Biliary manifestation of Erdheim-Chester disease mimicking Klatskin's carcinoma.

Erdheim-Chester disease (ECD) is a rare non-Langerhans form of histiocytosis, characterized by infiltration of foamy, lipid-laden histiocytes often affecting the lower extremities and resulting in symmetrical osteosclerosis. Internal organs involved include the lung and the kidneys, reflecting progressive disseminated granulomatous infiltration. Progression may be fatal, especially in cases of systemic extraosseous involvement.