Figure 103-1. Gastroschisis. The defect is to the right of the normal umbilicus, and the bowel is thickened and inflamed.

Associated anomalies are more common in infants with omphalocele than with gastroschisis, reflecting the more global abnormality of embryogenesis in omphalocele. About 50% to 60% of infants with omphalocele have at least one associated congenital anomaly involving the skeleton, gastrointestinal tract, nervous system, genitourinary system, and cardiopulmonary system.^7,8 In addition, infants with omphalocele have a higher incidence of chromosomal abnormalities and other conditions such as Beckwith–Wiedemann syndrome. A comparison of gastroschisis and omphalocele is summarized in Table 103-1.

Perioperative Management for Gastroschisis and Omphalocele

In contemporary practice, infants with gastroschisis can be safely delivered vaginally.^8,9 Studies comparing vaginal delivery with elective cesarean section for infants with gastroschisis demonstrated no significant differences in outcome.^10,11 Early delivery to minimize intestinal damage in gastroschisis patients has not been proved to be efficacious.^12,13 Fetal well-being has been advocated to be the primary determinant for gastroschisis. To prevent birth-related hepatic injury, cesarean section is preferable for prenatally diagnosed infants with giant omphaloceles.

After delivery, infants with either gastroschisis or omphalocele have similar initial management priorities. If necessary, an adequate airway with effective ventilation and oxygenation is established. The infant should be maintained under either an external warmer or a humidified incubator. An orogastric sump tube should be inserted early and placed on suction to prevent further intestinal distention. In gastroschisis, the herniated viscera should be examined to make certain that the mesentery is not twisted. In addition, the tightness of the opening of the abdominal wall should be assessed to ensure that there is sufficient perfusion of the bowel. The viscera should be covered with gauze plastic wrap to prevent further contamination, hypothermia, and volume depletion. Alternatively, the infant’s entire lower torso can be placed inside a plastic bowel bag. Regardless of the method, the initial therapeutic goal is to provide rapid, effective temporary coverage of the viscera. Adequate support of the herniated viscera must be provided to prevent intestinal ischemia. This can be done by placing the baby on his or her side, and placing support under the intestines. With large omphaloceles, the position of the infant’s liver and viscera may impair venous return from the inferior vena cava when the infant is supine, and these infants may preferentially require a left-side-down position to maintain normal hemodynamics. Intravenous dextrose and broad-spectrum antibiotics are administered. Infants with gastroschisis will have higher intravenous fluid requirements to maintain euvolemia. If the infant is not delivered at a center where definitive surgical care can be provided, urgent transport should be arranged.

Gastroschisis. Once the infant with gastroschisis has been stabilized, measures are taken to secure the viscera and, if possible, correct the abdominal wall defect. One option is to take the infant to the operating room, where reduction of the herniated viscera with primary fascial closure of the abdominal wall is an achievable goal in approximately 60% to 70% of infants with either gastroschisis. Gentle but definitive stretching of the abdominal wall is performed, and proximal decompression of the bowel is maintained with orogastric decompression. The defect may need to be enlarged to evaluate the intestinal tract fully and/or reduce the viscera into the abdominal cavity. The limiting factor in primary closure of a congenital abdominal wall defect is the increased intra-abdominal pressure generated by the reduction of the herniated viscera. Increased intra-abdominal pressure can lead to abdominal compartment syndrome. Features of neonatal abdominal compartment syndrome include impaired venous return caused by compression of the inferior vena cava, reduction of splanchnic blood flow leading to mesenteric ischemia, and respiratory compromise secondary to impaired diaphragmatic excursion. Intraoperative measurement of intragastric or intravesical pressure, end-tidal CO₂, central venous pressure, or regional oximetry may be helpful in determining the safety of primary abdominal wall closure. If the herniated viscera cannot be reduced primarily, the viscera is placed in a constructed Silastic pouch or performed silo. Daily partial reduction of the viscera within the silo is performed. This technique allows gradual reduction of the herniated viscera into the abdominal cavity, and complete reduction is usually obtained within 3 to 7 days. The infant is returned to the operating room for removal of the temporary silo with delayed primary closure of the abdominal wall defect (Fig. 103-5). Alternatively, a large abdominal wall defect may be effectively covered with abdominal skin flaps, with delayed repair of the ventral hernia months to years later (gross closure).

In some centers, all babies with gastroschisis are managed by placing a preformed silo at the bedside after the baby is born. Thereafter, the viscera is slowly reduced into the abdomen and eventual fascial closure is attained.¹⁴ Some studies caution that this practice may lead to longer ventilator and fluid requirements.^14,15 Another method that has been described in gastroschisis patients with noninflamed pliable intestines is to reduce the viscera with some sedation at the bedside, fold the umbilical cord stump over the skin closure, and place a pressure dressing over the defect.¹⁶ The use of the umbilical stump has been described even for patients requiring staged or silo closure.¹⁷ This method of closure has been shown to effect fewer days of mechanical ventilation in retrospective studies.^17–20

Omphaloceles. Given the high incidence of associated anomalies, infants with omphalocele should undergo diagnostic investigation, guided by the clinical presentation and physical examination. These studies include chest radiography, echocardiogram, and renal ultrasound, in addition to baseline blood work. Chromosomal analysis may be necessary. Until the decision is made with respect to the timing and method of repair, the omphalocele should remain covered and protected with a gauze dressing. If the omphalocele is ruptured or torn, immediate closure or coverage is necessary.

Closure of omphaloceles is dictated by the size of the defect, the amount of viscera extruded into the sac, and the abdominal domain. There is no standard definition of what constitutes a regular versus a giant omphalocele. Practically, a giant omphalocele has an abdominal wall defect larger than 4 cm, containing a portion of liver, and is difficult to dose primarily in the first days of life without physiologic compromise.

Omphaloceles with a small abdominal wall defect typically would have operative fascial closure with sac excision in the newborn period. Many techniques have been described to close giant omphaloceles including sac excision and temporary coverage with grafts, use of intraperitoneal tissue expanders,^21,22 and allowing the omphalocele sac to scar and then epithelialize in the latter technique.

The sac can be physically supported and left undisturbed, allowing epithelialization of the sac over several weeks to months. Antibiotic solutions or ointments are usually applied to control desiccation.^22–25 Delayed repair of the ventral hernia is required. This delay is particularly useful in the infant with a giant omphalocele and a small, underdeveloped abdominal cavity that prohibits primary closure.

