Solitary fibrous tumor arising from pelvic retroperitoneum: A report of two cases and a review of the literature

Solitary fibrous tumors (SFT) rarely arise in the pelvis. Here, we report two cases of SFT arising from the pelvic retroperitoneum. The first case involves a 64‐year‐old woman diagnosed with a 5‐cm pelvic mass. Magnetic resonance imaging revealed a solid and cystic mass with marked enhancement, but limited water restriction. During surgery, intraligamental tumor arising near the round ligament was resected. Pathologically, the tumor comprised dilated vessels and spindle‐shaped cells positive for STAT6 and CD34. The second case involves a 53‐year‐old woman diagnosed with a 4.5‐cm pelvic mass through computed tomography. Magnetic resonance imaging demonstrated a solid mass with multiple cysts with strong enhancement and slight water restriction. During surgery, the tumor was found in the retroperitoneum. Pathologically, spindle‐shaped tumor cells positive for STAT6 and CD34 had proliferated around the prominent hyalinized vessels. Although rare in the pelvis, SFT should be suspected when a mass with strong enhancement is found.