Accuracy of MRI in predicting deep myometrial invasion in endometrial cancer and the influence of leiomyoma, adenomyosis and the microcystic elongated and fragmented tumour pattern.

Introduction: The most common form of endometrial cancer is Type 1 endometrioid adenocarcinoma. Depth of myometrial invasion is the most important prognostic factor correlating with overall patient survival. The objective was to investigate how accurate magnetic resonance imaging (MRI) is in predicting the depth of myometrial invasion in preoperative assessment, and the influence of leiomyoma and/or adenomyosis, or microcystic, elongated and fragmented (MELF) pattern of invasion on MRI diagnostic performance.

Method: Retrospective audit of 235 endometrial cancer patients from the regional Gynaecology Oncology multidisciplinary meeting at Auckland City Hospital, between January 2020 and January 2021. Radiologist assigned stage was compared to histopathology. Presence of leiomyoma, adenomyosis and MELF pattern evaluated followed by analysis under a Biostatistician's supervision.

Results: Overall MRI diagnostic accuracy for depth of myometrial invasion was 86%. For deep myometrial invasion, MRI had a sensitivity of 72% and specificity 91%. Out of the misreported 32/235 cases, 16 demonstrated fibroids and/or adenomyosis leading to a sensitivity of 57% and specificity 93% for deep invasion, compared with 94% and 74% respectively in the population without, demonstrating statistical significance. Thirty seven cases with MELF pattern of invasion showed a sensitivity of 81% and specificity 80% for deep invasion, compared with 63% and 92% respectively in the group without, demonstrating no statistical significance.

Conclusion: MRI assessment of the depth of myometrial invasion in endometrial cancer has high accuracy. In the presence of background uterine fibroids/adenomyosis, pre-operative MRI accuracy of evaluating deep invasion shows a statistically significant reduction.