滑液膜肉瘤是一種罕見的軟組織肉瘤，其特點是臨床上緩慢生長的腫塊，具有局部 復發和晚期轉移的特性。一名36 歲的男子先前有輕微外傷史，這次臨床表現為左手臂腫 脹有一年的時間。最初的臨床和影像學認為的診斷是假性動脈瘤合併血腫。經由組織病理 學檢查及t(X;18) 染色體移位確診為滑液膜肉瘤。軟組織肉瘤合併廣泛出血和壞死可能會 跟良性病變極為相似。在文獻上，只有一個案例被提出是滑液膜肉瘤位於橈動脈，而臨床 上以假性動脈瘤來表現。對位於四肢的假性動脈瘤樣病灶或囊性軟組織的病變，臨床和放 射科醫師應該需要把滑液膜肉瘤列入鑑別診斷之中。

Synovial sarcoma is an uncommon soft tissue sarcoma, characterized by insidiously slowgrowing mass, local recurrence and late metastasis. A 36-year-old man with antecedent minor trauma history presented with left arm swelling for one year. The initial clinical and radiological impression was pseudoaneurysm with hematoma. Synovial sarcoma was diagnosed with histopathology and chromosomal t(X;18) translocation confirmation. Soft tissue sarcoma with extensive hemorrhage and necrosis may masquerade as a benign lesion. In the literature, only one case report with false aneurysm caused by synovial sarcoma located at radial artery has been published. The clinicians and radiologists should be aware of this entity and include synovial sarcoma in the differential diagnosis of pseudoaneurysm-like or cystic soft tissue lesions of the extremities.