1. Review the definition of the histiocytic disorders. 2. Review the classification of the major histiocytic disorders as well as the discriminating clinical features of these conditions. 3. Discuss the variety of radiologic findings in the histiocytoses and illustrate with selected case examples. 4. Illustrate the histopathologic findings.

1. Classification Schema of the Histiocytoses 2. Histologically nonmalignant proliferative disorders of dendritic cells a. Langerhans cell histiocytoses b. Juvenile xanthogranuloma c. Erdheim-Chester disease d. Dendritic cell histiocytoma 3. T-lymphocyte/macrophage activation disorders a. Hemophagocytic lymphohistiocytosis b. Rosai-Dorfman disease 4. Malignant disorders of the mononuclear phagocytic system a. Histiocytic sarcoma (dendritic cell or macrophage cell subtype)

1. The histiocytoses encompass a wide variety of disorders, including proliferative as well as overtly malignant conditions involving macrophages and dendritic cells. 2. These disorders typically present as multisystem disease involving the skin, bone, intrathoracic and abdominal organs, as well as the CNS. They may mimic many other conditions on imaging studies, and a joint approach to diagnosis with integration of the clinical and pathologic features is necessary.