Fetal Ovarian Cysts

Fetal ovarian cysts are fluid filled masses arising from the fetal ovary, measuring more than 20 mm in diameter.¹

As the quality of ultrasound imaging continues to improve, the number of cases diagnosed antenatally has increased.  Current incidence of clinically significant fetal ovarian cysts is thought to be about 1 in 2,500 live births.¹

 Fetal ovarian cysts are most commonly benign functional cysts.  It is hypothesized that these enlarged follicles form secondary to stimulation of fetal ovaries by maternal gonadotrophins or placental hormones.¹

Fetal ovaries normally undergo follicular development, therefore cysts <20mm in size are physiologic, not pathologic.² When the follicles grow beyond 20mm they are considered pathologic.  While most cysts are fluid filled, some become hemorrhagic and others undergo torsion, which may result in loss of the ovary.  Malignant fetal ovarian neoplasms have been reported only very rarely.^1,3

Fetal ovarian cysts are typically isolated and not associated with other fetal anomalies.  There may be additional findings on ultrasound that develop secondary to the ovarian cyst.  Ascites due to transudation or associated with cyst rupture may be found.¹ Polyhydramnios may be seen secondary to compression of bowel.¹ There are also reports of obstruction of bowel or ureters secondary to adhesions after ovarian torsion and necrosis.¹  Rarely, there can be significant bleeding into the cyst, which can require intrauterine transfusion ^4,5 

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Fetal ovarian cysts are diagnosed by ultrasound.  Most are detected incidentally in the third trimester after the patient presents for an ultrasound for growth or other routine follow up and a new cystic mass in the pelvis or lower abdomen of a female fetus is identified.^6,7  Ovarian cysts are typically intraabdominal cystic structures measuring 2-5cm which are seen superior to and parasagittal to the bladder.⁸  They are further classified as either simple or complex.  Simple cysts are round, unilocular, anechoic, and thin walled.¹  Pathognomonic features include “daughter cyst”, or smaller cyst within a cyst.⁹ This finding has been reported to be identified in 82% of ovarian cysts with 100% PPV.¹⁰  Complex cysts are thick walled with heterogeneous echogenicity, and may contain multiple septations, mobile internal echoes, appear solid, or have fluid-fluid levels.¹ Complex appearance often secondary to torsion or hemorrhage.¹ Torsion is suggested by mixed echogenicity or new fluid levels within the cyst.¹¹ Hemorrhage is represented by echogenic areas within the cyst.¹¹ Occasionally they are mobile and are seen to be in different locations on subsequent scans due to lax utero-ovarian ligaments or to autoamputation.¹² Color doppler may be helpful in evaluating ovarian cysts as ovarian cysts will be seen lateral to the bladder, and will have avascular walls and contents.

Any cystic or complex mass which can be found in the fetal abdomen can be confused with an ovarian cyst.  Once a mass is identified the remainder of the intraabdominal contents should be evaluated to ensure that the mass is not contiguous with them.  Specific sonographic features of the following structures should be identified:

• Urinary system: hydronephrosis, multicystic dysplastic kidney, dilated pole in duplex kidney, hydroureter, megacystis, urachal cyst. 
• Gastrointestinal: dilated stomach, dilated loops of bowel, meconium pseudocyst, enteric duplication cyst, mesenteric cyst, lymphangioma, hepatic cyst, cystic hepatic tumor, biliary cyst, splenic cyst, choledochal cyst.
• Genital: hydrocolpos, cloaca. 
• Other: adrenal cystic mass, teratoma, cystic neuroblastoma

The overall prognosis is generally excellent. Over 50% of these cysts will resolve spontaneously, occasionally during pregnancy but frequently within 6 months after birth.¹ A large meta-analysis reported that 53.8% of ovarian cysts resolved, especially if the cyst was <40mm and simple.⁷ The fetus with ovarian cysts is at risk for ovarian torsion, rupture of the cyst, or hemorrhage within the cyst.¹ Torsion is more common in cysts ≥40mm and is more common in complex cysts.⁷  Approximately 24% of simple cysts became complex by time of birth; with the greatest risk in cysts ≥40mm.⁷ 

Unfortunately, long term functional prognosis of the affected ovary is poor despite spontaneous cyst resolution. Of patients examined after cyst resolution by ultrasound; 53.6% of patients had an absent or undetectable ovary.¹³ Ovarian preservation was more likely if the cyst was simple (85%) compared with complex (16%).¹³ 

Prenatally, fetal ovarian cysts are managed conservatively with serial ultrasounds to detect hemorrhage, torsion, and polyhydramnios.¹ Torsion and bleeding into the cyst are not indications for delivery.  Aspiration of cyst prior to delivery has been performed, however, routine prenatal aspiration cannot be recommended as standard practice at this time due to heterogeneity of studies, and generally excellent outcomes with expectant management.⁷ Timing and mode of delivery should be as recommended for standard obstetric indications.  Fetal ovarian cysts are not an indication for preterm delivery, early term delivery, or cesarean delivery.¹ Pediatric surgery consultation and NICU consultation should be considered prenatally.

The optimal management strategy for these neonates remains controversial. If patients are asymptomatic, they are typically managed expectantly and are followed with serial ultrasounds to monitor the cyst.¹  Surgical interventions may be needed in neonates with cysts that are larger (>50 mm), complex, increasing in size, those that persist more than 6 months, and in symptomatic neonates.¹ Some experts recommend early surgical intervention for ovarian preservation.¹⁴ Surgery may be via laparoscopy or laparotomy, and cystectomy is preferred over oophorectomy for ovarian preservation, although this not always achievable.¹ Approximately 25% of patients who require surgery require oophorectomy.⁷ Cyst aspiration is sometimes performed in the neonate and may be considered to prevent ovarian torsion.¹ Patients and parents should be counseled about uncertainty regarding long term ovarian function, and importance of gynecology follow up.

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