Bile ducts and ductules are positive for CD56 (N-CAM) in most cases of extrahepatic biliary atresia.

The diagnosis of extrahepatic biliary atresia can be challenging as the histologic features can overlap with other pediatric cholestatic liver diseases. Several previous studies have noted that biliary epithelium is positive for CD56 in the setting of extrahepatic biliary tract disease. Thus, we explored the use of CD56 in evaluating liver biopsy specimens for extrahepatic biliary atresia. A total of 22 cases were selected and immunostained for CD56, including 14 cases of confirmed extrahepatic biliary atresia and 8 cases of other cholestatic liver diseases in which the differential diagnosis included extrahepatic biliary atresia. Bile ducts and proliferating ductules were positive for CD56 in 13 of 14 cases of extrahepatic biliary atresia. The staining intensity was generally strong with most cases showing positivity in more than two thirds of portal tracts. The one negative case was a very small biopsy (<0.3 cm), and sampling may have played a role. In contrast, 4 of 8 cases in the control group were completely negative for CD56, with the remaining cases showing weak and focal positivity. In conclusion, bile ducts and ductules are CD56 positive in most cases of extrahepatic biliary atresia, and CD56 immunostaining can be a useful supplemental stain for diagnosing extrahepatic biliary atresia in its early, ductular proliferative phase when used in conjunction with traditional hematoxylin and eosin morphology and clinical information.