Infants with repaired omphalocele usually have relatively prompt return of bowel function after definitive repair. In comparison, nearly all infants with gastroschisis have delayed intestinal function following closure. The use of total parenteral nutrition (TPN) is essential in the treatment of these infants because it allows nutritional support while the bowel inflammatory process resolves. It is not unusual for these infants to require up to 4 weeks after repair to have bowel function normalize, and time taken to achieve full enteral feeding is not affected by the use of erythromycin as a prokinetic agent.²⁶ Approximately 15% of infants with gastroschisis develop necrotizing enterocolitis (NEC), a diffuse, often life-threatening inflammatory complication of the neonatal intestinal tract.²⁷ In addition, infants with gastroschisis are at risk for nutrient malabsorption and intestinal dysmotility with inability to tolerate full enteral feeding. In particular, infants with gastroschisis and associated intestinal atresia may have pronounced intestinal dysmotility and may require long-term, sometimes lifelong, dependence on TPN for caloric intake.²⁸

Long-term outcome of infants operated on for gastroschisis or omphalocele is usually dependent on the morbidity and mortality of associated conditions rather than the abdominal wall defect itself. Surgical conditions such as undescended testicles, Meckel diverticulum, and adhesive small bowel obstruction are encountered with moderate frequency. Adhesive small bowel obstruction most commonly occurs in the first-year of life and requires operative management in the majority.²⁹ Most children with repaired abdominal wall defects enjoy satisfactory health and quality of life, although they have been reported to have a lower degree of physical fitness measured by exercise time and maximal oxygen consumption.³⁰

Umbilical Hernia

Anatomy and Embryology

Congenital umbilical hernia is the most common abdominal wall defect in infants and children. The umbilical ring begins to contract circumferentially after birth and normally is reinforced by the paired lateral umbilical ligaments (the obliterated umbilical arteries), the singular round ligament (the obliterated umbilical vein), the urachal remnant, and the transversalis fascia. Incomplete growth or impaired development of any one of these structures can lead to weakness at the umbilical ring and cause a congenital umbilical hernia.

Clinical Issues and Management

Congenital umbilical hernias generally do not pose significant problems during childhood. Rarely, an umbilical hernia presents with incarceration of intra-abdominal contents within the sac.³¹ Infants and children may also present with infection or drainage at the umbilicus from associated urachal or vitelline duct remnants. The incidence rate of congenital umbilical hernia has been reported to be 25% to 50% in black infants and 4% to 9% in white infants in the first few months of life.³² There is an increased incidence of umbilical hernia in premature infants, and there is a tendency for familial inheritance.

Diagnosis of umbilical hernia is usually made after separation of the umbilical cord remnant from the umbilicus and is often initially noted by parents or pediatrician. The size of the defect may vary from a few millimeters to several centimeters and is typically reducible and asymptomatic. Age and size of the defect are the most important factors determining spontaneous closure rates.³³ Many umbilical hernias spontaneously close within the first 2 to 3 years of life. Parents should be reassured that complications related to untreated umbilical hernia are rare. Given the high rate of spontaneous closure and the relatively asymptomatic nature of most umbilical hernias, operative repair is generally not performed during the first 2 years of life. Skin ulceration or an episode of incarceration should prompt earlier repair. Large defects with significant protrusion may necessitate surgery, and parents may desire repair if an older child appears to be self-conscious about the hernia.

Nearly all umbilical hernia repairs can be performed as outpatient surgical procedures. An incision is made along the umbilicus and the hernia sac is dissected free circumferentially. The sac is completely excised and primary fascial closure is performed. The umbilical skin is typically preserved and sutured to the fascial closure, and an acceptable cosmetic result is almost always achievable. Large umbilical hernias with redundant skin may require umbilicoplasty. The incidence of complications such as wound infection and recurrence is low.

Inguinal Hernia and Hydrocele

Anatomy, Embryology, and Pathophysiology

2 Inguinal hernias constitute one of the major surgical problems of infancy and childhood. Inguinal hernia repair is the most common elective general surgical procedure performed by pediatric surgeons. Three distinct anatomic types of inguinal hernias are observed in children: congenital indirect (99% of infants and children), direct (0.5%), and femoral (<0.5%). An indirect inguinal hernia is an abnormal, patent continuation of the peritoneum through the internal inguinal ring. The hernia sac originates lateral to the deep inferior epigastric vessels and descends along the spermatic cord within the cremasteric fascia. The sac can reside completely within the inguinal canal or descend through the external inguinal ring into the scrotum. A direct inguinal hernia originates medial to the deep inferior epigastric vessels and is external to the cremasteric fascia. The hernia sac protrudes directly through the posterior wall of the inguinal canal and can descend through the external inguinal ring and into the scrotum. A femoral hernia originates medial to the femoral vein and descends inferior to the inguinal ligament along the femoral canal. A femoral hernia never enters the scrotum or the labia.

The developing testicle is initially adjacent to the mesonephros and subsequently descends to the scrotum during the third trimester of gestation. The peritoneal extension that descends alongside the chorda gubernaculum of the testicle is called the processus vaginalis. A slightly higher incidence rate of right-sided indirect inguinal hernia is thought to reflect delay of right-sided testicular descent from the developing inferior vena cava and right external iliac vein. As the testicle descends into the scrotum, the processus vaginalis forms a serous covering around the testicle known as the tunica vaginalis. Normally, the patent processus vaginalis undergoes obliteration, closing the communication between the peritoneal cavity and the inguinal canal. A patent processus vaginalis can lead to a variety of anatomic conditions of the inguinal region (Fig. 103-6).

The incidence of patent processus vaginalis has been reported to be as high as 80% to 94% in newborn infants undergoing autopsy,³⁴ whereas in adulthood, the incidence is 20% to 30%. Infants with unilateral inguinal hernias have been found to have a patent contralateral processus vaginalis in 60% during the first few months of life. By the age of 2 years, 20% of these hernias were obliterated, and half of the remaining 40% became clinical hernias.³⁵ At least 30% of infants requiring placement of a ventriculoperitoneal shunt for hydrocephalus have been observed to have a patent processus vaginalis in the first few months of life, with a rapid decline in patency in older children.³⁶ These studies, along with contemporary use of laparoscopic exploration of the contralateral internal ring, demonstrate that although a patent processus vaginalis is common in infancy, there is some degree of obliteration that occurs with increasing age, and a patent processus vaginalis by itself does not constitute a clinical inguinal hernia.

