GASTROSCHISIS OMPHALOCELE WALL DEFECTS
Category: Pediatric Surgery
Abstract : Gastroschisis and omphalocele (abdominal wall defects, exomphalos, exumbilication) Gastroschisis and omphalocele are among the most frequently encountered congenital anomalies in pediatric surgery. Combined incidence of these anomalies is 1 in 2000 births, which means, for example, that a pediatric surgeon will see 2 such babies for every 1 born with esophageal atresia or tracheoesophageal fist
Gastroschisis and omphalocele (abdominal wall defects, exomphalos, exumbilication)
Gastroschisis and omphalocele are among the most frequently encountered congenital anomalies in pediatric surgery. Combined incidence of these anomalies is 1 in 2000 births, which means, for example, that a pediatric surgeon will see 2 such babies for every 1 born with esophageal atresia or tracheoesophageal fistula.
Although specialists such as neonatologists and pediatric surgeons are responsible for the care of these babies, this topic is included in a text of general pediatrics to bring about a more thorough understanding of these anomalies and enable physicians to care for these children more empathetically.
Many babies have correctable lesions and simply require routine pediatric care. For others, the abdominal wall defect is part of a larger constellation of unresolved problems, and further care by specialists is necessary. All of these children, however, require general management by pediatricians who have knowledge of their particular anomalies and their past surgical histories. For example, physicians should know if an associated malrotation was corrected (to prevent midgut volvulus) and whether an abnormally located appendix was removed (to prevent occurrence of atypical appendicitis).
Pathophysiology:
Embryology
Fetal growth and definition of form are orchestrated by processes that are specific regarding time and location. Growth spurts often are followed by delays. Cellular differentiation, proliferation, migration, and deposition are involved in the formation of new tissue. Initially, the embryo is flat within the umbilical ring, which is defined histologically by the junction of cylindrical epithelium of the epiblast (ectoderm) and the cuboidal epithelium of the amnion. Two layers comprise the embryo: the epiblast (ectoderm), which becomes either neuroectoderm or surface epithelium, and the hypoblast, which becomes the inner epithelium of gut-derived organs. Formation of a third germ layer (mesoblast) occurs along with the change in the embryo's shape. Elongation of the embryonic disc and longitudinal and lateral enfolding create a cylinder with a recognizable body plan.
Several processes combine to form the mesoblast cell layer, as follows:
• Apoptotic cell death with disruption of the epithelial basement membrane
• Phagocytosis of the dead cells with enlargement of the intercellular space
• Migration of ectoderm cells from the epithelial layer to the mesodermal layer
These processes take place in the following 3 areas:
• The primitive streak, which is a groove-like structure located in the dorsocaudal portion of the embryo
• The neural crest, which is located in the cranial half of the embryo at the transition of neuroectoderm and surface epithelium
• The umbilical ring
Proliferation of the neuroectoderm and underlying mesoderm, coupled with growth arrest at the umbilical ring, pushes the embryonic disc above the umbilical ring and beyond the underlying yolk sac like a growing mushroom. Simultaneously, the embryo folds ventrally, forming the thoracic and abdominal cavities distinct from the extraembryonic coelom. The amniotic cavity enlarges and bulges over the embryo, and the amnion attaches to the yolk sac and the connecting stalk, forming the umbilical cord. Caudal enfolding of the embryo incorporates the proximal yolk sac into the hindgut and allantois (a diverticulum of the yolk sac) into the urogenital sinus. The cloacal membrane covers the openings of the hindgut and urogenital sinus; the perineum lies between these openings. Elongation of the primitive gut and the urogenital sinus, and fusion of the surrounding mesoderm, coincides with the appearance of the urorectal septum.
In summary, the human embryo initially is disc-shaped and composed of 2 cell layers. It acquires a third cell layer as it grows above the umbilical ring and becomes cylindrical by elongation and inward folding. The body folds (cephalic, caudal, lateral) meet in the center of the embryo where the amnion invests the yolk sac. Defective development at this critical location results in a spectrum of abdominal wall defects. By the sixth week, rapid growth of the midgut causes a physiologic hernia of the intestine through the umbilical ring. The intestine returns to the abdominal cavity during the tenth week, and rotation and fixation of the midgut occur. This process does not occur in babies with gastroschisis or omphalocele, resulting in an increased risk of midgut volvulus.
Pathogenesis of omphalocele and gastroschisis
Abdominal wall defects occur as a result of failure of the mesoderm to replace the body stalk, which persists in a region normally occupied by somatopleure. Embryonic dysplasia causes insufficient outgrowth at the umbilical ring. Decreased apoptotic cell death and underdevelopment of the mesodermal cell compartment cause enlargement of the umbilical ring's diameter. The amnion does not apply itself to the yolk sac or connecting stalk but remains at the margin of the body wall defect, causing faulty development of the umbilical cord and a persistent communication between the intraembryonic body cavity and the extraembryonic coelom.
