RESUMO
Endometriosis constitutes the presence of ectopic endometrial glands and stroma outside the uterine endometrium, which is hormonally responsive and responds to pregnancy hormones as well. Decidualization is a physiologic process, where the normal endometrium readies itself for optimal accommodation of a pregnancy. A similar hormonal response can be seen with ectopic endometrium as well. As such, ovarian endometriomas and deep endometriosis implants can undergo decidualization. Overall, the progestational state of pregnancy favors an improvement in endometriosis, however, decidualization can lead to findings that can lead to increased size of endometriomas and deep infiltrative endometriosis implants, changes in imaging appearance and even complications, such as spontaneous hemoperitoneum in pregnancy. Awareness of this process can help prevent misdiagnosis of decidualized endometriomas as ovarian malignancy and recognize common imaging manifestations of hormonal effects of pregnancy on endometriosis.