Ultrasound Findings and O-RADS Malignancy Risk Stratification of Ovarian Collision Tumors.

Objectives: To describe the ultrasonographic signs of ovarian collision tumors and evaluate the malignancy risk using the O-RADS system.

Methods: This was a retrospective analysis of 25 ovarian collision tumors from 8739 patients between May 2010 and January 2020. All clinical characteristics, ultrasound images, and histological findings were collected and analyzed. Using the O-RADS lexicon descriptors, the O-RADS score was determined by two senior doctors. Lesions with O-RADS scores of 1 to 3 were classified as benign tumors, and lesions with O-RADS scores of 4 to 5 were classified as malignant tumors.

Results: The mean age of the 25 patients was 30.4 years. Histological findings showed that all tumors were a combination of mature cystic teratomas and cystadenomas/cystadenocarcinomas. There were 11 benign tumors of O-RADS 2 or 3, including 3 uniocular cysts, 3 dermoid cysts, and 5 dermoid cysts with an anechoic fluid cavity. There were 12 benign tumors of O-RADS 4, including 3 uniocular-multilocular cysts with solid components, 2 multilocular cysts with irregular walls, and 8 multilocular cysts with dermoid sacs. One borderline tumor of O-RADS 4 was a multilocular cyst with irregular septation. One malignant tumor of O-RADS 5 was a multilocular cystic tumor with solid components and ascites.

Conclusions: The most common ovarian collision tumor was the coexistence of a mature cystic teratoma and a cystadenoma. The O-RADS system was able to sensitively detect malignant tumors in this series. A typical dermoid cyst with an anechoic cavity or a multilocular cyst with a dermoid sac may signify a benign collision tumor.