Decidualized ovarian endometrioma

A 26-year-old asymptomatic woman (gravida 1, para 0) was referred to our department at 13 weeks of gestation because of sonographic evidence of a 7-cm left ovarian cyst (Figure, A). Repeat ultrasonography at 21 weeks of gestation demonstrated enlargement in diameter of the cyst to 10 cm with ground-glass echogenicity and several large vascularized papillary projections (Figure, B) and a thick septum (Figure, C). These appearances raised suspicion of early-stage ovarian malignancy. Exploratory laparotomy revealed a left ovarian mass adhering to the posterior uterine wall with multiple clear, red, or black blisterlike excrescences on the internal surface of the mass (Figure, D). The final pathologic report confirmed a markedly decidualized endometriotic cyst. The patient was discharged without postsurgical complications. The remaining pregnancy was uneventful. Pregnant hormonal milieu may change the size and morphologic appearances of ovarian endometriomas, mimicking malignancies on imaging and causing diagnostic dilemmas.