Biliary atresia

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Chapter 40 Biliary atresia

Mark Davenport

Overview

Biliary atresia (BA) remains a somewhat elusive disease, with our understanding confined as it is to its infancy but yet with the origin of BA essentially unknown. BA is potentially fatal, certainly if left to run its natural course (Hartley et al, 2009), but it can be treated effectively with expeditious surgery in a high proportion of patients. For the remainder, liver transplantation is an option, and indeed BA remains the single most common indication for liver transplant in the pediatric population.

BA is an occlusive panductular cholangiopathy affecting both intrahepatic and extrahepatic bile ducts. The most common classification divides BA into three types based on the most proximal level of occlusion of the extrahepatic biliary tree (Fig. 40.1). In types 1 and 2, in which there is a degree of preservation of structure of the intrahepatic bile ducts, blunting, irregularity, and pruning occurs, and dilation may be absent, even when the duct is obstructed. In the most common type of BA, type 3, the intrahepatic bile ducts are grossly abnormal with myriad small ductules coalescing at the porta hepatis. When retrograde cholangiography is possible, this is seen as a “cloud.” In approximately 5% of cases, extrahepatic formation of cysts containing clear mucus or bile can occur in the otherwise occluded biliary tree. Such cystic biliary atresia (Caponcelli et al, 2008) is distinguishable clinically and histologically from simple obstruction in a cystic choledochal malformation, where there is preservation of an epithelial lining and retention of a normal and often dilated intrahepatic biliary tree.

FIGURE 40.1 Classification of extrahepatic morphology in biliary atresia.

Etiologic Heterogeneity

BA is not one disease, certainly not one with a single cause. In all probability it is a phenotype resulting from a number of different etiologies. Three groups can be defined clinically: 1) biliary atresia splenic malformation (BASM) syndrome (Davenport et al, 1993, 2008), 2) cystic BA (Caponcelli et al, 2008), and 3) isolated BA (Table 40.1).

Table 40.1 Etiologic Heterogeneity in Biliary Atresia

Developmental biliary atresia is a term we use that includes BASM and cystic BA, for which the onset is almost certainly prenatal and is evident by the time of birth (Livesey et al, 2009). The onset of occlusion in isolated BA is much more contentious, and some authorities hold that the bile duct can be normal and patent at the time of birth and can then become occluded secondarily by virally mediated damage.

Biliary Atresia Splenic Malformation Syndrome

Although the association of BA with polysplenia had been recognized for some time, clarification of what constitutes BASM (Table 40.2) is only relatively recent (Davenport et al, 1993). The constellation of other anomalies is peculiar, and the reasons for this are still obscure. The common embryologic insult may simply be timing (30 to 35 days) rather than a specific genetic defect. Key genes are important in both bile duct development (JAG1, HNF-6 [ONECUT1]; Kohsaka et al, 2002) and visceral and somatic symmetry (INVS, CFC1; Bamford et al, 2000; Shimadera et al, 2007), although correlation with the human condition is patchy. A possible genetic link has recently been reported by a French group, who found an increased frequency of mutations in the CFC1 gene (on chromosome 2) compared with controls (Davit-Spraul et al, 2008).

Table 40.2 Spectrum of Anomalies in Biliary Atresia Splenic Malformation Syndrome

Organ System	Malformation	Notes
Splenic	Polysplenia, double spleen (95%); asplenia (5%)	No evidence of immune hypofunction
Situs determination	Inversus (50%)
Venous	Preduodenal portal vein (40%), portosystemic shunt (<2%); vena cava absence (50%)
Intestinal development	Malrotation (60%)
Cardiac	Atrial septal defect, ventricular septal defect, tetralogy of Fallot, etc. (~40%)	± Dextrocardia
Liver	Mirror image, normal, or symmetrical	Position dictated by abdominal situs
Biliary appearance	Atrophic or absent gallbladder	Often noninflammatory remnants with absence of common bile duct and obvious segmental appearance
Pancreas	Annular (<5%)
Miscellaneous	Immotile cilia syndrome, sacral agenesis

A maternal diabetic milieu seems to predispose to BASM in the same way that it can cause transposition of the great vessels and sacral agenesis, although these are not part of the usual spectrum of defects. The macroscopic appearance of the biliary tree and liver is also somewhat different from that of isolated BA, with frequent absence of the common bile duct and a miniscule gallbladder and small proximal remnant. The liver is also usually symmetric, whatever the abdominal situs.

