Abdominal Wall Defects in Neonates: Comprehensive Evaluation and Therapeutic Strategies

Abdominal wall defects are a relatively common congenital anomaly found in the pediatric population. These defects include 2 separate pathologies, gastroschisis and omphalocele, with divergent pathophysiological origins, clinical manifestations, and management strategies.

Although the mode and timing of delivery is somewhat controversial, particularly for gastroschischis, most evidence supports delivery in a high-volume tertiary care center with ready access to neonatal and pediatric surgical expertise.

Clinicians should be aware of a rare variant of gastroschisis, closure gastroschisis, because early recognition and treatment can affect patient outcomes, as well as complicated gastroschisis and giant omphalocele due to more challenging surgical considerations.

The 2 most common congenital abdominal wall defects are gastroschisis and omphalocele. Both are usually diagnosed prenatally with fetal ultrasound and affected patients are treated in a center with access to high-risk obstetrics, neonatology and pediatric surgery services.

The main distinguishing features between the 2 are that gastroschisis has no sac and the defect is to the right of the umbilicus, while an omphalocele typically has a sac and the defect is in the umbilicus.

Furthermore, patients with omphalocele have a high prevalence of associated anomalies, while those with gastroschisis have a higher likelihood of anomalies related to the gastrointestinal tract, the most common being intestinal atresia. As such, the prognosis in patients with omphalocele is mainly affected by the severity and number of other abnormalities and the prognosis of gastroschisis is correlated with the quantity and function of the intestine. Because of these distinctions, these defects have different management strategies and outcomes.

The goal of surgical treatment for both conditions is reduction of the abdominal viscera and closure of the wall defect; Primary closure or a variety of staged approaches can be used without damaging the intra-abdominal contents by direct injury or increased intra-abdominal pressure, or abdominal compartment syndrome.

In general, the long-term outcome is generally good. The ability to stratify patients, particularly those with gastroschisis, based on risk factors for increased morbidity could improve counseling and outcomes.

The 2 most common congenital abdominal wall defects are gastroschisis and omphalocele. Both are typically diagnosed prenatally by fetal ultrasound, and affected patients are treated at a center with access to high-risk obstetrics, neonatology, and pediatric surgery services. In this review, the distinguishing characteristics, current management strategies, and outcomes of patients with these defects are discussed.

 The incidence of congenital abdominal wall defects has been increasing, mainly due to the increased incidence of gastroschisis.1 Gastroschisis occurs in approximately 1 in 4,000 live births, with male preponderance, and has become the most common abdominal wall defect. most common in the last 30 years.3

A strong association has been observed with young maternal age. The overall incidence of omphalocele is 1 to 2.5 per 5,000 live births.4 An omphalocele results from the failure of the intestinal loops to return to the abdominal cavity after physiological herniation through the umbilical cord that occurs between the sixth and eleventh week of development.

Several mechanisms have been proposed for the pathogenesis of gastroschisis. One theory is that the defect arises from failure of the umbilical coelom to develop, leading to rupture of the small intestine outside the abdominal wall to the right of the umbilicus. An alternative explanation is that the embryonic structures are not incorporated into the umbilical cord.

Additionally, experts suggest that several environmental exposures and demographic risk factors contribute to its development.

> Clinical aspects

Gastroschisis is usually less than 4 cm in diameter, has no covering membrane or sac, and usually contains only small intestine, possibly with stomach or gonad. In almost all cases, it is present to the right of the umbilical cord.5 After birth, the intestine may appear quite normal or be thickened, coiled, and covered with a fibrinous shell.

Unlike patients with omphaloceles, those with gastroschisis do not usually have associated congenital anomalies, but are more likely to have bowel abnormalities, including atresias. Many affected patients are born prematurely and are usually small for gestational age. Those with atresia, perforation, necrosis, or volvulus fall into a separate category called "complicated gastroschisis."

Gastroschisis is frequently seen on mid-second trimester fetal ultrasound with features of a right-sided defect with floating bowel in the amniotic cavity. There are some ultrasound findings that raise concern for intestinal complications; Of these, intra-abdominal intestinal dilation appears to be the most reliable predictor of complex gastroschisis.6

Furthermore, elevated concentrations of α-fetoprotein in both maternal blood and amniotic fluid have been correlated with gastroschisis.

Closed gastroschisis is a rare variant of complicated gastroschisis in which the defect narrows in the uterus, resulting in strangulation and subsequent ischemia of the herniated intestine and atresia. More severe cases can lead to complete loss of the midgut with short bowel syndrome.

Affected patients have variable outcomes depending on the amount of intestine that is viable, but resulting in significantly higher rates of morbidity, mortality, and short bowel syndrome. If suspected on prenatal imaging, preterm delivery may be indicated.

