OVERVIEW: What every practitioner needs to know:
Omphalocele and gastroschisis are two of the most common congenital malformations of the anterior abdominal wall.
What are the typical findings for these two diseases?
Omphalocele: Omphalocele is a midline abdominal wall defect in which the rectus muscles insert widely on the costal margins and do not meet in the midline at the xiphoid. Herniated intra-abdominal organs protrude through the base of the umbilicus into a membranous sac consisting of peritoneum, Wharton’s jelly, and amnion. The membranous sac offers protection to the intraabdominal contents contained within the sac. The umbilical cord inserts into the membrane covering the omphalocele at a location far from the abdominal wall (see Figure 1). The omphalocele usually contains the small intestine and liver. The defect may be classified as “giant” due to the loss of abdominal domain and considerable size (see Figure 2). At times, the omphalocele sac may rupture and the protective effect of an intact membrane can be lost (see Figure 3).
Gastroschisis: Gastroschisis is anatomically characterized by evisceration of the abdominal organs through a small opening usually present to the right of the umbilicus (see Figure 4). Gastroschisis always includes the small intestine and may also include the stomach, colon, and gonads. There is not a membrane that covers the herniated viscera. The umbilical cord is present and found in the normal location. Gastroschisis is rarely associated with concomitant congenital anomalies. However, intestinal atresia is present in approximately 10% of infants due to an ischemic insult secondary to hernia with strangulation or torsion (see Figure 5). Gastroschisis is classified as simple if there is no associated bowel pathology and complex if there is associated bowel pathology.
A ruptured omphalocele may be misclassified as gastroschisis due to lack of an overlying membrane. However, omphalocele can be distinguished from gastroschisis based on the size and location of the defect.
What other disease/condition shares some of these symptoms?
The differential diagnosis of prenatally diagnosed anterior abdominal wall defects includes bladder exstrophy, cloacal exstrophy, cystic cord lesion, exomphalos (congenital umbilical hernia), urachal cyst, omphalocele and gastroschisis. These are differentiated based on postnatal physical examination and selected imaging studies.
Embryology of the abdominal wall
The embryo originates as a flat disk that develops four folds beginning at 3 weeks gestation; two lateral folds, which form the pleuroperitoneal cavity, the cephalic fold that brings down the developing heart, and the caudal fold, which brings up the bladder and allantois. At this time, the gut tube forms along the length of the embryo, connecting to the umbilicus at the yolk sac. At 5 weeks gestation, the midgut elongates and continues to grow within the umbilical cavity, then returns to the peritoneal cavity at 10 weeks gestation where it rotates and becomes fixed in place.
Embryology of the defects
Omphalocele is the result of the failure of the body folds to come together completely. It is usually due to failure of the lateral folds to meet together at the midline. The defect is always at the umbilicus. The rectus muscles insert too far laterally on the coastal margin and cannot be brought together in the operating room. This defect occurs early in embryogenesis and for this reason, is often associated with other congenital anomalies.
The cause of gastroschisis remains somewhat unclear with a variety of possible explanations that have been proposed. One theory is that gastroschisis results from a lack of development of the umbilical cavity or coelom. When the bowel grows, it has no space in which to herniate and develop, causing it to rupture outside of the body wall. Other theories include a malformation caused by abnormal involution of the right umbilical vein at approximately 28-32 days of gestation, disruption of the right omphalomesentric artery within the extraembryonic coelom. Alternatively, gastroschisis may be the result of disruption of the abdominal wall in development caused by teratogens including radiation, aspirin, pseudoephedrine, acetaminophen, or maternal smoking.
How are abdominal wall defects diagnosed?
Diagnosis of either gastroschisis or omphalocele is usually made based on routine prenatal ultrasound. Omphalocele is generally detected at 18 + 6 weeks gestational age while gastroschisis is detected at 20 + 7 weeks gestational age. The sensitivity of prenatal ultrasound is 75% for omphalocele and 83% for gastroschisis. Prenatal ultrasound can also detect associated anomalies including cardiac anomalies, which are common in omphalocele. Results of prenatal ultrasound can be used to guide prenatal counselling. Moreover, the appearance of the fetal intestine can be characterized with specific attention to progressive dilation suggesting threatened bowel. A serial US every 4 weeks is recommended to assess fetal growth and intestinal development or dilation.
What role do laboratory studies have in confirming the diagnosis?
Elevated alpha fetoprotein (AFP) in both maternal serum and amniotic fluid as well as acetylcholinesterase levels in amniotic fluid correlate with the presence of abdominal wall defects.
