Chapter 396. Abdominal Wall Defects

Gastroschisis is congenital abdominal wall defect though which intraperitoneal contents protrude (Fig. 396-1). The defect occurs to the right of the umbilical cord and can range in size from 2 to 5 cm. The bowel typically appears edematous and inflamed and may be covered by a fibrinous peel. The most commonly eviscerated organs include the intestines and gonads. Gastroschisis occurs in younger mothers,1 with a total incidence of one in 3000 live births.2 Several studies have reported a recent increase in the incidence of gastroschisis.3-5

Pathogenesis

Gastroschisis occurs during the sixth or seventh week of gestation. The right umbilical vein naturally involutes, leaving one umbilical vein and two umbilical arteries. It is hypothesized that the right abdominal wall suffers from vascular compromise, which results in gastroschisis.6,7 This explains why gastroschisis always occurs to the right of the umbilicus. Two other hypotheses exist for the formation of gastroschisis. One involves the defective development of the mesenchyme on the anterior abdominal wall. Anecdotally, omphalocele membrane rupture and subsequent growth of skin to the right and lateral to the umbilicus was documented by ultrasound; the newborn appearance was that of a gastroschisis.8

Epidemiology

Maternal and environmental factors have been implicated in the development of gastroschisis. In animal models, folic acid deficiency, maternal hypoxia, and salicylates have been linked to abdominal wall defects.9 The use of vasoconstrictive agents, such as pseudoephedrine, cocaine, and cigarettes, in early pregnancy have been postulated to increase the risk of gastroschisis.10 Maternal use of salicylates and acetaminophen has also been implicated in the development of gastroschisis.11 Elevated atrazine levels, a chemical found in pesticides in drinking water, has recently been correlated with a regional increased incidence of gastroschisis in the United States.12

Infants with gastroschisis tend to be born prematurely. There is some evidence that gastroschisis infants allowed to deliver after 36 weeks have a stillborn rate of approximately 10%.13 Consequently, mothers of gastroschisis infants are induced to deliver at 36 to 37 weeks, when lung maturity is reached.

Ten percent of infants with gastroschisis have an associated intestinal atresia of varying lengths. It is thought that the atresia results from in utero segmental intestinal volvulus. This is made more likely by the fact that the intestines float in the amniotic fluid without the protection of the peritoneal cavity. Occasionally, the gastroschisis defect closes completely around the mesenteric pedicle, causing the midgut to be ischemic and reabsorbed prior to birth.

The intestines of infants with gastroschisis have an inherent dysmotility. In most gastroschisis infants, this manifests as a prolonged ileus after closure of the abdominal wall. The average time to start feeds after abdominal wall closure is 21 days, with the average time to full feeds of approximately 28 days, but the intestinal dysmotility can be prolonged, necessitating the need for parenteral nutrition for months to years.14 In a smaller percentage of gastroschisis infants, the intestinal dysmotility can be prolonged, necessitating the need for parenteral nutrition for months to years.

Gastroschisis has a higher risk of developing necrotizing enterocolitis as advancement in feedings progress. The incidence of necrotizing entercolitis after gastroschisis repair can be as high as 18.5% and can occur up to several weeks after abdominal wall closure.15 Symptoms of NEC include abdominal distention, high gastric residuals, and vomiting. Bowel rest, gastric decompression, and intravenous antibiotics are hallmarks of treatment.

Prenatal Diagnosis and Management

The diagnosis of gastroschisis is usually made using prenatal ultrasound. Ultrasonography can detect abdominal wall defects at or beyond 14 weeks of gestation. At this time in normal development, the fetal midgut would have returned to the abdominal cavity. Follow-up ultrasound should be performed if an abdominal wall defect is noted in order to detect other potential associated anomalies. Perinatologists usually pay attention to the degree of intestinal edema and dilation. The accuracy of prenatal screening ultrasound detection of abdominal wall defects ranges from 57% to 95% for gastroschisis.1,2,16

Fetal MRI has also increased in popularity to evaluate fetal abnormalities. MRI is very sensitive and can determine the detail of complex anomalies for accurate prenatal diagnosis and better prenatal counseling.17 A small retrospective case series has reported that prenatal MRI may be useful in predicting primary versus staged closures of abdominal wall defects by calculating an exteriorized ratio (ER). ER is the volume of exteriorized viscera divided by volume of the abdominal cavity. This series found all patients with an ER less than 1 were able to be primarily closed. The authors claim that this information can be used to predict postnatal surgical intervention more accurately.18 Nonetheless, in contemporary practice, prenatal ultrasound gives enough detail for perinatologists and pediatric surgeons alike. In addition, during prenatal counseling, the parents are prepared for either a primary or staged repair.

