Bowel Obstruction in the Newborn 

Bowel obstruction is one of the most common surgical emergencies in newborns. Successful management depends on timely diagnosis and appropriate intervention.^{[1, 2]} An accurate history and physical, corroborated by simple radiologic studies, usually leads the physician to the correct diagnosis. Fortunately, the outlook for babies undergoing surgery for intestinal obstruction is excellent.

A newborn who vomits bile may have ileus from sepsis or necrotizing enterocolitis, but proximal intestinal obstruction is a possible etiology. The physician must be vigilant and not overlook the following potential catastrophes:

• Volvulus (twisting) of the entire midgut can occur.
• In high jejunal atresia, where there is a sizable gap in the mesentery, the distal small bowel may wind around the ileocecal vessels like an “apple peel,” and the apical loop of intestine may twist and infarct.
• Congenital bands can compress and obstruct the intestine, or they can act as a fixed point around which a loop of intestine flips and obstructs both efferent and afferent ends, creating a closed-loop obstruction.
• Fluid-filled intestinal duplications may, like bulky ovarian cysts or a “floating spleen,” twist and cause strangulation obstruction (gut infarction).

In these circumstances, prompt surgical intervention is necessary to salvage the intestine and prevent the development of short-gut syndrome. Fortunately, the frequency of these notable circumstances is small.

Babies who have distal intestinal obstruction present with abdominal distention, delayed passage of meconium, and absence of transitional stools (meconium mixed with feces derived from ingested breast milk or formula).

Plain radiographs have a diagnostic pattern: multiple loops of dilated proximal small bowel and an absence of air in the distal colon and rectum. A Gastrografin (diatrizoate) enema is diagnostic and may be therapeutic in babies with meconium ileus or meconium plug syndrome, in which the intestine is obstructed by inspissated intraluminal contents.

The obstruction may be complete (atretic) or incomplete (stenotic).

Small bowel or colonic atresias may be accompanied by mesenteric defects, since the etiology in these instances is an in utero mesenteric vascular accident.

Congenital intestinal obstruction may also be caused by developmental failure in canalization, creating an intestinal lumen. These anatomic locations include the following:

• Esophagus
• Antrum (stomach)
• Duodenum
• Rectum: A shelflike partition may develop just above a normal-appearing anal canal.

Other anorectal anomalies are readily diagnosed by inspection of the baby’s perineum. The baby’s anus is imperforate; the rectum tapers, ending as a fistula to bladder, urethra, or scrotum in males and vagina or perineum in females.

In intestinal stenosis, the bowel and mesentery appear entirely normal; the obstruction is caused by an intraluminal mucosal partition that may or may not be fenestrated. Stenosis occurs in the esophagus, stomach (antrum), duodenum, small intestine, or anus.

Hypertrophic pyloric stenosis is termed “congenital,” but it is actually an acquired disorder. It is termed congenital to distinguish it from cicatricial stenosis caused by peptic ulcer disease.

In aganglionic megacolon, Hirschsprung disease, faulty intestinal innervation causes a functional obstruction that is manifested by a transition zone delimiting dilated intestine from intestine of normal caliber. Paradoxically, it is the aganglionic intestine that has the normal caliber, and before the etiology of the disease was understood, surgeons removed the dilated (normal) intestine, assuming that it was flaccid or atonic. The absence of ganglion cells, however, causes the opposite effect: aganglionic bowel can only contract, whereas peristalsis demands sequential contraction and relaxation.

The gastrointestinal (GI) tract arises from the yolk sac. At 3-4 weeks’ gestation, it becomes a distinct entity; however, a connection, the vitelline (omphalomesenteric) duct, may persist as a Meckel diverticulum. The alimentary tube is divided into 3 sections on the basis of its blood supply: foregut, midgut, and hindgut.

The foregut includes the following:

• Esophagus, stomach, and duodenum - These are vascularized by multiple sources
• Thyrocervical, intercostal, celiac axis, and superior mesenteric vessels

The midgut includes the following:

• Jejunum and ileum
• Ascending and proximal transverse colon - These are supplied by the superior mesenteric vessels

The hindgut includes the following:

• Distal colon - This is supplied by the inferior mesenteric vessels
• Rectum - This is supplied by the internal iliac vessels

Foregut anomalies

Duodenal atresia involves a pathophysiologic mechanism that is different from the one that causes atresias in other parts of the intestine. It is believed to result from a failure of canalization of the duodenal lumen. Before 8 weeks’ gestation, the duodenum is solid; vacuoles then form and coalesce to create a lumen. If this process is incomplete, an atresia or a web may develop.

A duodenal web is a band of mucosa that obstructs the duodenal lumen. Usually, webs have perforations; thus, the obstruction is incomplete. Occasionally, they may stretch distally within the lumen of the duodenum like a windsock. A surgeon must guard against assuming that the web originates where the duodenum changes in caliber. A tube pushed through a gastrostomy into the duodenum tents the duodenal wall at the site of the web’s origination; this is where the duodenum should be opened to excise the web.

Duodenal atresia may be associated with an annular pancreas, in which a band of pancreatic tissue encircles the duodenum.

