Retrorectal Extraosseous Ewing Sarcoma/Primitive Neuroectodermal Tumor in a 59-Year-Old Man Mimicking a Tailgut Cyst: A Case Report :

Abstract

Ewing sarcoma is a rare, aggressive small round-cell sarcoma that predominantly affects children and young adults. Extraosseous pelvic presentations are uncommon, particularly in older adults. We report the case of a 59-year-old man who presented with progressive asthenia, constipation, and intermittent rectal bleeding. Pelvic ultrasound and magnetic resonance imaging demonstrated a large multiloculated presacral mass with cystic and enhancing solid components, initially raising the possibility of a tailgut cyst. Contrast-enhanced computed tomography showed a heterogeneous pelvic mass with marked upstream colonic dilatation; no distant metastases were identified on CT of the chest, abdomen, and pelvis. A core biopsy was reported as an extraosseous Ewing sarcoma/primitive neuroectodermal tumor. The lesion was considered unresectable at multidisciplinary review because of its extent and local relationships. Systemic chemotherapy was initiated, but the patient's clinical condition deteriorated after two cycles. This case highlights the nonspecific and potentially cystic-appearing imaging presentation of extraosseous Ewing sarcoma in the retrorectal space and the diagnostic challenges posed by this rare presentation in an older adult.