> Management

The optimal mode and timing of delivery for patients with gastroschisis is controversial. Some experts have advocated the use of routine cesarean delivery to avoid injury to the exposed intestine, but the published literature has not shown a difference in outcomes in babies born by cesarean section versus vaginal delivery.7

Similarly, certain centers deliver early to reduce inflammatory peel in the intestine. However, data have not shown conclusive evidence to support this view, and the risks associated with prematurity argue against this practice. 8, 9

Therefore, the method of delivery should be left to the discretion of the obstetrician and the parents. Most authors and physicians encourage delivery at a tertiary center with immediate access to neonatal and pediatric surgery.10, 11

The Canadian Pediatric Surgery Network reviewed data on infants with gastroschischis from 18 pediatric surgical centers and concluded that delivery outside of a perinatal center requiring transfer was a significant predictor of complications.12

Once the baby is born, resuscitation, fluid intake, and gastric decompression should begin immediately. Given the significant heat loss and evaporation these patients experience due to exposed viscera, the intestine should be wrapped in warm gauze soaked in saline and the lower half of the infant placed in an intestinal bag.

The primary goal of surgical repair is to reposition the intestine into the abdominal cavity without traumatizing the intestine or avoiding increased intra-abdominal pressure. The intestine should be inspected for obstructive bands, mats, perforations, or atresia. Several options are available for surgical treatment, including:

• Primary reduction with surgical closure of the fascia

• Silo placement with serial reductions and delayed surgical closure of the fascia

• Primary reduction without fascial closure

• Delayed reduction without fascial closure

The last 2 surgical procedures are commonly referred to as "sutureless" closure.

Primary reduction in the operating room involves transportation, general anesthesia, division of the umbilical vessels and urachus, and suturing of the fascia and skin. Alternatively, surgeons can place a preformed spring-loaded silo into the abdominal defect at the bedside.13

Serial reductions are then performed daily or twice daily with the aid of gravity until the contents have reached the level of the fascia. This slow reduction allows intestinal edema to be gradually reduced and allows intestinal reduction without increasing intra-abdominal pressure. It is important that the reduction takes place between 3 and 5 days. Any type of surgical closure or sutureless closure can be performed.

Sutureless closure involves covering the abdominal defect with the umbilical cord or a synthetic dressing such as a self-adherent foam dressing and allowing closure by secondary intention. We have reported a technique of primary sutureless closure of gastroschisis using a negative pressure/vacuum wound dressing.14 This procedure involves initial placement of a silo with gradual reduction of intra-abdominal contents.

Subsequently, the defect is mainly closed with adhesive tape and vacuum rolled. This procedure can be performed at the bedside without anesthesia and without the need to go to the operating room. It has the advantage of gentle reduction of the silo without increasing intra-abdominal pressure and without causing compartment syndrome. It is also an easily reversible procedure because the tape and wound vacuum can be easily removed if abdominal pressure increases after closure.

A randomized control study comparing sutureless versus sutured gastroschisis closure found no difference in complications.15 Advantages of this method include lack of transportation, avoidance of anesthesia, and better cosmetic outcome.

Most series report a hernia rate of 60% to 84%, of which the majority close spontaneously; with vacuum wound closure, the herniation rate is much lower.16 Biosynthetic patches or nonabsorbable meshes can also be used for closure when primary fascial closure cannot be achieved.

Abdominal compartment syndrome can be a complication after bowel reduction. Intra-abdominal pressures greater than 15 to 20 mm Hg indicate compartment syndrome. This pressure can be determined with the use of intragastric or intravesical catheters.

Worrying signs also include increased peak or mean inspiratory pressures, need for vasopressor support, or metabolic acidosis. Immediate decompressive laparotomy or closure release with silo placement should be performed if abdominal compartment syndrome is suspected. Given this complication, the approach for the type of closure must be decided based on conditions such as prematurity, abdominal dominance, and degree of respiratory difficulty.

For patients with gastroschisis and an associated atresia or perforation, management is more complex. The care of these babies should be individualized according to their gestational age, weight and clinical status, as well as the length and condition of the intestine. Possible techniques include primary anastomosis with closure if the intestine is in good condition; creation of stomata with closure; or reduction of unrepaired bowel in the abdomen with closure and repeat surgery for establishment of bowel continuity in the future.

Postoperatively, a delay in the recovery of intestinal function is common as a result of abnormal intestinal motility, which is frequently observed in these patients.

During this period of dysmotility, gastric decompression and parenteral nutrition should be provided until enteral feeding is reinitiated. If no intestinal improvement is seen after 4 to 6 weeks, imaging studies may be performed to evaluate for the presence of intestinal atresia which is often difficult to visualize due to the coiled intestine.