Midgut anomalies

At 6-10 weeks’ gestation, growth of the midgut outstrips the capacity of the abdominal cavity, and the midgut is extruded into the extracoelomic space. When the peritoneal cavity has sufficiently grown, the midgut returns and rotates around the axis of the superior mesenteric vessels; the duodenum passes under the superior mesenteric vessels, and the colon passes over them. This establishes the C loop of the duodenum and the rectangular course of the colon. Malrotation results when the GI tract fails to complete this process.^[3]

The portions of the intestine that are fixed to the retroperitoneum include the duodenum and the ascending colon, as well as the hepatic flexure, the splenic flexure, and the descending colon. This arrangement maximizes the base of the midgut mesentery, extending from the left upper quadrant (ligament of Treitz) to the right lower quadrant (ileocecal valve).

Without normal rotation of the intestine, the colon remains medial to the duodenum and the peritoneal bands; attaching the ascending colon to the retroperitoneum obstructs the duodenum. These are called Ladd bands in honor of the surgeon who developed the operation to correct this anomaly.^[4] Without fixation of the mesentery to the retroperitoneum, the superior mesenteric vascular pedicle retains a narrow base; hence, it is liable to twist during peristalsis, causing midgut volvulus.

Jejunoileal atresia is a condition acquired during fetal development and not a preprogrammed embryonic anomaly. In their classic work on fetal dogs, Louw and Barnard elucidated the pathophysiology of jejunoileal atresia.^[5] The extent of intestinal loss and the appearance of the atretic intestinal segment varied according to the timing and degree of the disruption of the mesenteric blood supply.

Atresias may be single or multiple. Interruption of the main superior mesenteric blood supply results in atresia of the jejunum and proximal ileum; the distal ileum is preserved because of retrograde blood flow from the ileocolic vessels. Other abdominal conditions occurring in utero, such as gastroschisis or intussusception, may be associated with intestinal atresia as a result of kinking, stretching, or other conditions that disrupt the blood flow to the fetal bowel.

Meconium ileus is the earliest manifestation of cystic fibrosis, an autosomal recessive condition characterized by abnormalities in cellular membrane physiology and chloride ion transport that contribute to progressive respiratory failure, derangements in cellular secretory patterns, and diminished mucosal motility. Of newborns with cystic fibrosis, 10-20% present with meconium ileus, an association first described by Landsteiner in 1905.^[6]

Meconium plug syndrome refers to inspissated meconium that obstructs the colon; it may signal Hirschsprung disease but not cystic fibrosis. Conditions that predispose to dysmotility of the neonatal bowel (eg, maternal preeclampsia, maternal diabetes mellitus, maternal administration of magnesium sulfate, prematurity, sepsis, and hypothyroidism) may be responsible for the formation of the meconium plug. A contrast enema can be both diagnostic of and therapeutic for this condition.

Hirschsprung disease, first described in 1886 by Harold Hirschsprung, is a disorder of the neuroenteric pathways in the distal colon that results in a bowel that is tonically contracted. The normal bowel, in response to an antegrade peristaltic wave, reflexively relaxes downstream, allowing propagation of the peristaltic wave. This reflex is controlled by neuroenteric ganglion cells, which are present in the submucosal layer of the intestine and migrate from the neural crest distally along the bowel to reach the rectum at about 7-10 weeks’ gestation.

Hirschsprung disease is congenital absence of neuroganglion cells; consequently, the peristaltic relaxation phase is not distally conducted to the affected intestine, which does not appropriately relax, causing a functional obstruction.

Because of the antegrade embryonic migration of ganglion cells, Hirschsprung disease usually affects a continuous segment of bowel that extends from the rectum proximally to the level of normal ganglionated bowel. This is termed the transition zone. The extent of the aganglionic segment varies with each patient.

Hindgut anomalies

At 4-6 weeks’ gestation, the hindgut separates into the urogenital sinus and the anorectum, which then undergoes canalization. The distal third of the anus develops from ectoderm and becomes the anal pit, whereas the proximal portion of the anal canal is derived from mesoderm. An anal membrane covers the canal until 8 weeks’ gestation, when it perforates and becomes a patent anus. Imperforate anus results if this sequence of events improperly occurs.

Duodenal stenosis, duodenal atresia, and annular pancreas result from aberrations of foregut formation. Malrotation and jejunal and ileal atresia arise from maldevelopment of the midgut. Meconium ileus involves the distal ileum. Hirschsprung disease (aganglionic megacolon), meconium plug syndrome, and imperforate anus involve the hindgut. Enteric duplications occur in all 3 locations. (See Pathophysiology.)

Genetic factors

Congenital anomalies, such as trisomy 21 (40% of patients), imperforate anus, and congenital cardiac disease, are present in 50% of babies with duodenal atresia. Chromosomal anomalies are rare (< 1%) in babies with jejunoileal atresia.