Clinical Issues

Inguinal hernias occur in 1% to 3% of all children and in 3% to 5% of premature infants. There is no known inheritance pattern, but there is an increased incidence of inguinal hernia in children with connective tissue disorders such as Ehlers–Danlos syndrome and Marfan syndrome. There is a 6:1 predominance of males to females. At least 30% of children are younger than 6 months at the time of operative repair. Inguinal hernia more commonly presents as right-sided (56.2%) compared with left-sided (27.5%) or bilateral (16.2%).³⁷

Most infants and children have a history of an intermittent inguinal mass or bulge that may descend into the scrotum or labia. The hernia may become more pronounced during times of increased intra-abdominal pressure, such as crying or having a bowel movement. Most inguinal hernias in children reduce spontaneously or are reducible with gentle, manual pressure along the inguinal canal. Female infants may have an ovary and fallopian tube in the hernia sac, identified clinically as a firm, slightly mobile, nontender mass in the labia or the inguinal canal. Most parents or pediatricians give a characteristic history that is sufficient to warrant inguinal exploration, even in children in whom the hernia cannot be clinically demonstrated at the time of examination. Depending on institution and surgeon preference, infants and children with a strong history consistent with inguinal hernia and an equivocal clinical examination may be offered ultrasound or diagnostic laparoscopy to effectively confirm the diagnosis before groin exploration.³⁸

Incarceration is a common consequence of untreated inguinal hernia and presents as a nonreducible mass in the inguinal canal, scrotum, or labia.³⁹ Clinical symptoms and signs are related to the duration of incarceration. If the incarceration has been present for several hours, the infant may be inconsolable and have feeding intolerance, pain, abdominal distention, vomiting, and lack of flatus or stool, signaling complete intestinal obstruction. The affected groin may become quite edematous, and a reactive scrotal hydrocele may evolve. Elevation of the infant’s lower extremities with a pillow may help encourage spontaneous reduction. Attempts at manually reducing an incarcerated inguinal hernia should be performed by an experienced surgeon. If necessary, sedation to calm the infant before attempting manual reduction may be cautiously used. Ice packs should be avoided in infants and children. Following successful reduction of an incarcerated hernia, expedient elective repair of the hernia should be performed after the edema has subsided. If reduction of an incarcerated hernia requires several attempts and is difficult, overnight inpatient observation is warranted to rule out reduction of strangulated bowel; fortunately, this is an uncommon occurrence in the pediatric population. Inability to reduce an incarcerated hernia is a clear indication for urgent operative exploration and repair. Incarcerated inguinal hernia must be differentiated from an acute, noncommunicating hydrocele, or inguinal lymphadenitis. With acute hydrocele, it is usually possible to transilluminate the hydrocele and palpate normal cord structures above the scrotal mass. In addition, symptoms of bowel obstruction are absent with acute hydrocele. Acute lymphadenitis typically is associated with fever, erythema, and tenderness, and there may be a history of lower-extremity infection on the ipsilateral side. If the inguinal mass is not reducible and an incarcerated hernia cannot be excluded, urgent groin exploration is required.

Operative Considerations and Outcome

The diagnosis of inguinal hernia in an infant or a child is an indication for operative repair. The rationale for elective repair is to prevent the complications associated with incarceration. At least 71% of infants who require operative reduction of incarcerated inguinal hernia are younger than 11 months.⁴⁰ Therefore, an approach emphasizing timely elective repair of inguinal hernia is warranted, particularly during infancy. Delay of elective repair may be necessary in premature, extremely low–birth-weight (<1,500 g) infants and in children with other conditions such as congenital heart disease, pulmonary disease, infection, or metabolic disease.

Elective inguinal hernia repair in the pediatric age group is usually performed as an outpatient surgical procedure using general anesthesia, although spinal anesthesia is an effective alternative in selected high-risk infants.⁴¹ A regional caudal block or local inguinal nerve block using local anesthetic is useful to diminish perioperative pain and increase patient comfort. These techniques, along with the use of rapid-acting general anesthetics, allow the vast majority of children to be discharged home within hours of operation. Overnight observation and monitoring are required for high-risk infants and children with disorders that increase anesthetic risk for postoperative apnea.

Repair of pediatric inguinal hernia relies on high ligation of the hernia sac at the internal inguinal ring. Sensory nerves deep to the external oblique aponeurosis should be identified and preserved. Careful identification and dissection of the hernia sac from the vas deferens and the testicular blood supply must be performed. The vas deferens must be carefully dissected free from the sac, and direct handling or pinching of the vas with forceps is avoided. The absence of a vas deferens or a blind-ending vas may be observed in children with cystic fibrosis (CF). In female infants, opening the hernia sac to visualize the ovary and fallopian tube may help avoid inadvertent injury to these structures during suture ligation of the sac. The distal component of the hernia sac is opened widely, and any fluid in the sac is evacuated. If the internal inguinal ring is attenuated or enlarged, it can be repaired with a few sutures. Experience with laparoscopic inguinal hernia repair using purse–string suture closure of the patent internal ring without direct inguinal exploration has been described.⁴² The testicle is returned to its scrotal position by gentle traction on the gubernaculum, and the spermatic cord is carefully aligned along the inguinal canal. Postoperative pain is managed with oral acetaminophen for 24 to 48 hours; older children may require postoperative narcotics. In addition, abnormalities of the vas deferens may be associated with genitourinary anomalies. A renal ultrasound should be permed to rule out kidney malformations.

Operative exploration of the asymptomatic contralateral groin remains controversial but is often performed in infants younger than 2 years because of the reported 60% to 70% incidence of a patent processus vaginalis on the opposite side.⁴³ In a survey of the surgical section of the American Academy of Pediatrics, 65% of the respondents perform contralateral exploration in male patients younger than 2 years, and 84% perform exploration for female infants up to 4 years of age.⁴⁴ Direct visualization of the contralateral groin can be performed using a laparoscope inserted either through the umbilicus or through a side-viewing laparoscope inserted through the hernia sac. Experience with diagnostic laparoscopy demonstrates that approximately one-third to one-half of children have a patent processus vaginalis on the contralateral, asymptomatic groin, with higher rates in infants younger than 1 year.^45,46 This approach avoids unnecessary contralateral groin exploration in about half of all children who undergo surgery for unilateral inguinal hernia. However, the presence of a patent processus alone does not necessarily translate into a clinically significant hernia, and via systematic review, the reported risk of developing a metachronous contralateral inguinal hernia following open unilateral hernia repair in children is 7.2%.⁴⁷

The major risk of inguinal hernia repair in infants and children is related to general anesthesia. Complications in pediatric inguinal hernia repair include wound infection, injury to the vas deferens or testicular vessels, injury or displacement of the testicle, and recurrence. Fortunately, all these complications are infrequent. The overall complication rate is higher for children requiring emergent operation for incarcerated or strangulated hernia. Recurrent inguinal hernia following elective repair is unusual and may be an indication of an underlying connective tissue disorder such as Ehlers–Danlos syndrome.