In babies with omphalocele, failure of central fusion at the umbilical ring by growth of the mesoderm causes defective abdominal wall closure and persistent herniation of the midgut. The abdominal viscera are contained within a translucent sac, which is composed of amnion, Wharton jelly, and peritoneum. The umbilical vessels radiate onto the wall of the sac. In 50% of cases, the liver, spleen, and ovaries or testes accompany the extruded midgut. Possible explanations of the embryology of abdominal wall defect in gastroschisis include the following:
• Defective mesenchymal development at the body stalk-abdominal wall junction results in a dysplastic abdominal wall that may rupture with increased abdominal pressure.
• Abnormal involution of the right umbilical vein or a vascular accident involving the omphalo-mesenteric artery causes localized abdominal wall weakness that subsequently ruptures.
• Rupture of a small omphalocele with absorption of the sac and growth of a skin bridge between the abdominal wall defect and the umbilical cord has been chronicled on prenatal ultrasound.
Pathogenesis of Other abdominal wall defects
In umbilical cord hernias, the umbilical ring is oversized but the amnion is applied normally around the yolk sac and connecting stalk.
Urachal remnants and omphalomesenteric duct malformations result from absent or deficient apoptotic cell death of the epithelium of the urachus and yolk stalk, which, in normal embryogenesis, cause these structures to disappear.
Abnormal development of the lower body wall results from defective enfolding of the caudal pole of the embryo and deficient incorporation of the yolk sac and allantois; this is associated with malformation of external genitalia. Bladder exstrophy (hypogastric omphalocele) has an incidence of 3.3 in 100,000 births. The bladder develops during the fifth to ninth gestational weeks, and urine mixes with amniotic fluid by the tenth week. Normally, the bladder can be visualized by ultrasound by the end of the first trimester. The bladder mucosa is soft and pliable at birth, but within 48 hours' exposure, it becomes firm and polypoid and prone to malignant degeneration. Surgical closure is staged and varied, but the goal of reconstruction is voluntary urination with continence and correction of the associated vesicoureteral reflux.
Characteristic findings include the following:
• Anterior vagina and rectum, which may be prolapsed
• Epispadias, bifid clitoris or penis and scrotum
• Dorsal chordee
• Poor urinary sphincter control
• Waddling gait due to outward and downward rotation of the anterior pelvic ring and pubic symphysis diastasis
Prune belly syndrome (abdominal wall dysplasia) occurs as a result of increased apoptotic cell death in the body wall placode, which leads to insufficient mesodermal cell deposition. Retention of an abnormally large amount of yolk sac causes attenuation of the abdominal musculature. Muscle fibers are absent and replaced by a thick collagenous aponeurosis. Intercellular conduction of electrical impulses is disturbed, which leads to faulty muscular contractions and ineffective peristalsis.
Characteristics of prune belly syndrome include a thin, flaccid abdominal wall and hypertrophy of the bladder wall with dilation of the bladder, ureters, and renal collecting system, which may be associated with obstruction of the prostate urethra at its junction with the bladder neck. Incidence is 1 in 30,000-50,000 births. Approximately 95% of patients are male. Patients are infertile, since absence of prostate and seminal fluid precludes normal sperm development. Surgical repair includes reconstruction of the urinary collecting systems and the abdominal wall, along with bilateral orchiopexies.
Faulty development of the urorectal septum leads to anal agenesis and nondivision of the cloaca. Cloacal exstrophy (lower midline syndrome, see Images 19-25) has an incidence of 1 in 200,000-400,000 births. Chromosomal abnormalities are associated with low-set ears, fetal uropathy leading to oligohydramnios, pulmonary hypoplasia, and compression abnormalities, such as indented thorax, deformed digits, talipes, bowed limbs, and dislocated hips.
Characteristic features include the following:
• Bladder exstrophy with a central strip of everted intestine
• Duplicated colon and appendix, or colonic atresia and imperforate anus (agenesis of the hindgut)
• Sacral and neurologic anomalies, such as myelomeningocele, hydromyelia, and diastematomyelia
Frequency:
• In the US:
Combined incidence of omphalocele and gastroschisis is 1 in 2000 births. Epidemiologic data compiled over the last 40 years show that the incidence of omphalocele has remained constant and is associated with increased maternal age. An inherited predilection is indicated by its occurrence in twins, in consecutive children, and in different generations of the same family. Incidence of gastroschisis is increasing, and it is associated with young maternal age and low gravity. Prematurity and low birth weights, secondary to in utero growth retardation, are more common in babies with gastroschisis.
Mortality/Morbidity:
• Over the past 30 years, the survival rate of babies with gastroschisis and omphalocele has steadily improved, from approximately 60% in the 1960s to more than 90% currently. The observed decline in morbidity and mortality has resulted from improvements in the care of low birth weight and premature babies, particularly those who, because of open abdominal wounds and extruded intestine (gastroschisis), are especially prone to hypothermia, dehydration, sepsis, and hypoglycemia. Anesthetic management and surgical techniques have improved and the development and availability of excellent parenteral nutrition for these and other surgical patients has had a significant impact.
