Magnetic resonance imaging findings, prognosis, and treatment of fetal ovarian cysts

Introduction

Fetal ovarian cysts (FOCs) typically occur in the abdominal cavity of female fetuses during the third trimester with an incidence of approximately 1 in 2,600 (1,2). Although the ovaries are generally dormant during the fetal period, follicular development can still occur. The exact mechanism of FOCs remains unclear, but the widely accepted theory suggests that exposure to fetal pituitary gonadotropin, placental human chorionic gonadotropin, and maternal estrogen stimulates the ovaries, promoting follicular development and maturation (2,3). Additionally, conditions such as gestational hypertension, preeclampsia, diabetes, and thyroid dysfunction may lead to excessive estrogen secretion, further promoting follicular cyst development (4-6).

With the widespread adoption and advancement of prenatal diagnosis, the detection of FOCs has become increasingly prevalent (7). Accurate prenatal diagnosis is crucial for assessing fetal prognosis, guiding surgical decisions, and avoiding unnecessary induction of labor. Ultrasound remains the primary method for prenatal assessment, capable of detecting a wide range of fetal abnormalities. However, with the advancements in magnetic resonance imaging (MRI) technology, fetal MRI has emerged as a critical complementary tool to ultrasound for assessment of structural and developmental abnormalities. Fetal MRI enhances the diagnostic accuracy of abdominal tumors and cystic lesions and can aid in characterization of the lesion in relationship to surrounding anatomic structures, offering clinicians more comprehensive and clear images. In cases where fetal position, oligohydramnios, or maternal habitus limit the effectiveness of ultrasound, MRI serves as an accurate alternative for prenatal evaluation of fetal structures. The MRI characteristics of FOCs can exhibit significant variability, especially in the case of complex cysts.

At present, there is no consensus on the treatment of FOC. Ovarian cysts are typically considered benign lesions. A study suggested that they may resolve spontaneously after birth without intervention (8). However, certain types of cysts may give rise to complications such as cystic torsion, hemorrhage, necrosis, and other serious consequences, potentially leading to ovarian loss and other adverse outcomes (7,9,10). In such cases, active surgical intervention is recommended.

This study presents the MRI findings from 22 cases of FOCs and analyzed their prognosis and treatment. The aim was to assess the impact of MRI characteristics on the progression and management of FOCs. We present this article in accordance with the STROBE reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2024-2493/rc).

Methods

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Medical Ethics Committee of Northwest Women’s and Children’s Hospital (No. L2024-028). The requirement for individual consent for this retrospective study was waived. By searching “fetal abdomen” of the examination site on the Picture Archiving and Communication System (PACS) of Northwest Women’s and Children’s Hospital between January2016 and June2024, we confirmed the number of cases undergoing fetal abdominal MRI examination. The inclusion criterion was fetal ovarian lesions suspected by MRI examination. The exclusion criteria were as follows: (I) induced labor; (II) loss to follow-up; and (III) fetal non-ovarian cysts confirmed by surgery and pathology.

All pregnant women underwent MRI examination with a 1.5 Tesla (T) magnetic resonance system (GE Signa HDxt1.5T MR; GE Healthcare, Chicago, IL, USA). The scanning sequences included single-shot fast spin-echo (SSFSE), fast imaging with relaxation modulation (FIRM), and diffusion-weighted imaging (DWI). FOCs were divided into a simple cysts group and a complex cysts group according to Nussbaum’s criteria (11), with simple cysts showing a homogeneous signal with a thin wall and complex cysts showing a heterogeneous signal with hemorrhage, fluid-fluid level, or an unclear cystic wall. These ovarian cysts were also divided into an operation group and a non-operation group according to whether surgery was performed. The MRI findings and prognosis of the two groups were analyzed respectively. Imaging analysis was carried out by two radiologists with 10 years of experience in obstetric radiology. Differences of opinion were discussed until a consensus was reached.

Clinical features were recorded, including age, gestational age of initial diagnosis, and treatment. MRI features, including the location, unilateral/bilateral, size (the largest diameter), morphology, margin (regular or irregular), cystic wall, the signal characteristics, and fluid-fluid level, were recorded.

