Omphalocele & Cystic Hygroma

This case study presents a 35-year-old white female who was referred to the UAMS High-Risk Obstetrical Clinic due to advanced maternal age. The patient and her husband received genetic counseling. This was the patient's first pregnancy. She presented with no obvious complications.

A routine obstetrical ultrasound exam was performed by an ARDMS certified obstetrical sonographer using a 3.5 MHz transabdominal transducer. The sonogram showed a single intrauterine pregnancy with an estimated gestational age of 17 weeks, 4 days (7.5 weeks). 

On examination of the fetal head a large cystic mass presented around the posterior of the neck. The nuchal fold measured 9.5mm and the nuchal ligament could be seen within the cystic mass. These findings are consistent with the diagnosis of cystic hygroma.

Cystic hygromas are caused by a delay or absence of the communication between the jugular lymph sacs and the internal jugular veins during fetal development. Late communication of the sacs to drain into the internal jugular vein results in the dilation of lymph sacs into cystic spaces, increased posterior nuchal measurement, and neck webbing. Complete obstruction of the jugular lymphatic is often associated with fetal hydrops, which is frequently fatal (Sanders, 1996). Another probable cause of cystic hygroma is abnormal budding of lymphatic endothelium. Increased nuchal thickness (nuchal lucency) can be detected at 10 weeks (Stevens 1998).

Elevated AFP occurs in 40-50% of cases and amniotic fluid is often reduced. Ultrasounds of cystic hygromas show a thin walled cystic mass on the posterolateral aspect of the neck. While small cystic hygromas can spontaneously disappear, most, 85%, are larger than the fetal head. Identification of the nuchal ligament within the cyst constitutes the most specific sign for diagnosis of cystic hygroma. (Nyberg, 1990)

Cystic hygromas are associated with syndromes such as multiple pterygium, Turners, Noonan, Pena-Shokeir and Roberts Syndrome. About 60% of Cystic hygromas are chromosomal abnormalities, most having Turners Syndrome, a minority having Downs Syndrome. (Sanders, 1996) If cystic hygroma is the only anomaly present and is small, serial exams should be performed every 3-4 weeks to watch for progression to fetal hydrops. The majority of reported cases of cystic hygroma have undergone elective termination of the pregnancy, therefore, the mortality rate of cystic hygroma detected with ultrasound can not be certain. However, case reports of pregnancies following a spontaneous conclusion (fetuses not electively terminated) suggest a mortality rate of 80-90%. (Nyberg, 1990)

On examination of the abdomen, herniated abdominal viscera were noted. The viscera were contained within a membrane. These findings are consistent with the diagnosis of an omphalocele.

An omphalocele is a transparent sac of amnion that contains herniated abdominal viscera; it is attached at the base of the umbilical cord. Omphaloceles occur in 1 in 4,000 births. Abdominal circumference cannot be accurately measured and polyhydramnios is often present. The embryonic mid-gut herniation is usually reduced by 11 weeks, so care should be taken not to confuse physiological gut herniation at this age with an omphalocele. (Cyr 1986; Lines & Milman 1996) Omphaloceles can be detected with certainty at 14 weeks or after. (Sanders, 1996) Omphaloceles containing gut are said to result from a midline defect of abdominal muscles, fascia and skin resulting in herniation of the viscera. The membrane containing the viscera is comprised of two layers: the peritoneum and amnion. Presence of a membrane surrounding the viscera distinguishes an omphalocele from gastroschisis in which herniated viscera is free floating in the amniotic fluid and is not contained by a membrane. (Nyberg, 1990)

At least 50% of fetuses with Omphaloceles have defects elsewhere. Some things sonographers should look for are heart defects, facial abnormalities, limb body-wall complex, spinal distortion, findings associated with trisomy 13 & 18 and signs of Beckwith-Wiedemann Syndrome which include renal, liver and spleen enlargement. (Sanders, 1996) If there are no associated anomalies, serial ultrasound examinations should be done every 4 weeks. The mortality rate is 10%, similar to that for gastroschisis. After birth surgical repair of herniated viscous is required and resumption of intestinal function usually follows. Detection of any concurrent anomalies increases the likelihood of chromosome abnormalities and an increased perinatal mortality rate of 80%. The presence of chromosomal abnormalities and cardiovascular malformations increase the mortality rate to nearly 100%. (Nyberg, 1990)

On completion of the Sonographer's examination, the obstetrician gave the patient the option of having an amniocentesis to determine the presence of chromosomal abnormalities. The obstetrician informed the patient that the possibility of chromosome defects was greatly increased due to the presence of two anomalies. The patient and her husband decided to have the procedure, which was performed under sonographic guidance without complications. The obstetrician's dictated report stated there was a high suspicion for trisomy 18. The results of the amniocentesis showed there were no chromosomal abnormalities. However, due to the high perinatal mortality rate the couple chose to terminate the pregnancy.

This case study shows the role of ultrasound in diagnosing an omphalocele and cystic hygroma in a second trimester intrauterine pregnancy.

Disclaimer:

One of the authors (TJDuB) is the author and owner of the software BASIC BABY (BBII).

References:

References:

Cyr DR, Mach LA, Schoenecker SA, et al (1986): Bowel Migration in the Normal Fetus: Ultrasound detection. Radiology; 616:119-121.

Lines ML & Milman RM (1996): Chapter 6, Abdomen in DuBose TJ (editor) Fetal Sonography; W. B. Saunders Company, Philadelphia, p. 305.

Nyberg, D.A., Mahony B.S., Pretorious D.H (1990). Diagnostic Ultrasound of Fetal Anomalies; 238-243; 405-416

Sanders, R.C. (1996): Structural Fetal Abnormalities; The Total Picture.; 149-151; 158-159

Stevens S.L. (1998): The Use of Nuchal Lucency as a Screening Tool in First Trimester Sonography; J Diagnostic Medical Sonography,; 14:251-254.