[A case of fibrous histiocytoma of the appendix with twisted stalk].

A 74-year-old man consulted this hospital with the chief complaint of lower right abdominal pain on February 13, 1998. He was hospitalized, subjected to abdominalechography and CT, and diagnosed as having subileus caused by an intraperitoneal tumor. Surgery was performed on February 25, 1998. When the abdomen was incised, a chicken egg-sized tumor at the end of theappendix were found. In addition, the stalk of the appendix was twisted. Appendectomy was therefore performed. Upon histopathological examination, it was found that the submucosal tumor originated at the end of the appendix, and proliferation of spindle-shaped fibroblast-like cells and histocytic oval cells was observed in the tumor. Since various histiocyte markers were positive upon immunohistological examination, the tumor was considered to be of histiocytic origin. However, the tumordid not exhibit polymorphism, heteromorphism, or mitotic figures which would confirm a diagnosis of malignant fibrous histiocytoma. It was thus diagnosed as a fibrous histiocytic tumor on the borderline between malignant and benign. We report the present case because the occurrence of a primary fibrous histiocytoma in an appendix of which the stalk is twisted is very rare.