Background/Purpose: Neonates who have ovarian torsion caused by an ova
rian cyst often lose their ovary because the torsion and infarction oc
curred antenatally. Because ultrasound scan has been so effective in d
iagnosing ovarian cysts in utero, we have a better understanding of th
eir natural history and can select appropriate cases for cyst decompre
ssion in utero to prevent torsion. The authors reviewed experience wit
h seven fetuses who had fetal ovarian cyst. Methods: During a 26-month
period, seven patients were referred for the evaluation of fetal ovar
ian cyst. The mean gestational age at presentation was 31.9 +/- 3.6 we
eks (+/-SD; range, 27 to 37 weeks). There was no history of maternal r
isk factors such as diabetes mellitus or fetal risk factors such as hy
perthyroidism or placentomegally. All seven cases involved isolated un
ilateral cysts without associated anomalies or chromosomal abnormaliti
es. Mean initial cyst diameter was 3.4 +/- 1.7 cm (+/-SD; range, 1 to
6.1). Indications used for ovarian cyst decompression included anechoi
c cysts with a diameter greater than or equal to 4 cm, a cyst ''wander
ing'' about the abdomen on serial sonograms, or demonstrating rapid en
largement (>1 cm/wk). Results: All but one cyst progressed in size dur
ing observation, One fetal ovarian cyst (diameter, 2 cm) subsequently
regressed spontaneously and another (diameter, 2.1 cm) stabilized duri
ng prenatal ultrasound surveillance. One ''cyst'' observed with a diam
eter of 3.5 cm proved to be a persistent cloaca. Four fetal ovarian cy
sts met criteria for decompression. Because of fetal position, decompr
ession could not be performed in one. One cyst (seen before defining c
riteria for decompression) with a diameter of 5 cm was observed only a
nd underwent torsion, Two cysts (diameters, 6.1 cm and 4 cm) were deco
mpressed in utero under local anesthesia with ultrasound guidance, of
95 mL and 35 mL, respectively, High cyst fluid progesterone (12,041 an
d 1,990 ng/dL, respectively) and testosterone (1,298 and 2,900 ng/dL,
respectively) confirmed the etiology of the cyst as ovarian. Neither c
yst recurred, and postnatal ultrasound scan confirmed resolution. Ther
e was no maternal or fetal morbidity or mortality and only the patient
observed before development of criteria for decompression lost her ov
ary because of torsion. Conclusions: Fetal ovarian cysts tend to prese
nt as isolated unilateral lesions in normal fetuses in the third trime
ster. Spontaneous regression of fetal ovarian cysts may occur, Fetal o
varian cyst decompression, in select cases, may preserve ovaries at ri
sk for torsion. Copyright (C) 1997 by W.B. Saunders Company.