Biliary atresia is an inflammatory and fibrosing disease of extrahepatic bile ducts and represents an important cause of neonatal cholestasis. Early diagnosis is crucial to prevent progression to biliary cirrhosis. Biliary atresia cases are almost always treated with hepatoportoenterostomy (or Kasai procedure), a technique named after its creator, surgeon Morio Kasai, that aims at restoring the bile flow to the small bowel, hence slowing progression to cirrhosis.² The procedure yields variable results, with most patients progressing to biliary cirrhosis and ultimately requiring liver transplantation.³ In fact, biliary atresia is the most common indication for liver transplantation in pediatric patients.

Liver biopsy evaluation plays a key role in the diagnosis of biliary atresia. Awareness about the early changes in the disease and the possible pitfalls is critical in the histologic evaluation of these cases.

In the United States, biliary atresia occurs at a frequency of 1 in 15,000 live births with seasonal clustering of the disease and higher rates in nonwhite infants.⁴ European and Asian studies have demonstrated rates ranging from 1:6,000 in Taiwan to 1:20,000 live births in France, but no seasonal variation was identified.⁵, ⁶, ⁷ Female gender, advanced maternal age, and multiparity are associated with slightly increased risk for the disease.⁸,⁹ Splenic malformation and other syndromic features are present in about 10% of cases. Reports of familial biliary atresia are exceptionally rare¹⁰ and studies of twin infants showed discordance of presentation.¹¹,¹²

Biliary atresia can be broadly classified as nonsyndromic (or perinatal), syndromic (or embryonic), and cystic. Nonsyndromic biliary atresia accounts for 80% of cases and is not typically associated with other malformations. Syndromic biliary atresia represents about 10% of cases and encompasses a heterogeneous group of patients, who present with early onset jaundice and, many times, absent extrahepatic biliary tree. Macroscopic splenic malformations are classically described in syndromic biliary atresia, a condition named biliary atresia-splenic malformation syndrome. Biliary atresia-splenic malformation syndrome typically occurs together with other malformations, including situs inversus, intestinal malrotations, portal vein anomalies, and cardiac defects. The syndrome occurs more frequently in females, has a higher association with maternal diabetes, and has a worse outcome following Kasai procedure.¹³,¹⁴ Syndromic cases are often referred to as “early” or “embryonic” forms and nonsyndromic biliary atresia as “late” or “perinatal,” presuming that timing of disease in syndromic cases is different than nonsyndromic biliary atresia. More recent studies have demonstrated that this temporal classification may be too simplistic and therefore should be avoided until studies with better definitions and better group homogeneity are made available.¹⁵ The cystic variant of biliary atresia represents 8% of patients and is characterized by cystic dilatation of the atretic biliary remnants. Some cases can be detected prenatally, and jaundice may occur early or late. Cystic biliary atresia appears to have a better prognosis than syndromic and nonsyndromic cases.¹⁶

Biliary atresia is a multifactorial disease, and its exact etiology remains unclear. Recent studies suggest that developmental, environmental, and immune elements play a role in the disease. Infectious etiologies have been proposed but never confirmed, whereas the clustering of biliary atresia cases in Australia livestock suggests that toxins can lead to the development of disease.¹⁷,¹⁸ Mutations in the CFC1 gene have been associated with biliary atresia-splenic malformation cases.¹⁹

Jaundice is the first and most important manifestation of biliary atresia, occurring anywhere from birth to 8 weeks of age. In most cases, infants are born at full term and are healthy in the first weeks of life. Acholic stools and dark urine may be present, but are often unrecognized by parents. Patients who present later in the course of disease often have hepatosplenomegaly. Conjugated hyperbilirubinemia (>2 mg/dL) and extremely high levels of γ-glutamyl transpeptidase (GGT) are typical. Recent studies show that conjugated bilirubin levels are slightly elevated in the asymptomatic early stages of disease and suggest that serum bilirubin concentrations or stool color cards can be useful as newborn screening tools.²⁰

When the diagnosis of biliary atresia is suspected, abdominal ultrasound is performed to rule out anatomical anomalies, such as choledochal cysts, polycystic liver/kidney disease, Caroli disease, and tumors. In biliary atresia, ultrasonographic evaluation demonstrates an absent or abnormal gallbladder. When present, portal hypertension can usually be identified on ultrasound. Other possible findings include an absent common bile duct, the “triangular cord” sign (triangular echogenic density present immediately above the porta hepatis), and an abnormal gallbladder shape.²¹

Following abdominal ultrasound, hepatobiliary scintigraphy is performed to evaluate the patency of the extrahepatic biliary tree using a technetium-labeled iminodiacetic acid analogous compound as a marker. Absent excretion of the marker into the bowel strongly supports the diagnosis of biliary atresia. This test is found to be 100% sensitive and 93% specific when patients are pretreated with phenobarbital.²² Magnetic resonance cholangiography is another imaging modality of high diagnostic accuracy.²³

