Imaging description

Decidualization is the physiological transformation of endometrial tissue into the dense highly vascularized cellular matrix known as decidua that occurs in the endometrium of the uterus during pregnancy [1]. The same process can occur in the ectopic endometrium within endometriomas, and may result in the development of solid nodules in endometriomas during pregnancy (Figure 78.1).

Importance

Decidualization of endometriomas may be misdiagnosed as ovarian cancer or malignant transformation, resulting in unnecessary surgery during pregnancy.

Typical clinical scenario

Adnexal masses (excluding physiological corpus luteal cysts of early pregnancy) are seen in 0.5 to 1.2% of pregnancies, and 11% of these are endometriomas [2]. Despite the relative frequency of endometriomas in pregnancy, decidualization resulting in an appearance that mimics malignancy seems rare, with only a handful of reported cases [3–7]. Most of these cases have resulted in surgery during pregnancy because of the suspicious imaging findings [3–7].

Differential diagnosis

The development of solid nodules in an endometrioma could also indicate superimposed malignancy. While malignant transformation of an endometrioma during pregnancy has not been reported, this remains a potential concern when solid nodules develop within an endometrioma irrespective of whether the patient is pregnant or not.