The statistical software SPSS 23.0 (IBM Corp., Armonk, NY, USA) was used for statistical analysis. Continuous variables were expressed as mean ± standard deviation (SD). If continuous variables were normally distributed by Shapiro-Wilk test, independent sample t-test was used for comparison; if they were not, Wilcoxon rank-sum test was performed. The corresponding threshold was calculated using the receiver operating characteristic (ROC)curve. Fisher’s exact test was used for categorical variables. A P value <0.05 indicated statistical significance.

Results

In total, we found 552 cases of fetal abdominal MRI examinations. Among them, 25 cases met the inclusion criteria, of which 2 cases were induced labor, 1 case was lost to follow-up, and the remaining 22 cases were included (Figure 1).

Figure 1 A flowchart of the cases enrollment and exclusion. MRI, magnetic resonance imaging.

Clinical features

The age of the 22 pregnant women ranged from 20 to 34 years old. The mean age of those in the simple cysts group was 29.79±3.62 years, whereas that of the complex cysts group was 29.37±4.41 years, which had no statistical difference (Table 1, independent sample t-test, P=0.815). The gestational age of initial diagnosis was 30–37 weeks, which had no differences between the simple cysts group and complex cysts group (Table 1, independent sample t-test, P=0.909).

Imaging features

There were 21 cases with unilateral cysts and 1 with bilateral cysts. Among them, there were 14 simple cysts and 8 complicated cysts. The maximum diameters ranged from 20 to 96 mm. There was no statistical difference between the simple cysts group and the complex cysts group in the maximum diameters (Table 1, independent sample t-test, P=0.682), whereas there was a statistical difference between the operation group and the non-operation group in the maximum diameters (Table 2, independent sample t-test, P<0.01). The critical value was 5.8 cm, for which the sensitivity was 77.8% and specificity was 100% (Figure 2). There was no statistical difference between the operation group and the non-operation group in cyst type, the T2 signal, and cystic wall (Table 2, Fisher’s exact test, P>0.99, P=0.609, P=0.544). All cysts showed hypointensity on T1-weighted imaging (T1WI). Simple cysts showed uniform hyperintensity on T2-weighted imaging (T2WI) (Figure 3). Of the 8 cases of complex cysts, 5 showed mixed and slight hypointensity on T2WI (Figure 4), and 3 cases showed fluid-fluid level. All cysts had clear boundaries and regular morphology. The cyst walls were unclear in 3 cases of complex cysts and clear in the rest (Table 3).

Figure 2 The ROC curve of maximum diameter. ROC, receiver operating characteristic.

Figure 3 Fetal simple ovarian cyst. (A) The coronal T2WI shows a round hyperintense mass on the left side of the fetal abdominal cavity. The size is about 62 mm × 45 mm × 48 mm. The boundary is clear, the margin is regular (arrow). The cystic wall is thin and uniform. (B)The mass on T1WI is uniform hypointense (arrow). (C) Two hyperintense masses can be seen on both sides of the fetal bladder on the coronal T2WI, the size of which is about 26 mm × 26 mm × 26 mm on the right side and 20 mm × 20 mm × 20 mm on the left side, with clear boundaries and regular margin (arrow). (D) The coronal T1WI shows hypointense masses (arrow). T2WI, T2-weighted imaging; T1WI, T1-weighted imaging.

Figure 4 Fetal complex ovarian cyst. (A) Coronal T2WI shows a round mixed-signal mass in the abdominal cavity of the fetus, with slightly low signal and linear high signal. The size of the mass is about 70 mm × 66 mm × 65 mm. The boundary is clear, the margin is regular (arrow). (B) The coronal T1WI shows the mass is uniform hypointense (arrow). (C) The coronal T2WI shows a round slight hypointense mass in the left side of the fetal abdominal cavity. The size is 59 mm × 51 mm × 51 mm. The boundary is clear, the margin is regular (arrow). (D) The coronal T1WI shows the mass was uniform hypointense (arrow). T2WI, T2-weighted imaging; T1WI, T1-weighted imaging.