Hydrocele

A hydrocele is a fluid collection that resides in the tunica vaginalis in the scrotum or the processus vaginalis in the inguinal canal. A hydrocele may be present at birth, or it may occur acutely as a result of an incarcerated hernia or torsion of the appendix testis. On examination, a hydrocele transilluminates with a bright handheld light. A hydrocele is described as either communicating or noncommunicating depending on whether there is direct patency between the hydrocele and the peritoneal cavity. A history of intermittent fluctuation in the size of the hydrocele is generally diagnostic for communicating hydrocele. A communicating hydrocele is synonymous with a patent processus vaginalis, and, therefore, a communicating hydrocele is treated operatively in the same fashion. In male patients, a hydrocele of the cord is a collection of fluid in the processus vaginalis separate from the tunica vaginalis. In female patients, fluid trapped in the processus vaginalis is considered a hydrocele of the canal of Nuck. In noncommunicating hydrocele, the isolated fluid collection is typically asymptomatic and tends to spontaneously resolve before age 12 months. Operative management of noncommunicating hydrocele is usually reserved for lesions that persist after this age, acute enlargement of the hydrocele, or if there is any question of communication.

GASTROINTESTINAL DISORDERS

Neonatal Intestinal Obstruction

3 A variety of congenital anatomic defects, inherited metabolic diseases, and acquired physiologic disorders may present as intestinal obstruction in a newborn. Neonatal intestinal obstruction is characterized clinically by bilious emesis and is often associated with abdominal distention. Bilious emesis in a neonate must be considered to be acute mechanical intestinal obstruction until proven otherwise. Emergent surgical evaluation is warranted for any newborn with bilious emesis. Table 103-2 provides differential diagnoses for neonatal intestinal obstruction along with salient features of the history, physical examination, and diagnostic studies.

The clinical presentation of neonatal intestinal obstruction depends, in part, on the site of obstruction and the age of the infant. Clinical examination of the infant typically provides the surgeon with a preliminary diagnosis and helps guide further diagnostic studies. Abdominal distention is a characteristic physical finding with distal bowel obstruction, whereas the abdomen may be flat in proximal obstruction. The presence of bile in the gastric contents or stool provides clinical evidence of the location of an obstruction relative to the ampulla of Vater. Bilious emesis in an infant or child should be considered an anatomic obstruction requiring emergent surgical evaluation. An infant with bilious emesis who has already passed meconium and has tolerated feeding is unlikely to have intestinal atresia and more likely to have intestinal malrotation with midgut volvulus. If volvulus is suspected, emergent evaluation must be performed to diagnose and prevent catastrophic bowel injury or death.

Definitive diagnosis of neonatal intestinal obstruction may often be made by physical examination and readily available radiologic studies. Incarcerated inguinal hernia is an important cause of neonatal bowel obstruction, and examination leads to a straightforward diagnosis. Some congenital conditions have clearly recognizable features and may be associated with anatomic intestinal obstruction. For example, infants with trisomy 21 have a higher probability of having duodenal atresia or Hirschsprung disease than the general population. An approach to imaging the neonate suspected of having an intestinal obstruction is to obtain a plain abdominal radiograph, followed by either a contrast enema or an upper gastrointestinal series. Plain films of the newborn abdomen can be extremely useful because swallowed gas acts as a contrast agent. For example, duodenal atresia gives rise to a dilated, gas-filled stomach and duodenum proximal to the obstruction; the remainder of the bowel remains gasless, giving rise to the “double-bubble” appearance on plain films. Other causes of proximal intestinal obstruction may lead to a microcolon on contrast enema, which is a small, unused but otherwise normal colon. If a retrograde contrast enema does not pass into the dilated segment of bowel, an upper gastrointestinal series may be useful to identify a more proximal obstruction. Upper gastrointestinal series is also the most useful diagnostic test for intestinal malrotation.

Several medical conditions of the newborn appear clinically similar to mechanical intestinal obstruction (see Table 103-2). In particular, bilious emesis from ileus secondary to neonatal sepsis is not uncommon. Congenital hypothyroidism is an infrequent and medically treatable condition that can produce delayed intestinal motility that mimics mechanical intestinal obstruction.

Intestinal Atresia or Stenosis

Embryology and Anatomy

The embryonic intestine undergoes segmental development during the third week of gestation. The septum transversum demarcates the developing foregut from the midgut. The midgut can be considered a tubular structure that progressively undergoes several predictable, developmental stages: (a) elongation; (b) herniation from and reduction into the coelomic cavity; (c) rotation; and (d) fixation of the mesentery to the posterior body wall.

Several different types of intestinal atresia are clinically observed (Fig. 103-7). Type I atresia is an intraluminal web or diaphragm that can either be complete or fenestrated with intact seromuscular layers of bowel. Type II and IIIa atresia are believed to be a result of in utero mesenteric vascular accidents. Experimental interruption of the fetal mesenteric blood supply in utero leads to this type of atresia.^48,49 Type IIIb atresia, also known as the apple-peel or Christmas tree deformity, has complete mesenteric discontinuity, with the distal bowel concentrically surrounding a singular mesenteric blood supply. Type IV atresia has multiple segmental areas of discontinuous bowel. Type IIIb and IV atresia are thought to be consequences of major and multiple fetal mesenteric vascular interruption.

At least 90% of infants with congenital intestinal obstruction of the small bowel have complete atresia, whereas the remaining children have either stenoses or fenestrated intraluminal webs. The most common location is the distal ileum, and multiple areas of atresia are discovered in 3.6% to 20% of these infants.³⁸ Infants with fenestrated intraluminal webs may have a small, often eccentric opening only millimeters in diameter. These infants may not have obstructive symptoms until the introduction of solid food at 6 to 12 months of age and present with feeding intolerance, failure to thrive, or abdominal pain.

Congenital colonic atresia is a distinctly unusual condition. In a contemporary series of 277 infants treated with intestinal atresia, only 21 children had colonic atresia.⁵⁰ Similar to small bowel atresia, colonic atresia is believed to reflect fetal mesenteric vascular injury. Given the distal nature of colonic atresia, initial feeding may be well tolerated and definitive diagnosis may be delayed for several days. The diagnostic evaluation and surgical treatment of colonic atresia is identical to the approach used for small bowel atresia. Colonic atresia may be associated with abdominal wall defects, skeletal or cardiac defects, or coexisting intestinal atresia.

Clinical Presentation

The actual incidence rate of congenital intestinal atresia is unknown. Reported estimates in the United States are 3.5 to 3.75 cases per 10,000 total births.⁵¹ Infants with jejunal or ileal atresia have a low incidence rate of significant associated anomalies. Approximately 10% of infants with gastroschisis have intestinal atresia or stenosis secondary to mechanical interruption of the mesenteric vascular supply.

Detection of maternal polyhydramnios on routine prenatal ultrasound screening can be an indication of proximal bowel obstruction caused by the interruption of normal amniotic fluid absorption in the fetal gut.⁵² Following delivery, the classic clinical presentation of intestinal atresia is bilious emesis, abdominal distention, and failure to pass meconium. The degree of abdominal distention depends on the site of obstruction, the infant’s age, and the efficacy of proximal decompression. Abdominal distention may be absent with proximal intestinal atresia. Distal intestinal atresia may lead to abdominal distention with visible or palpable intestinal loops on examination. Rectal examination and evaluation of stool character remains important when intestinal obstruction is suspected.

