Fetal Abdominal Cysts

What Is a Fetal Abdominal Cyst?

A fetal abdominal cyst is a generic term that describes an abnormal fluid-filled bubble-like mass in the fetal abdomen. Usually, they are benign structures found on prenatal ultrasound, which is quite good at differentiating between cysts and solid tumors. Fetal abdominal cysts can vary in size from tiny cysts that are smaller than a pea to large grapefruit-sized cysts that can displace the other abdominal organs. Serial ultrasound exams during pregnancy can track the growth or regression of a cyst. Most fetal cysts are singular and involve a single organ system such as the ovary, intestine or liver.

Types of Abdominal Cysts

In a female fetus, the most common diagnosis is an ovarian cyst. These cysts usually appear in the third trimester of pregnancy. The sizes vary but rarely exceed 6 to 7 centimeters. Usually, there is a single cyst containing thin fluid and arising from one ovary. Because of the potentially large size of an ovarian cyst, it may be difficult to determine whether it originates from the right or left ovary. 

In both male and female fetuses, an enteric duplication cyst can originate from the gastrointestinal tract including the mouth, tongue, esophagus, stomach, small intestine, large intestine and rectum. These lesions can appear earlier in gestation and tend to be fixed in the same position. Enteric duplications are spherical or tubular structures within the intestinal wall and can communicate with the inside of the intestine (lumen) or be completely separated from it. Sometimes, they may show movement with digestion.

Genitourinary cysts can originate from the urinary system, such as the kidney or bladder.

Mesenteric cysts are generated from the swelling of lymphatic vessels in the mesentery (the membrane connecting the bowel to the abdomen). Although they can occur in any part of the digestive tract, both enteric duplications and mesenteric cysts are more commonly seen in the small intestine.  

Sometimes, the cyst represents a dilated loop of bowel and is a sign of fetal intestinal atresia. This is an interruption in the digestive tube in any point that prevents the normal progression of the intestinal contents.

Choledochal cysts, a rare type of cyst, involve the biliary tract and are relatively fixed near the liver.  

What Causes Fetal Abdominal Cysts?

Ovarian cysts are caused by the powerful effects of pregnancy hormones from the mother that travel into the female fetus and stimulate the developing ovaries to form cysts. Mesenteric cysts represent obstructed lymphatic drainage from the gut, while enteric duplication cysts occur within the wall of the trachea (windpipe), esophagus, stomach or intestine and can develop in any segment of the intestine. It is unclear what causes enteric duplication or choledochal cyst. 

How Are Fetal Abdominal Cysts Diagnosed?

Usually, the characteristics and position of the cyst will suggest the diagnosis. However, sometimes an accurate diagnosis can be difficult to obtain. In these cases, serial prenatal ultrasounds or MRI imaging help narrow the diagnosis. Only a comprehensive postnatal evaluation can confirm the final diagnosis. 

While any hollow structure in the abdomen can form a cyst, the most common fetal abdominal cyst is a benign cyst on the ovary in a female fetus. Ovarian cysts usually involve only one side and only cause problems if the cyst grows so large that it twists along with the ovary and pinches off its blood supply (ovarian torsion). Ovarian cysts usually appear in the third trimester, grow with the fetus and disappear within few weeks after birth once the pregnancy hormones have left the baby’s body. Sometimes, ovarian cysts don’t disappear on their own and must be removed with surgery. It is extremely rare that they include cancer. 

Lymphatic cysts and enteric duplications grow with the fetus and can be associated with progressive dilation of the bowel due to obstruction or cause an excess of amniotic fluid, called polyhydramnios.

In most cases, the discovery of an abdominal cyst is not an indication for earlier delivery or caesarian section. Significant polyhydramnios can cause a spontaneous preterm delivery.

How Are Fetal Abdominal Cysts Treated?

Fetal intervention is reserved primarily for large cysts which are mostly ovarian in origin. During this prenatal procedure, ultrasound is used to guide a small needle into the cyst and remove the fluid in order to reduce the risk of ovarian torsion. 

In most other cases, the abdominal cyst is usually followed through the pregnancy without intervention. At delivery, neonatologists and pediatric surgeons will manage the care of your baby depending on the baby’s condition. To confirm the diagnosis, an ultrasound, abdominal x-ray, CT scan or MRI may be needed. The specific details of the subsequent care plan including surgery, if needed, will depend on the findings of these studies.

After birth, ovarian cysts, unless very large, are usually observed for 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 removed with surgery — either through an abdominal incision or with minimally invasive surgery. 

The other causes of fetal cysts usually require surgery to correct. The timing of the surgery depends on the urgency of the problem and the overall health of the baby. In case of bowel obstruction in the newborn, the surgery will usually be performed on the first day of life.

At Lurie Children's, the experts in The Chicago Institute for Fetal Health provide care for fetal abdominal cysts. 

What Are the Long-Term Effects and Outcomes of Fetal Abdominal Cysts? 

In most cases, the outcomes are excellent without any long-term complications.  

Mesenteric cysts rarely cause any symptoms and frequently disappear in the first year of life. They are usually followed with ultrasound for a period of time to confirm the diagnosis and ensure that they are not growing.

If needed, the recovery after surgery for an ovarian cyst is quick and the patient can be discharged on the same day of the procedure.   

In cases of enteric duplication cysts, a part of the intestine must be removed. This is usually a short segment and does not affect the baby’s overall growth and nutrition. The procedure is usually performed between 6 and 12 months of age and typically requires a few days of recovery in the hospital.

Surgery for intestinal atresia is more complex. Newborns are admitted to the neonatal intensive care unit (NICU) for multidisciplinary care and remain there until they recover from surgery and demonstrate an ability to eat and grow normally. The length of stay is quite variable depending on the severity of the atresia and can range from a few weeks to a few months. However, most babies treated for intestinal atresia eventually eat and grow normally with an excellent long-term outcome. Learn more about fetal intestinal atresia.