MRI Findings of Ovarian Carcinosarcoma: A Retrospective Comparison With Endometrioid Carcinoma.

Purpose Ovarian carcinosarcoma is a rare and highly aggressive ovarian malignancy composed of epithelial and mesenchymal components, and its preoperative diagnosis remains challenging because of nonspecific imaging features. This study aimed to identify MRI findings useful for differentiating ovarian carcinosarcoma from ovarian endometrioid carcinoma by comparing their imaging characteristics. Materials and methods We retrospectively reviewed patients who underwent pelvic MRI between January 2002 and December 2025 for suspected malignant ovarian tumors and were subsequently diagnosed with ovarian carcinosarcoma or ovarian endometrioid carcinoma on postoperative histopathology. Patient age and MRI findings were analyzed. Evaluated MRI features included tumor size, laterality, morphology, margin characteristics, tumor architecture, signal heterogeneity on T2-weighted images, morphology of solid components, presence of a stained-glass appearance, mille-feuille-like layered pattern, hemorrhage, enhancement characteristics, necrosis, lymphadenopathy, ascites, and peritoneal dissemination. Apparent diffusion coefficient (ADC) values of solid tumor components were measured. Imaging findings were compared between groups using Fisher's exact test and the Mann-Whitney U test. Results Among 12 cases of ovarian carcinosarcoma, the maximum tumor diameter ranged from 5.7 to 21.5 cm (mean, 11.6 ± 4.8 cm). Tumors were unilateral in 11 cases. An irregular tumor margin was observed in 6 cases, solid-dominant components in 7 cases, nodular solid components in 12 cases, the presence of a mille-feuille sign in 2 cases, lymphadenopathy in 6 cases, peritoneal dissemination in 8 cases, and ascites in 9 cases. The mean ADC value of the solid component in ovarian carcinosarcoma was 0.952 ± 0.186 × 10⁻³ mm²/s. Significant differences between ovarian carcinosarcoma and ovarian endometrioid carcinoma were observed for patient age (67.6 years vs. 56.9 years, p=0.003), margin irregularity (6/12:50% vs. 3/45:6.7%, p=0.002), predominance of solid components (7/12:58.3% vs. 11/45:24.4%, p=0.037), nodular morphology of solid portions (12/12:100% vs. 25/45:55.6%, p=0.005), presence of the mille-feuille sign (2/12:16.7% vs. 0/45:0%, p=0.041), and peritoneal dissemination (8/12:66.7% vs. 9/45:20%, p=0.004). Laterality, overall tumor shape, the presence of hemorrhagic components, and mean ADC value did not differ significantly between the two groups. Conclusion On MRI, ovarian carcinosarcoma tends to present as a mass with irregular margins, predominantly nodular solid components with partial cystic components, and frequent peritoneal dissemination. Recognition of these characteristic findings may help differentiate ovarian carcinosarcoma from ovarian endometrioid carcinoma and improve preoperative diagnostic accuracy in patients with malignant ovarian tumors.