Diagnosis

Following history and physical examination, plain radiographic abdominal films should be obtained. Plain films in jejunal or ileal atresia demonstrate marked gaseous distention of the proximal intestine with gasless distal small bowel and colon. Haustral markings are normally not apparent in the neonatal colon, and, therefore, discrimination between small bowel and colon in the newborn is difficult without intraluminal contrast. A contrast enema is generally obtained to confirm the diagnosis of jejunoileal atresia. A diminutive, unused but otherwise normal microcolon is typical of proximal intestinal obstruction. The inability to reflux contrast into the proximal, dilated small bowel segment is diagnostic for congenital intestinal obstruction. This radiographic finding, in conjunction with the clinical setting, warrants operative exploration. An upper gastrointestinal series is unnecessary and may increase the risk of further emesis and aspiration in the newborn with obstruction. Incomplete obstruction from a fenestrated intraluminal web may require more sophisticated imaging techniques such as catheter-directed enteroclysis.

Treatment

Anatomic lesions causing neonatal intestinal obstruction require operative treatment. Whereas malrotation with midgut volvulus requires emergent diagnostic workup and operative intervention, obstruction resulting from intestinal atresia is generally not associated with life-threatening physiologic disturbances. Therefore, initial treatment is aimed at treating any other associated problems, confirming diagnosis, and preparing the infant for an operation. During this period, the infant should always have an orogastric or nasogastric tube in place to provide proximal decompression of the obstructed bowel.

The operative strategy in treating intestinal atresia is to restore gastrointestinal tract continuity while preserving as much intestinal length as possible. The operation is straightforward and an end-to-end or end-to-oblique (end-to-back) anastomosis is typically performed (Fig. 103-8). Short-segmental bowel resection and excision of an intraluminal web or diaphragm are done when necessary. Visual inspection and instillation of intraluminal saline or air to exclude distal atresia or web prior to anastomosis is important to evaluate patency of the downstream bowel. The size discrepancy between the proximal and distal bowel is usually considerable, and delayed postoperative bowel motility is common. Some surgeons advocate the use of technical procedures to improve emptying of the proximal bowel by reducing overall bowel diameter. These procedures include resection, plication, and tapering enteroplasty. Complex atresia associated with apple-peel deformity or multiple segmental atresias may require multiple serial anastomoses to preserve as much bowel length as possible. The ileocecal valve is preserved whenever possible, allowing improved tolerance of enteral nutrition in infants with limited small bowel length. It is estimated that approximately 40 cm of small bowel without an ileocecal valve, compared with 15 to 20 cm with an ileocecal valve, is sufficient for long-term enteral feeding tolerance in the neonate.⁵³ Contemporary management of colonic atresia includes primary anastomosis when technically possible.

Results and Outcome

Currently, the overall survival rate for infants treated for intestinal atresia or stenosis (including duodenal atresia) exceeds 93% in most large series.^50,54 Mortality in these infants is generally related to cardiac anomalies, birth weight less than 2 kg, and associated congenital anomalies.⁵⁵ Infants with a limited amount of intestinal length for nutritional absorption (short bowel syndrome with less than 40 cm) usually require long-term TPN and are at moderate to high risk for sepsis and liver injury. Infants with normal gastrointestinal length may still have prolonged intestinal dysfunction and dysmotility for several weeks.

Congenital Duodenal Obstruction

Causes of duodenal obstruction in the newborn include duodenal atresia or stenosis, duodenal intraluminal web, and annular pancreas. Because of the common embryologic basis, clinical presentation, and treatment, these entities are considered jointly.

Embryology and Anatomy

The duodenum is derived from both the caudal segment of the foregut and the cranial segment of the midgut. Duodenal development is intimately related to the developing pancreaticobiliary system. The fetal pancreas arises from paired dorsal and ventral foregut diverticula during week 6 of gestation. The dorsal anlage gives rise to the body and tail of the pancreas as well as the main pancreatic duct. The ventral anlage migrates 180 degrees to fuse with the dorsal gland, forming the uncinate process and the distal portion of the duct of Wirsung (Fig. 103-9). An annular pancreas is characterized by glandular persistence surrounding the duodenum at the site of the embryonic ventral anlage. It is invariably associated with intrinsic duodenal obstruction, and a patent accessory pancreatic duct is common (Fig. 103-10).⁵⁷

It is believed that congenital duodenal obstruction results from abnormalities of pancreatic development, failure of duodenal recanalization, or vascular compromise to the duodenum. Duodenal atresia may occur with or without seromuscular continuity, and an intraluminal duodenal web may occur with or without fenestration. The most frequent location for duodenal atresia is in the descending duodenum distal to the ampulla of Vater. Most series report a 5% to 10% incidence of duodenal atresia proximal to the ampulla, giving rise to nonbilious gastric contents and emesis. Another important variant is a periampullary web projecting distally into the duodenal or jejunal lumen, forming a “wind-sock” deformity (Fig. 103-11). In this instance, the ampulla must be clearly identified before excision and repair because of the proximity of the ampulla to the web.

Clinical Presentation

The incidence rate of congenital duodenal obstruction is estimated to be about 1 in 6,000 to 10,000 births.⁵⁸ About 30% of these infants have trisomy 21.⁵⁹ Infants born with duodenal atresia should be examined with a high degree of suspicion for trisomy 21 and undergo routine karyotype analysis. Other associated anomalies such as congenital heart disease, genitourinary tract malformations, and musculoskeletal disorders are common in these infants, and appropriate preoperative workup is necessary.

Congenital duodenal obstruction most commonly presents in the first 24 to 48 hours of life with feeding intolerance and bilious emesis; duodenal obstruction proximal to the ampulla of Vater results in nonbilious emesis. On physical examination, infants with untreated duodenal obstruction may have a palpable epigastric mass, and gastric peristaltic waves may be visible. The collapsed and unused distal small intestine typically does not produce diffuse abdominal distention. Partial duodenal obstruction from a fenestrated web may not produce symptoms in the newborn period, and delayed diagnosis is common.

Diagnosis

Prenatal diagnosis of duodenal atresia is possible given contemporary fetal ultrasound techniques. Following birth, infants with suspected duodenal atresia should obtain plain abdominal radiographs. The classic radiographic finding of duodenal atresia is a double bubble from the air-filled stomach and duodenum (Fig. 103-12). In complete duodenal obstruction, no gas is seen distal to the duodenum; in this setting, the plain film is sufficiently diagnostic that no further imaging of the gastrointestinal tract is necessary. If there is incomplete obstruction, gas may be seen distally in the small or large intestine. Infants with suspected incomplete obstruction at the duodenal level may have either a fenestrated web or volvulus secondary to malrotation. Given the need for emergent operative intervention in malrotation with acute volvulus, an urgent upper gastrointestinal series with contrast should be strongly considered to exclude a neonatal surgical emergency. Importantly, all anatomic lesions causing neonatal duodenal obstruction require operative repair using a similar approach.

