A Rare Large Cystic Adenomatoid Tumor of the Uterus: Diagnostic Challenges and Focused Literature Review

Uterine Adenomatoid Tumor (AT) is a rare benign mesothelial neoplasm, usually small and incidental. Large cystic presentations are exceptional and can mimic adnexal or uterine malignancy. The Leiomyoadenomatoid Tumor (LAT) variant combines mesothelial and smooth-muscle components, adding diagnostic difficulty. The Leiomyoadenomatoid Tumor (LAT) is a rare benign uterine lesion characterized by a proliferation of interlacing smooth muscle fibers admixed with glandular elements and fibrous tissue, forming well-demarcated nodules. A 53-year-old postmenopausal woman presented with diffuse pelvic pain and one month of progressive abdominal distension. Preoperative laboratory tests, including measurement of serum CA-125, were within normal limits. No elevation of tumor markers was observed, supporting the benign nature of the lesion and helping to exclude malignant ovarian or uterine tumors in the differential diagnosis. Ultrasound revealed a 16 × 10 cm unilocular anechoic cystic lesion, and pelvic MRI showed a large heterogeneous solid-cystic uterine mass with low T1/T2 signal in the solid part, high T1 hemorrhagic areas in the cystic part, and moderate peritoneal effusion, contiguous with the posterior uterine wall. Serum CA-125 was within normal limits. Laparotomy identified a 17-cm cystic mass attached to the right uterine wall, and total hysterectomy with bilateral adnexectomy was performed. Histopathology demonstrated intersecting bundles of bland spindle cells (smooth muscle) with a peripheral cyst lined by attenuated mesothelial epithelium, without atypia, necrosis, or significant mitotic activity (1/10 HPF). Cytology of hemorrhagic peritoneal fluid showed benign mesothelial clusters. Immunohistochemistry (cytoblock) was calretinin-positive and PAX8-negative, confirming mesothelial origin. TRAF7 mutational testing was not performed in this patient, which represents a limitation of this case report. Postoperative Course and Long-Term Follow-Up: The postoperative course was uneventful, with no hemorrhagic, infectious, or thromboembolic complications. Pain was well controlled, and recovery was rapid. Clinical and pelvic ultrasound follow-up at three and six months showed no recurrence or local complications. The patient remained asymptomatic, and the CA-125 level was within the normal range, confirming the favorable prognosis and benign behavior of the Leiomyoadenomatoid Tumor. LAT is a rare benign uterine lesion that may present as a large symptomatic mass mimicking malignancy. Recognition of its dual mesothelial and smooth-muscle nature through histopathology and immunohistochemistry is essential to avoid overtreatment. Surgical excision is curative, and prognosis is excellent. This study was conducted in accordance with the ethical principles of the Declaration of Helsinki. Institutional ethics committee approval was obtained, and written informed consent was obtained from the patient for publication of the clinical data and related images.