Definition: Fetal ovarian cysts represent cystic lesion confined to the lower abdomen of a female fetus, when the stomach, bladder and both kidneys appear normal. The diagnosis is made by exclusion of other cystic lesions (either unilateral or bilateral) confined to the fetal abdomen. The cysts may achieve a considerable size, reaching up to 5 cm for large cysts. The cysts can be unilateral or bilateral, unilocular or multilocular.

Prevalence: Fetal ovarian cysts are not rare. In the last 10 years we have encountered 45 cases of which 12 showed signs of in -utero torsion.

Etiology: There is controversy with respect to the genesis of these cysts. Evidence suggests that excessive stimulation of the fetal ovary by hCG from the placenta may be a significant factor in cyst formation. This would explain the increased incidence of cysts in infants of mothers with diabetes, pre-eclampsia or rhesus isoimmunization.

Ultrasound features: These criteria are diagnostic of fetal ovarian cyst in most cases:

1. Presence of a cystic structure that is regular in shape and located at one side of the fetal abdomen.
2. Integrity of the urinary and gastrointestinal tracts.
3. Female sex of the fetus. The diagnosis is always presumptive. Torsion can be suspected when intracystic flocculation is observed followed by sedimentation on the sloping part of the cyst. Most cases of fetal ovarian cysts are diagnosed in late second trimester of pregnancy or in early third trimester.

Ultrasound scan of the fetal abdomen showing an ovarian cyst. (S-Stomach , B-Bladder)

A huge fetal ovarian cyst with a liquid/solid sediment interface, representing torsion of the cyst.

Intra-operative picture of the cyst described in fig. above

Prognosis: Continuous ultrasound monitoring of antenatally diagnosed fetal ovarian cysts is recommended. The tendency of simple cysts to regress near term or in the early neonatal period does nor justify in-utero therapy and certainly does not necessitate induction of labor before lung maturity is ascertained. In cases where fetal ovarian cysts show evidence of in-utero torsion, induction of labor may be considered provided lung maturity has been established.