Tumor-like ovarian endometriosis with pregnancy decidua reaction: A case report and review of the literature

Abstract

We describe a case of bilateral ovarian tumor-like lesions detected during pregnancy. It is important to highlight that these masses were not detected for the first time during pregnancy; the patient had already been aware of them 2 years prior, during pregnancy preparation, when an ultrasound examination revealed bilateral space-occupying ovarian lesions. These lesions did not exhibit any increase in size during regular follow-ups until pregnancy. At 17 weeks of gestation, fetal ultrasound showed significant enlargement of the bilateral ovarian lesions. The patient underwent pelvic magnetic resonance imaging, which revealed cystic masses in both the ovaries with septations and multiple nodular and flocculent projections on the walls and septations, exhibiting features resembling malignant tumors. The cystic fluid within each cyst predominantly showed slightly short T1 and long T2 signal characteristics. The final diagnosis of lesions occupying the ovarian space was endometriotic cysts with a decidual reaction associated with pregnancy, which was confirmed on postoperative pathological examination. Subsequently, at 19 weeks of gestation, the patient underwent a “laparoscopic excision of the left ovarian lesion and right ovarian lesion stripping.” The patient recovered well postoperatively and successfully delivered a baby at 39 weeks of gestation. Endometriosis with decidual reaction during pregnancy is rare and ectopic decidual tissue can easily be confused with neoplastic lesions using imaging results. In addition, clinicians must remain vigilant about the special conditions that ectopic decidual tissue may cause, such as cyst rupture, massive hemorrhage, dystocia, and even fetal death.

Background

Decidual reaction is a normal response of the pregnant uterus. If this reaction occurs at a site other than the uterine cavity, it is referred to as ectopic decidua. Although decidual reaction is mostly regarded as a benign reaction during pregnancy, it is noteworthy that in some cases, decidual reaction can present as tumor-like lesions and even induce complications, such as cyst rupture and hemorrhage, which can directly threaten the safety of the mother and the fetus.

The current clinical management of adnexal masses in pregnancy is characterized by a significant conflict. However, there is a need to avoid the potential risk of over-intervention on pregnancy outcomes, and it is important to be vigilant about the serious consequences of missed diagnosis of malignant lesions or delayed treatment.

In view of the many diagnostic and therapeutic challenges associated with ectopic meconium and the potential risks it may pose during pregnancy, this report describes a case of endometriosis in a patient with bilateral ovarian meconium reaction that resembled a tumor lesion on imaging. By reviewing the relevant literature and combining the clinical experience of this case, we aimed to provide a more scientific and rational basis for the clinical diagnosis and treatment of decidual reaction.

Case presentation

A 30-year-old pregnant woman was admitted to the hospital for evaluation of “bilateral space-occupying ovarian lesions.” Two years ago, during pregnancy preparation, an ultrasound examination revealed bilateral space-occupying ovarian lesions (a cystic-solid mass on the left side, measuring 11.6 × 5.8 cm, and a cystic mass on the right side, measuring 4.5 × 4.4 cm), which did not increase in size upon regular follow-up. At the time of fetal ultrasound at 17 weeks of gestation, the patient had significantly enlarged bilateral ovarian lesions (the left ovarian lesion measured 16.0 × 7.4 cm, and the right ovarian lesion measured 5.4 × 4.7 cm). The patient, with a history of hypertension and a maximum blood pressure of 145/100 mmHg prior to pregnancy, had been taking oral labetalol hydrochloride 50 mg before this visit, denied smoking and alcohol use, and reported a family history of hypertension and diabetes. Laboratory tests showed negative tumor markers. Magnetic resonance imaging (MRI) examination was performed to further clarify the nature of the lesions. Pelvic MRI scan revealed the following: (a) pregnant uterus and (b) a cystic mass in each ovary, with the left ovary showing a larger mass measuring 15.5 × 11.0 × 7.0 cm, and the right ovary showing a smaller mass measuring 5.3 × 4.2 × 2.0 cm. The cystic masses within both ovaries had thickened walls, with septations inside the cysts; multiple nodular or flocculent protrusions are visible on the walls and septations. The signal of the fluid within each cyst varied, predominantly showing slightly short T1 and long T2 signals (Figure 1). Imaging diagnosis showed possible bilateral endometriotic ovarian cysts with decidual reaction; however, cystic adenocarcinoma could not be ruled out.

