A fetal abdominal cyst is a liquid-filled structure seen within a baby’s abdomen, usually found on routine ultrasound, before birth. The location of the cyst often suggests from which organ in the abdomen the cyst originates. Modern ultrasound is quite good at differentiating between liquid and solid, so these cysts rarely turn out to be tumors or solid masses. Furthermore, serial ultrasound exams done over a matter of time can be helpful in revealing the growth or regression of a cyst.
Fetal abdominal cysts are thought to be caused by the effects of powerful pregnancy hormones from the mother that travel into the fetus and stimulate the developing ovaries to form cysts.
Intestinal atresias (see fetal intestinal atresia) can be first found as abdominal cysts. Similarly, urinary obstruction causing collections of urine in the kidneys, ureters or bladder can produce cystic structures in the fetal abdomen (see information within the fetal urology pages). Under the best of circumstances, serial ultrasounds during the pregnancy will reveal the correct origin of these cysts.
Cysts in the urachus, a structure left over from early formation in the fetus, are another benign cause for a fetal cyst, as are choledochal cysts arising from the fetal gallbladder.
While any hollow structure in the abdomen can form a cyst, far and away the most common fetal abdominal cyst is a benign cyst on the ovary of a female fetus.
This type of cyst is a normal occurrence for a female fetus and usually disappears within weeks after birth, after the pregnancy hormones have left the baby’s body. Unless the cyst becomes so large that it twists and pinches off its blood supply, they rarely cause problems. Other rare ovarian cysts don’t disappear on their own and must be removed with surgery. They can include very rare cancers.
Very uncommon are cysts that arise from the fetal spine, either anterior meningomyelocele (see fetal spina bifida) or sacrococcygeal teratoma. Both of these are very serious problems.
When a baby is born with an abdominal cyst, usually the first order of business is to carefully image the cyst, as imaging done after the birth is more precise than that done before birth. Ultrasound, Xray, CT, MRI or a contrast study may be necessary depending on what is suspected.
Ovarian cysts, unless very large, are usually observed for a matter of weeks or months with the expectation that they will go away on their own. If they don’t go away after a reasonable period, they are deemed not to be the result of mother’s hormones and are removed with surgery — either through an abdominal incision or with minimally invasive surgery.
Other causes of fetal cysts usually require surgery to correct. The timing and the manner of surgery, either through a traditional incision or with minimally invasive surgery when possible, depend on the urgency of the problem and the overall health of the baby.