[Imaging features of osseous and extra-osseous involvement in Erdheim-Chester disease]

Erdheim-Chester disease is a rare form of systemic non-Langerhans cell histiocytosis characterized by infiltration by lipid-laden or foamy histiocytes. Osseous involvement, major diagnostic criteria, is constant and characteristic. It presents as metaphyseal and diaphyseal osteosclerosis, mainly affecting the long bones of the lower limbs. A few cases with axial skeleton involvement have been reported. Extra-osseous lesions may affect the retroperitoneum, lungs, skin, heart, brain and orbits. Prognosis depends mainly on the extra-osseous disease, mainly heart and lung involvement. Diagnosis is based on the combination of radiographic features, nuclear medicine features and nearly pathognomonic immunohistochemical profile.