Treatment

Following expedient treatment of any associated life-threatening medical conditions and preoperative evaluation, the operative goals are to restore gastrointestinal continuity without sacrificing intestinal length or absorptive surface area. Because most lesions causing congenital duodenal obstruction are near the ampulla of Vater, great care must be exercised in treatment to avoid inadvertent injury to the ampulla or the pancreas.

Congenital duodenal atresia is treated by duodenoduodenostomy. Duodenal obstruction secondary to annular pancreas is also treated by duodenoduodenostomy. Direct division of annular pancreas is not performed because this does not address the underlying intraluminal duodenal obstruction, and there is significant risk of injury to the accessory pancreatic duct (see Fig. 103-10).

Duodenoduodenostomy is performed by making a transverse incision in the dilated, proximal duodenum and a longitudinal incision in the unused, downstream duodenum. The lumens are sutured together to form a diamond-shaped anastomosis (Fig. 103-13).⁶⁰ Downstream duodenal patency should be demonstrated by passing a catheter or infusing saline or air distally to avoid overlooking synchronous distal intestinal atresia. Successful and efficacious laparoscopic duodenal atresia repair has also been reported.⁶¹

Duodenal webs are excised through a longitudinal duodenotomy. The wind-sock duodenal web must be clearly identified because the visible transition from the distended, proximal duodenum to the small, downstream duodenum may be several centimeters distal to the base of the web. The ampulla of Vater must be unequivocally identified before duodenal web excision to avoid injury. Closure of the longitudinal duodenotomy is performed transversely to avoid narrowing of the duodenum.

There is usually great size discrepancy between the dilated, proximal pouch and the distal duodenal lumen, leading some surgeons to advocate procedures designed to reduce the diameter of the proximal duodenum in an effort to facilitate improved postoperative bowel motility. The efficacy of these procedures, which include tapering duodenoplasty and duodenal plication, has been described in anecdotal fashion without randomized comparison.

Results and Outcome

After successful operative repair of duodenal atresia or stenosis, delayed gastric emptying is common and typically manifests as enteral feeding intolerance. Patience and persistence are essential during the postoperative period. Surgical outcomes after repair of congenital duodenal obstruction are excellent,^59–62 with perioperative survival exceeding 95%. Perioperative mortality is generally related to other congenital anomalies and, in particular, congenital heart disease in infants with trisomy 21. Other late problems may be encountered that reflect gastroduodenal motility issues such as poor gastric emptying, gastroesophageal reflux, and duodenal dilatation. These symptoms may appear several months to years following repair and, therefore, long-term surgical follow-up remains important.

Anorectal Malformations (Imperforate Anus)

Embryology

By week 5 of gestation, the fetal cloaca is identifiable with the adjacent hindgut, allantois, and vestigial tailgut (Fig. 103-14). The mesoderm of the urorectal septum extends caudally to fuse with the cloacal closing plate. Fusion of the lateral cloacal ridges completes division of the cloaca into the rectum and the urogenital sinus. The caudal aspect of the urorectal septum forms the perineal body. The anal membrane normally ruptures during week 8 of gestation, completing the patency of the distal rectum to the skin. Further development of the urogenital sinus leads to the formation of the urethra and the bladder. In female infants, the uterus and the proximal vagina develop from the müllerian ducts. The diverse anatomic variation observed with anorectal malformations is thought to reflect anomalous or interrupted development of these structures during normal embryogenesis.

Anatomy and Classification

The normal anatomy of the anus and the rectum is reviewed in previous chapters. Normally, the rectum descends to the perineum and ultimately to the anal orifice through a striated muscle complex in the pelvis resembling a funnel. The striated muscle complex is under voluntary control and is responsible for providing fecal continence (Fig. 103-15). Contiguous portions of the levator ani, the external sphincter, and the puborectalis muscles compose the striated muscle complex. These anatomically indistinct components of the muscle complex act together to provide control of defecation. The concept of the striated muscle complex and anatomic relationships leading to normal fecal continence with respect to anorectal malformations has evolved from both clinical and anatomic data as described by Peña.⁶³

Because of the variety of anorectal malformations observed, different classification systems have been proposed in an attempt to characterize the defects. A summary of the Wingspread Classification is provided in Table 103-3. This anatomically descriptive classification scheme is useful in planning the operative management of anorectal malformations.

In male subjects, the two most common anorectal malformations observed are low imperforate anus with a perineal fistula (Fig. 103-16) and high anorectal agenesis with a rectoprostatic urethral fistula (Fig. 103-17). Male patients without a visible perineal fistula are assumed to have high imperforate anus with a rectourethral fistula until proven otherwise. In female subjects, the most common malformation encountered is low imperforate anus with a fistula from the rectum to either the perineal body or the vaginal vestibule (Fig. 103-18). As these malformations result from developmental arrest at various times during migration of the urogenital septum, considerable anatomic variability exists in both male and female subjects.

A common anatomic feature of imperforate anus is incomplete rectal descent to the perineum. Consequently, the rectum is not completely within the striated muscle complex. The caudal portion of the striated muscle complex remains a solid mass of striated muscle, whereas the cephalad portion may be normally positioned circumferentially around the rectal pouch. In low imperforate anus, the rectum nearly reaches the perineum, and the configuration of the striated muscle complex surrounding the rectum more closely approximates normal. With high imperforate anus, less striated muscle surrounds the rectal pouch. All anorectal malformations are considered to have some component of striated muscle complex hypoplasia and dysfunction, although the physiologic effects are variable. Low anorectal lesions have a more favorable prognosis for fecal continence than intermediate or high lesions.

Classic delineation between low and high anorectal malformations is made anatomically at the pubococcygeal line. The vast majority of low lesions have associated perineal or vestibular fistulas. High imperforate anus has a blind-ending rectal pouch above the pubococcygeal line and, therefore, above the striated muscle complex (or levator ani).

Associated Anomalies

Associated anomalies in infants with anorectal malformations are common and may be found in more than 70% of patients. The VACTERL (vertebral, anal, cardiac, tracheal, esophageal, renal, and limb) association is important and requires consideration in any infant with imperforate anus. Vertebral anomalies are common and include sacral dysplasia and agenesis. Infants with sacral anomalies commonly have high imperforate anus and sacral nerve dysfunction that can lead to poor long-term fecal continence and neurogenic bladder. A variety of spinal cord malformations can also be observed in these infants, including tethered spinal cord syndromes and some myelodysplastic syndromes. During the neonatal period, these spinal lesions may be detected by using ultrasound or magnetic resonance imaging (MRI), and surgical treatment may be necessary within the first 8 to 18 months of life. Tracheoesophageal fistula with or without esophageal atresia is estimated to occur in about 10% of infants with anorectal malformations. Renal anomalies are the most common associated abnormalities with anorectal malformations and include both upper and lower tract conditions. Genitourinary screening in the form of a renal ultrasound and voiding cystourethrogram is routinely performed. Cardiac anomalies are common and screening echocardiography is clinically indicated. Limb abnormalities, in particular, involvement of the radius, complete the associated anomalies defined by the acronym.

