Decidualized endometrioma mimicking malignancy: A case report and literature review of magnetic resonance imaging findings

Decidualized endometrioma results from the hypertrophy of endometrial stromal cells, which occurs during pregnancy due to increased progesterone levels. Differentiating decidualized endometrioma from ovarian malignancy can be challenging. However, various types of imaging findings can help us identify decidualized endometrioma and avoid unnecessary surgical intervention during pregnancy. We present a case of decidualized endometrioma, with a focus on the magnetic resonance imaging (MRI) features that aid in its accurate diagnosis. CASE REPORT A 33-year-old woman (gravida-1-para-0) at 13 weeks gestational age was incidentally discovered to have a right ovarian cystic lesion during a prenatal examination. Transvaginal ultrasonography revealed a 6.7-cm, well-defined, and echogenic cystic lesion in the right ovary with mural nodules. The largest mural nodule was approximately 1.1 cm. No obvious blood flow was revealed through color Doppler ultrasonography. However, after 3 weeks, the cyst enlarged slightly (7.0 cm), and a color Doppler ultrasound revealed blood flow in the mural nodule [Figure 1]. MRI revealed a 7.0-cm, septated cystic lesion with a hyperintense signal on T1-weighted images and hypointensity on T2-weighted images (T2WI), suggesting the presence of hemorrhagic content. The mural nodules were hyperintense on T2WI, were relatively isointense to the placenta, and had a high apparent diffusion coefficient (ADC) value [1.76 × 10−3 mm2/s; Figure 2]. Because ovarian malignancy was suspected, the patient underwent laparoscopic right oophorocystectomy. The surgical findings revealed a large (7.0 cm × 4.5 cm) right ovarian cystic lesion with chocolate-like content, and the solid parts measured approximately 2.0 cm × 1.5 cm. Adhesion between the cystic lesion and cul-de-sac was also noted. The pathology report revealed decidualized stromal tissues with some endometrial lining cells and a focal presence of hemosiderin-laden macrophages. This result suggested decidualized endometrioma. The patient was discharged from the hospital 2 days after surgery and received regular prenatal care.

Most ovarian masses found in pregnant women are benign lesions, and <1% of patients with ovarian masses are diagnosed with ovarian cancer.[] A study indicated that teratomas, endometriomas, and cysts are the most common adnexal masses that develop during pregnancy.[] Decidualized endometrioma is a special type of endometrioma that is only observed in pregnant women. Endometrial stromal cells are stimulated by progesterone, leading to the formation of hypervascular mural nodules.[] Although the prevalence of decidualized endometrioma is unclear, a small cohort study reported that 16% of patients with endometrioma may undergo decidualization during the first trimester.[] The size of decidualized endometriomas can increase gradually with gestational age.[] Decidualized endometriomas can be asymptomatic, and they can spontaneously regress after childbirth. Therefore, surgical excision is not necessary. Through ultrasonography, single or multiloculated cystic lesions with homogeneous echogenic content can be detected. In addition, mural nodules with vascularity are typically observed on color flow Doppler ultrasound images.[] A case report described a decidualized endometrioma that presented with mural nodules that rapidly vascularized without size enlargement.[] Another study reported “smoothly” lobulated nodules, which are common in decidualization.[] On MRI, endometriomas typically present T1 hyperintensity and T2 hypointensity (T2 shading) due to hemorrhagic content. The fluid–fluid level has been reported in several cases.[] Mural nodules may be lobulated or papillary, hyperintense on T2WI, and isointense to the placenta. The mural nodule mainly comprises decidual cells with abundant cytoplasm, and it tends to be the cause of T2 hyperintensity.[] A single-center retrospective study suggested that solid components with a height of <11.1 mm indicates the presence of benign lesions.[] After reviewing the literature, we identified 10 case reports that described a total of 13 decidualized endometrioma cases with MRI findings.[,,,] The main MRI characteristics of these cases and the present case are summarized in Table 1. On diffusion-weighted imaging (DWI), decidualized endometriomas may exhibit high signal intensity due to the T2 shine-through effect. A single-center retrospective study reported that computed DWIs with b = 1500 s/mm2 and the ADC value can be used to differentiate endometrioma from ovarian malignancy through the evaluation of mural nodules. The result of that study indicated that relative to ovarian malignancies, decidualized endometriomas have a significantly higher ADC value (2.01 ± 0.26 × 10−3 mm2/s), whereas ovarian cancer has a lower ADC value (1.08 ± 0.20 × 10−3 mm2/s).[] This finding may be attributed to higher cellularity in malignant tissues than in decidualized tissues. In our case, the mean ADC value was 1.76 × 10−3 mm2/s, which suggested decidualized endometrioma. In conclusion, the characteristic imaging features of decidualized endometrioma, particularly T2 hyperintensity, low height, and mural nodules with high ADC values on MRI, can help clinicians to differentiate decidualized endometrioma from ovarian malignancy. A careful review of clinical history and imaging findings can aid in making accurate diagnoses and avoiding unnecessary surgery. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that her name and initial will not be published and due efforts will be made to conceal her identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

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