fibrous scarring and luminal narrowing. Most stricture arise as sequelae of operative injury, with cholecystectomy the typical culprit.^55,95 Other causes include the biliary insults associated with chronic pancreatitis, choledocholithiasis, external blunt trauma, and subhepatic abscess; some cases have no clearly identifiable cause.^51,85,97 Primary sclerosing cholangitis represents an idiopathic variant characterized by multiple irregular strictures and special clinical and histologic features. The same cholangiographic appearance can sometimes result from a known cause of biliary stricturing; this circumstance is often referred to as secondary sclerosing cholangitis (Chapter 5).

Biliary obstruction also can result from an exotic cause: parasite or fungal infections, aneurysms of the celiac axis, or duodenal diverticula.^57,92

Biliary obstruction is usually suspected from the clinical history, physical examination, and laboratory abnormalities.^8,15,20 In addition to the clinical features common to any type of cholestasis, patients may have clues that hint at biliary blockage: abdominal pain, fever (implying bacterial cholangitis), an abdominal mass or palpable gallbladder, or a history of prior biliary tract surgery. Elevated serum bilirubin and alkaline phosphatase levels are the rule, but jaundice may be absent if obstruction is incomplete or focal.

Although a sensitive diagnostic procedure, clinical evaluation is not perfect. Its specificity is only about 75%, meaning that some patients with nonobstructive cholestasis are apt to be wrongly diagnosed. Radiologic techniques are therefore valuable adjuncts in securing a diagnosis.

Several imaging techniques are available.^2,26,53,68 Ultrasonography and computed tomography are useful initial procedures that can noninvasively confirm obstruction by demonstrating dilated bile ducts proximal to the site of blockage. Such dilatation may be missing, however, in early or intermittent obstruction, or when the ducts are fibrotic as in primary sclerosing cholangitis or cirrhosis. Moreover, the level and nature of the obstruction are not always defined. The conclusive investigation is direct cholangiography: contrast material is injected into the ducts, either by endoscopic retrograde or percutaneous transhepatic routes, and direct visualization of the ductal lumen is possible (Figure 4-15). This technique provides a sensitive and specific means of diagnosing obstruction and also defines the site and cause in almost all patients.

The liver in biliary obstruction is basically an innocent victim, suffering the consequences of events proceeding somewhere distally in the bile ducts. These consequences -- increased biliary pressure and bile stasis -- produce a succession of histologic changes in the liver. These changes are further modified by the duration, degree, and cause of the blockage and added to by such complicating factors as biliary infection. As a result, the histologic features are often nonspecific and provide only indirect evidence for duct obstruction. Liver biopsy specimens are therefore more apt to suggest than establish a diagnosis of biliary obstruction.

The major features of acute biliary obstruction include canalicular cholestasis and portal tract alterations.^61,66,82 Canalicular cholestasis, typically the earliest change, is identified by canalicular bile plugs and accompanying hepatocellular injury and inflammatory response, as described earlier (Figure 4-16). Large or periportal bile infarcts are particularly indicative of biliary obstruction, but they are usually seen with high-grade occlusion and are uncommon lesions in biopsy specimens. Canalicular cholestasis may be absent if the blockage is partial or sporadic.

The portal tract abnormalities appear only after one or two weeks of obstruction. The affected tracts become edematous and inflamed with neutrophils and scattered lymphocytes, other mononuclear cells, and occasional eosinophils (Figure 4-17). Of more diagnostic use, however, are the changes in bile ducts.

A consistent finding is the proliferation of bile ductules, characteristically along the borders of portal tracts (Figure 4-18).^61,66 This marginal ductular proliferation involves most portal areas, usually to varying degrees, although the larger tracts are often most conspicuously affected. The proliferated ductules have small but well-defined lumens and are lined by uniform cuboidal epithelium, sometimes with hyperchromatic or variably sized nuclei. Neutrophils commonly cluster around the ductules, but this is seen with any type of ductular proliferation and does not imply bacterial cholangitis. The ductules appear to derive from preexisting bile ducts that have grown elongated and tortuous in response to increased intraluminal pressure; in microscopic sections these sinuous ducts are seen as multiple ductular profiles.⁸³

Ductular proliferation at portal tract margins, although characteristic of biliary obstruction, is not a specific feature. Nevertheless, when it is prominent and widespread, obstruction should be suspected.^75,78

The interlobular bile ducts demonstrate further abnormalties. Their epithelium commonly appears irregular and focally hyperplastic as the lining cells enlarge, develop reactive nuclear changes, and proliferate (as evinced by mitoses). At times, the duct dilates and the epithelium flattens from the increased luminal pressure. Edema accentuates the periductal connective tissue, and inflammatory cells (including neutrophils) gather. Other ductal changes are more specific for obstruction than ductular proliferation, but unfortunately, they are uncommon.

