Langerhans'-cell histiocytosis is part of the histiocytosis syndromes, which are characterized by an abnormal proliferation of Langerhans' cells [134] . The Langerhans cells are differentiated cells of monocyte-macrophage lineage that function as antigen-presenting cells. The origin of the expanded population of Langerhans' cells is unknown; in adults, the only consistent epidemiologic association is with cigarette smoking. These cells may form tumors, which may affect various parts of the body. Most cases of pediatric Langerhans'-cell histiocytosis are observed in children between ages 1 and 15 years, with usually bone involvement (80%) including the skull. The tumors produce a punched-out appearance on bone X-ray, and can cause fracture without apparent traumatism. Langerhans'-cell histiocytosis can also affects various organs including the lung [135] .