Incidentally Discovered Primary Renal Leiomyosarcoma in a Middle Aged Female Presenting with Symptoms of Incomplete Abortion: A Rare Case Report

Background Primary renal leiomyosarcoma (LMS) is an exceptionally rare malignant mesenchymal tumor, constituting <1.5% of all primary renal malignancies. Diagnosis is difficult because clinical and radiologic features overlap with other renal neoplasms. Case Presentation We describe a 37-year-old woman, notably younger than the typical age reported for renal LMS, who presented with abnormal uterine bleeding and incomplete abortion. During gynaecologic imaging, an incidental exophytic right-renal mass was detected. CECT and CT angiography revealed a heterogeneously enhancing lesion with necrosis abutting adjacent structures. The patient underwent laparoscopic radical nephrectomy. Histopathological examination showed fascicles of spindle cells with pleomorphism, atypical mitoses, and necrosis involving <50% of tumor area. Immunohistochemistry confirmed smooth muscle differentiation with positivity for vimentin, desmin, and SMA, while negative for cytokeratin, S100, and HMB-45. A final diagnosis of well-differentiated primary renal leiomyosarcoma (FNCLCC grade 1, stage pT3aNxMx) was rendered. The postoperative course was uneventful, and the patient remains well at 3-month follow-up. Conclusion This case is novel for its incidental detection during gynaecologic evaluation for incomplete abortion and for occurring in a young female patient (37 years), whereas most reported renal LMS present later in life and at higher grade. These features underscore the importance of considering LMS in atypical contexts and highlight the need for awareness among both urologists and gynaecologists.