Maternal serum markers aid in the prenatal diagnosis of abdominal wall defects. On the maternal triple test, α-fetoprotein is elevated in all gastroschisis cases. Acetyl-cholinesterase is also elevated in the amniotic fluid of patients with gastroschisis. Karyotype analysis may be indicated in gastroschisis fetuses that have evidence of additional anomalies.

Prenatal diagnosis allows the opportunity to educate families about their infant with an abdominal wall defect. A multidisciplinary team approach has been shown to reduce maternal anxiety.19 Families meet with perinatologists, neonatologists, and pediatric surgical subspecialists to discuss the birthing plan as well as medical and surgical management of the infant. Current recommendations for the perinatal management of gastroschisis include birth in a facility with immediate pediatric surgical availability. Normal labor and vaginal delivery are encouraged.

Management

At birth, gastroschisis infants lose fluid and body heat due to the large exposed surface area. In addition, the intestines are suspended on a thin, narrow mesenteric pedicle. Measures to decrease heat and temperature loss, decrease kinking of the mesentery and prevent desiccation and ischemia of the exposed viscera are mandatory within minutes after the baby’s birth. This can be accomplished by wrapping the bowel in saline-moistened gauze and then wrapping the infant in clear thermoplastic wrap. The bowel must be supported to prevent vascular compromise. If transport is necessary, it is best accomplished in the lateral position to minimize tethering of the mesentery. Gastric decompression and venous access should be secured. Appropriate fluid resuscitation is required to maintain adequate urine output and acid-base balance. Antibiotics should be started. The infant can then be evaluated for other anomalies. The pediatric surgeon will inspect the bowel for ischemia, necrosis, perforation, and atresia. Any inflammatory peel should not be removed.

The goal of surgical treatment for gastroschisis is ultimate closure of the muscle, fascia, and skin; this will confer the greatest chance of survival and least morbidity. Bedside reduction without sedation was introduced in 1998 for infants who were stable from a thermodynamic and cardiorespiratory standpoint.20 Most centers perform definitive closure in the operating room under general anesthesia. Primary fascial and skin closure are possible in one half to two thirds of patients.

In one third to one half of the cases, primary closure will not be possible. Many options exist for staged closure of gastroschisis. The most common method is to place a protective silo over the intestine. The silo may be preformed and spring-loaded or be a piece of silastic sheeting fashioned by the surgeon at the time of the operation. The intestine within the silo is gradually reduced in the abdominal cavity for 5 to 14 days after silo placement. The goal is to expand the abdominal compartment slowly and decrease the physiology effects of abdominal compartment syndrome. At the end of this period, the infant is taken to the operating room. In majority of cases, primary fascial closure can be achieved. However, if fascial closure cannot be achieved, a synthetic or biologic patch may be used to close the fascial defect. The most common synthetic patch used is polytetrafluoroethylene (PTFE or Gore-Tex; W.L. Gore and Associates, Flagstaff, AZ). Recent reports using lyophilized porcine small intestinal submucosa (Surgisis; Cook Biotech, West Lafayette, Indiana)21 or an acellular dermal matrix (AlloDerm; LifeCell Corp., Branchburg, NJ) to create a scaffolding for cellular reconstruction has shown some success. During the period of gradual intestinal reduction, the infant may require mechanical ventilation. Alternatively, the skin may be closed over the abdominal wall defect without closing the fascia (Gross repair). The resulting ventral hernia is fixed in a single or multiple-staged operation within the first year of life.

Closure of the abdomen may be complicated by abdominal compartment syndrome. After returning the viscera in the abdominal cavity, the surgeon watches for signs of tightness around the viscera. These include decreasing ventilation, loss of pedal pulses, loss of urine output, and discoloration of the intestine. If abdominal compartment syndrome is suspected, prompt evisceration and placement of a silo is performed. If intestinal atresia is present, repair of the atresia is deferred for 6 weeks from fascial closure to allow for resolution of intestinal serositis. Infants with undescended testes are allowed a year of natural descent. If the testes are not in the normal intrascrotal position in a year, an orchiopexy is recommended.