Prognosis and treatment

A total of 7 simple cysts shrunk and disappeared postnatally, and 1 simple cyst disappeared prenatally. There were 6 simple cysts treated with surgery within 1 month after birth including 1 case of pedicle torsion and 1 case with hemorrhage. In the complex cysts group, 4 cases disappeared postnatally and 1 case disappeared prenatally; 3 cases were treated with surgery including 2 cases of pedicle torsion and 1 case with hemorrhage. There was no statistical difference in the number of surgery cases between two groups (Table 1, Fisher’s exact test, P>0.99). A total of 13 cases (59%) resolved spontaneously among all cysts.

Discussion

Fetal MRI examination

In recent years, there has been an increasing focus on the prenatal diagnosis of fetuses. Ultrasound is the primary method for prenatal assessment, capable of detecting a variety of fetal diseases. However, with the small imaging field, poor soft tissue acoustic contrast, oligohydramnios, and bone, ultrasound has not been able to facilitate a definite diagnosis of some diseases. Fetal MRI is most often used to supplement the abnormalities detected by ultrasound (12). MRI examination has the advantages of multi-orientation, non-radiation, and good soft tissue contrast resolution (13). With the development of MRI technology, especially the popularity of rapid MRI scanning sequences, such as the rapid MRI T2WI scanning technology SSFSE, the scanning time is only a few seconds each layer, which makes MRI an increasingly important supplement for prenatal diagnosis. FOCs are mostly benign lesions disappearing spontaneously after birth; their correct prenatal diagnosis is of great value. Fetal MRI enhances the diagnostic accuracy of abdominal tumors and cystic lesions and can aid in characterization of the lesion in relationship to surrounding anatomic structures (3,14).

MRI features

Currently, the criteria established by Nussbaum et al. are widely used to differentiate between complex and simple cysts (11,15). “Simple cysts” are characterized by being completely anechoic, thin walled, and are frequently unilocular. In contrast, “complex cysts” which denote intracystic hemorrhage, may be thick walled, partially anechoic with a fluid-fluid level (formed by cyst fluid and liquid hematoma), or partially anechoic with a retracting clot and septations (septa formed by strands of organized hematoma). The International Ovarian Tumor Analysis (IOTA) has recently been proposed for the classification of FOCs (16).

FOCs have characteristic MRI manifestations. Some ovarian cysts typically present with uniform hyperintensity, whereas others may demonstrate mixed signals or slight hypointensity on T2WI due to hemorrhage or torsion. In our study, MRI classification criteria for FOCs were established based on the classification criteria of ultrasound. Simple cysts showed hyperintensity on T2WI, whereas complex cysts showed mixed signal, fluid-fluid level, and unclear cystic wall on T2WI. Both simple and complex cysts showed uniform hypointensity on T1WI which can distinguish them from solid abdominal tumors. In our cases, 8 complex cysts were identified, 5 with mixed signals, and 3 with fluid-fluid level. Complex cysts with mixed signals on T2WI may be misdiagnosed as solid tumors. Due to this, T1WI and DWI should be used for differentiation. Complex cysts show uniform hypointensity on T1WI and unrestricted diffusion on DWI, whereas abdominal solid tumors show isointensity or uneven hypointensity on T1WI and uneven restricted diffusion on DWI. Simple cysts should be differentiated from other abdominal cystic diseases, such as mesenteric cysts, intestinal duplication, and choledochal cysts (17,18). FOCs are mostly located in the lower abdomen, between the bladder and the kidney, with thin wall and a regular shape, whereas mesenteric cysts are found higher up with unclear cystic wall, and irregular shape. Intestinal duplications are also located in the upper abdomen, with thick walls and irregular shape. Choledochal cysts are mostly located in the right upper abdomen, with thin walls and irregular morphology. When an ovarian cyst is large and difficult to distinguish from other cystic lesions in the abdominal cavity, accurate diagnosis can be facilitated by noting the sex of the fetus and the gestational week when the cyst is found.

