Integrally calcified solitary fibrous tumor in the retroperitoneum: a case report and review of the literature.

Solitary fibrous tumor (SFT) is a rare stromal neoplasm and usually occurs in the thoracic cavity. We here report a case of retroperitoneal SFT with prominent calcification. A 64-year-old man presented with an incidentally detected retroperitoneal mass in the right upper abdomen. Imaging tests indicated an integrally calcified mass. The lesion was observed for 2 years and laparoscopically resected according to the patient's wish. Microscopically, the mass was mostly occupied by calcification and proliferous spindle cells were scattered with positive CD34 expression. We diagnosed morphologically benign SFT and the patient remained disease-free 1 year after the excision. There has been no report of such integrally calcified SFT. Retroperitoneal SFT is difficult to make a preoperative diagnosis, and careful follow-up after the excision is recommended because morphological malignancy does not always correspond to clinical malignancy.