Decidualized endometrioma in a non‐pregnant woman

Decidualization of endometriotic ovarian cysts was first described at the beginning of the 20th century. This phenomenon occurs in response to the altered hormonal environment during pregnancy. Specifically, progesterone induces hypertrophy of the endometrial stromal cells and transforms the tissue of the ovarian cyst into decidual tissue1. Decidualized endometriomas have always been associated with pregnancy and frequently mimic malignant lesions2, 3. To the best of our knowledge, decidualized endometrioma in a non-pregnant woman has not previously been reported. We present the case of a 40-year-old, non-pregnant, nulliparous woman with no known history related to endometriosis, except for a sister with deep endometriosis. Following the advice of her gynecologist, the patient had been taking micronized progesterone (200 mg/day) for 1 year, for 14 days a month, as luteal phase support. She was booked into our outpatient clinic for ultrasound examination of a uterine myoma. She complained of only mild, occasional abdominal discomfort unrelated to her menstrual cycle. Ultrasound examination confirmed the presence of a uterine subserous myoma (International Federation of Gynecology and Obstetrics (FIGO) Type 6) measuring 3 cm. Moreover, in the left adnexal region, a multilocular, solid cyst with ground-glass echogenicity and multiple solid components was visualized (Videoclip S1). The cyst was divided into two loci and contained at least three papillary projections, the largest measuring 24 mm in length. All papillary projections were highly vascularized on power Doppler, and a color score of 4 was assigned by the examiner (Figure 1 and Videoclip S1). The cyst was fixed in the adnexal region (negative sliding sign), it was painless during the examination and its maximum diameter measured 5.5 cm. No healthy ovarian tissue was seen (negative crescent sign). The examiner classified this cyst as probably malignant, and the suspected diagnosis was endometrioid borderline ovarian tumor4, 5. Computed tomography was performed to determine the stage of the disease. No other lesions were seen and FIGO Stage 1A was assigned. In consideration of the patient's desire for pregnancy, after appropriate counseling, a fertility-sparing approach was chosen. The patient underwent left salpingo-oophorectomy with peritoneal washing and multiple peritoneal samplings. To our surprise, the histological diagnosis was ovarian endometrioma with an edematous intracystic vegetative component, showing mucinous and squamous metaplasia, and stroma with features of pseudodecidualization with diffuse eosinophilia (Figure 2). It is well-known that decidualized endometriomas may mimic malignant ovarian lesions. The present case shows that low-level intake of cyclic progesterone may also induce decidual transformation of ovarian endometriomas. In our case, we believe that an accurate ultrasound examination before the administration of progesterone therapy, showing an endometriotic ovarian cyst, would have helped us consider the diagnosis of decidualized endometrioma. Data sharing is not applicable to this article as no new data were created or analyzed in this study. Videoclip S1 Grayscale and power Doppler ultrasound imaging, intraoperative view and histological findings in a non-pregnant woman with a multilocular, solid cyst, located in the left adnexal region, which was ultimately diagnosed as ovarian decidualized endometrioma. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.