Uterine angiomyolipoma presenting as a rapidly enlarging retroperitoneal mass in the early postpartum period.

Uterine angiomyolipomas (AMLs) are exceptionally rare benign mesenchymal tumors that can closely mimic malignant uterine or retroperitoneal neoplasms when large or highly vascular. We describe the case of a healthy 29-year-old postpartum woman who presented with acute abdominal pain three months after delivery and was found to have a rapidly enlarging 10-cm hypervascular mass arising from the right uterine cornua with extension into the retroperitoneum. The imaging appearance and interval growth were highly concerning for a retroperitoneal sarcoma. She underwent diagnostic laparoscopy, which was converted to open resection with multidisciplinary assistance due to deep retroperitoneal involvement. Frozen section was nondiagnostic, prompting total abdominal hysterectomy. Final pathology demonstrated a benign AML composed of smooth muscle, blood vessels, and adipose tissue. The patient recovered uneventfully. This case highlights a rare benign entity that can convincingly simulate sarcoma both clinically and radiographically, emphasizing the diagnostic and surgical challenges when malignancy cannot be excluded.