Giant primary retroperitoneal granulosa cell tumor in a post-oophorectomy patient: A rare case report and a literature review

Introduction Primary retroperitoneal granulosa cell tumors (GCTs) are exceedingly rare, particularly in patients with prior bilateral oophorectomy, posing significant diagnostic challenges. Case Presentation A 69-year-old woman with multiple comorbidities and a history of hysterectomy with bilateral oophorectomy presented with a large retroperitoneal mass. Preoperative imaging demonstrated a well-defined fluid collection measuring 142 × 193 × 130 mm in the infra-pancreatic region, along with a tissue mass up to 59 × 50 × 33 mm in the left para-aortic area. These findings were consistent with a retroperitoneal mass. Tumor markers were non-contributory. Intraoperatively, the mass was identified as a giant retroperitoneal cyst and completely drained and excised via laparoscopic drainage and Pfannenstiel laparotomy. The definitive diagnosis was established post-operatively by pathohistological examination, which confirmed the lesion to be a Granulosa Cell Tumor. Conclusion This case underscores the importance of considering rare extra-gonadal GCTs in the differential diagnosis of retroperitoneal masses, even in post-oophorectomy patients. Complete surgical excision and long-term surveillance remain essential due to the risk of late recurrence.