Abstract
Follicular dendritic cell sarcoma is a rare malignant neoplasm originating from follicular dendritic cells, and most of them develop in lymph nodes of the head and neck. One third of follicular dendritic cell sarcomas occur in the extranodal sites such as the tonsils, mesentery, and retroperitoneal organs, but those of mediastinal origin are rare. Here, we present the case of a 16-year-old female with a large follicular dendritic cell sarcoma of posterior mediastinal origin. The tumor was found by a chest X-ray mass examination at her high school, and she had no subjective symptoms or significant past medical history. The tumor was diagnosed as a follicular dendritic cell sarcoma by computed tomography-guided needle biopsy. Although the tumor compressed the mediastinal organs and showed moderate uptake in 18-fluorodeoxyglucose positron emission tomography imaging, it was completely resected through posterolateral incision. Histological examination revealed that spindle-shaped tumor cells formed fascicular or storiform pattern with cellular pleomorphism. By immunohistochemical examination, the tumor cells were found to be positive for CD21 and follicular dendritic cell antigen. Two years after surgery, the patient remains alive with no signs of tumor recurrence.