The gene for cystic fibrosis is carried by as many as 4% of Ashkenazi Jews and 1% of people of Asian descent. Since 1988, when the genetic mutation that causes cystic fibrosis was localized to q31.2 locus on chromosome 7, more than 1400 mutations have been identified in this gene, which contains 230,000 base pairs and codes for a protein called cystic fibrosis transmembrane conductance regulator (CFTCR).^[6]

Abnormalities in CFTCR disrupt membrane ingress and egress of the chloride ion, which subsequently affects sodium transport as well. The meconium of affected babies is thick and sticky; this, coupled with the poor motility of an immature intestine, leads to intraluminal obstruction of the terminal ileum. A contrast enema reveals the characteristic finding of microcolon resulting from the proximal obstruction.

The genetic defects responsible for Hirschsprung disease consist of abnormalities on more than 1 chromosome (termed oligogenic inheritance) and include the RET proto-oncogene, located at chromosome 10q11.21. In Hirschsprung disease, RET interacts with a protein termed EDNRB, encoded by the gene EDNRB, which is located on chromosome 13.

Six other genes are associated with Hirschsprung disease, including GDNF on chromosome 5, EDN3 on chromosome 20, SOX10 on chromosome 22, ECE1 on chromosome 1, NTN on chromosome 19, and SIP1 on chromosome 2. Variations in RET and EDNRB must coexist for Hirschsprung disease to develop; however, the specific mechanism is not yet clear.

Recently, syndromic cases of Hirschsprung disease (associated with other defects of the autonomic nervous system) were shown to be caused by mutations in the homeobox gene PHOX2B. Mutations in RET and related signaling pathways and modifier genes on 3p21, 9q31, and 19q12 may lead to a failure of migration of the enteric neural crest cells during fetal development. Hirschsprung disease may be a model for understanding other disorders of bowel motility.

The incidence of malrotation of the midgut with clinical symptoms is 1 case per 6000 newborns. As many as 1 in 100 newborns have some asymptomatic anomaly of fixation, rotation, or both. It also occurs with congenital diaphragmatic hernia, gastroschisis, and omphalocele. Obstructive symptoms usually manifest during the first month of the life (50% of cases), and 90% of cases occur before the end of first year; however, in many instances, diagnosis is delayed until adulthood.^[7]

Duodenal obstruction from an atresia or web affects as many as 1 in 6,000-10,000 infants. Duodenal atresia is present in 4% of infants with trisomy 21. In this context, a congenital heart defect is often present. Atresia of the jejunum or ileum occurs more frequently (1 case per 1500 births).

Cystic fibrosis, which occurs in 1 infant per 3000 live births, is reported in 10-20% of babies with meconium ileus.^[8] It is the most common genetic disease in people of European origin.

Hirschsprung disease affects 1 in 4500-7000 newborns; it is more common in white infants and affects males 4 times more frequently than females. Hirschsprung disease is hereditary in approximately 12.5% of patients; this subset of patients typically has involvement of the entire colon (total colonic aganglionosis).

Isolated imperforate anus has an incidence of 1-3 cases per 10,000 births, and a female predominance is observed. Administration of folic acid during pregnancy has been shown to reduce the incidence of imperforate anus to 1 case per 10,000 births.

The morbidity and mortality from malrotation and midgut volvulus are directly related to the magnitude of bowel loss. The mortality may be as high as 65% if 75% or more of the small bowel is found to be necrotic. Survivors may develop short-gut syndrome, with the attendant complications of malabsorption and malnutrition.

The Ladd procedure corrects the partial duodenal obstruction and prevents midgut volvulus but does not change the intestinal dysmotility, which may be associated with malrotation; hence dysmotility symptoms such as constipation may persist.

For duodenal atresia, the prognosis is generally good, and normal bowel function can be expected. For jejunoileal atresia, long-term outcomes are generally excellent if sufficient bowel is present for absorption and growth.

The long-term outlook for a patient with meconium ileus depends on whether the infant has cystic fibrosis. If the infant does have cystic fibrosis, bowel function and nutritional status depend on the severity of the cystic fibrosis and the effectiveness of its management. If cystic fibrosis is not present, outcome is excellent.

Most patients with meconium plug syndrome have an excellent outcome after relief of the obstruction, and no further intervention is required. If laparotomy is necessary to evacuate the meconium, another diagnosis should be considered, such as Hirschsprung disease, which is associated with meconium plug syndrome in 4% of patients. A rectal biopsy should be performed in these cases.

The outcome for most patients with Hirschsprung disease is good both in terms of continence and stool frequency; however, bowel dysmotility, manifested by refractory constipation or recurrent episodes of enterocolitis, may persist despite removal of the aganglionic colon and rectum.

A report of 26 patients in a case-controlled investigation suggests that Doppler-flow studies of the splanchnic circulation prior to surgery may predict the likelihood of normal bowel function postoperatively.^[9]

Long-term complications may include bowel obstruction from adhesions or internal hernia, acquired aganglionosis, disordered motility in the proximal colon or small bowel, internal sphincter achalasia, or functional megacolon caused by stool-holding behavior. The latter children require complex interdisciplinary care to ensure an adequate quality of life, even after a successful pull-through procedure.^[10]

For patients with imperforate anus, outcome depends on the precision of the surgery, the severity of the sacral and perineal musculature deficiency, and the degree of colonic dysmotility.