Clinical Presentation

The incidence rate of anorectal malformations is estimated at 1 in 2,524 to 5,000 live births,⁶⁴ with a slightly higher rate in males. Careful examination of the neonatal perineum reveals the diagnosis. If unrecognized and left untreated, high imperforate anus eventually leads to signs and symptoms of complete bowel obstruction characterized by abdominal distention, feeding intolerance, and bilious emesis. Because of the nearly uniform rectourethral or rectovesicular fistula in males with high lesions, some of these infants will pass meconium or gas through the urethra during urination. In contrast, infants with low malformations typically pass meconium through a perineal or vestibular fistula within the first 24 hours of life. Occasionally, infants with large perineal fistulas are not diagnosed with an anorectal malformation until progressive constipation is noted weeks to months after birth.

In male infants, more than 95% of low malformations are associated with either a thin anal membrane or a fistula to the perineum or the scrotal raphe. The presence of a “bucket-handle” skin deformity at the presumptive anal dimple is also diagnostic of a low lesion. Infants with high malformations typically lack anal skin dimpling, have a flat gluteal contour, and may have little or absent contraction of the external sphincter with cutaneous stimulation. In female infants, 90% to 95% of low malformations have a perineal or vestibular fistula. In both male and female infants, a perineal fistula may not become apparent in the first 12 to 24 hours of life until meconium progresses distally through the rectum into the fistula.

Diagnosis

Because surgical treatment of a high or intermediate anorectal malformation is different from that of low lesion, a primary diagnostic goal is to determine whether an infant with imperforate anus has a high or low malformation. A secondary diagnostic goal is to determine the specific anorectal malformation as it relates to the rectourethral or rectovesicular fistula.

Clinical examination of an infant with low imperforate anus almost always reveals an external fistula to the perineum or the vestibule. The classic radiographic study of newborns with imperforate anus is the Wangensteen-Rice invertogram, with a lateral view of the pelvis obtained 12 to 24 hours after birth with the infant in a head-down position. This technique has been largely replaced by ultrasound-directed imaging.⁶⁵ Real-time ultrasound is currently well-accepted as an accurate method of determining the distal extent of the rectal pouch. Computed tomography (CT) imaging and MRI can be useful in evaluating the pelvic striated muscle complex in difficult cases and, in particular, cloacal malformations. MRI is also useful in evaluation of the distal spinal cord in these infants.

If there is a suspected perineal fistula or covered anus, diagnostic needle aspiration under anesthesia may be useful. Aspiration of meconium not only localizes the rectum or fistula but can also provide an estimation of the distance between the perineum and the rectum or the fistula. In general, low lesions are within 1 cm of the perineum. An infant not clearly found to have a low lesion by physical examination, radiographic studies, or examination under anesthesia should be considered to have a high anorectal malformation and treated accordingly.

A voiding cystourethrogram is generally the procedure of choice for defining the rectourethral or rectovesical fistula. In some instances, cystoscopy is a useful adjunct before repair of high imperforate anus. For example, an infant with a large rectourethral fistula may require cystoscopic guidance of a urinary catheter to avoid inadvertent placement of the catheter through the fistula and into the rectum.

Treatment

Imperforate anus by itself is not a life-threatening condition, and, in many instances, observation for 12 to 24 hours may help delineate the presence or absence of a fistula. The surgical management of anorectal malformations has been well described elsewhere⁶³ and a brief summary follows below.

Low Malformations. Definitive repair of most low anorectal malformations can be performed in the newborn period with perineal procedures that do not require diverting colostomy. Simple dilatation of the fistula or unroofing of a covered anus may relieve the anatomic obstruction. For more complex anal stenoses or anterior perineal fistulas, a formal perineal anoplasty may be required. A common perineal procedure performed is cutback anoplasty, in which the anterior fistula or anal orifice is opened posteriorly by dividing the perineum to the external sphincter. More complex alternative approaches may be preferred in female infants with low vaginal or anterior perineal fistulas. These lesions generally require circumferential mobilization of the anterior fistula with transposition to the center of the external sphincter. Anterior reconstruction of the perineal body is then performed. Transposition anoplasty is designed to position the neoanus within the center of the external sphincter and separate the neoanus from the vaginal introitus.

Intermediate and High Malformations. Infants determined to have an intermediate, high, or indeterminate anorectal malformation generally require diverting divided colostomy as initial surgical management. Care must be taken to ensure that the proximal diverting colostomy provides adequate length and mobility of the distal colon in anticipation of eventual anorectoplasty. A divided colostomy is preferred over a loop colostomy by many surgeons to provide maximal fecal diversion from the downstream rectourinary fistula. Following diverting colostomy, a distal contrast study into the rectal pouch can also define the fistula and delineate the position of the rectum relative to the perineum.

Anorectoplasty is generally performed when the infant is approximately 8 to 12 months of age. Many different approaches have been described, and considerable personal and institutional variation is common. No single approach has superior results, and all have technical merits and difficulties. The common surgical objectives in the treatment of anorectal malformations include (a) relief of the rectal obstruction; (b) creation of a new anus; (c) position the rectum as normally as possible within the striated muscle complex; and (d) divide the rectourinary fistula. In addition, preservation of the surrounding structures (prostate, urethra, seminal vesicles, vaginal wall) is essential.

For repair of high and intermediate anorectal malformations, the most widely used procedure in the United States is the posterior sagittal anorectoplasty described in detail by Peña.⁶³ The infant is placed prone and a posterior sagittal incision following the gluteal crease is used. The external sphincter and the striated muscle complex are divided posteriorly along the midline to expose the rectal pouch. A muscle stimulator is used to define and map the striated muscle complex and to confirm symmetric dissection along the midline. Typically, the rectal pouch can be adequately dissected by this approach to allow enough length to reach the perineum. Infrequently, a combined abdominoperineal approach is required. The mobilized rectal pouch is opened and the rectourinary fistula identified and closed directly. The rectal pouch is placed centrally within the striated muscle complex, which is reconstructed circumferentially around the rectum. The neoanus is centered within the external sphincter and the mucosa is sutured to the perineum.

