Retroperitoneal primitive neuroectodermal tumor in an adult: A rare case report and review of the literature

Primitive neuroectodermal tumor (PNET) and Ewing's sarcoma (EWS) are small round cell tumors occurring mainly in children and adolescents. Their occurrence in adults is rare. The abdominal cavity and retroperitoneal PNET/EWS are also relatively rare, grow rapidly in size, compressing surrounding organs/large vessels, and make surgical resection difficult. We report one such rare occurrence of a retroperitoneal PNET in 41-year-old male who presented with abdominal pain and constipation. Contrast enhanced computed tomography abdomen showed large lobulated necrotic hypodense enhancing lesion extending from epigastrium to hypogastrium and involving entire abdomen. Excision of retroperitoneal mass with omentectomy was done. Microscopic examination revealed a malignant small round cell tumor with homer wright rosettes and the tumor cells were positive for CD99.