MRI appearances of uterine malignant mixed müllerian tumors.

Objective: Uterine malignant mixed müllerian tumors (MMMTs) are rare aggressive tumors with a high incidence of lymphatic, peritoneal, and pulmonary metastases. Preoperative differentiation from endometrial adenocarcinoma would be beneficial because their prognoses differ.

Materials And Methods: We retrospectively reviewed MRI examinations of 51 histologically confirmed MMMTs. Tumor size, growth pattern, and imaging characteristics were recorded. Data were compared with MRI appearances of 73 endometrial adenocarcinomas.

Results: On T1-weighted images, MMMTs were predominantly isointense to myometrium (76%) and endometrium (71%), with heterogeneous texture in 33% of cases and hyperintense foci in 27% of cases. On T2-weighted images, 92% of MMMTs were hyperintense to myometrium and either hypointense (55%) or isointense (41%) to endometrium. In 12% of cases, large heterogeneous MMMTs obliterated uterine architecture and were aggressive in appearance, whereas in 88% of cases, the appearances were indistinguishable from those of endometrial adenocarcinoma. Significantly more MMMTs than endometrial adenocarcinomas had cervical invasion (p = 0.008) and nodal enlargement (p = 0.00008). Dynamic contrast-enhanced images (available for 19 of 51 patients) obtained at less than 1 minute after administration of contrast agent showed MMMT enhancement to be hypointense (42%; 5/12 patients) or isointense (33%; 4/12 patients) to myometrium; between 1 and 4 minutes after administration of contrast agent, tumors were hypointense (58%; 7/12 patients); and at more than 4 minutes after administration of contrast agent (n = 18), MMMTs were isointense in 56% of cases. This finding is significantly different from that for endometrial adenocarcinoma, where enhancement is less than that of myometrium in 90% of cases (p = 4 × 10⁻⁸).

Conclusion: MMMTs do not have a pathognomonic MRI appearance. However, radiologic suspicion should increase in the presence of large heterogeneous infiltrative tumors or when tumoral enhancement equals or exceeds that of myometrium.