Figure 1.

(a) T1WI transverse position; (b) T2WI transverse position; (c) T2WI sagittal position, mixed-signal occupancy of the left ovary with multiple thick separations (solid line arrow); (d) Ultrasound image with intact left ovarian envelope, poorly transmissive, with detailed dense weak light spots and separation (solid line arrow); (e) T1WI transverse position; (f) T2WI transverse position; (g) T2WI sagittal position, posterior uterine masses of long/short T1 and long T2 signal foci of possible right ovarian origin (dashed arrows) and (h) Ultrasound image, the envelope of the right ovary is intact with good translucency, multiple separations are visible within it, and a little blood flow signal is visible in the periphery (dashed arrow).

The patient underwent “laparoscopic left ovarian lesion excision and right ovarian lesion stripping” at 19 weeks of gestation. Intraoperatively, both ovaries exhibited blister-like lesions with marked thickening of the cyst walls and the presence of yellow-brown mucus in the cystic fluid. Microscopically, the cyst wall appeared rough with numerous small, scattered protrusions, and coffee-ground-like material was observed attached to it (Figure 2). Pathology revealed bilateral ovarian endometriotic cysts with a decidual reaction to pregnancy in both the left and right ovaries. Postoperatively, we performed ritodrine hydrochloride pumping, phloroglucinol 80 mg BID, oral drotaverine hydrochloride to inhibit contractions, cefazolin sodium for antibiotic prophylaxis, oral dydrogesterone, and vaginal insertion of urtrogestan to protect the fetus, along with labetalol hydrochloride 50 mg TID, and nifedipine 30 mg QD for hypotensive treatment. The patient was discharged from the hospital 7 days postoperatively and delivered a healthy child at 39 weeks and 3 days of gestation; both the patient and the newborn were in good condition after the delivery.

Figure 2.

(a) Gross examination revealing grayish-white to grayish-red tissue of the cyst wall and (b) Microscopic findings (HE staining): Under 40× magnification, both the left and right ovarian cyst linings demonstrated irregular surfaces with numerous scattered small protrusions (solid arrow).

Discussion

The decidua reaction refers to a series of changes in the endometrial tissues during pregnancy, such as capillary dilation as well as the thickening and curvature of the endometrial glands. These changes are stimulated by embryo implantation and progesterone action. The reaction serves to protect and nourish the placenta and provides a safe environment for fetal growth and development. The decidua reaction is often associated with pregnancy but has also been reported in nonpregnant and postmenopausal women.^1–3 Ectopic decidua can occur in tissues and organs outside the endometrial region, such as the ovaries, cervix, plasma surface of the uterus, and appendix as well as periaortic and pelvic lymph nodes. ⁴ There are two main theories regarding the origin of ectopic decidua. One theory suggests that it occurs on the basis of endometriosis and is a decidualization reaction to the hormonal changes of pregnancy. Another theory posits that the peritoneum and Müllerian ducts have a common embryonic origin, both being derived from the coelomic epithelium and mesenchyme. Consequently, coelomic mesenchymal pluripotent cells can transform into decidual cells under the influence of progesterone, allowing the decidua reaction to occur in the peritoneum, on the serous surface of the abdominopelvic cavity, and on the surface of the greater omentum.^5,6 Therefore, some refer to the endometrial-origin ectopic decidua as endometriosis decidua, while the mesenchymal metaplasia-origin ectopic decidua is referred to as deciduosis.

In the present case, the patient had a history of hypertension. Studies have shown that women with hypertension are at a higher risk of being diagnosed with endometriosis via laparoscopy. ⁷ Both ultrasound and MRI revealed cystic lesions with internal septations in both ovaries. The left ovary contained a larger, multicystic lesion with varying signals within each cystic sac, predominantly characterized by slightly shorter T1 and longer T2 signals. We speculate that the lesion’s morphology and the cystic fluid’s signal characteristics may be related to ectopic endometrial cyclic bleeding and the decidua reaction; an encapsulated old hemorrhage within the lesion is covered by new hemorrhage, subsequently forming a multilocular cystic structure. The presence of accumulated blood from different time periods, combined with increased secretion of mucinous material from the endometrial glands due to the decidua reaction, mucinous material being high in protein content, could account for the variable signals from one cyst to another. This phenomenon may also be a significant reason for the notable enlargement of the lesion during pregnancy.

