Histiocytic sarcoma: PET-CT evaluation of a rare entity.

Histiocytic sarcoma is a rare malignancy of hematopoietic origin. Lymph nodes, skin, and extranodal sites, especially gastrointestinal tract, are commonly involved. Some cases reported in the past as non-Hodgkin's lymphoma are now classified as histiocytic sarcoma by detailed immunohistochemical studies. Patients with clinically localized disease have a good prognosis whereas those with lymphatic involvement have an aggressive course. In our case, histiocytic sarcoma was detected, originating from the skin over the left shoulder associated with disseminated lymphadenopathy. A positron emission tomography/computed tomography examination was done for evaluating the extent of the disease which showed pathologic increased 18F-fluorodeoxyglucose uptake in the lymph nodes, indicating widespread disease. The pertinent literature is reviewed.