> Forecast

Long-term outcomes and survival of patients with gastroschisis are generally excellent, with survival rates greater than 90% in large series.17, 18 Outcomes are poorer in patients with an associated finding, such as atresia, perforation, necrosis. or volvulus.19

However, a single-center study that focused on quality of life using a validated survey demonstrated high mean quality of life scores that were independent of severity after 2 years of age, which were comparable to the results published from healthy children.20

Potential long-term problems that may be seen in these patients include cholestasis, recurrent nonspecific abdominal pain, intestinal obstruction, and need for scar revision.

> Clinical aspects

Omphalocele is a large defect, usually larger than 4 cm, covered by an amniotic membrane, containing intestines and other abdominal organs, including the liver and often the spleen and gonad. 5

Patients with omphalocele often have other congenital anomalies, chromosomal abnormalities, or syndromes. Additionally, omphaloceles can be combined with pentalogy of Cantrell, cloacal exstrophy, and the rare omphalocele, bladder exstrophy, imperforate anus, and spinal anomaly (OEIS) complex.

Babies with omphalocele are usually diagnosed prenatally. Fetal ultrasound features include a hernia contained in a membranous sac. Additional associated abnormalities may also be identified on prenatal ultrasound; However, up to one-third of patients with isolated defects present with other anomalies postnatally.

A giant omphalocele contains liver and has a defect of at least 5 to 10 cm in diameter. In addition to an underdeveloped abdominal wall cavity, these patients commonly also have pulmonary hypoplasia. Giant omphaloceles are associated with a high rate of morbidity and mortality. Surgical treatment for these patients is also challenging. twenty-one

> Management

Most patients with omphalocele are born at term. Some experts advocate delivery by cesarean section if there is an extra abdominal liver to avoid liver injury during a vaginal delivery. However, neither of the two types of childbirth has been shown to be superior.

Initial management involves obtaining venous access and initiating fluid resuscitation, as well as gastric decompression with a naso- or orogastric tube. A cardiopulmonary evaluation of the newborn and a complete evaluation of associated anomalies is mandatory.

As such, an echocardiogram x-ray and an abdominal ultrasound should be performed. Additionally, blood glucose level should be monitored because hypoglycemia may be an indication of Beckwith-Wiedemann syndrome, which occurs in 12% of patients with omphalocele.

The management approach for infants with omphalocele depends on the size of the defect, gestational age at birth and weight, and the existence of associated anomalies. In a stable patient with a small defect, a primary repair with surgical closure may be possible. The sac may be removed or inverted before fascial closure.

If the sac adheres to the liver, some defects may need to be left in place to prevent liver injury and bleeding. More commonly, however, due to the size of the defect, loss of dominance of the peritoneal cavity, or instability of the infant, primary closure is not possible and various techniques for coverage and closure are used.

Normally staggered or delayed closure 5 of the defect is used. Often used is eschar – eschar therapy, sometimes referred to as the “paint and wait” technique, in which a topical agent, most commonly silver sulfadiazine, is applied daily to the sac. It creates a gradual eschar with subsequent epithelialization, leaving a ventral hernia.

This process takes weeks to months to complete and can be combined with pressure bandages once the sac is thick enough to slowly reduce the contents to the abdomen.

Posterior closure may involve mobilization of skin flaps, separation of components,22 the use of tissue expanders,23 or a patch. 24 A recent report describes a series of patients using a serial taping method to gradually reduce abdominal contents.25 With all of these techniques, it is important to avoid kinking of the hepatic veins that can occur with liver reduction. This can lead to metabolic acidosis and may require further surgery to reposition the liver.

Another possible complication that may arise before primary repair or during topical therapy before the eschar has completely formed is sac rupture. A variety of methods can be used to manage a ruptured sac, depending on the size of the tear and the condition of the baby, including suture repair, skin closure, and patching.

> Forecast

The main determinant of the prognosis of infants with omphalocele is the association with structural or chromosomal abnormalities that can occur in up to 80% of affected patients. Significant cardiac abnormalities are seen in approximately one-third of patients with omphaloceles.

Survival rates range from 70% to 95%, with most mortality due to associated abnormalities.26,27 Additionally, several long-term medical problems have been found in patients with large omphaloceles, including disease due to gastroesophageal reflux, pulmonary insufficiency, asthma and feeding difficulties.28 and 29 Patients with giant omphaloceles have increased morbidity due to greater viscero-abdominal disproportion leading to prolonged mechanical ventilation and a longer hospital stay.

Future goals in the care of patients with gastroschisis are primarily directed at preventing damage to the exposed intestine as a result of amniotic fluid.

Amniotic fluid exchange, 30, 31, 32 nitric oxide, 33 diuretics, 34 and fetal surgery 35, 36, 37 have been tested in animal models with limited success.

The other areas of focus include the timing of delivery and the role of intra-abdominal intestinal dilation, as described herein.