Ovarian collision tumors: imaging findings, pathological characteristics, diagnosis, and differential diagnosis.

Collision tumors are uncommon neoplasms in which elements of differing histologic origins coexist in a single mass. Ovarian collision tumors are a rare subtype of such lesions. The identification of collision tumors by radiologic examinations is essential to ensure that comprehensive biopsies are performed to guide appropriate treatments. According to the clinical and imaging findings of 12 patients and reviews of previous studies, ovarian collision tumors are mixtures of different combinations of epithelial tumors, germ cell tumors, and sex-cord-stromal tumors. The smaller tumors are usually located inside ("nested tumor") or on the wall ("back to back") of the larger tumors. Each type of ovarian collision tumors presents specific CT/MRI features in accordance with their histologic origins and collision patterns. Knowledge of the imaging features of ovarian collision tumors is crucial to aid preoperative diagnostic accuracy.