Epidemiology

A clear difference in incidence is seen across the globe. The highest is reported in Taiwan, at one in 5000 live births (Hsiao et al, 2008). In Japan, the incidence is one in 10,000 (Nio et al, 2003), with national studies from the United Kingdom and France reporting an incidence of one in 17,000 and 19,000, respectively (Chardot et al, 1999; Livesey et al, 2009; Serinet et al, 2006). Although there are no national studies in North America, smaller regional studies suggest an incidence closer to that of Europe (Yoon et al, 1997) but with some interracial variation (The et al, 2007). Significant regional differences within the United Kingdom have also been observed, again ascribed to variations in racial origin and the nature of the BA. For example, developmental BA is more common in white infants than in those of Asian origin (Livesey et al, 2009).

A distinct female predominance in seen in those with developmental BA that is not seen in the isolated BA group for unknown reasons (Davenport et al, 1993, 2006; Livesey et al, 2009). A seasonal variation in incidence has also been observed in some regionally based studies (Yoon et al, 1997; The et al, 2007), although this has not been confirmed in the larger, national studies (Chardot et al, 1999; Livesey et al, 2009).

Pathophysiology

The macroscopic appearance of the extrahepatic biliary tree ranges from being inflamed and hypertrophic yet intact to being an atrophic negligible remnant with absent parts. The histologic appearance within the liver appears more consistent with early portal tract inflammation, a mononuclear cell infiltrate, bile duct plugging, and proliferation and fibrosis giving way to overt biliary cirrhosis from about 3 months on.

The nature of the mononuclear infiltrate has assumed a degree of importance, and many authors suggest this is the specific primary destructive element of BA (Davenport et al, 2001; Mack et al, 2007). Although not necessarily uniformly applied across the spectrum of BA, the infiltrate is largely composed of CD4+ T lymphocytes, specifically Th1 (Mack et al, 2004) and CD56+ natural killer (NK) cells (Davenport et al, 2001; Shivakumar et al, 2009), which exhibit markers for proliferation (CD71+) and activation (particularly LFA-1+ but also CD25+). Infiltrating CD8+ cells appear to lack markers of activation—such as perforin, granzyme B, and Fas ligand (Ahmed et al, 2001)—in contrast to other diseases such as primary biliary cirrhosis (see Chapter 9).

Expression of cell adhesion molecules, proteins involved in cell-cell binding, is an important precursor to an immune-active cell infiltrate. Both interstitial cell adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 are important in binding circulating leukocytes by interaction with cell-surface integrins, and they are expressed on sinusoidal and biliary epithelium of infants with BA (Dillon et al, 1997; Davenport et al, 2001).

Expression of soluble(s) ICAM-1 and sVCAM-1 in the circulation is also increased (Minnick et al, 1998; Davenport et al, 2005), as is seen in other immunologically mediated liver diseases such as primary biliary cirrhosis and sclerosing cholangitis; levels of sVCAM-1 at the time of presentation have been shown to be prognostic (Davenport et al, 2005). Increasing levels of various other cytokines (interleukin [IL]-2, tumor necrosis factor [TNF]-α, IL-18) can also be shown postoperatively (Fig. 40.2), but most discriminate poorly between patients who would clear their jaundice and those who would not; conversely, some cytokines (IL-2, interferon [IFN]-γ, IL-4, IL-10, TNF-α, and sICAM-1) were better predictors of subsequent need for early transplantation (Narayanaswamy et al, 2007).

