From Benign Polyp to High-Grade Endometrial Sarcoma: A Case Report with Imaging Correlation.

Uterine adenosarcoma with sarcomatous overgrowth (ASSO) is an exceptionally rare and aggressive subtype of uterine sarcomas, characterized by high mitotic activity, deep myometrial invasion, and an elevated risk of recurrence and metastasis. We report the case of a 79-year-old institutionalized woman with a history of hypertension, type 2 diabetes, chronic hepatitis B, and mild Alzheimer's disease. During routine hepatic ultrasound surveillance, an incidental 26 mm endometrial lesion was detected. Initial diagnostic hysteroscopy revealed a benign endometrial polyp. However, due to the patient's institutionalization and absence of gynecologic symptoms, no specialized follow-up was conducted. Four years later, she presented with profuse postmenopausal bleeding. Imaging revealed a markedly enlarged uterus with a 12-13 cm heterogeneous endometrial mass containing cystic and hemorrhagic areas, demonstrating diffusion restriction and significant contrast enhancement on MRI, with no radiologically suspicious lymphadenopathy. Hysteroscopy demonstrated a giant polyp with a broad implantation base; histology suggested sarcomatous transformation. Definitive diagnosis after total hysterectomy with bilateral salpingo-oophorectomy confirmed high-grade ASSO with homologous sarcomatoid overgrowth, consistent with endometrial stromal sarcoma. This case illustrates the progressive malignant transformation of an initially benign-appearing lesion in a patient with significant comorbidities and limited follow-up. It underscores the importance of clinical vigilance, regular monitoring, and interdisciplinary coordination in the evaluation of uterine enlargement in asymptomatic postmenopausal women.