Other accepted and practiced surgical approaches to imperforate anus include a sacroperineal approach as proposed by Stephens,⁶⁶ and an approach that uses components of endorectal dissection as attributed to Rehbein.⁶⁷ Both these surgical procedures are characterized by blind pull-through of the distal rectum to the perineum without direct visualization of the striated muscle complex. Experience with laparoscopic dissection and division of the rectourinary fistula with perineal pull-through reconstruction has been reported.⁶⁸ It appears that personal preference, experience and familiarity rather than differences in outcome dictate the selection of procedure. In general, diverting colostomy in all of these procedures is maintained until the anorectoplasty has completely healed, after which the colostomy is closed electively.

Results, Complications, and Outcome

Mortality following anorectoplasty is related to the presence of associated congenital anomalies other than imperforate anus. A careful review of 284 infants undergoing repair of anorectal malformations observed an 18.7% mortality,⁶⁹ suggesting that this group is at moderate to high risk for complications and death secondary to coexisting congenital anomalies.

Complications are similar to other gastrointestinal surgical procedures and include infection, leak, recurrent fistula, or anastomotic stricture. Leak or stricture formation is observed in 5% to 10% of infants undergoing tapering rectoplasty during posterior sagittal anorectoplasty. Anorectal strictures are treated by gradual postoperative anal dilatation for weeks to months. Recurrent rectourethral fistula or urethral stricture is uncommon.

Long-term functional outcome in infants with low malformations is generally good given the relatively normal descent of the distal rectum within the striated muscle complex. Infants with higher lesions have a less predictable prognosis and are much more likely to have difficulty with fecal continence. Currently, the outcomes appear to be independent of the type of surgical reconstruction performed and more related to anatomic patient factors, including degree of rectal descent, integrity of the striated muscle complex, and sacral innervation. Few or perhaps none of these children have completely normal bowel habits after operation. About half of the infants have acceptable to good results with episodic fecal soilage that can be improved with bowel management programs enemas and cathartics.^70–72 A comprehensive bowel management program is essential in preventing fecal impaction and subsequent motility dysfunction in the rectum. The remaining children require major adjustments in lifestyle secondary to fecal incontinence, chronic constipation, or fecal smearing and odor. In some instances, socially acceptable continence can be assisted by the use of daily antegrade enemas via a cecostomy or appendicostomy. In other situations, a permanent diverting colostomy may be desirable.

Necrotizing Enterocolitis

Pathophysiology

4 NEC is a neonatal disease characterized by an initial intestinal mucosal injury that may ultimately progress to transmural bowel necrosis. NEC is the most frequently encountered neonatal surgical emergency and a major cause of morbidity and mortality in the premature infant. Despite its frequency and extensive study, the pathogenesis remains obscure, and surgical treatment is directed largely at controlling the complications of intestinal necrosis. The development of NEC occurs in association with a variety of associated conditions, including perinatal stress, sepsis, respiratory failure, hypoxemia, hypotension, and congenital cardiac defects. In general, NEC is observed in the premature infant with multiple risk factors and potential etiologic events and conditions. Current clinical and experimental data support the concept that the pathophysiology of NEC remains enigmatic and multifactorial.

The intestinal mucosal injury observed in NEC is likely to be the end result of an ischemic insult in a susceptible host. Normally, the neonatal pulmonary and systemic vascular smooth muscle undergoes rapid structural and physiologic changes shortly after birth. The premature infant appears to be particularly vulnerable to vasoconstriction. With regard to NEC, it is hypothesized that hypoperfusion and ischemia of the premature neonatal intestinal tract may be the result of uncontrolled splanchnic vasoconstriction. This situation may be worsened in critically ill premature infants with low cardiac output states impairing oxygen delivery to the intestines.

A common characteristic of NEC is the host inflammatory response to the initiating mucosal injury. Experimental data are consistent with an important role for inflammatory mediators in the propagation of intestinal injury in NEC.⁷³ More than 90% of cases of NEC occur after the initiation of enteral feeding, and several studies document that the osmolarity or rate of initial feeding may be important. Although controversy exists, most neonatal centers now avoid rapid advancement of hyperosmolar enteral feedings and attempt to prevent excessive fluid volume in premature infants.^74,75 A multicenter, randomized controlled clinical trial using Bifidobacterium and Lactobacillus as a probiotic given with initial feeding demonstrated significant reduction in death from NEC in very low–birth-weight premature infants.⁷⁶

The most common site of involvement of NEC is the terminal ileum and right colon. NEC may be localized, segmental, or it may involve the entire gastrointestinal tract. Histopathologic examination of intestinal tissue from infants with NEC demonstrates submucosal edema, hemorrhage, and microvascular thrombosis leading to transmural necrosis. The histopathology of NEC resembles that of experimental intestinal ischemia, with areas of reversible mucosal injury adjacent to areas of transmural necrosis. Dissection of intraluminal gas through the injured mucosa leads to gas within the bowel wall, known as Pneumatosis intestinalis. The finding of pneumatosis intestinalis is a classic radiographic and pathologic feature of NEC. Initially, the gas may be localized in the submucosa or lymphatic vessels, but it may dissect into the muscularis, the portal venous tract, or into the subserosa. Intestinal perforation, inflammatory phlegmon, and diffuse peritonitis are common with advanced NEC.

Clinical Presentation

Over the past three decades, advancements in technology, prenatal care, and neonatology have improved overall outcome in premature infants who were previously unable to survive. In the United States alone, low–birth-weight infants (less than 2,500 g) account for more than 250,000 births a year. At least half of all infants with NEC are extremely low–birth-weight infants weighing less than 1,500 g. In a study of 302 infants with NEC treated over two decades, the average birth weight fell from 1,645 to 1,505 g, and in similar fashion, the mean gestational age fell from 32.4 weeks to 30.4 weeks.⁷⁷ NEC is estimated to occur in 1 to 3 of 1,000 live births and 30 per 1,000 low-birth-weight births.⁷⁸ NEC may also occur in term infants, and in this group, it has a tendency to involve the colon and may present without classic signs.⁷⁹ The actual incidence of NEC remains difficult to determine because the diagnosis is subjective; classic signs on physical examination and diagnostic imaging are not always uniformly present. The classic clinical signs of NEC include abdominal distention, feeding intolerance, bilious emesis, and either occult or gross blood in the stool. Gastrointestinal mucosal bleeding is present in the vast majority of cases (80% to 90%) but is rarely significant from a hemodynamic standpoint. On physical examination, abdominal tenderness with distention is common, and individual loops of thickened or fixed bowel may be palpable. Edema, erythema, crepitus, or discoloration of the abdominal wall suggests intestinal necrosis, perforation, or intra-abdominal abscess (Fig. 103-19). Hematochezia or guaiac-positive stool is typical. Systemic signs of inflammation and sepsis such as temperature instability, apnea, bradycardia, hypoxemia, acidosis, and thrombocytopenia are also common. The primary diagnostic goal during initial clinical evaluation is to determine whether irreversible, transmural intestinal necrosis is present. There is no single physical finding or laboratory test that makes this distinction.

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