Introduction

Fetal ovarian cysts are abdominal tumors frequently diagnosed after 29 weeks’ gestation, upon activation of the hypothalamic-pituitary-gonadal axis¹. Of unilateral predominance, their incidence is 1 in 2 500 live births.

Most cases are small and resolve spontaneously without clinical problems. However, some may present complications such as torsion, thus requiring an emergency C-section².

Etiology is unknown; hormone stimulation, in the form of beta-hCG, fetal gonadotropins and maternal estradiol, is considered the main cause. In most cases, the interruption of hormone stimulation at birth leads to spontaneous regression¹.

Case report

We present the case of a 33-year-old woman, gravida 2, with one prior cesarean delivery at 38 weeks of a healthy fetus and no other relevant medical history. The patient came at 13.3 weeks for her first trimester screening, in which the ultrasound scan found no fetal alterations (Figure 1).

Figure 1 Abdominal perimeter At 13.3 weeks gestation. 

The pregnancy evolved normally. Structural ultrasound at 20.3 weeks showed anatomical integrity without anomalies and an abdominal circumference in the 74th percentile, one week larger than expected at fetometry (21.3 weeks gestation) (Figure 2).

Figure 2 Abdominal perimeter at 20.3 weeks, one week older than expected when dated by last menstrual period 

In the follow-up ultrasound scan at 27.5 weeks, the estimated weight was 1 548 g, in the 68th percentile. The abdominal circumference, in the 85th percentile, was 2 weeks and 4 days larger than expected when dated by last menstrual period (30.2 weeks).

At 32.3 weeks, we observed an abdominal fetal tumor. The evaluation by maternal-fetal medicine reported the abdominal circumference was in the 94th percentile, two weeks larger than expected when dated by last menstrual period (34.3 weeks). It also evidenced a well-defined abdominal tumor in the left flank under the stomach measuring 3.83 x 4.7 cm, with probable diagnosis of meconium peritonitis. It was decided to monitor the fetus, with no indication for surgery (Figure 3).

Figure 3 Abdominal tumor in left flank under the stomach, measuring 3.83 x 4.7 cm, at 32.3 weeks gestation. 

In the following week, abdominal circumference was over the 97th percentile, two weeks and 3 days larger than expected at fetometry (35.3 weeks). The tumor in the left flank had grown to 5.53 x 4.52 cm, with adjacent bowel wall thickening, unaltered hemodynamics, normal amniotic fluid, and a reactive nonstress test. Given these findings, it was decided to continue monitoring until term (Figure 4).

Figure 4 Abdominal tumor in left flank had grown to 5.53 x 4.52 cm at 33.3 weeks gestation. 

One week later, tumor diameter remained stable and fetal wellbeing tests were within normal ranges, so cesarean delivery was programmed at 37 weeks. Surgery was performed without complications; the female newborn weighted 3 150 g, measured 48 cm, had an Apgar score of 8 out of 9, and a Silverman score of 2, without need for supplemental oxygen.

Within the first 24 hours after birth, an abdominal ultrasound of the newborn revealed a septated cystic mass in the left lower quadrant, which was diagnosed as probable meconium peritonitis. A CT scan showed an abdominal mass withnprobable diagnosis of left meconium peritonitis versus complex left ovarian cyst.

The patient was programmed for a left exploratory laparotomy. Upon finding a cystic mass dependent of the left ovary, left salpingo-oophorectomy was performed. On the second day, the newborn was discharged without complications; she presented no late complications in the pediatric follow-up.

The pathology report described a cystic nodule measuring 4.5 x 3.0 x 3.0 cm; its histological section revealed a unilocular cyst with smooth internal walls and friable blood-like contents. The de finitive histopathologic diagnosis was left ovarian serous cystadenoma with torsion (Figure 5).

Figure 5 Left ovarian cyst with torsion, weighing 14 g and measuring 4.5 x 3.0 x 3.0 cm. 

Discusion

Risk factors for fetal ovarian cyst formation include a disruption in blood flow to the primary gonad, fetal hypothyroidism, and congenital adrenal hyperplasia. Maternal and fetal cysts may coexist, which could support a shared etiology¹.

Probable diagnoses for a fetal abdominal mass include hydronephrosis, megacystis, anal atresia, urachal cyst, meconium pseudocyst, hydrometrocolpos or fetal cyst³.

While cysts may cause fetal anemia or compression, or present rupture during the prenatal period, the most common complication is intracystic hemorrhage, followed by torsion. To date, consensus has not been reached on how to properly manage this condition, nor on the opportune moment for surgery⁴.

In order to evaluate the torsion of a fetal ovarian cyst in abdomen (not in pelvis), measuring the peduncle is more effective than measuring the cyst’s diameters. However, these values have to be obtained by abdominal ultrasound of the patient, which is a complex, unavailable technique in the antenatal period⁵.

Follow-up is recommended every two weeks after diagnosis; cysts larger than 4 cm present the most complications. If the ultrasound features are those of a simple cyst, it is preferable to wait until after delivery for surgery⁴.

Intracystic hemorrhage is an important parameter to predict torsion. Possible scenarios that could prompt surgery while acting in the best interest of our patients include complications of torsion, suspicion of an adnexal mass and abdominal obstruction. Performing a C-section after lung maturation in ovarian torsion may save the fetus’ life and ovary from necrosis; the time between diagnosis and surgery must be no longer than two weeks⁴.

In conclusion, fetal ovarian cysts have a low frequency, despite being the main cysts diagnosed in the prenatal period. The case we presented illustrates the difficulty of obtaining an antena-tal diagnosis, as well as the importance of close monitoring until term, in the absence of complications. Finally, it also highlights the need for a comprehensive neonatal assessment at birth.