PREGNANCY AND DELIVERY MANAGEMENT:
Parental counseling is advised soon after the diagnosis is made, including emphasis on associated anomalies, genetic syndromes, morbidity, mortality, and expected results following surgical intervention. The family must be advised that surgical correction may be staged or repeated interventions necessary based on the severity of the defect. Educational materials should be provided to the family.
The significant risk of intrauterine growth restriction or stillbirth warrants close fetal monitoring in the third trimester. Early intervention may be necessary if potential serious abnormalities are identified. Delivery should be planned at a tertiary care center to better coordinate the obstetrical, neonatal, and pediatric surgical care.
The preferred optimal mode of delivery of infants with abdominal wall defects has not been determined. Contemporary studies indicate that 53% of children with gastroschisis and up to 80% of the children with omphalocele are delivered by cesarean section. Yet, there does not appear to be a consistent difference in the neonatal outcome between infants delivered vaginally or those delivered by cesarean section. At present, most clinicians advocate delivery at term unless other associated problems exist, requiring preterm delivery.
Key considerations in the management of gastroschisis and omphalocele are:
Stabilize the patient, administer IV fluids, and protect the herniated bowel or omphalocele sac. Place an orogastric tube to prevent further distention of the bowel. Place the infant in a bowel bag to protect the bowel and reduce insensible fluid losses.
Reduce the evisceration: Management is dictated by the severity of the defect, the degree of herniated viscera, and the effect of infant physiology. Successful reduction must not negatively impact end organ perfusion or ventilation. Thus, ventilatory pressures, oxygenation, and urine output are all carefully monitored and reduction is abandoned when compromise occurs with attempts at full reduction. In this situation, staged reduction is indicated. While staged reduction is generally accomplished in 5 to 7 days in gastroschisis, staged reduction in a “giant” omphalocele may take months. In the event of severe or lethal anomalies, the infant may undergo palliative therapy alone.
Identify and treat the associated anomalies.
Recognize and treat complications.
Early neonatal management is directed to limit fluid and protein loss and prevent hypothermia. The exposed viscera are immediately covered by enveloping the infant partially in a plastic bowel bag to minimize handling of the bowel and reduce insensible fluid losses. The clear bag provides close observation of the bowel or omphalocele. Avoid saline-soaked dressings applied directly to the bowel or omphalocele and the use of plastic wrap to secure the dressing. The bowel is examined for vascular compromise and, if present, the bowel should be carefully untwisted to restore perfusion. If this is unsuccessful, it may be necessary to enlarge the abdominal wall defect emergently with a lateral extension of the fascial opening. Orogastric tube placement, IV fluid administration, and broad-spectrum antibiotics follow. After initial stabilization in the neonatal ICU, the infant is transported to the OR for surgical reduction.
Fluid requirements in neonates with these abdominal wall defects within the first 24 hours of life–especially in cases of gastroschisis–exceed the usually accepted maintenance requirements for a normal newborn. These infants may require as much as 150-300 cc/kg in the first day of life to support tissue perfusion. The end points of adequate fluid resuscitation are an appropriate heart rate, blood pressure, urine output of 1-2 cc/kg/hr, and normal base deficit. An appropriate combination of crystalloids and colloids should be used, and naso-gastric losses should be replaced. This increasing requirement has been attributed to antenatal peritonitis, increased insensible loss due to exposed viscera, and excessive fluid transudation as third space loss from inflamed bowel wall. This can be further aggravated in the presence of lymphatic and venous obstruction secondary to incarceration of the bowel within the defect.
SURGICAL MANAGEMENT OF GASTROSCHISIS:
After initial stabilization in the neonatal ICU, the infant is transported urgently to the operating room. The type of repair performed is related to the degree of bowel inflammation, and the relative size discrepancy between available abdominal cavity and the amount of herniated viscera.
Primary abdominal wall closure is the preferred technique; a staged repair is reserved for when primary closure is not possible. The newborn is given general anesthesia, and the herniated viscera is carefully reduced into the abdominal cavity. Attempts should be made to determine if additional intestinal anomalies are present. This may be difficult due to the thickened, inflamed bowel. The feasibility of primary closure is assessed by estimates of intraoperative intra-abdominal pressures, ventilatory pressures, and lower body perfusion to avoid the development of abdominal compartment syndrome. Intra-abdominal pressure can be determined from gastric or bladder pressure measurements. A value of more than 20 mmHg indicates that no further reduction should be attempted. Infants suffering intrauterine or perinatal bowel injury may require bowel resection with temporary intestinal stoma. Alternatively, if an atretic segment exists but there is no free perforation or necrosis, the atretic segments are reduced with planned re-exploration at 4-6 weeks once the inflammatory peel has diminished and permits re-anastomosis.
