In female newborns, ovarian cysts are the most frequent type of abdominal tumor (1). The incidence of ovarian cysts has been estimated at more than 30% (this estimate is based on an investigation of stillborns or infants who died within 28 days of birth) (2). In the most of cases, the size of ovarian cyst is small, seeming to resolve spontaneously and are of no clinical significance. However ovarian cyst often presents complication such as torsion and seems to be an indication for surgical intervention. According to the common use of antenatal ultrasonography, the incidence of ovarian cysts have been increased both in utero and in the female newborn. There is some debate about the appropriate treatment of fetal ovarian cysts. Here we presented 17 clinical cases and the relation between pre- and post-natal sonographic findings and postnatal course of fetal ovarian cysts.

Between November 1990 and May 2005, 17 cases of fetal ovarian cysts were diagnosed at the Yonsei University College of Medicine, Seoul, Korea. We retrospectively analysed pre- and post-natal medical records and ultrasonography of 17 infants. Prenatal transabdominal ultrasound scans were performed and the maximum diameter of all cysts was measured. When completely anechoic and with a thin wall, the cyst was defined simple (3). Cysts, which presented themselves echogenic, with a fluid-debris level, a retraction clot or a septation were defined complex (Fig. 1,3) (3-6). The data was analyzed with respect to the age of gestation at the point of diagnosis, sonographic findings, accompanying malformations, and postnatal outcome. With regard to postnatal outcome, we were interested in confirming the prenatal diagnosis, as well as frequency of surgery, the indications leading to surgery, the surgical methods employed and pathologic findings. In post-operative cases, the patients were brought in for follow up at 1, 4 months after surgery and rest of the cases, follow up was done at 1, 4, 10, 16, 24 months with transabdominal sonography. The diagnostic status was 'suspicion of ovarian cyst' as other differential diagnosis could not be completely excluded.

In a total of 17 cases, 10 fetuses (60%) had an ovarian cyst on the right side, 5 (29%) on the left side, and 2 (11%) had bilateral cysts. The mean gestational age at the time of initial diagnosis was 33.5 weeks (range 30-38 weeks). Maternal diabetes, fetal hypothyroidism or accompanying malformation was not observed in all cases.

Ovarian cysts are the most frequent, prenatally diagnosed intra-abdominal cysts (1). The etiology of fetal ovarian cysts is still unknown, but hormonal stimulation is generally considered to be responsible for the disease (fetal gonadotrophins, maternal estrogen and placental human chorionic gonadotrophin) (1). The association of fetal ovarian cysts with maternal diabetes or fetal hypothyroidism has been described (7,8). However, we observed no such diseases in our patients.

When a cystic abdominal mass is diagnosed in the female fetus, differential diagnosis should be established for mesenteric and urachal cysts, intestinal duplication anomalies, cystic teratoma, and intestinal obstruction (9-11). A differential diagnosis between ovarian cysts and one of these conditions cannot be made with intrauterine sonography. Because ovarian cysts are almost always functional and benign tumors, the question of malignancy is not important in prenatal diagnosis (12). Also accompanying malformations are extremely rare. As a result, the question of emergence and nature of any complications, such as torsion, plays a significant role, as these can be an indication for surgical intervention in what would otherwise be an instance of an inconspicuous cyst. In addition, polyhydramnios or ascites (the result of transudation), as a result of partial obstruction of the gastrointestinal tract, may be present (1,13,14). However we observed no such complications or accompanying malformation in our patients.

Once the prenatal diagnosis of a probable ovarian cyst has been made, it is most important to perform serial ultrasound examinations to detect any structural change (size, appearance) in the mass or complications (hydramnios, ascites, torsion). A normal ovarian cyst has a smooth border and is without an internal structure. If there is intracystic bleeding or torsion, the cyst acquires a heterogeneous structure, in part with internal septa. Bleeding within an ovarian cyst usually arises in connection with torsion. For that reason, postnatal surgery for all fetal ovarian cysts which are complex, irrespective of their size, has been recommended (15,16). Sonographic findings of adnexal torsion are not specific (17). If the cyst did not induce the symptoms, no intervention was necessary, because the cyst regressed spontaneously (18,19). We observed spontaneous resolution in both cases complex ovarian cysts which were managed conservatively even when the size increased at birth.

As to uncomplicated cysts, the data describe a high risk of torsion for cysts with a diameter greater than 5 cm (15,20). Aspiration of the cyst to reduce its size (and so that one can investigate its contents) can be performed prenatally. However, the value of cyst aspiration is a point of controversy. Ultrasonic guided puncture may not only prevent torsion, but it may also eliminate the need for newborn laparotomy (1,10,20). However, it can result in intracystic bleeding and lead to subsequent diagnostic difficulties (2). Sometimes, the hole produced by aspiration closes again and the cyst reforms. In our patient, one case of cyst aspiration was performed successfully, but oophorectomy was done after birth because the cyst with internal septum had reformed. In addition, there is a small risk of infection of the amniotic cavity and premature labor. Aspiration of the cysts is recommended only if it is huge enough to impair spontaneous delivery or cause distension of the fetal abdomen.

In summary, an ovarian cyst is not a life-threatening condition, so that further diagnostic procedures can be carried out in the first few days of life. It is natural that postnatal symptomatic cysts demand intervention. Postnatally asymptomatic fetal ovarian cysts smaller than 5 cm in diameter, even exceeding 5 cm at initial diagnosis, with tendency to regress should be closely monitored pre- and postnatally until spontaneous resolution. If they regress spontaneously, no surgical intervention is necessary independent of their sonographic appearances.