Fetal Cystic Hygroma

Cystic hygroma in late pregnancy is a malformation of the lymphatic system. The lymphatic system is comprised of vessels, distinct from both arteries and veins, which are present in both organs and tissue. The lymphatic system’s role is to help eliminate unwanted material from the human body. A cystic hygroma that develops late in pregnancy is considered to be a form of vascular (meaning vessel) malformation. When this condition develops during the third trimester in a fetus with previously normal appearing anatomy, it is most commonly located in the anterior cervical triangle, a region in the front of the neck. The cysts that develop may be small (microcystic) or large (macrocystic). Lymphangioma is another term used to describe these cysts. The cystic hygroma may be confined to one area or diffusely spread out.

Frequency

The exact incidence of cystic hygromas late in pregnancy is unclear. The available literature varies widely with estimates anywhere from 1 in 1,000 births to 1 in 12,000 births depending on the data included in the study (e.g., terminations, stillbirths, deaths after delivery).

Diagnosis

Fluid-filled cystic spaces, along the sides and back of the neck and divided by thin tissue (septae), are the common ultrasound findings. Solid components should not be present in a cystic hygroma in late pregnancy. Other potential findings are fluid in the fetal skin (edema), abdomen (ascites), and in the space that surrounds the lungs (pleural effusion) or heart (pericardial effusion). Nonimmune hydrops is defined as fluid present in at least two of the aforementioned spaces. The presence of nonimmune hydrops often carries a poor prognosis. Lymphatic malformations may be diagnosed in the chest, abdomen, retroperitoneum (towards the back) or inguinal (groin) region. It is important to distinguish a cystic hygroma from a cervical teratoma. Teratomas usually have solid as well as cystic components. Calcifications within the mass are thought to be diagnostic of teratoma.

Management Options and Outcomes

A detailed fetal anatomy survey should be performed after a cystic hygroma is detected with particular focus on whether nonimmune hydrops (fluid accumulation in two or ore spaces) has developed. The fetal survey may reveal anomalies in the heart, face, spine, kidneys/bladder and/or the diaphragm. An amniocentesis is recommended in all cases of cystic hygroma because of the increased likelihood of associated chromosomal abnormalities. An amniocentesis is a procedure in which a needle is inserted under ultrasound guidance to remove some amniotic fluid (the fluid contains fetal cells) to test for a chromosomal abnormality.

Candidacy for Fetal Treatment

Few cases of lymphangioma have undergone in utero drainage by ultrasound-guided cyst aspiration. There is little data to support in utero decompression to prevent progression to nonimmune hydrops or facial deformity. In Japan, some groups have attempted in utero sclerotherapy in which a chemical is injected to decrease the size. There are no reports of this being performed in the United States.

Cystic hygromas can often cause a significant increase in the amount of amniotic fluid, referred to as polyhydramnios. Polyhydramnios in fetuses with large cystic hygromas may be severe to the point that the mother develops respiratory difficulties and preterm labor. In such cases, an amnioreduction may be recommended. An amnioreduction is similar to an amniocentesis in that a needle is inserted into the fetal space under direct ultrasound guidance. The difference, however, is that rather than removing a small amount of amniotic fluid, several liters are drained to alleviate the maternal symptoms. It is not uncommon for the amniotic fluid to again accumulate over days to weeks resulting in the amnioreduction being repeated.

The risk of airway compromise is of greatest concern in those fetuses with a cystic hygroma that develops after 30 weeks of gestation. In such cases, delivery by EXIT procedure (Ex-utero Intrapartum Treatment) may be necessary. An EXIT procedure is a specialized type of cesarean section whereby an airway is established (i.e., placement of a breathing tube) before delivery of the fetus. The mother is deeply anesthetized so that adequate gas exchange is maintained between the uterus and placenta. This allows up to 1 hour for laryngoscopy, bronchoscopy and, if necessary, tracheostomy with or without partial resection of the mass before clamping and cutting the umbilical cord. This type of specialized delivery more commonly occurs only in tertiary medical centers with highly skilled teams.

Surgical Management

After birth, cystic aspiration is usually of little benefit unless a large, dominant cyst requires urgent decompression. Overall, the reason aspiration is not particularly beneficial is that the cysts rapidly reaccumulate. Sclerosing, chemical agents have been used as an alternative to resection. No prospective trials confirming the efficacy of this treatment have been reported.

Complete resection is possible in only 75% of cases based on a study by Hancock et al in 1992. Even in those case where complete resection does occur, the cystic hygroma can grow back as many as 10% to 27% of cases. The rate for tumor regrowth is greater in those cases in which only a partial resection was achieved. Recurrence rates range from 50% to 100% depending on the scientific study.

The infant with a large cystic hygroma often has an unstable airway. If an EXIT procedure is not indicated, then resection should proceed as soon as the diagnostic evaluation is completed. If the mass is small enough as to not compromise the airway, then removal may occur on a more elective basis. Complete resection of the mass often is not possible. Thus, the surgeon may focus on resection of as much of the mass as possible without sacrificing vital structures.

Newborn Care

The mortality of cystic hygroma diagnosed prior to 30 weeks of gestation and associated with nonimmune hydrops is virtually 100%. There is also a high incidence of associated chromosomal abnormalities. Significant neurologic problems can result from injury to cranial nerves, especially the facial nerve (VII). Horner syndrome, due to injury to the sympathetic chain and diaphragmatic paralysis from phrenic nerve injury, has occurred during resection of cystic hygromas. The long-term outcome and care of the newborn depends on whether complete resection is achieved, though complete resection is unlikely if there is extensive involvement of the floor of the mouth, tongue, larynx, or trachea.

Additional Information

The lymphatic system develops at the end of the 5^th week of pregnancy from the six primary lymph sacs that sprout at that time. Some theorize that cystic hygromas result from the failure of specific neck lymph sacs (the jugular lymph sacs) to join the lymphatic system. Isolated cystic hygromas presenting late in pregnancy do not tend to be associated with other abnormalities. Prenatally diagnosed cystic hygroma has a 50% to 60% incidence of chromosomal abnormalities.

Additional Resources

Fisher R, Partington A, Dykes E. Cystic hygroma: comparison between prenatal  and postnatal diagnosis. J Pediatr Surg. 1996;31:473-476.

Hancock BJ, St-Vil D, Lebs FI, et al. Complications of lymphangiomas in children. J Pediatr Surg. 1982;27:220-225.