Introduction/Background Solitary fibrous tumors are rare spindle neoplasms that are usually located in the pleura. These tumors can rarely be seen in extrapleural areas. Localization in the pelvic region is also quite rare. This study aims to provide information about the follow-up and treatment of a patient diagnosed with a solitary fibrous tumor located in the extrapleural adnexal area on the right.

Methodology The treatment and follow-up process of a patient diagnosed with a solitary fibrous tumor in the pelvis are presented retrospectively in this study.

Results Our patient, a 42-year-old female, presented with complaints of right groin pain. Imaging revealed a semi-solid lesion containing large cystic areas that extended into the abdominal cavity, measuring 242x231x112 mm. Suspicious areas were observed in the pelvic tissue for invasion, and the patient was suspected of having uterine sarcoma. Tumor markers (CA125, CA19–9, CEA, CA15–3) examined prior to the case were normal.

Conclusion The appearance of extrapleural solitary fibrous tumors (ESFT) in the pelvis is extremely rare. A definitive diagnosis is primarily based on characteristic microscopic appearance along with immunohistochemical examinations. Therefore, considering ESFT in the differential diagnosis is important in pelvic masses since it does not have a pathognomonic radiological imaging finding. In our case, the tumor was observed to invade the pelvic sidewalls inside the abdomen. Invasion of the external iliac artery and vein was also observed. The external iliac vein was excised and reconstructed. Even though the tumor has been completely removed, careful follow-up is required for ESFT due to its potential for malignancy.

Disclosures Total abdominal hysterectomy and bilateral salpingo-oophorectomy were performed on the patient. Pathology results showed a CD34, STAT6, bcl-2, and CD99 diffusely positive inhibin weakly positive staining with a hemangiopericytoma-like vascular pattern. The final pathology resulted in a solitary fibrous tumor with the potential for aggressive behavior.