Omphaloceles, also known as exomphalos (rare plural: exomphali), are congenital midline abdominal wall defects at the base of the umbilical cord insertion, with herniation of gut (or occasionally other structures) out of the fetal abdomen.
The estimated occurrence can be up to 1:4000 of live births .
Typically a large anterior abdominal wall defect will be present, through which liver and/or bowel herniate, covered by a peritoneal membrane as well as amnion. The umbilical cord typically inserts at or near the apex. As the midline herniation is normal in a fetus until around gestational age 11-12 weeks, this abnormality is only identified on the second-trimester scans.
Some suggest that the formation of an omphalocele may be due to the failure of the medial segments of the two lateral embryonic wall folds to fuse at approximately 3-4 weeks post conception. This defect at the umbilical ring allows the abdominal content to herniate into a sac comprised of an outer layer of amnion and an inner layer of peritoneum and often Wharton's jelly.
General pathogenesis includes teratogenic effects by early pregnancy use of antithyroid drugs .
Isolated cases are often sporadic.
Associated anomalies are high (27-91% ) and are thought to be more common in smaller omphalocele containing bowel only .
Such anomalies include:
- chromosomal anomalies: can occur in 20-50% of cases; the risk of an associated chromosomal anomaly is higher when the omphalocele is detected earlier in gestation
- other syndromic associations
- other fetal gastrointestinal anomalies: which confer a poor prognosis
- fetal CNS anomalies
- fetal cardiac anomalies: can occur in 50% of cases
- fetal genitourinary anomalies
- fetal skeletal anomalies
- omphalocele-radial ray (ORR) complex
- raised maternal alpha-fetoprotein (MSAFP)
- multiple bowel loops (and on occasion liver) herniate into a membrane-covered defect (i.e. not free-flowing) and are usually seen as hyperechogenic content (non-fluid filled bowel)
- the umbilical cord insertion is directly into the omphalocele
- may also show evidence of polyhydramnios
- the abdominal circumference may be smaller as a result
- an allantoic cyst is often present
In neonates, radiographs show herniated bowel loops covered by a membrane.
CT, although not routinely used in neonates, permits direct visualization of herniation content +/- evidence of any malrotation.
- as with CT, allows better direct visualization of the herniation through the abdominal wall
- the herniated liver is often of low T2 signal and the bowel of high T2 signal
Treatment and prognosis
An omphalocele is associated with higher morbidity and mortality than gastroschisis, primarily due to a higher incidence of associated congenital anomalies. Smaller omphaloceles are thought to carry a worse prognosis due to increased risk of associated abnormalities.
Mortality rates can approach 80% when associated anomalies are present and increase to ~100% when chromosomal or cardiovascular anomalies exist. However, if found in isolation, then the associated mortality rate decreases to ~10% .
History and etymology
The word omphalocele is derived from the Greek words "omphalos" (Ομφαλός) meaning naval, and "cele", meaning pouch .
For imaging appearances consider:
- gastroschisis: smaller paraumbilical defect usually to the right of midline, usually containing only bowel loops and not covered by a membrane
- physiological gut herniation: this diagnosis should only be entertained in early pregnancy prior to 11.4 weeks or in gestation with crown-rump length less than 55 mm. The physiologic midgut herniation should not exceed 7 mm in diameter
- limb-body wall complex: large defect usually to the left of midline
- umbilical hernia: abdominal wall hernia