In the presence of a large defect causing significant visceral-abdominal disproportion or evidence of abdominal compartment syndrome with primary reduction, an alternative approach must be taken. The herniated viscera are placed into a silastic silo, which in turn is secured either to the fascia with suture or below the fascia with a spring-loaded ring. Over the ensuing days the bowel gradually returns to the abdomen by gravity and gentle reduction of the bowel within the silo (see Figure 8). Once fully reduced, the fascial defect and skin are closed (see Figure 9). At times, the fascia cannot be closed, primarily due to excessive tension. When primary fascial closure cannot be accomplished, prosthetic mesh is utilized. Non-absorbable material, e.g., Gore-Tex, or absorbable, biologic matrix, e.g., AlloDerm or Surgisis, is placed and skin is used to cover the prosthetic. Rarely, there is insufficient skin to cover the defect and the prosthetic remains exposed, requiring either delayed excision or replacement with a biologic substitute.
In special circumstances, for example, infants with structural cardiac anomalies, lethal chromosomal anomalies, or extreme prematurity, bedside reduction and the use of prosthetic pre-formed silo may be preferable. Alternatively, elevation of skin flaps to close the skin defect, leaving a fascial defect, or the use of sclerosing agents like silver sulfadiazine to paint the external omphalocele membrane to promote fibrosis and eventual epithelialization, have been utilized. These techniques result in large ventral hernias that become quite challenging to close due to the loss of abdominal domain (see Figure 10). Often, multiple operations are needed to achieve final closure. Again, these methods should only be utilized in patients with severe associated anomalies that limit the possibility of using other strategies for closure.
Bedside suture-less closure with negative pressure dressing has also emerged as a suitable option for gastroschisis closure. Bedside closure offers many advantages including the fact that it obviates the need for general anaesthesia. Bedside closure has equivalent rates of mortality, length of stay, and feeding parameters as operative closure. Bedside closure may be associated with an increased risk of umbilical hernia, however, newer data suggest that most of these hernias resolve without the need for operative repair.
What are the adverse effects associated with each treatment option?
In both gastroschisis and in omphalocele, the best results are achieved with primary closure with or without the use of prosthetic mesh. There is no survival difference between the appropriately chosen primary or staged closure. Although in some studies, immediate repair has been shown to increase the number of ventilator days required, randomized controlled trials failed to demonstrate any difference in the length of stay, time to return to full enteral feeds, days of parenteral nutrition, and overall morbidity and mortality. Available biomaterials further enhance our ability to achieve closure for all abdominal wall defects without intra-abdominal hypertension and with good cosmetic outcomes. The choice between primary or staged reduction
What are the long-term outcomes of omphalocele/gastroschisis?
Mortality: Postnatal survival in cases of gastroschisis and omphalocele largely depends on the presence or absence of associated anomalies, the remaining intestinal length, and the degree of visceral-abdominal disproportion. Mortality has markedly decreased in recent years due to improved prenatal diagnosis, in concert with advances in surgical and medical management.
Overall mortality has been found to be approximately 8% to 28% in cases of gastroschisis. Survival for simple gastroschisis is nearly 100%. Mortality for complex gastroschisis may be as high as 28%. Death usually results from cholestatic liver disease secondary to intestinal failure and the need for prolonged total parenteral nutrition.
Mortality in omphalocele has been reported to be only approximately 15% without associated anomalies, but increases, up to 61% if other anomalies are present. In patients with omphalocele and a major cardiac anomaly, mortality approaches 80%. No difference in the survival outcome between giant and minor omphalocele has been reported.
Gastrointestinal function: Long-term gastrointestinal problems are seen in only 7-10% of children with abdominal wall defects and are generally related to the degree of intestinal loss from intestinal atresia or injury. Small bowel obstruction occurs in approximately 25% of infants with gastroschisis and approximately 13% of those with omphalocele. Eighty-five percent occur in the first year of life. Gastro-esophageal reflux disease affects nearly one half of patients with large defects, and may be complicated by the development of esophagitis and esophageal stricture. Cryptorchidism, inguinal hernia, and recurrent abdominal wall hernia are more frequent in children with abdominal wall defects.
Cosmetic outcome: Cosmetic results are described as excellent or good in the majority of patients. Few patients require umbilical reconstruction due to lack of umbilicus or scar revision later in life.
Physical and intellectual development and quality of life: Long-term follow-up reveals normal growth and development of these children, in the absence of additional congenital anomalies. More than two thirds of these children achieve developmental milestones at the appropriate time, but up to one third demonstrate delayed development in growth and achievement of developmental milestones.