One such change is acute cholangitis, characterized by neutrophils infiltrating into bile duct epithelium (Figure 4-19). When flagrant this may manifest as obvious ductal suppuration, but it is more often represented by scattered neutrophils situated between epithelial cells together with a more prominent infiltrate around the duct. Acute cholangitis (in this histologic sense) need not signify biliary infection, although this is likely when more than an occasional intraepithelial neutrophil is present. The correlation, however, between bile cultures, symptoms of bacterial cholangitis, and portal tract abnormalities is imperfect.^64,77 The differential diagnosis of acute cholangitis is detailed in Chapter 5.

In addition, the ducts may exhibit ductal cholestasis wherein bile pigment forms intraluminal masses and stains the biliary epithelium. This observation virtually assures biliary obstruction, but is noted in only about 10% of cases.^36,66 The ducts (or ductules) may also leak bile into and around the portal tract. This pool of biliary material, referred to a bile lake (or bile extravasate), provokes a local xanthogranulomatous response and may ultimately come to resemble a periportal bile infarct (Figure 4-20). Although highly specific for obstruction, bile lakes are a late feature rare in biopsy specimens.⁶⁶

As bile duct blockage continues, the features of acute obstruction persevere, but changes indicating chronic obstruction gradually develop and increasingly dominate the histologic picture. The key features include chronic cholestasis and fibrosis.

Chronic cholestasis, as discussed above, is characterized by alterations in the periportal or periseptal region. The hepatocytes in this zone become swollen and vacuolated; they frequently contain stainable copper and copper-associated protein, and Mallory bodies may appear. The neighboring connective tissue is pale, edematous, and inflamed with lymphocytes, neutrophils, and macrophages. Proliferated bile ductules and fibrosis join in the process, extending out from the portal tract between affected hepatocytes to erode and irregularly replace the bordering parenchyma.

Fibrosis in chronic obstruction takes several forms. Layers of periductal fibrosis may encircle the bile ducts, particularly the larger ones, producing a concentric "onion-skin" appearance. The attendant ductal epithelium can appear injured, atrophic or hyperplastic with papillary infoldings (Figure 4-21). Rarely the epithelium is destroyed and the duct disappears; this is more characteristic of primary sclerosing cholangitis than the usual biliary obstruction.^71,72

In addition, a distinctive pattern of biliary fibrosis derives from the combination of the active periportal fibroplasia seen with chronic cholestasis and the fibrosis provoked by continuing marginal bile ductular proliferation. Cellular zones of fibrous tissue, accompanied by inflammatory cells and ductules, expand the portal tract and project into the parenchyma (Figure 4-22). Eventually these fibrous spurs link with adjacent portal tracts to yield portal-portal fibrous septa. As additional septa form, individual liver lobules are surrounded, leaving behind islands of liver cells with lobulated geographic configurations often likened to jigsaw puzzle pieces. These are sometimes enveloped by a narrow edematous rim of laminar collagen fibers as chronic cholestasis persists.

Hepatocyte hyperplasia, manifest by thickened liver-cell plates, develops in some instances of biliary fibrosis; in some instances, this may give rise to portal hypertension.^69,96 However, despite the bridging fibrosis, normal vascular architecture within the parenchymal islands is maintained: centrilobular veins are correctly located in relation to portal structures. Cirrhosis (in the strict sense) is therefore not yet present. This distinction is of importance because biliary fibrosis, even when severe, may regress if obstruction is relieved, whereas true cirrhosis is presumably irreversible.^71,98

Nonetheless, continued obstruction ultimately does generates architectural abnormalities and nodular parenchymal hyperplasia: an obstructive (or secondary) biliary cirrhosis is thus established. Progression to cirrhosis probably depends upon such factors as the cause, degree, and intensity of the occlusion as well as the occurence of complications like bacterial cholangitis, but the exact determinants are unclear. Nevertheless, many months to years of obstruction are generally required.^81,96 (One exception is biliary atresia in newborns, which can lead to cirrhosis within several months.) Obstructive biliary cirrhosis is an infrequent biopsy diagnosis: before cirrhosis has time to develop either the obstruction is relieved or the patient dies, commonly because of malignant occlusion or sepsis.

