Primary Langerhans Cell Histiocytosis of the Extrahepatic Bile Duct Occurring in an Adult Patient.

Background: Langerhans cell histiocytosis is characterized by an abnormal proliferation of neoplastic Langerhans cells. Langerhans cell histiocytosis commonly affects the pediatric population, whereas presentation in adults remains a rare event. 'I'he presentation of Langerhans cell histiocytosis is highly variable, but the involvement of skin, bone, and lung is very common. Langerhans cell histiocytosis presenting as a bile duct mass is rare and usually occurs as part of a multiorgan system disease. Case Report: We present a case of Langerhans cell histiocytosis confined to the extrahepatic bile duct in a 62-year-old female patient with sclerosing cholangitis. The mass was composed of mononuclear cells with cleaved nuclei that were positive for CD68, S100, and CD1a as assessed by immunohistochemistry. Conclusion: This is the first report of Langerhans cell histiocytosis limited to the extrahepatic bile duct in an adult patient. We discuss the clinical manifestations and the challenges encountered in the diagnosis and treatment of this rare entity.