Primary Uterine Primitive Neuroectodermal Tumour Mistaken for Leiomyosarcoma in an Adolescent Girl: A Very Rare Case With Many Diagnostic and Therapeutic Challenges.

Primary uterine primitive neuroectodermal tumours (PNETs) are exceedingly rare and typically reported in postmenopausal adults. We describe a 14-year-old adolescent girl who presented with one month of rapidly progressive abdominal distension, lower abdominal pain and nausea. Imaging (ultrasound, contrast-enhanced (CE) CT, and MRI) revealed a large heterogeneous uterine mass with necrosis, enlarged pelvic nodes and suspected peritoneal and pulmonary deposits; serum lactate dehydrogenase was markedly elevated. Preoperative findings suggested leiomyosarcoma, but the patient developed haemoperitoneum before the planned biopsy and required emergency laparotomy. The uterine corpus was largely replaced by a friable vascular tumour. A total abdominal hysterectomy with bilateral salpingo-oophorectomy and omentectomy was performed. Histopathology showed a small round cell tumour with rosette formation. Immunohistochemistry (IHC) was strongly positive for CD99 and FLI‑1 and Ki‑67, all confirming PNET of the uterine corpus. Preoperative PET/CT demonstrated multifocal metastatic disease. Postoperatively, she was treated with an Ewing sarcoma‑based chemotherapy protocol (vincristine, doxorubicin, cyclophosphamide/ifosfamide and etoposide (VDC/IE)), but unfortunately, she died 10 months after surgery. Uterine PNETs may mimic more common uterine sarcomas on imaging and may present at an advanced stage. Morphology can overlap with other small round cell tumours. Therefore, IHC with markers such as CD99 and FLI‑1, and, where feasible, molecular testing for EWSR1 rearrangement, are essential for accurate diagnosis. Management typically requires multimodal therapy involving a combination of surgery, radiotherapy and/or systemic chemotherapy. Ewing sarcoma regimens such as VDC/IE are often used because of the shared biology. While on one hand, among adolescents, fertility preservation poses an additional ethical and therapeutic challenge, on the other hand, rapid, individualised decision‑making is also required to prevent clinical deterioration. This case highlights the diagnostic and therapeutic dilemmas faced, the need to consider PNET in the differential diagnosis of aggressive uterine masses even in adolescents, the important role of ancillary testing like IHC and molecular studies for a definitive diagnosis and the difficulties in balancing life‑saving surgery and fertility preservation when disease is advanced.