孤立纖維腫瘤是一相當罕見的梭狀細胞腫瘤，它通常長在助膜的地方，但近年來，在身體其他部位陸陸續續有人發表出來，因此長在助膜外的孤立纖維腫瘤往往被誤診或未能辨識。我們報導一例59歲男性患者，入院主訴為急性尿液瀦流。影像學檢查發現介於膀胱和直腸之間有一直徑約10公分的異質性軟組織腫瘤。經直腸超音波切片病理診斷為惡性梭狀細胞腫瘤。病患接受腫瘤完全切除手術。微觀下，此病變是一界線明確的腫瘤，它由無規則的梭狀細胞雜亂的排列而成，中間夾雜著大小不一的膠原纖維。另外，亦可見豐富的上管及呈現血管外皮細胞瘤的型態。在免疫組織學上，腫瘤細胞對desmin和S-100呈現陰性反應，對CD34和bcl2呈現瀰漫的陽性反應。最終的臨床病理診斷為孤立纖維腫瘤。此病患到目前為止仍定期於門診追蹤，健康情形良好。總結來說，孤立纖維腫瘤應晚入骨盆腫瘤的鑑別診斷中。文中並作文獻回顧。

Solitary fibrous tumors (SFTs) are rare spindle cell neoplasms that were originally de-scribed in the pleura but can occur in a variety of sites, as a consequence of which extrapleural examples often go unrecongnized or misdiagnosed. We report an SFT arising in the pelvis in a 59-year-old male with presentation of acute urinary retention. Image studies showed a huge (10 cm in maximum diameter) hetrogenous soft tissue tumor between the urinary bladder and rectum. Transrectal sonoguided biopsy suggested malignant spindle-cell tumor or leiomyosarcoma. The tumor was excised completely. Microscopically, the lesion was well circumscribed, and com-posed of pattern-less spindle cells without mitoses, in a variably collagenous background. Abun-dant vasculature and focal hemangiopericytoma-like pattern were noted. Immunohistochemically, the tumor cells were negative for desmin and S-100 but diffusely positive for CD 34 and bc1-2. The overall features suggest a solitary fibrous tumor. So far, the patient is regularly followed at our out-patient clinic with a benign clinical course. In conclusion, SFT should e included in the differential diagnosis of tumors arising in the pelvis. The literature is also reviewed. (J Urol R.O.C.,10:168-172,1999)