Omphalocele

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Omphalocele

Definition

An omphalocele occurs when the abdominal wall does not close properly during fetal development. The extent to which abdominal contents protrude through the base of the umbilical cord will vary. A membrane usually covers the defect.

Description

An omphalocele is an abnormal closure of the abdominal wall. Between the sixth and tenth weeks of pregnancy, the intestines normally protrude into the umbilical cord as the baby is developing. During the tenth week, the intestines should return and rotate in such a way that the abdomen is closed around the umbilical cord. An omphalocele occurs when the intestines do not return, and this closure does not occur properly.

Genetic profile

In one-third of infants, an omphalocele occurs by itself, and is said to be an isolated abnormality. The cause of an isolated omphalocele is suspected to be multifactorial. Multifactorial means that many factors, both genetic and environmental, contribute to the cause. The specific genes involved, as well as the specific environmental factors are largely unknown. The chance for a couple to have another baby with an omphalocele, after they have had one with an isolated omphalocele is approximately one in 100 or 1%.

The remaining two-thirds of babies with an omphalocele have other birth defects, including problems with the heart (heart disease), spine (spina bifida ), digestive system, urinary system, and the limbs.

Approximately 30% of babies with an omphalocele have a chromosome abnormality as the underlying cause of the omphalocele. Babies with chromosome abnormalities usually have multiple birth defects, so many babies will have other medical problems in addition to the omphalocele. Chromosomes are structures in the center of the cell that contain our genes; our genes code for our traits, such as blood type or eye color. The normal number of chromosomes is 46; having extra or missing chromosome material is associated with health problems. Babies with an omphalocele may have an extra chromosome number 13, 18, 21, or others. An omphalocele is sometimes said to occur more often in a mother who is older. This is because the chance for a chromosome abnormality to occur increases with maternal age.

Some infants with an omphalocele have a syndrome (collection of health problems). An example is Beckwith-Wiedemann syndrome , where a baby is born larger than normal (macrosomia), has an omphalocele, and a large tongue (macroglossia). Finally, in some families, an omphalocele has been reported to be inherited as an autosomal dominant, or autosomal recessive trait. Autosomal means that males and females are equally affected. Dominant means that only one gene is necessary to produce the condition, while recessive means that two genes are necessary to have the condition. With autosomal dominant inheritance , there is a 50% chance with each pregnancy to have an affected child, while with autosomal recessive inheritance. the recurrence risk is 25%.

Demographics

Omphalocele is estimated to occur in one in 4,000 to one in 6,000 liveborns. Males are slightly more often affected than females (1.5:1).

Signs and symptoms

Anytime an infant is born with an omphalocele, a thorough physical examination is performed to determine whether the omphalocele is isolated or associated with other health problems. To determine this, various studies may be performed such as a chromosome study, which is done from a small blood sample. Since the chest cavity may be small in an infant born with an omphalocele, the baby may have underdeveloped lungs, requiring breathing assistance with a ventilator (mechanical breathing machine). In 10–20% of infants, the sac has torn (ruptured), requiring immediate surgical repair, due to the risk of infection.

Diagnosis

During pregnancy, two different signs may cause a physician to suspect an omphalocele: increased fluid around the baby (polyhydramnios) on a fetal ultrasound and/or an abnormal maternal serum screening test, showing an elevated amount of alpha-fetoprotein (AFP). Maternal serum screening, measuring analytes present in the mother's bloodstream only during pregnancy, is offered to pregnant women usually under the age of 35, to screen for various disorders such as Down syndrome , trisomy 18 , and abnormalities of the spine (such as spina bifida). Other abnormalities can give an abnormal test result, and an omphalocele is an example.

An ultrasound is often performed as the first step when a woman's maternal serum screening is abnormal, if one has not already been performed. Omphalocele is usually identifiable on fetal ultrasound. If a woman's fetal ultrasound showed an omphalocele, polyhydramnios, or if she had an abnormal maternal serum screening test, an amniocentesis may be offered.

Amniocentesis is a procedure done under ultrasound guidance where a long thin needle is inserted into the mother's abdomen, then into the uterus, to withdraw a couple tablespoons of amniotic fluid (fluid surrounding the developing baby) to study. Measurement of the AFP in the amniotic fluid can then be done to test for problems such as omphalocele. In addition, a chromosome analysis for the baby can be performed on the cells contained in the amniotic fluid. When the AFP in the amniotic fluid is elevated, an additional test is used to look for the presence or absence of an enzyme found in nerve tissue, called acetylcholinesterase, or ACHE. ACHE is present in the amniotic fluid only when a baby has an opening such as spina bifida or an omphalocele. Not all babies with an omphalocele will cause the maternal serum screening test to be abnormal or to cause extra fluid accumulation, but many will. At birth, an omphalocele is diagnosed by visual/physical examination.

Treatment and management

Treatment and management of an omphalocele depends upon the size of the abnormality, whether the sac is intact or ruptured, and whether other health problems are present. A small omphalocele is usually repaired by surgery shortly after birth, where an operation is performed to return the organs to the abdomen and close the opening in the abdominal wall. If the omphalocele is large, where most of the intestines, liver, and/or spleen are present outside of the body, the repair is done in stages because the abdomen is small and may not be able to hold all of the organs at once. Initially, sterile protective gauze is placed over the abdominal organs whether the omphalocele is large or small. The exposed organs are then gradually moved back into the abdomen over several days or weeks. The abdominal wall is surgically closed once all of the organs have been returned to the abdomen. Infants are often on a breathing machine (ventilator) until the abdominal cavity increases in size since returning the organs to the abdomen may crowd the lungs in the chest area.

Prognosis

The prognosis of an infant born with an omphalocele depends upon the size of the defect, whether there was a loss of blood flow to part of the intestines or other organs, and the extent of other abnormalities. The survival rate overall for an infant born with an isolated omphalocele has improved greatly over the past forty years, from 60% to over 90%.

Resources

ORGANIZATIONS

Foundation for Blood Research. PO Box 190, 69 US Route One, Scarborough, ME 04070-0190. (207) 883-4131. Fax: (207) 883-1527. <http://www.fbr.org>.

WEBSITES

Adam.com. "Omphalocele." Medlineplus. U.S. National Library of Medicine. <http://medlineplus.adam.com/ency/article/000994.htm>.

Catherine L. Tesla, MS, CGC

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Omphalocele

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