Outcomes

Simple gastroschisis is an isolated abdominal wall defect that occurs in 89% of all gastroschisis patients with an all-cause mortality of 3%.22 Complex gastroschisis is associated with other gastrointestinal anomalies such as intestinal atresia, perforation, necrosis, or volvulus and has a reported mortality rate of 9%.22 Infants with complex gastroschisis are more likely to have bronchopulmonary dysplasia and cardiac disease. Interestingly, infants with simple gastroschisis have a higher likelihood of having genitourinary anomalies (5%). The median length of stay was twice the number of days for initial hospitalization in complex gastroschisis as compared to simple cases. In simple gastroschisis cases, the most common complications included sepsis and ileus. On the other hand, patients with complex gastroschisis were more likely to have gastrointestinal complications such as necrotizing entercolitis, small bowel resection, and sepsis. Almost one quarter of complex patients required an ostomy during hospitalization. A significantly larger proportion of complex gastroschisis cases were male.22

Most centers report a 50% to 80% primary closure rate for gastroschisis. The average length of mechanical ventilation was 5.7 days, with an average length of initial hospitalization of 66 days. Complications occurred in 70% of children, with the most common complications including ileus (28%), catheter infection (25%), and sepsis (15%). Thirty-eight percent of children required reoperation during the initial hospitalization. One half required rehospitalization, and 35% required further operations beyond the initial hospitalization.

All infants with gastroschisis have intestinal nonrotation. A formal Ladd procedure is not performed with a primary or a staged closure. Parents are warned that infants with gastroschisis can have bowel obstruction secondary to adhesions or less commonly volvulus, for the rest of their lives.

At long-term follow-up, only 7.1% of gastroschisis patients report frequent gastrointestinal problems. Few patients reported concerns regarding physical exercise. Most parents described the cosmetic and physiologic results as good or excellent. Developmental assessment shows 32% with delayed walking or sitting. However, 77% start school on time. Growth is only 9% below the third percentile for weight and 14% below the third percentile for height.1

Omphalocele is a congenital defect of the midline anterior abdominal wall, where the extruded abdominal organs are covered by a protective membrane (Fig. 396-2). The fascial defect and eviscerated organs are contained within the umbilicus. The defect can range in size from 2 to 15 cm. The incidence of omphaloceles is one in 7500 live births, a rate that has remained stable over the past few decades.2

Pathogenesis

Omphaloceles result from failure of fusion of the lateral embryonic folds at the umbilical ring. The viscera within the omphalocele can include any part of the GI tract, liver, spleen, bladder, and/or gonads and are covered with an opaque sac. This sac is composed of peritoneum, amnion and Wharton’s jelly. The umbilical cord inserts into the sac. The viscera develop without the flat anterior abdominal wall, encouraging globular-shaped liver development and intestinal rotational anomalies.

Etiology and Pathophysiology

Unlike gastroschisis, omphalocele is associated with additional abnormalities in up to 60% of infants.23 These associated anomalies may include structural defects of the heart, kidneys, limbs, and face. Omphaloceles have been associated with trisomy 13, 14, 15, 18, and 21 as well as other genetic syndromes. Beckwith-Weidemann syndrome (BWS), a defect in chromosome 11p15.5, consists of omphalocele, macrosomia, macroglossia, hypertrophy of solid organs, and a predisposition for developing childhood cancers.1,24 Since omphaloceles are often associated with several other anomalies, it is postulated that omphaloceles develop as a part of a field defects early in development. Alternatively, omphaloceles may result from a change in a basic cellular process that has far-reaching consequences, such as alternations in protein methylation seen in BWS. In one study, maternal consumption of multivitamins around the time of the gestation reduced the risk of isolated omphalocele by 60%.25

Unlike gastroschisis, infants born with omphaloceles are relatively protected from heat and fluid loss by the intact membrane covering the viscera. Small, covered omphaloceles usually do not have any physiologic consequences. Larger omphaloceles pose more physiologic and surgical challenges.

Giant omphaloceles are defined as defects greater than 5 cm in diameter that contain liver. In utero, the liver develops outside of the abdominal cavity, resulting in a globular liver and a limited abdominal domain. The omphalocele membrane is fragile and cannot support the underlying viscera. Giant omphaloceles are more likely to be associated with respiratory compromise due to pulmonary hypoplasia. In addition, the lack of muscular support in the epigastrium makes it difficult to have a coordinated diaphragmatic contraction. Some of these infants will require prolonged ventilatory support.

Unlike the gastroschisis patients, omphalocele patients do not have impaired gastrointestinal function when the sac remains intact. They have variable rotational anomalies. A Ladd procedure may be considered at the time of final closure.