This cirrhosis is characteristically micronodular with garland- or jigsaw-shaped nodules (as described with biliary fibrosis) that are enclosed by broad fibrous septa (Figure 4-23). The features of acute and chronic obstruction are variably present: canalicular cholestasis, ductular proliferation, a neutrophil-rich inflammatory infiltrate, concentric periductal fibrosis, or chronic cholestatic changes can all be noted. At times inspissated bile is found within proliferated ductules; bile lakes may also be identified. Although all these features point to a biliary origin, in late stages they may vanish. The appearance then resembles any end-stage cirrhosis, and an etiologic diagnosis is not possible.^52,63,73

The diagnosis of biliary obstruction is seldom based solely on morphologic findings, although it can be suspected when particular histologic features are present. These distinctive features include acute cholangitis, ductal cholestasis, periportal bile infarcts, and bile lakes. Unfortunately, depending upon the duration and degree of obstruction, only a minority of cases possess these clues. Of greater diagnostic use then are such portal tract alterations as bile ductular proliferation (especially at the portal tract margins), portal edema, and portal infiltration with prominent neutrophils. These changes, although not specific, suggest biliary obstruction with an 80% to 85% accuracy.^75,76,82 Most apt to be missed are cases with incomplete or intermittent obstruction, such as with bile duct strictures or recurrent bouts of choledocholithiasis; the portal tracts in these instances may be misleadingly normal or may only show minor inflammatory infiltration or fibrosis.

The differential diagnosis involves those conditions with portal tract alterations that resemble those of biliary obstruction. The distinction may not be possible histologically, and clinical and radiographic data are often required to establish the proper diagnosis.

Drug-induced cholestasis may sometimes display portal tract inflammation and even bile duct damage (including acute cholangitis), along with canalicular cholestasis. Although many agents are potentially responsible, notable culprits include chlorpromazine, erythromycin derivatives, chlorpropamide, phenylbutazone, and total parenteral nutrition.^56,101,137 These cases may be distinguished by the typical absence of marginal ductular proliferation and the presence of conspicuous eosinophil infiltrates or epithelioid granulomas, although neither is an invariable or conclusive finding of drug toxicity.^103,114

Ductular cholestasis can also mimic biliary obstruction by its proliferated bile ductules and portal neutrophils, but the presence of ductular bile pigment is distinctive.^27,40 Moreover, in liver transplantation obstructive-type features may be seen with resolving acute rejection; the context and radiographic results are again useful.⁸⁴

Chronic biliary obstruction can be confused with chronic hepatitis because they both share such features as a mononuclear portal infiltrate and periportal fibrosis. Copper stains together with clinical and radiologic information usually solve this problem.

This category encompasses a miscellany of conditions whose focus is the hepatic lobules and the liver cells rather than the large or small bile ducts. Given the pathogenetic range of cholestasis, these conditions include a wide variety of both primary and secondary cholestatic disorders. Pragmatically they can be separated into two histologic groups: pure cholestasis and compound cholestasis. Pure cholestasis, as the name implies, designated the presence of cholestasis alone, whereas in compound cholestasis some additional lobular or hepatocellular abnormality is evident. This distinction is usually straightforward, although there is some overlap, particularly with drug-induced injuries.

Pure Cholestasis

This pattern is characterized by canalicular cholestasis unadorned by other histologic alterations (Figure 4-24). Canalicular bile plugs, mild hepatocellular damage, and in prolonged cases, cholestatic rosettes are therefore noted, but hepatocellular necrosis is absent and lobular and portal inflammation are missing or minimal.¹³⁵ Such synonyms as simple or bland cholestasis further emphasize the austere morphologic picture. Pure cholestasis is potentially an early manifestation of any cholestatic condition, but the disorders commonly associated with this pattern are specified in Table 4-4 and briefly discussed below. Pure cholestasis is generally an innocuous process, usually presenting with pruritus followed by mild jaundice. It is typically a reversible process and does not result in progressive liver disease. Because the various pure cholestatic conditions show the same histologic pattern, the distinction is primarily based on clinical circumstances.

