When Benign Masquerades as Malignant: A Case of Expansively Growing Ovarian Leiomyoma Challenging Preoperative and Intraoperative Diagnosis.

Ovarian leiomyoma (OL) is an exceedingly rare benign tumor that originates from ovarian smooth muscle cells and accounts for approximately 0.5%-1% of all benign ovarian neoplasms. To date, around 100 cases have been documented worldwide. OL is often asymptomatic and is typically discovered incidentally, presenting as a small, well-circumscribed, noninvasive solid or cystic mass within the ovary. We report a case of a 22-year-old woman who presented with Abnormal Uterine Bleeding (AUB). Imaging identified a solid left adnexal mass. Laparoscopic exploration revealed features suggestive of malignancy, leading to surgical resection. The final diagnosis was established through histopathological and immunohistochemical examination. Intraoperative findings revealed a diffusely invasive, irregular, multilobulated mass involving multiple paracervical ligaments (broad ligament, round ligament, and proper ovarian ligament) and associated with ascites-features highly suggestive of malignancy. However, pathological assessment confirmed a benign ovarian leiomyoma. This case illustrates that OL can, in rare instances, show locally aggressive and disseminated growth patterns that mimic malignancy. Recognizing these atypical presentations is crucial for accurate intraoperative judgment and for guiding fertility-preserving surgical strategies in young patients who wish to retain reproductive potential.