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Although they are most often benign and often undergo spontaneous resolution, fetal ovarian cysts can cause ovarian torsion with the potential risk of loss of an ovary or ovarian function. Because ovarian torsion often occurs before birth, management during pregnancy remains controversial. Some experts advocate in utero decompression via fetal intervention, whereas other experts recommend expectant management.
An ovarian cyst of <20 mm in diameter is considered physiological and represents a maturing follicle. A cyst of >20 mm in diameter is considered abnormal.
With improved ultrasound resolution, the incidence of ovarian cysts detected in a fetus has increased and is currently estimated to be approximately 1 in 2500 live births.
The ovaries arise mainly from the genital ridge and mesonephros. The gubernaculum becomes the ovarian ligament and connects the ovary to the uterine fundus. The ovary descends no further than the level of the uterine fundus. Because the fetal pelvis is shallow and the ovary originates as an abdominal organ, fetal ovarian cysts are most often seen as an abdominal mass.
The fetal ovary is normally dormant, but follicular cysts may develop, likely secondary to exposure to fetal pituitary gonadotropins, placental human chorionic gonadotropins, and maternal estrogens.
A simple cyst may contain a single septation. A small, round anechoic structure within a cyst, or the “daughter cyst sign,” is considered pathognomonic for an ovarian cyst (Figures 1 and 2).
Postnatal surgical specimens and histologic analysis suggest that complex ovarian cysts may result from primitive gonadal dysgenesis caused by vascular compromise.
Fetal ovarian cysts are typically rare, incidental findings in the third trimester of pregnancy and are not associated with genetic or structural anomalies. Secondary obstruction of the fetal bowel or kidneys can occur and is thought to result from adhesions in the presence of ovarian torsion, causing ovarian necrosis.
The differential diagnosis of a fetal intra-abdominal cyst is broad and can be narrowed by determining the organ of origin and the location and appearance of the surrounding structures. As discussed in other anomalies presented in this Consult, several genitourinary abnormalities can present with a fetal abdominal or pelvic cystic mass. These include simple renal cysts, multicystic dysplastic kidneys, hydronephrosis, urachal cysts, and hydrocolpos.
Other potential etiologies for an abdominal cyst include gastrointestinal findings, such as enteric duplication cysts, meconium pseudocysts, or choledochal cysts. Enteric duplication cysts are cystic structures consisting of all three bowel wall layers that often share a common wall with normal small bowel. A meconium pseudocyst occurs after bowel perforation and can be seen as an irregular, thick-walled mass that conforms to the peritoneal contours and liver surfaces. In addition, bowel dilation, intraperitoneal calcifications, and ascites may be seen. Choledochal cysts, which are dilations of the common bile duct, are most commonly unilocular cysts that are located in the right upper quadrant of the fetal abdomen adjacent to the liver. If these become very large, they can extend into the abdomen and displace other organs.
In addition, lymphatic malformations can present as intra-abdominal masses, although the most common sites are the fetal neck, head, and axilla. Intra-abdominal lymphatic malformations often present as large, thin-walled, multilocular cysts with multiple septations, commonly located in the small bowel mesentery.
Cystic sacrococcygeal teratoma, which is more likely to occur in female fetuses, can present as a purely cystic, midline pelvic structure; however, it usually contains cystic and solid components and grows in the sacrococcygeal region with external extension.
Fetal ovarian cysts are typically sporadic findings. If no further abnormalities are noted on ultrasound and the family history is unremarkable, no genetic evaluation beyond standard aneuploidy screening is typically recommended.
Pregnancy and Delivery Management
Once a fetal ovarian cyst is diagnosed, serial ultrasound examinations have been recommended to assess changes in size or complexity of the cyst. The most common complication of an ovarian cyst is torsion, which has been reported in as many as 15% to 34% of fetuses with cysts measuring 30 to 59 mm.
Because of the high risk of torsion, prenatal cyst decompression by percutaneous aspiration has been suggested, particularly for cysts of ≥40 mm in diameter or for those with rapid growth, defined as ≥10 mm per week.
However, some experts argue that spontaneous resolution of ovarian cysts, particularly small, simple cysts, can occur both prenatally and postnatally. Thus, conservative management is a reasonable approach.
To date, optimal management of fetal ovarian cysts is uncertain.
Timing of delivery should not be affected by the presence of a fetal ovarian cyst, as the risk, timing, and duration of torsion cannot be predicted, and early delivery would not necessarily preserve ovarian function.
The presence of an ovarian cyst should not alter the mode of delivery; cesarean delivery should be performed for the usual obstetrical or medical indications.
Prognosis
Most small, simple fetal ovarian cysts resolve spontaneously after birth because of cessation of exposure to maternal and placental hormones.
Postnatal surgical treatment is often recommended for large cysts. Most operations can be performed in the newborn period laparoscopically with minimal morbidity, with the goal of ovarian preservation. However, one study with long-term follow-up reports that a follicular ovary was detected only in 39% of cases, with a higher likelihood of preservation of function in simple cysts (85%) vs hemorrhagic cysts (16%).
Fetal ovarian cysts typically present as unilateral intra-abdominal cystic structures in the third trimester of pregnancy, likely because of follicular stimulation from maternal and placental hormones. Spontaneous resolution of fetal and neonatal ovarian cysts can occur. The most common complication is ovarian torsion. The risk of torsion is higher in the prenatal period than after birth. Management includes serial ultrasound examinations to assess changes in size and complexity. Some experts advocate for decompression for cysts of ≥40 mm in diameter or those that demonstrate rapid growth of ≥10 mm per week to minimize the risk of torsion. However, the risks and benefits of prenatal intervention remain controversial. The diagnosis of fetal ovarian cysts should not alter the timing and mode of delivery. If postnatal surgical intervention is indicated, the goal of treatment is ovarian preservation. Simple cysts tend to have more favorable long-term outcomes than complex cysts.
References
Trinh T.W.
Kennedy A.M.
Fetal ovarian cysts: review of imaging spectrum, differential diagnosis, management, and outcome.
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