Unusual imaging presentation of gossypiboma with pelvic bone involvement: a case report and radiologic review of the literature.

Gossypiboma, although rare, is a serious surgical complication with potential medicolegal implications. We report a case of a 70-year-old female presenting with a progressively enlarging painless mass in the left iliac region, initially suspected to be a pelvic sarcoma. The patient had a history of femoral intramedullary nailing performed 16 years ago for a femoral shaft fracture, followed 2 years later by exchange nailing and iliac bone grafting due to non-union. Ultrasonography revealed a lobulated, avascular mass with acoustic shadowing. Computed tomography (CT) demonstrated a hypodense lesion causing erosion of the left anterior superior iliac spine (ASIS), while magnetic resonance imaging (MRI) revealed a well-defined mass with a whorled pattern. Histopathology confirmed the diagnosis of gossypiboma with foreign body material. Uniquely, to our knowledge, this is the first reported case of gossypiboma located at the ASIS mimicking neoplastic bone erosion, presenting radiologically as a pelvic bone defect. This distinctive imaging appearance carries important diagnostic implications, particularly for musculoskeletal radiologists, and broadens the known spectrum of gossypiboma-related complications following orthopedic surgery.