What Is Omphalocele?
Omphalocele, also known as exomphalos, is a birth defect of the abdominal wall where an infant's organs—such as the intestines, stomach, or liver—protrude through the navel. This condition is rare, affecting roughly 1 in every 3,000 births.
A key feature that distinguishes omphalocele from other abdominal wall defects is the presence of a protective membrane, or sac, that encloses the protruding organs. This transparent sac is formed from layers of the peritoneum (the lining of the abdomen) and the amnion (the inner layer of the placenta). While alarming in appearance, this sac provides a crucial barrier, protecting the delicate organs from direct exposure to amniotic fluid in the womb and from injury during delivery.
The condition originates very early in pregnancy. Around the sixth week of gestation, it is normal for the fetal intestines to temporarily move into the umbilical cord because the abdomen is not yet large enough to hold them. An omphalocele results when these organs fail to move back into the abdominal cavity as expected by the 10th to 12th week of pregnancy. This can often be identified on a prenatal ultrasound.
Omphaloceles vary significantly in size, from small defects containing only a loop of intestine to giant ones holding most of the abdominal organs. The size of the defect and which organs are involved influence the complexity of the baby's treatment and overall prognosis. In cases of large or giant omphaloceles, the baby's abdominal cavity may be too small to accommodate the organs immediately after birth, often requiring a staged surgical repair.
Omphalocele is frequently associated with other health issues and is less commonly an isolated defect. These can include chromosomal abnormalities and specific genetic syndromes. Because of this high rate of association, a prenatal diagnosis of omphalocele typically prompts a thorough evaluation to check for other potential heart, spine, or organ anomalies. The presence of these associated conditions is a key factor in an infant's long-term prognosis.
Genetic Causes and Associated Syndromes
A primary cause of omphalocele is linked to the baby's genetic makeup. In many instances, the abdominal wall defect is not an isolated event but rather one feature of a broader condition affecting the body's development. Understanding these underlying factors is key to providing comprehensive care.
Chromosomal Abnormalities
A significant number of infants with omphalocele have a variation in their chromosomes, most commonly an extra copy of a specific chromosome, a condition known as a trisomy. The most frequent ones seen are Trisomy 18 (Edwards syndrome) and Trisomy 13 (Patau syndrome), with Trisomy 21 (Down syndrome) occurring less often. Because chromosomes carry instructions for the entire body's development, an extra one can disrupt many processes simultaneously, leading to a pattern of features that includes not only the omphalocele but also potential heart defects and other developmental challenges.
Specific Genetic Syndromes
Beyond changes to whole chromosomes, omphalocele is a hallmark feature of several genetic syndromes.
Beckwith-Wiedemann syndrome is the most common syndrome associated with omphalocele. It is an overgrowth condition caused by changes on chromosome 11 that affect genes controlling growth. Babies with this syndrome are often larger than average, may have an enlarged tongue, and are at an increased risk for certain childhood cancers, which makes ongoing screening an important part of their care.
Pentalogy of Cantrell is a rare and complex condition characterized by a specific combination of five birth defects affecting the chest and abdomen. The omphalocele is typically located high on the abdomen and occurs alongside a split sternum (breastbone), a defect in the diaphragm, an issue with the pericardium (the sac around the heart), and a congenital heart defect. Not all babies have all five features, but the combination of a high omphalocele with heart and chest wall issues points toward this diagnosis.
OEIS Complex , also known as cloacal exstrophy, is an acronym for its primary features: Omphalocele, Exstrophy of the bladder (bladder is open and exposed), Imperforate anus (no normal anal opening), and Spinal defects. This syndrome represents a severe developmental issue affecting the lower torso. Managing this condition requires a large, multidisciplinary team of surgeons and specialists to address each complex anatomical challenge.
CHARGE syndrome is another condition where an omphalocele can sometimes be present. The name is an acronym for its most common characteristics: Coloboma (eye gap), Heart defects, Atresia of the choanae (blocked nasal passages), Retardation of growth, Genital abnormalities, and Ear anomalies. For these children, the omphalocele is part of a wide-ranging condition impacting vision, hearing, breathing, and growth.
Maternal and Environmental Risk Factors
While genetic factors are significant, research also points to certain maternal health characteristics and environmental exposures that may increase the risk of an omphalocele. These factors are not direct causes but are associated with a higher likelihood of the condition developing during the critical early stages of pregnancy.
Key associated factors include:
- Maternal Health: Increased risk is associated with mothers over 40, as well as those who are overweight or obese. Certain metabolic conditions, such as abnormalities in how the body processes vitamin B12, have also been identified as potential risk factors.
- Substance Exposure: The use of tobacco, alcohol, or certain medications like selective serotonin reuptake inhibitor (SSRI) antidepressants during the first trimester has been linked to a higher incidence of omphalocele.
- Nutrition: While research is ongoing, some studies suggest a link between very high doses of certain supplements, like vitamin E, and an increased risk. Conversely, some nutrient deficiencies have been shown to cause abdominal wall defects in animal studies, highlighting the delicate nutritional balance required for healthy development.
Theories on Developmental Failure
The development of an omphalocele is a specific interruption in the highly orchestrated process of early fetal growth. Scientists have proposed several key theories that pinpoint critical moments in the first trimester when this process can go wrong.
The most widely accepted theory centers on the failure of a normal developmental stage called physiological herniation. Around the sixth week of pregnancy, the fetal intestines grow so rapidly they temporarily extend out of the small abdomen and into the umbilical cord. By the 10th to 12th week, the abdomen has grown large enough to accommodate the intestines, which should then rotate and return. An omphalocele is thought to occur when this crucial return journey fails, leaving the organs permanently outside in their protective sac.
Another theory points to an even earlier process involving the fundamental folding of the embryo. In the first few weeks, the embryo transforms from a flat disc into a cylindrical body as its sides fold towards the middle. Think of the early embryo as a flat sheet that needs to fold and "zip up" at the front to create the torso. If this zipper does not close completely at the navel, a persistent opening remains, creating the defect through which abdominal organs can protrude.
A more specific theory proposes a failure in myogenesis—the formation of muscle. The abdominal wall muscles develop from cells that migrate from the sides toward the body's midline, a process essential for strengthening the wall and narrowing the umbilical ring. If these muscle cells fail to migrate completely or do not develop sufficiently, the umbilical ring remains weak and wide. This structural flaw prevents the natural opening from closing after the intestines are meant to return, essentially leaving the gate open for an omphalocele to form.