Prenatal Diagnosis and Management

Maternal serum α-fetoprotein is elevated in 90% of omphalocele cases. If an amniocentesis is performed, karyotype analysis should be performed. The amniotic fluid will not have elevated acetyl-cholinesterase levels, as is typically seen with gastroschisis. In the fetus with omphaloceles, prenatal ultrasonography should be used not only to document the presence of the abdominal wall defect, but to identify other associated anomalies. The accuracy of fetal ultrasound in detecting omphaloceles is 70% to 98%.1,2,16 Fetal MRI may be considered in omphalocele infants with multiple defects if this modality can give more information to the parents to ensure a safe pregnancy and birth. Cesarean sections are recommended in cases of giant omphalocele to prevent dystocia and omphalocele rupture. In these cases, a vaginal delivery may result in injury to the liver, which can be fatal.

Management

The omphalocele sac must be carefully inspected for its integrity. Physical exam and radiologic studies of the infant should focus on identifying additional anomalies, in particular structural cardiac problems. This initial evaluation should include a chest X-ray, cardiac echocardiogram, and renal ultrasound. If the sac is intact, closure of the omphalocele is relatively elective. Priority then should focus on defining and initiating management of any cardiac anomalies.

Smaller defects are closed primarily. The sac is removed at the time of closure unless it is adherent to the liver. Closure of giant omphaloceles is not advised in the neonatal period. Giant omphaloceles are usually treated with topical agents to induce eschar formation and gradual epithelialization. Forcing the liver and other viscera into the abdominal cavity is impossible and may lead to abdominal compartment syndrome. Complete epithelialization can take weeks to months. Infants may require a stabilization device to support the liver and the viscera during this process. Occupational therapists create these devices in the newborn period. Current agents in use include silver sulfadiazine cream, dilute povidone-iodine solution, and triiodomethane-petroleum gauze. If iodinated agents are used, the infant must be monitored for thyroid suppression. Sulfadiazine can cause immune suppression.

Complete epithelialization can take weeks to months. Infants may require a stabilization device to support the liver and the viscera during this process. Occupational therapists create these devices in the newborn period. Depending on the size of the defect and comorbidities, staged fascial closure is performed between the ages of 6 to 12 months. The fascia may then be closed primarily or approximated with prosthetic material. Alternatively, giant omphaloceles may be managed by closing only skin over the viscera in the newborn period. The resulting ventral hernia will close sequentially over the next few months. This method is known as the Gross closure. If the sac is ruptured, a silo such as that used in a gastroschisis staged repair can be used.

Postoperative management provides respiratory support, nutritional support, and wound care. Limited use of antibiotics may be necessary. The wound should be monitored frequently for evidence of cellulitis and fasciitis. Gastric decompression is required until evidence of GI function is noted. Some of these infants may require long-term ventilation due to pulmonary hypoplasia.

Outcomes

Overall survival in children with abdominal wall defects with no other major congenital anomalies is excellent at greater than 90%.24,26 In a study of postoperative outcomes, neonates who were unable to be closed primarily had a prolonged length of stay and time to full enteral feeds.24 Omphalocele patients achieved primary closure in almost 60% of cases.1 Some of the infants may require long-term ventilation due to pulmonary hypoplasia, which may be associated with the mechanical limitations of the chest and abdominal wall. Average length of respiratory support was 4.5 days, and average length of initial hospitalization was reported at 29.1 days. Complications occur in 83% of patients, with the most common complication being wound infection (15%), sepsis (12%), and ileus (12%). Oral feeding is started without complication in 46% and delayed in 23% of patients. Reoperation during the initial hospitalization occurs in 31% of patients. Fifty-eight percent require readmission and 46% require further surgery.

Long term, only 10% of children report gastrointestinal disturbances with frequent difficulty. Seven percent report restriction with sports activities. Cosmetic results are good or excellent in most. Twenty percent report abdominal wall hernia, 27% have a developmental delay in sitting or walking, but 93% start school at the appropriate age. About 20% of patients have poor weight gain but height is normal in most.1

Midline abdominal defects can occur during the seventh to eighth week of gestation. Defective fusion of the cranial fold is associated with failure of the septum transversum and fibrous pericardium to develop. These defects, if combined with thoracoabdominal ectopia cordis, intracardiac defects, omphalocele, cleft sternum, and diaphragmatic defects, define the Pentalogy of Cantrell. Lower midline abdominal wall defects can result in cloacal or bladder extrophy, imperforate anus, and neural tube defects.

These more complicated anomalies require a multispecialty and multidisciplinary approach, often requiring multiple operations for repair.