FIGURE 40.2 Postoperative plasma tumor necrosis factor (TNF)-α levels in biliary atresia (n = 21), showing progressive increase whether clearance of jaundice was achieved (good, n = 11) or not (poor, n = 10).

(Modified from Narayanaswamy B, et al, 2007: Serial circulating markers of inflammation in biliary atresia: evolution of the post-operative inflammatory process. Hepatology 46:180-187.)

Resident (Kupffer cells) or systemic/recruited macrophages and monocytes seem to play a dual role in BA, as both the presenters of antigenic material in the first place and as the initiating driver for fibrosis in the development of chronic liver disease. Tracy and colleagues (1996) first showed increases in resident macrophages (CD68+) with marked expression of the lipopolysaccharide receptor CD14+. Increased levels of both CD68+ cells and circulating markers of CD68+, TNF-α, and IL-18, have been shown to predict outcome post-Kasai (Kobayashi et al, 1997; Narayanaswamy et al, 2007).

Viral Hypothesis of Biliary Atresia

The most recent study is one from Hannover, Germany, in which liver biopsies from 74 infants obtained at the time of portoenterostomy were tested for a panel of DNA and RNA hepatotropic viruses (Rauschenfels et al, 2009). One or more viruses was detected in about one third of infants, and the rate of detection increased with infant age, which suggested that observed viral infection was more likely to be a secondary finding rather than a specific cause.

One problem with the viral hypothesis is the lack of an explanation as to why such ubiquitous organisms only damage the biliary tree in such a small fraction of infants and children. It may be that such infants are in some way susceptible to cholangiocyte damage and require a (viral) trigger to set off an immune-mediated destructive process (Mack, 2007).

RNA gene expression studies in rotavirus-induced murine models have shown upregulation of many proinflammatory genes, among them the IFN-γ inducers IRF7 and IRF9 (Carvalho et al, 2005). Similar gene-expression profiling in human BA samples has also shown overexpression of immune regulatory genes and differences between isolated and syndromic forms (Bezerra et al, 2002; Zhang et al, 2004).

A number of studies have shown different but specific elements of genetic variation between patients with isolated BA and unaffected control subjects. Thus, susceptibility may be imparted by polymorphisms in a number of relevant genes. Examples of this include vascular endothelial growth factor (VEGFA; Lee et al, 2010), macrophage migration inhibitory factor (MIF, Arikan et al, 2006), and intercellular adhesion molecules (ICAMs; Arikan et al, 2008).

Most recently, maternal microchimerism, a novel mechanism of immune damage, has been suggested based on the observation that male infants with BA have a threefold increase in cells of maternal origin in their livers (Hayashida et al, 2007). These were later shown to be maternal-origin chimeric CD8+ T cells and CD45 NK cells capable of initiating immune cholangiolar damage (Muraji et al, 2008).

Clinical Features

The cardinal features of BA are conjugated jaundice persisting beyond 14 days of age, pale and unpigmented stools, and dark urine in an otherwise healthy, term neonate. Liver fibrosis and cirrhosis are later developments, even in infants with intrauterine BA evident at birth (Makin et al, 2009); therefore ascites and marked hepatosplenomegaly are rarely seen before 3 months. Fat malabsorption occurs by stealth, and these infants will fall behind in their growth (Livesey et al, 2009). Fat malabsorption can also cause fat-soluble vitamin K deficiency, and some infants (<3%) will be seen with a possibly catastrophic bleeding tendency and a raised international normalized ratio (INR).

A proportion of infants (approximately 5%) will be seen initially with an abnormal antenatal ultrasound (US) scan (Caponcelli et al, 2008). These will be shown to have cystic BA, with the “cyst” evident from at least 20 weeks’ gestation. This has no untoward effects during pregnancy but clearly needs thorough investigation postnatally. The differential diagnosis for these infants, if the cyst is actually recognized as of hepatobiliary origin, is that of a cystic choledochal malformation, better known as a choledochal cyst (Hinds et al, 2004).