A Very Rare Case of Ovarian Collision Tumor with Contralateral Endometriotic Cyst: Fertility-Sparing Surgical Management

Abstract Ovarian collision tumors are rare entities where two histologically distinct neoplasms coexist in the same ovary without interaction, often mimicking malignancy. Fertility-sparing surgery is crucial in young women. We present a unique case of a 25-year-old woman with progressive abdominal distension. Imaging revealed a large complex mass. Laparoscopic fertility-preserving surgery uncovered a 30 cm serous cystadenoma and a 5-7 cm mature cystic teratoma in the right ovary, along with a 4x5 cm endometriotic cyst in the contralateral ovary. A total of 12.5 litres of f luid was aspirated. Histopathology confirmed a collision tumor. Postoperatively, the patient experienced transient difficulty walking due to a sudden 12 kg weight loss but recovered fully with preserved ovarian function. This is the first reported case of a unilateral ovarian collision tumor with a contralateral endometriotic cyst. The case emphasizes the importance of considering collision tumors in differential diagnoses and the efficacy of laparoscopic fertility-sparing approaches.