OP09.01: Decidualization of endometrioma during pregnancy mimicking a malignant ovarian tumor

The aim of this study is to provide the description of ultrasound (US) findings of a rare entity that occurs during pregnancy in patients with ovarian endometrioma, whose echo pattern changes by hormonal influences and mimics a malignant ovarian tumor. Seven cases are described in which an ovarian mass was discovered during pregnancy. We reported the patient's age, weeks of gestation, tumor size, echo pattern, and blood flow observed by ultrasonography, and tumor marker CA-125. The results are summarized in Table 1. The average age is 34 years. The tumor was bilateral in one case. In all cases, US findings show the presence of papillae and color Doppler study shows intense vascularization, score 4 according to the IOTA consensus. The tumor marker CA-125 shows a minimal elevation in five cases, and there was no information in two cases. Patients 1 to 5 underwent a minimally invasive approach, with histological result of endometriosis with extensive stromal decidualization. Two patients were managed throughout the pregnancy and the complex ultrasonographic patterns resolved on their own. There are few published cases and almost all show US findings similar to our cases. Until more evidence becomes available regarding the echo pattern and blood flow mimicking a malignant ovarian tumor, surgical treatment cannot be avoided, although in two cases the ovarian echo-pattern was normalized after delivery. This opens a new expectation in highly selected cases and is followed closely. In our experience conservative surgery has had satisfactory results; all patients gave birth without complications.