Collision Tumour of the Ovary: Mature Cystic Teratoma and Benign Mucinous Cystadenoma.

A collision tumour is defined as the coexistence of two or more histologically and pathogenetically distinct tumours without any histological intermixing in the same organ or tissue. This article reports a case of an ovarian collision tumour consisting of a mature cystic teratoma and a benign mucinous cystadenoma in a 28-year-old premenopausal woman. Ultrasound of the pelvis showed an enlarged right ovary with a 7.0 cm x 6.0 cm x 5.0 cm cyst. The tumour marker was normal. Macroscopic examination of the cyst revealed a dermoid cyst with some haemorrhagic areas. The histopathological examination showed a dermoid cyst that matched the characteristics of a mature cystic teratoma and a benign mucinous cystadenoma, both located in the right ovary. Recognition of collision tumours by gynaecologists, radiologists, and pathologists is vital. Detailed histopathological evaluation is essential for accurate diagnosis and for tailoring appropriate therapy according to the distinct biological behaviour of the individual tumour components.