Phenotypic variant of diffuse uterine leiomyomatosis presenting as cellular leiomyoma with retroperitoneal extension: A case report

Introduction: Diffuse uterine leiomyomatosis (DUL) is a rare benign smooth-muscle disorder characterized by diffuse myometrial involvement and uterine enlargement. Its radiologic appearance may mimic malignant or extra-uterine disease, creating diagnostic uncertainty. We report an unusual case of DUL with retroperitoneal extension presenting as a giant abdomino-pelvic mass. Case Report: A nulliparous woman in her 40s presented with abdominal pain and dyspepsia for six months with recent weight loss, without menstrual complaints. Examination revealed a markedly distended abdomen with a large abdomino-pelvic mass. Serum CA-125 was elevated (276 U/mL), while other tumor markers were within normal limits. Magnetic resonance imaging demonstrated a 26 × 16.5 × 17.5 cm T2-isointense mass occupying the abdomen and pelvis with extra-peritoneal/retroperitoneal insinuation. Differential diagnoses included diffuse leiomyomatosis, leiomyosarcoma, and ovarian neoplasm. Treatment options were discussed, and exploratory laparotomy, was performed with multidisciplinary team. Intraoperatively, a large fleshy mass with multiple projections arising from a normal uterus was identified, extending into the retroperitoneal and paravesical spaces. The appearance differed from diffuse uterine leiomyomatosis, with no evidence of peritoneal leiomyomatosis. She underwent total abdominal hysterectomy with bilateral salpingo-oophorectomy. Postoperatively she developed sudden hypotension requiring emergency re-exploration during which around 1500 mL blood clots were evacuated and a small bleeder of 2 mm in retroperitoneal space was identified and secured. Histopathology revealed a spindle cell neoplasm with increased cellularity, while immunohistochemistry showed Ki-67 greater 5% and negative S100 excluding malignancy. At one year follow-up, the patient was asymptomatic with no evidence of recurrence. Conclusion: Diffuse uterine leiomyomatosis is a rare benign entity that may present as a massive abdomino-pelvic mass with atypical retroperitoneal extension, closely mimicking malignant disease. Preoperative diagnosis remains challenging despite advanced imaging. Histopathology and immunohistochemistry are essential for definitive diagnosis. Multidisciplinary surgical management and careful postoperative monitoring are crucial for favorable outcomes.