Clinical features

FOCs are diagnosed after 28 weeks (8,10); Souganidis et al. reported that they are found at 32–36 weeks (19). FOCs, which are mostly unilateral with few bilateral cases and vary in size, can spontaneously regress, with nearly 50% involuting either pre- or post-natally (8,20,21). At present, studies on FOC regression have mainly focused on the type and size of the cyst (2,5,8,22-24). The prenatal spontaneous regression rate of simple ovarian cysts is 20% (8), and spontaneous regression of simple ovarian cysts is more common than that of complex ovarian cysts (5). For simple ovarian cysts less than 5 cm or 4 cm in diameter, postpartum surgical treatment is not necessary (2,22); otherwise, surgical treatment can be taken into consideration (23,24). For complex cysts, some regression can happen, but active surgical treatment is recommended (22).

All cases in our study were initially diagnosed at 30–37 weeks of gestation, 95% (21/22) were unilateral and 59% (13/22) underwent non-operative management. The rate of non-operative management of simple cysts was 8/14. The prenatal spontaneous regression rate of simple cysts was 1/14, which was lower than that reported in previous literature (8). The non-operative rate of complex cysts was 5/8, including 1 case of prenatal regression. There was no statistical difference between simple cysts and complex cysts in the number of cases undergoing non-operative management. The mean maximum diameter of cysts in the surgical group was (62.11±21.60) mm and (37.62±10.28) mm in the non-surgical group, which had statistical significance. The critical value was 5.80 cm, slightly higher than the standard of 5 cm in previous research (2,22).

There is no consensus regarding the management and treatment of FOCs, and the treatment plan depends on different medical institutions. There is a higher risk of complications for persistent or enlarged cysts, such as pedicle torsion, hemorrhage, intestinal obstruction, cyst rupture, and even autoamputation of the ovaries (25). Some studies have shown that simple cysts with a maximum diameter of 3–4 cm are still at risk of torsion (3,26). The probability of torsion for cysts over 50 mm is 33% (22). The risk of occurring complications of complex cysts is 34% (5). Regarding the prediction of complications and surgery of FOCs, cysts size, imaging findings (simple or complex), and cyst progression during follow-up are important determinants (27). In our study, there was no statistical difference in the number of torsion cases and surgery cases between the simple cysts group and the complex cysts group. The average maximum diameter of the torsion cysts was 5.97 cm, accounting for 3/8 of the number of cysts with maximum diameter exceeding 5 cm, which was basically consistent with literature (22). This may be due to the fact that ovarian cysts in the fetal period were located in the abdominal cavity and had large mobility, so they were prone to torsion.

Limitations

First of all, this was a retrospective study. The main limitation is the sample size, which is the current situation of most studies on FOCs. In future, we hope to establish multi-center research to increase the sample size. Second, some cases were managed based on clinical experience and prophylactic surgical interventions, so the number of cysts that would have regressed in the surgical group is unknown. In future study, we propose to establish collaborative frameworks with clinicians to standardize diagnostic protocols, thereby enhancing the precision of MRI characteristics and statistical validity.

Conclusions

The MRI findings of FOCs are various, especially complex cysts which are prone to misdiagnosis as solid tumors. Accurate recognition of complex cyst features on MRI is crucial for diagnosis. For newborns with ovarian cysts, whether to operate or observe after birth depends on the size of the cysts and its dynamic changes. Our study suggests that cysts smaller than 5 cm can typically be managed conservatively with dynamic monitoring. MRI classification of cysts has little effect on prognosis. Both simple cysts and complex cysts bear the risk of torsion. If cysts regress after birth, conservative management may continue. However, if cysts enlarge or if abdominal pain develops, prompt surgery is necessary to preserve ovarian tissue and prevent autoamputation.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2024-2493/rc

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2024-2493/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Medical Ethics Committee of Northwest Women’s and Children’s Hospital (No. L2024-028). The requirement for individual consent for this retrospective study was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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