Malignant neoplastic lesions cannot be completely ruled out based on imaging characteristics, because of the rapid short-term enlargement of bilateral lesions with thick cystic walls and multiple nodular and flocculent protrusions visible on the walls, similar to the case reported by Machida ⁸ et al. (papillary vegetation, with ultrasound suggesting improved blood flow manifestations). They concluded that comparing the MRI signals of the lesion with those of the placenta could aid in identifying ectopic decidua and malignant ovarian tumors. Vegetation have the same signal intensity as the placenta in both T1 and T2, while malignant tumors exhibit low to high signal in T1 and high signal in T2. Additionally, ectopic ovarian decidua reaction must be differentiated from ovarian cystadenomas. Both can present as single or multiple cystic lesions, and sometimes differentiation is challenging, with the final diagnosis relying on pathological examination.

Decidualization is a benign reaction during pregnancy and commonly occurs at 4–6 weeks of gestation. ⁶ Most ectopic decidua are asymptomatic and require no special treatment. However, several reports in the literature suggest that ectopic decidua can develop tumor-like lesions, which may be associated with risks, such as cyst rupture, pain, hemorrhage, dystocia, and even fetal death.^9–14 These conditions should be treated accordingly. We conducted a literature review on eight reported cases of ovarian endometriosis with decidual reaction during pregnancy (Table 1). This condition is often asymptomatic and is typically discovered incidentally on ultrasound, making diagnosis challenging. Ultrasound and MRI play a critical role in the initial evaluation of the disease. Ultrasound often reveals cystic masses, some of which may contain solid or liquid components, while MRI typically shows high signal intensity on T2-weighted imaging. However, pathological examination remains the gold standard for establishing a definitive diagnosis. A literature review of the eight cases indicates that surgical intervention is the primary treatment approach. Overall, the prognosis is favorable. The uniqueness of this case lies in the following two aspects. First, it was difficult to exclude the possibility of malignancy in the original lesion. Second, considering the lesion’s potential for malignant transformation, significant rupture/hemorrhage risk due to its large size, and possible fetal compromise through mass effect or hemorrhagic shock, we ultimately performed laparoscopic precision resection through multidisciplinary collaboration. This approach not only avoided overtreatment but also ensured the safety of both the mother and the fetus, providing a valuable reference for selecting the optimal surgical timing and minimally invasive technique for such complex cases.

Table 1.

Clinical and imaging characteristics of ovarian endometriosis with decidua reaction during pregnancy: a summary of eight cases.

Feature	Results
Number of cases	8 cases
Mean age (range)	32.8 years (24–41 years)
Mean gestational age (range)	15 weeks (8–25 weeks)
Clinical presentation	Abdominal pain (1 case), incidental finding (6 cases), recurrent vaginal bleeding (1 case)
Ultrasound features	Cystic mass (100%). Of these, liquid echo (2 cases), combining real components (3 cases)
MRI features	High signal intensity on T2-weighted images (4 cases), no mention of MRI (4 cases)
Pathological confirmation	100%
Management	Surgical intervention (100%)
Prognosis	Favorable

MRI: magnetic resonance imaging.

Based on the experience from this case, we recommend the establishment of a dynamic risk assessment system for adnexal masses during pregnancy. This system should focus on monitoring the growth rate of the mass, changes in blood flow, and fluctuations in indicators such as CA125. Additionally, a radiomics feature comparison database should be developed to improve the ability to differentiate between benign and malignant lesions. The current research findings will provide a scientific basis for establishing a clinical diagnosis and making treatment decisions, helping physicians strike a reasonable balance between avoiding overtreatment and preventing delays in necessary care.

Conclusions

Ovarian endometriosis with a decidua reaction during pregnancy is rare. The possibility of this condition should be considered when an ovarian lesion with space-occupying characteristics is encountered during pregnancy. Ultrasound and MRI aid in the diagnosis and differential diagnosis of this condition, but sometimes pathology is ultimately required for clarification. Although ectopic decidual changes are inherently benign, clinicians must remain vigilant about the risk of complications when making a treatment decision. In the future, a multidisciplinary collaboration mechanism could be established to dynamically assess the nature of the mass, its growth rate, and hemodynamic changes.