• Long-term morbidity from gastroschisis is related to intestinal dysfunction and wound problems.
• Short gut syndrome may be caused by a number of factors. An antenatal mesenteric vascular accident or constriction of the extruded intestine's mesentery by a small abdominal wall defect may cause an obstructed, shortened intestine with diminished absorptive capacity. Gut necrosis may complicate excessively tight closure of the abdominal wall defect by impeding splanchnic blood flow with resultant intestinal ischemia and necrotizing enterocolitis (NEC), or it may occur consequent to closed loop obstruction caused by adhesions or midgut volvulus. Loss of intestinal length exacerbates the dysfunction consequent to antenatal exposure of the intestine to amniotic fluid.
• Management of babies with short gut syndrome also has improved significantly as a result of providing nutrition by parenteral and enteral routes, obtaining venous access and treating catheter sepsis, and optimizing gut adaptation with innovative surgical procedures and aggressive treatment of bacterial overgrowth within stagnant intestinal loops. Even so, babies with short gut as a consequence of gastroschisis comprise a large percentage of children undergoing intestinal transplantation.
• Poor healing of the abdominal wound usually results in a ventral hernia, which may require secondary surgical repair.
• Paradoxically, babies with small (unimpressive) omphaloceles are most likely to have associated abnormalities, including intestinal problems (Meckel diverticulum, atresia), genetic syndromes (Beckwith-Wiedemann), and congenital heart disease.
• Babies with giant omphaloceles usually have small, bell-shaped, thoracic cavities and minimal pulmonary reserve; reduction and repair of the omphalocele frequently precipitates respiratory failure, which may be chronic and require a tracheotomy and long-term ventilator support. The authors recently cared for a baby with giant omphalocele and diaphragmatic hernia. Both conditions are associated with pulmonary hypoplasia, and when they are combined, the severity of the pulmonary deficit precludes survival, even with Extracorporeal Membrane Oxygenation (ECMO) support, as provided for our patient.
• Even with successful repair, which usually requires a synthetic patch, and good clinical outcome, the location of the child's liver is central, directly beneath the patch, rendering it more vulnerable to trauma. Race: No geographic or racial predilection exists for omphalocele or gastroschisis. Sex: The male-to-female ratio is 1.5:1.
Physical:
• Omphalocele
o In babies with omphaloceles, the size of the abdominal wall defect ranges from 4-12 cm, and the location of the defect may be central, epigastric, or hypogastric.
o Although the ease of surgical reduction and repair correlate with the size of the abdominal wall defect, a small omphalocele is no guarantee of an uncomplicated clinical course. Associated genetic syndromes involving multiple organ systems, or abnormalities of the intestine, such as an atresia or a patent omphalomesenteric duct, are potential problems.
o With a large omphalocele, dystocia may occur and result in injury to the baby's liver; hence, a cesarean section may be indicated.
o The omphalocele sac is usually intact, although it may be ruptured in 10-20% of cases. Rupture may occur in utero or during or after delivery.
o Babies with the Beckwith-Wiedemann syndrome (ie, exomphalos, macroglossia, gigantism) have large, rounded facial features, hypoglycemia from hyperplasia of the pancreatic islet cells, and visceromegaly.
They may have genitourinary abnormalities, and they are at risk for development of Wilms tumors, liver tumors (hepatoblastoma), and adrenocortical neoplasms.
o Pentalogy of Cantrell describes an epigastric omphalocele associated with a cleft sternum and anterior diaphragmatic hernia (Morgagni), cardiac defects (eg, ectopia cordis, ventricular septal defect [VSD]) and an absent pericardium.
o Giant omphaloceles have large central or epigastric defects. The liver is centrally located and entirely contained within the omphalocele sac. The abdominal cavity is small and undeveloped, and operative closure is very difficult. The thoracic cavity is also small. Associated pulmonary hypoplasia or restrictive lung disease may be present.
• Gastroschisis
o The defect is fairly uniform in size and location; a 5-cm vertical opening to the left of the umbilical cord.
o However, the extent of intestinal inflammation and resultant edema and turgor greatly affect reduction and closure of the abdomen. Inflammation so distorts the bowel's appearance that it may be difficult to determine if associated intestinal atresia is present.
o Once reduction and closure is obtained, inflammation resolves, and the intestine softens and regains a normal appearance. Correction of associated intestinal atresia is best left until this time, usually 3 weeks after the first operative procedure.
o Intestinal dysfunction takes longer to normalize, from 6 weeks to several months.
o If gastroschisis is identified, perform serial examinations to assess intestinal integrity and amniocentesis to monitor lung maturity.
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