Benign recurrent intrahepatic cholestasis designates a familial condition distinguished by multiple, transient episodes of cholestasis. It is an uncommon disorder: fewer than 100 cases have been reported since the original description by Summerskill and Walshe in 1959.¹³¹ The onset, duration, and frequency of the cholestatic attacks vary widely. Usually the episodes first appear in childhood or early adulthood and consist of a flu-like prodrome succeeded by pruritus and jaundice. These symptoms resolve spontaneously, usually in three or four months, but they may last for only a few days or may persist for as long as two years. Further attacks then occur after an interlude that averages about 15 months but may range from a few months to over 20 years. No clinical, laboratory, or histologic abnormalities are present between attacks, and there are no long-term sequelae, even after repeated episodes over many years. The pathogenesis is not established, but an inherited abnormality in bile acid metabolism has been proposed.^{104,105,118,123}

Intrahepatic cholestasis of pregnancy refers to an unusual self-limited form of gestational cholestasis. Symptoms typically develop during the third trimester (although the onset may be earlier), continue for the duration of the pregnancy, and disappear rapidly with delivery. A reappearance with subsequent pregnancies is common. Other than the discomfort of pruritus and occasional fat malabsorption, the mothers suffer no serious consequences and develop no long-term liver disease. The fetus, however, is vulnerable to intrauterine distress, premature delivery, or death, particularly in severe cases, and routine fetal monitoring has been advocated.^102,125,126

This disorder appears to represent one manifestation of an underlying inherited sensitivity to estrogens. Affected women therefore develop cholestasis not only when pregnant but also when using synthetic estrogens such as oral contraceptives. Furthermore, mothers and sisters of these women frequently display the same predisposition to estrogen-related cholestasis, and pedigree studies in some families have supported a Mendelian dominant transmission.¹¹² This susceptibility is particularly expressed in certain ethnic groups and geographic areas: up to 10% of pregnancies in regions of Chile and Scandinavia are complicated by intrahepatic cholestasis as contrasted with less than 0.1% of North American and European pregnancies.¹²⁵

Drug-induced pure cholestasis is classically produced by estrogenic and androgenic steroids.¹¹³ Although many patients receiving these agents develop subtle and subclinical evidence of liver dysfunction, only rarely does overt cholestasis arise. This typically appears within a few months of usage and quickly vanishes once the drug is stopped. The development of estrogen-related cholestasis probably requires a genetic predisposition, accounting for both the common familial history and the overlap with intrahepatic cholestasis of pregnancy. A similar propensity is proposed for androgen-induced examples, but has not extensively investigated. The cellular mechanism is unclear, but proposals include changes in the physical properties of hepatocyte plasma membrane or the production of cholestatic metabolites.¹³³ Other drug-induced cholestasis is generally associated with some degree of hepatocellular necrosis and attendant inflammation, although when these changes are minimal, the appearance may be that of pure cholestasis.

Sepsis is a celebrated cause of cholestasis, especially in infants and young children, but also occasionally in adults. Pure cholestasis commonly comprises the underlying histologic alteration; it may be joined by minor nonspecific changes including Kupffer cell hyperplasia, mild fatty change, or a mild scattering of lymphocytes within portal tracts.^109,130,136 This subject is further addressed in Chapter 8.

In patients with malignant neoplasms, pure cholestasis may develop as a paraneoplastic process, occurring without direct tumor involvement or biliary obstruction. Hodgkin's disease is the notorious example, but non-Hodgkin's lymphomas, renal cell carcinoma, and prostatic carcinoma have also been implicated.^{106,115,117,121,124} This is a rare event: in the face of malignancy, cholestasis is more apt to represent a terminal event in advanced metastatic disease.

An eclectic collection of disorders, this category includes many types of acute or chronic hepatocellular disease. Often cholestasis is a minor component of the overall picture, and the correct diagnosis is obvious histologically and clinically. At times, however, the cholestasis is prominent enough to confound the diagnosis. The approach for the pathologist is to mentally subtract the cholestatic features from the histology and to assess the remaining abnormalities in concert with clinical information. Complete descriptions of these conditions are presented elsewhere, and only brief comments are included here.

