This leaflet is to help you understand what a fetal mesenteric cyst is, what tests you need, and the implications for you and your baby.

What is a Mesenteric Cyst?

A fetal mesenteric cyst is a single cyst or more commonly a collection of cysts in the lower part of the baby’s abdomen. Mesenteric cysts can be located in several places inside the abdomen. They can be located inside the mesentery of the bowel, which is the structure containing blood vessels and lymph channels (small tubes that contain fluid) and which connects the bowel to the back side of the baby’s belly. They can be connected to the mesentery by a small stalk of tissue or located partially in the mesentery and partially behind the abdominal cavity. 

Mesenteric cysts are one form of lymphangioma, which is formed by a blockage of flow of lymphatic or tissue fluid. Lymphangiomas can be located anywhere in the body. When they are located in the mesentery of the bowel, they are called mesenteric cysts. Mesenteric cysts are also known as a mesenteric lymphangioma, a mesenteric cystic lymphangioma or an abdominal cystic lymphangioma. 

How does a Fetal Mesenteric Cyst happen?

Mesenteric cysts are rare and found in 1 of 20,000 children who become hospitalised. No one really knows why they happen, but it is thought that they occur due to damage to the lymphatic channels during the first 6-12 weeks of fetal life. 

Should I have more tests done?

Many women will choose to have more tests done to know more about the condition of the baby. The tests available depend on where you live. All babies with a cyst or cysts in the abdomen should have a detailed ultrasound to look for additional problems and to try to figure out what the reason for the cyst is. The baby’s legs should be evaluated to see if there are additional cysts in the legs. 

One test to ask about is an amniocentesis to make sure that the chromosomes are normal in the baby.  Sometimes, it is difficult to determine what kind of cyst is in the baby’s abdomen, and in these cases, your doctor might recommend a fetal MRI. There is currently no prenatal treatment for mesenteric cysts in the fetus. 

What are the things to watch for during pregnancy?

While you may wish to know for sure exactly where the mesenteric cyst is located, it is often difficult to tell this prenatally. Most babies with mesenteric cysts will have additional ultrasound examinations. These ultrasound examinations will focus mostly on the baby’s growth and cyst size. Some mesenteric cysts have been seen to become bigger between scans. Sometimes, the baby develops fluid inside the abdomen called ascites and under the skin called edema. Sometimes, there is extra amniotic fluid (polyhydramnios) which can make the pregnancy uncomfortable for the mother.

What does it mean for my baby after it is born?

After the baby is born, it will be transferred to a neonatal intensive care unit, where additional studies will be performed. The baby will have X-rays taken to further evaluate the abdomen and a surgeon will be consulted. A CT scan or an MRI may be performed to further evaluate the baby. The baby may not be fed until these tests are completed. 

A decision will be made about when the mesenteric cyst will be removed and how this will be done. Depending on your surgeon, this may be done with an incision into the baby’s abdomen, or with instruments inserted through small incisions into the abdomen and visualised through a light tube inserted in the belly. If the cysts extend to areas not safely able to be surgically removed, sclerosing agents (substances that can produce controlled scarring) may be needed to clear the cysts. The goal is to completely remove the cysts so that they do not recur. 

In the long term, the outcome for most children is excellent. There are some children who have long-term issues which are related to the amount of bowel that is removed and additional malformations. Occasionally a child will have “short gut syndrome” because a large piece of the bowel needs to be removed along with the mesenteric cyst. Unfortunately, prenatal ultrasound is not able to predict which children will have this problem. 

Will it happen again?

Most cases of mesenteric cyst are sporadic, meaning that they are very unlikely to happen again in future pregnancies. 

What other questions should I ask?

  • Does this look like a typical mesenteric cyst?
  • Are you sure of the diagnosis or could it be something else?
  • Do you see additional abnormalities in my baby?
  • How often will I have ultrasound examinations done?
  • Are there any other tests that are recommended?
  • What will you be looking for during these examinations?
  • Where should I deliver?
  • Where will the baby receive the best care after it is born?
  • Can I meet in advance the team of doctors who will be looking after my baby when it is born?

Last updated September 2022