Retroperitoneal synovial sarcoma. A report of four cases.

Synovial sarcoma most commonly affects the extremities, especially the lower thigh and knee region; other primary sites, in contrast, have been only infrequently reported. Therefore, we undertook this study of four synovial sarcomas arising in the retroperitoneum. This group, whose ages ranged from 17-57 years (mean, 36 years), comprised three males and one female. The nonspecific clinical presentations consisted of pain and/or a mass; diverse preoperative radiographic procedures merely served to reinforce the impression of a retroperitoneal mass. Histologically, all four examples revealed a typical biphasic pattern. Two cases showed a predominant spindle cell component; two others disclosed a more even distribution of the spindle-cell and epithelioid-cell elements, one of these containing, in addition, broad areas of stromal calcification. Follow-up data, obtained for two patients, indicated that both died as a direct result of peritoneal sarcomatosis. The differential diagnosis of selected spindle-cell and biphasic neoplasms known to arise in the retroperitoneum will be discussed.