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Biliary atresia: Wikis

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Biliary atresia
Classification and external resources

Operative view of complete extrahepatic biliary atresia.
ICD-10 Q44.2
ICD-9 751.61
OMIM 210500
DiseasesDB 1400
eMedicine ped/237
MeSH C06.130.120.123

Biliary atresia is a rare condition in newborn infants in which the common bile duct between the liver and the small intestine is blocked or absent. If unrecognised, the condition leads to liver failure but not (as one might think) to kernicterus. This is because the liver is still able to conjugate bilirubin, and conjugated bilirubin is unable to cross the blood-brain barrier. The cause of the condition is unknown. The only effective treatments are certain surgeries, or liver transplantation.

Contents

Symptoms and diagnosis

Initially, the symptoms are indistinguishable from neonatal jaundice, a common phenomenon. Symptoms are usually evident between one and six weeks after birth. Besides jaundice, other symptoms include clay colored stools, dark urine, swollen abdominal region and large hardened liver (which may or may not be observable by the naked eye). Prolonged jaundice that is resistant to phototherapy and/or exchange transfusions should prompt a search for secondary causes. By this time, liver enzymes are generally measured, and these tend to be grossly deranged, hyperbilirubinaemia is conjugated and therefore does not lead to kernicterus. Ultrasound investigation or other forms of imaging can confirm the diagnosis. Further testing includes radioactive scans of the liver and a liver biopsy.

Biliary atresia is a very rare disorder. About one in 10,000 to 20,000 babies in the U.S are affected every year. Biliary atresia seems to affect girls slightly more often than boys. Within the same family, it is common for only one child in a pair of twins or only one child within the same family to have it. Asians and African-Americans are affected more frequently than Caucasians. There does not appear to be any link to medications or immunizations given immediately before or during pregnancy.

Pathophysiology

There is no known cause of biliary atresia. There have been many theories about ethiopathogenesis such as Reovirus 3 infection, congenital malformation, congenital CMV infection, autoimmune theory. This means that the etiology and pathogenesis of biliary atresia are largely unknown. However, there have been extensive studies about the pathogenesis and proper management of progressive liver fibrosis, which is arguably one of the most important aspects of biliary atresia patients. As the biliary tract cannot transport bile to the intestine, bile is retained in the liver (known as stasis) and results in cirrhosis of the liver. Proliferation of the small bile ductules occur, and peribiliary fibroblasts become activated. These "reactive" biliary epithelial cells in cholestasis, unlike normal condition, produce and secrete various cytokines such as CCL-2 or MCP-1, Tumor necrosis factor (TNF), Interleukin-6 (IL-6), TGF-beta, Endothelin (ET), and nitric oxide (NO). Among these, TGF-beta is the most important profibrogenic cytokine that can be seen in liver fibrosis in chronic cholestasis. During the chronic activation of biliary epithelium and progressive fibrosis, afflicted patients eventually show signs and symptoms of portal hypertension (esophagogastric varix bleeding, hypersplenism, hepatorenal syndrome(HRS), hepatopulmonary syndrome(HPS)). The latter two syndromes are essentially caused by systemic mediators that maintain the body within the hyperdynamic states.

Treatment

If the intrahepatic biliary tree is unaffected, surgical reconstruction of the extrahepatic biliary tract is possible. This surgery is called a Kasai procedure (after the Japanese surgeon who developed the surgery, Dr. Morio Kasai) or hepatoportoenterostomy.

If the atresia is complete, liver transplantation is the only option. Timely Kasai portoenterostomy (eg < 60 postnatal days) has shown better outcomes. Nevertheless, a considerable number of the patients, even if Kasai portoenterostomy has been successful, eventually undergo liver transplantation within a couple of years after Kasai portoenterostomy.

Recent large volume studies from Davenport et al. (Ann Surg, 2008) show that age of the patient is not an absolute clinical factor affecting the prognosis. In the latter study, influence of age differs according to the disease etiology—i.e., whether isolated BA, BASM (BA with splenic malformation ), or CBA(cystic biliary atresia).

It is widely accepted that corticosteroid treatment after a Kasai operation, with or without choleretics and antibiotics, has a beneficial effect on the postoperative bile flow and can clear the jaundice; but the dosing and duration of the ideal steroid protocol have been controversial ("blast dose" vs. "high dose" vs. "low dose"). Furthermore, it has been observed in many retrospective longitudinal studies that steroid does not prolong survival of the native liver or transplant-free survival. Davenport at al. also showed (hepatology 2007) that short-term low-dose steroid therapy following a Kasai operation has no effect on the mid- and long-term prognosis of biliary atresia patients.

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