To determine the accuracy of transvaginal ultrasonography (TVS) and pelvic magnetic resonance imaging (MRI) in preoperative staging of endometrial cancer in comparison to frozen section (FS) for the assessment of myometrial invasion, considering permanent section as the gold standard.

A retrospective longitudinal study of all endometrial carcinomas diagnosed in our institution between March 2012 and October 2018 was conducted. Women with histologically confirmed endometrial malignancy, planned for surgery as primary treatment and submitted either to TVS, MRI and/or intraoperative FS followed by comprehensive surgical staging were eligible.

From a total of 187 endometrial carcinomas, 156 were eligible for the study. The most frequent histology was endometrioid carcinoma (n=115), followed by serous carcinoma (n=25); the majority presented a FIGO stage IA (n=85) or IB (n=21). TVS, MRI and FS presented a sensitivity 56 %, 71 % and 67 % [95 %CI 0.35-0.75; 0.49-0.87; 0.45-0.84] and a specificity of 90 %, 78 % and 94 % [95 %CI 0.79-0.97; 0.58-0.91; 0.84-0.98], respectively. FS was the method with the lowest overestimation rate (6.5 %, 95 %CI 0.02-0.16), whereas MRI showed the lowest underestimation rate (29.2 %, 95 %CI 0.13-0.51). Agreement was superior between MRI and FS (Pa=0.79, K=0.56) and secondly between MRI and TVS (Pa=0.78, K=0.47).

Intraoperative FS presents the higher specificity and the lowest overestimation rate, while MRI seems to be the exam with the highest sensitivity in the evaluation of myometrial invasion. Agreement between the different methods is reasonable, suggesting that the best alternative will be highly dependent on the availability and experience of each institution.