Acute hepatitis (Chapter 2), particularly due to hepatitis A virus, is sometimes dominated by canalicular cholestasis: canalicular bile plugs are prominent and the portal tracts may show changes suggesting biliary obstruction. Clinically, this histologic pictures is accompanied by a prolonged course with jaundice persisting up to five months.^110,129

Chronic hepatitis (Chapter 3) generally displays canalicular cholestasis only when severe hepatocyte dysfunction has supervened, although rare exceptions are recorded. Finding chronic cholestasis, however, in the setting of chronic hepatitis should prompt a consideration of primary biliary cirrhosis and primary sclerosing cholangitis: either may be confused with chronic active hepatitis, and a careful look for bile duct damage and loss is necessary.^107,134

When advanced or severe, alcoholic liver disease is often complicated by canalicular cholestasis.¹²² Nonetheless, in some instances fatty change alone, without alcoholic hepatitis or cirrhosis, is found with prominent cholestasis (Chapter 7). This fatty change, either macrovesicular or microvesicular in nature, may be accompanied by bile ductular proliferation and portal inflammation. The clinical features (as well as the histologic appearance) may therefore imitate biliary obstruction; some patients manifest evidence of liver failure.^100,119,132

A lengthy list of drugs and toxins may cause canalicular cholestasis combined with variable hepatocyte damage and inflammatory infiltration (Chapter 12). These added changes range in degree from mild liver cell swelling and focal necrosis to more striking injury and portal inflammation that may prompt the consideration of acute viral hepatitis.^103,114 Moreover, a few agents -- chlorpromazine, tolbutamide, and thiabendazole among them -- may produce chronic cholestasis, sometimes accompanied by damage and loss of bile ducts.^114,137 As with most drug-induced reactions, the histology is usually not definitive, and the clinical history is manifestly important for a correct diagnosis.

Venous outflow obstruction with sinusoidal congestion and dilatation may be joined by canalicular cholestasis, particularly when hypoperfusion or shock supervene (Chapter 11).^116,120 Rarely amyloidosis with diffuse hepatic involvement may present with marked cholestasis, presumably because bile canaliculi are compressed (Chapter 17).^108,111,127 Finally, any type of chronic liver disease with fibrosis or cirrhosis may assume some degree of cholestasis with decompensation.

These disorders result from inherited defects in bilirubin metabolism. They are, strictly speaking, not cholestatic in nature: bile secretion is not disturbed and no clinical or laboratory features of cholestasis other than hyperbilirubinemia are present. The liver histology -- with the one striking exception of Dubin-Johnson syndrome -- is normal and does not contribute to the diagnosis. They therefore merit only a brief discussion.^138,140,141

Gilbert's syndrome, which afflicts about 5% of the population, is a benign and banal variant of familial unconjugated hyperbilirubinemia. The underlying defect is incompletely understood and the mode of inheritance uncertain, but a decrease in bilirubin conjugation by glucuronyltransferase is observed in most patients. Although Gilbert's syndrome may present with slight jaundice, more often it is recognized because of mildly elevated serum bilirubin levels on biochemical screening panels. The liver is morphologically normal, and no treatment is required.

The rare Crigler-Najjar syndrome originates from either an absence of hepatic glucuronyltransferase (referred to type I) or a marked reduction in its activity (known as type II). Type I, inherited as an autosomal recessive trait, produces a severe unconjugated hyperbilirubinemia that usually results in kernicterus and early death; liver transplantation has been successfully employed in treatment.¹³⁹ Crigler-Najjar type II, in contrast, is a milder disease with typically a benign clinical course.

Two unusual forms of hereditary conjugated hyperbilirubinemia are described, Dubin-Johnson syndrome and Rotor syndrome. Both are benign autosomal recessive disorders produced by a defect in canalicular excretion of conjugated bilirubin. The characteristic feature of the Dubin-Johnson syndrome (lacking in Rotor syndrome) is the dark gray or black color of the liver imparted by the accumulation of coarsely granular brown pigment within hepatocytes. Principally centrilobular in distribution, the pigment collects within lysosomes along the pericanalicular pole of the liver cell and stains with acid fast, Fontana, and PAS stains (Figure 4-25). Although resembling lipofuscin, the granules are typically larger and more variable in size and ultrastructural appearance. The nature and origin of the pigment is obscure.