The ‘daughter cyst sign’: a sonographic clue to the diagnosis of fetal ovarian cyst

The first sonographic diagnosis of ovarian cyst was reported in a living fetus in 19751. Since then these cysts have been increasingly recognized in newborns as a result of being identified prenatally on ultrasound examination. Whatever the postnatal age, ovarian cysts are considered to be abnormal when they are ≥ 20 mm in diameter, otherwise they are diagnosed as maturing follicles. A maturing follicle (diameter < 20 mm) is physiological and occurs in all preovulatory phases. They vary in size from 40 µm to 20 mm and occur in 34% of stillbirths and neonates that die in the first 28 days of life2. When a fetal ovarian cyst is suspected prenatally, problems of confirming its ovarian origin and detecting complications must be overcome. We recently reviewed the records of 12 newborns referred over a 6-year period to our pediatric surgery department for the management of an abdominal cystic mass, which was consistent with a fetal ovarian cyst. Prenatal sonographic images, which were generated by several operators who were not specifically trained to look for this sign, were retrospectively analyzed. Fourteen cystic intra-abdominal masses were found in 12 fetuses (two cases of bilateral cysts). In each case, the ultrasound findings were consistent with fetal ovarian cyst being the most likely diagnosis (see later). The mean gestational age at the time of diagnosis was 31 weeks. In 11 fetuses no other malformation was found. Amniocentesis performed in two cases revealed normal female karyotypes. In the remaining fetuses, fetal gender was ultrasonographically determined as female. Prenatal puncture of the mass was never performed. Within the first 2 days of life, abdominal ultrasonography was performed to determine subsequent procedures, i.e. expectant management when the cyst was uncomplicated and measured < 4 cm in diameter, transabdominal puncture when the cyst was uncomplicated and > 4 cm in diameter, or surgery when the cyst was symptomatic, bilateral or sonographically complicated. In three cases in our series (one with a complicated cyst and two with simple cysts) a single, round, anechogenic structure, or 'daughter cyst', was found within the fetal ovarian cyst, adjacent to the wall (Figure 1). One of the simple cysts became complicated after birth. The diameters of the 'mother cysts' ranged between 24 and 46 mm with a mean diameter of 35 mm. The largest diameters of the 'daughter cysts' were 12, 15 and 18 mm, and the mean diameter was 13 mm. Fetal ultrasound scan at 34 weeks' gestation showing the gross ovarian cyst containing the small 'daughter cyst'. All newborns underwent postnatal scans that confirmed the diagnosis of ovarian cyst. The diagnosis of fetal ovarian cyst is most likely to be made during a routine ultrasound examination3, or following an obstetric complication caused by the cyst. When a fetal intra-abdominal cystic structure is found, the diagnosis of an ovarian cyst might be suspected when: the fetal gender is confirmed as female; discovery is made in the third trimester of pregnancy; the location is above and distinct from the bladder, and below and distinct from the stomach and gallbladder; and an abnormality involving the intestinal, urinary and vertebral tracts has been excluded. Nussbaum et al.4 thus categorized fetal ovarian cysts according to ultrasound criteria into two groups: simple (uncomplicated) and complicated. The sonographic features of uncomplicated cysts are: anechogenic, round, > 20 mm in diameter, unilocular, intrapelvic or more often intra-abdominal, unilateral or seldom bilateral, thin-walled, and more or less mobile with the mother's positions. Sonographic features of complicated cysts are: heterogeneous with hyperechogenic components, thick-walled, containing free-floating material, with intracystic septations, and mobile after adnexal torsion; the absence of color Doppler flow is 100% and therefore highly specific for torsion5, 6. There is no established correlation between the sonographic findings and the histological nature of the cyst but prenatal histological diagnosis does not affect management, only the ultrasonographic features (i.e. whether complicated or uncomplicated). Fetal ovarian carcinoma has been rarely reported (one bilateral ovarian carcinoma was described in a 30-week fetus by Ziegler in 19457). Henrion et al.8 reported that ovarian malignancy represents 3.5% of neonatal ovarian masses. A review of the literature reveals that 85–90% of total fetal ovarian masses are cystic (follicular and/or luteinic origins) and 10–15% are organic (< 3% are carcinomas and 7–12% are represented by teratomas, mucinous and serous cystadenomas). Torsion represents the main complication of fetal ovarian cysts. The exact frequency is difficult to establish. Torsion occurred prenatally in 38% of the cases in Brandt's series9. At birth, surgery is performed when the sonographic appearance is complicated thus providing an exact diagnosis. Using these criteria, Brandt et al.9 found that 92% of newborns who underwent surgery for suspected torsion of the ovary presented prenatal ultrasound characteristics of a complicated cyst. Furthermore, there are no features that would predict the occurrence of this complication10. The 'daughter cyst' sign was defined, thanks to technical improvements in high-resolution ultrasonography, by Lee et al.11. They described this sonographic sign in 23 female newborns and infants with intra-abdominal cysts (excluding those of biliary and urinary origin). This sign consists of the existence, within or outside the main cyst, of a small (2–8 mm), round, anechogenic structure resembling a small cyst. This feature confirmed the ovarian origin of the cysts in Lee's study with a sensitivity of 82% and specificity of 100%11. As far as we know this sign has not previously been described prenatally. To establish this diagnosis the examiner needs a multifrequency transabdominal transducer with maximum zoom on the cystic mass. Of course, this 'daughter cyst' sign can be asserted only if a normal fetal bladder is clearly identified; indeed the main differential diagnosis is the existence of an ureterocele, which can present as a very similar image12. As far as pathophysiology is concerned, this 'daughter cyst' sign might be explained by the hormonal dysfunctions responsible for the genesis of follicular and luteinic cysts, which are the most common13. Immature hypothalamus–pituitary–ovarian feedback is thought to be responsible for gonadal hyperstimulation in severely premature fetuses before 28 weeks' gestation; maturation may be delayed or abnormal in cases of fetal ovarian cyst in the third trimester. The 'daughter cyst' probably corresponds to an excessively developing intra-ovarian follicle just before ovulation occurs. This ultrasonographic appearance is identical to a de Graaf follicle with cumulus oöphorus obtained during ultrasound monitoring in assisted conception treatment. Thus, this feature indicates the ovarian origin. Although not sensitive, the 'daughter cyst' sign seems to be highly predictive of the ovarian origin of female fetal intra-abdominal cysts. E. Quarello*, G. Gorincour*, T. Merrot , L. Boubli*, C. d'Ercole eqdivers@wanadoo.