Children with isolated defects typically participate in normal activities and education without any compromise in their quality of life. Most children start kindergarten at the usual age. Restrictions in physical exercise and sports are reported in fewer than 10% of children.
What is the frequency of abdominal wall defects?
The incidence of gastroschisis is 3-4/10,000 live births. Its overall incidence has been globally increasing over the past few decades, independent of maternal age.
The incidence of omphalocele is 1/110 fetuses by prenatal ultrasound at a gestational age of 18 weeks; however, this decreases to 1/4,000 live births due to fetal demise. Omphalocele is more common in male infants than female infants.
What are the risk factors for development of abdominal wall defects?
Risk factors for gastroschisis include young maternal age, low socioeconomic status, absence of maternal father, poor maternal prenatal care, and primigravida status as well as poor nutritional status and lack of prenatal vitamins. Maternal obesity is known to be protective. Use of illegal drugs during pregnancy is also a known risk factor.
Risk factors for omphalocele include advanced and very young maternal age and maternal obesity. Nutrition risk factors include lack of prenantal vitamins including folic acid, and poor glycemic control. In vitro fertilization is also a known risk factor.
Other clinical manifestations that might help with diagnosis and management
Associated malformations: The presence of associated systemic malformations or physical findings characteristic of chromosomal abnormalities suggest omphalocele.
Omphalocele: In descending order of frequency, anomalies include cardiac (septal defects, tetralogy of Fallot and ectopia cordis) gastrointestinal tract (diaphragmatic hernia, intestinal duplications, and atresia), musculoskeletal system (see Figure 11), genitourinary system, and central nervous system. Chromosomal abnormalities are observed in 40% of infants with omphalocele, including trisomy 18, trisomy 13, trisomy 21, Turner syndrome, Klinefelter syndrome, and triploidy. Genetic syndromes associated with omphalocele include Beckwith-Weidemann Syndrome (omphalocele, macroglossia, hemihypertrophy, ventricular septal defect (VSD)), pentalogy of Cantrell (omphalocele, anterior diaphragmatic hernia, sternal cleft, ectopia cordis, cloacal exstrophy) (see Figure 12), Goltz syndrome, Marshall-Smith Syndrome, Meckel-Gruber syndrome, and CHARGE syndrome (coloboma of the eye, heart defects, atresia of the nasal choanae, retardation of growth and/or development, genital and/or urinary abnormalities, and ear abnormalities and deafness). Due to co-existence of the high prevalence of secondary defects, newborns should undergo comprehensive evaluation that includes a genetic profile and karyotyping.
Gastroschisis: Gastroschisis is rarely associated with a chromosomal abnormality. Typically, infants born with gastroschisis are small for gestational age. Intestinal atresia (see Figure 5) is the most common associated anomaly and is among the leading causes of congenital short gut. Skeletal dysplasias, arthrogryposis, craniosynostosis, and unspecified dwarfism have been observed.
What complications might you expect from the disease or treatment of the disease?
Complications in abdominal wall defects are influenced by birth weight, gestational age at birth, and the presence of associated anomalies. Immediate postoperative complications can be seen in up to 70% to 80% cases of gastroschisis and omphalocele and include postoperative ileus with associated reoperation rate of up to 28%, sepsis, delay in achieving full oral feedings, catheter-related infections, and acute renal failure. Two main causes of postoperative morbidity in newborns with an abdominal wall defect are sepsis and acute renal failure.
Additional complications of necrotizing enterocolitis (NEC), subsequent short bowel syndrome, prolonged parenteral nutrition, cholestasis, and intestinal failure-associated liver disease are seen with gastroschisis. The incidence of NEC may be reduced by the introduction of early enteral feeding and the use of breast milk. The use of a prosthetic silo can result in silo detachment, an increased rate of infection, and subsequent loss of abdominal domain, especially in large defects associated with giant omphaloceles. Again, the presence of associated anomalies in omphalocele further complicates the postoperative course and, if severe, may delay definitive repair of the abdominal wall defect.
How can omphalocele/gastroschisis be prevented?
There are no known preventive interventions to date for these defects.
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- OVERVIEW: What every practitioner needs to know:
- What are the typical findings for these two diseases?
- What other disease/condition shares some of these symptoms?
- How are abdominal wall defects diagnosed?
- What role do laboratory studies have in confirming the diagnosis?
- What are the adverse effects associated with each treatment option?
- What are the long-term outcomes of omphalocele/gastroschisis?
- What is the frequency of abdominal wall defects?
- What are the risk factors for development of abdominal wall defects?
- Other clinical manifestations that might help with diagnosis and management
- What complications might you expect from the disease or treatment of the disease?
- How can omphalocele/gastroschisis be prevented?