Liver biopsy is performed in nearly all infants with suspected biliary atresia. The main purpose of the biopsy is to confirm the diagnosis of biliary tract obstruction by histology and to exclude diseases that may mimic biliary atresia. Following scans and liver biopsy, patients undergo intraoperative cholangiogram, the gold standard for the diagnosis of biliary atresia. The presence of biliary obstruction on intraoperative cholangiogram confirms the diagnosis of biliary atresia and is usually followed by hepatoportoenterostomy at the time of examination.

On liver biopsies, the histologic findings of biliary atresia are not entirely specific, requiring correlation with clinical and laboratorial findings. Microscopically, there is marked cholestasis in the form of canalicular, hepatocellular, and ductular bile accumulation. Features of large bile duct obstruction are almost always present, including portal edema, fibrosis, and ductular proliferation (Figs. 14.2 and 14.3). Mild neutrophilic infiltrates typically accompany the proliferating bile ductules. In addition, the lobular parenchyma may show centrilobular hepatocyte swelling with or without features of cholate stasis, namely periportal hepatocellular swelling, cytoplasmic rarefaction, and Mallory-Denk bodies. Periportal accumulation of copper-binding protein is sometimes present. Extramedullary hematopoiesis is often seen and needs to be differentiated from inflammation. The presence of significant inflammation, apoptosis, or confluent necrosis should raise the possibility of an alternative diagnosis, such as neonatal hepatitis (Table 14.1). Giant cell transformation of hepatocytes, a feature classically described in neonatal hepatitis, can occur in biliary atresia (Fig. 14.2). Liver biopsies performed at earlier stages will demonstrate less conspicuous findings and may be harder to differentiate from other processes (Fig. 14.4). Later, portal-based fibrosis can progress to bridging and nodularity. The loss of native bile ducts also occurs in the later stages of disease.²⁴ Occasionally, bile duct plate malformations may be present and have been reported to predict a worse clinical outcome.²⁵

Typically, a Kasai procedure is performed at the time of intraoperative cholangiogram. In this procedure, a loop of small intestine is anastomosed to the hepatic hilum, after the biliary remnant and portal fibrous plate have been resected. The resected specimen that results from a Kasai procedure consists of a fibrotic/atrophic segment of the extrahepatic bile duct (Fig. 14.5). Proper orientation of the specimen by the surgeon and the pathologist is a key step in the evaluation of a Kasai specimen. The proximal aspect of the specimen contains the portal plate and surrounding liver parenchyma. Distally, the specimen contains a segment of common hepatic duct, the cystic duct, and gallbladder, and finally a segment of common bile duct. The gallbladder is typically smaller than normal and might not have a lumen. Sampling should include the portal plate and consecutive sections of the extrahepatic biliary tree, including the gallbladder remnant. Sections of the atretic bile duct demonstrate partial to total luminal occlusion by fibrosis and variable inflammation (Fig. 14.6). Evaluation of the portal plate is recommended because the presence of large-caliber bile ducts (150 to 200 µm) within the portal plate is associated with a better clinical prognosis, while scant small bile ducts in the portal plate sections are associated with a worse prognosis and lower survival (Fig. 14.7).²⁶,²⁷,²⁸

Explant specimens from patients who have failed a Kasai procedure and proceeded to liver transplantation will show a shrunken and cirrhotic liver with the typical features of biliary cirrhosis. Histologically, incomplete nodule formation can confer a “geographic” appearance. Features of large bile duct obstruction are present throughout the specimen. At this stage, inflammation, injury, and loss of interlobular bile ducts may be present. Prolonged cholestasis will result in cholate stasis. Extramedullary hematopoiesis and giant multinucleated hepatocytes are less common, unless liver transplantation occurs at an early stage of disease. Hepatocellular carcinoma is a rare complication, reported in less than 1% of biliary atresia patients.²⁹ Large regenerative nodules are described in patients that have undergone Kasai procedure and may mimic hepatocellular neoplasms.³⁰

As described by Alagille and colleagues,⁴⁰,⁴¹ this disease, also known as arteriohepatic dysplasia, is characterized by bile duct loss, cholestatic liver injury, and distinct extrahepatic malformations, including congenital heart disease, dysmorphic facies (inverted triangle with broad forehead and pointy chin, mild hypertelorism, and deep-set eyes), posterior embryotoxon in the eye, butterfly-shaped vertebrae, and renal abnormalities.⁴²,⁴³ Nonsyndromic cases are also described and include a vast number of diseases discussed later in this chapter.