Overview of Intestinal Obstruction
Important anatomic sites to consider include the following:
Esophagus: Esophageal atresia
Stomach: Antral web/pyloric stenosis
Duodenum: Duodenal atresia
Jejunum: Jejunal atresia
Ileum: Ileal atresia
Colon: Colonic atresia
Rectum: Rectal atresia
Anus: Imperforate anus
See the images below.
Faulty embryogenesis may result from the following:
Genetic factors: Duodenal atresia and its association with trisomy 21
Environmental exposure in utero may lead to VACTERL syndrome (vertebral anomalies, anal atresia, and cardiac, tracheoesophageal, renal/radial, and limb anomalies)
Thromboembolic event(s) may lead to mesenteric vascular accident (small bowel atresia)
The mechanism by which intestinal obstruction occurs may be intrinsic, extrinsic, or intraluminal, as follows:
Intrinsic: The obstructed bowel may be in continuity, partitioned by a web (duodenal atresia), or it may be discontinuous, segmented with a gap in the mesentery
Extrinsic: There may be compression by a band (malrotation, Meckel diverticulum) or by a duplication cyst, twisting by a volvulus, or kinking in an incarcerated hernia (inguinal or Morgagni)
Intraluminal: Obstruction may occur by inspissated, thick meconium (meconium ileus)
See the following images.
Complete or incomplete
Bowel obstruction may be complete (atresia) or incomplete (stenosis, fenestrated web). Other considerations include the following:
Malrotation and/or volvulus
Conditions that may be associated with bowel obstruction in the newborn include the following:
Gastroschisis-associated intestinal atresia
Malrotation: Associated with abdominal wall defects and congenital diaphragmatic hernia
Tracheoesophageal fistula: Associated with esophageal atresia
Meckel diverticulum or pancreatic rest: May serve as lead points in intussusception
Short gut: Loss of intestinal length
Massively dilated proximal intestine and diminutive distal segment (colonic atresia)
Intestinal perforation may be associated with the following:
Antenatally: Meconium peritonitis (complicated meconium ileus, which is associated with cystic fibrosis)
Postnatally: Premature infants with inadequate peristalsis proximally and diminutive distal intestine, with/without inspissated stool may lead to perforation
Developmental Immaturity may be associated with the following:
Inadequate peristalsis in micro premature infants (<26 weeks' gestation) plus immunologic immaturity plus bacterial overgrowth may lead to necrotizing enterocolitis, with/without perforation
Small left colon syndrome (infants of diabetic mothers) may simulate Hirschsprung disease.
See the image below.
Intestinal obstruction is a frequent indication for surgical intervention in newborns. The incidence is an estimated 1 in 2000 live births.
Cardinal signs of intestinal obstruction are the following  :
History of maternal polyhydramnios
Delayed passage of meconium
Failure to pass transitional stools
An accurate history and physical examination, corroborated by simple radiologic studies, usually leads to the correct diagnosis. Fortunately, the outlook for babies undergoing surgery for intestinal obstruction is excellent.
Anatomy of neonatal obstruction
Any location within the gastrointestinal tract may be the site of intestinal obstruction. Note the following:
Esophagus: Proximal esophageal atresia is usually associated with a distal tracheoesophageal fistula
Antrum of the stomach: Obstruction may occur, but it is exceedingly rare; 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
Duodenal obstruction: Uniquely caused by incomplete canalization, or creation of a lumen in the solid intestinal anlage  ; it is frequently associated with Down syndrome
Intestinal obstruction: May be complete (atresia) or incomplete (stenosis); 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 
Bilious emesis may reflect ileus secondary to sepsis or necrotizing enterocolitis, but proximal intestinal obstruction is also an etiology
Midgut volvulus: In a baby who has previously tolerated feedings, the physician must be vigilant not to overlook midgut volvulus, or twisting, of the midgut, the portion of the intestine that is supplied by the superior mesenteric vasculature
Small bowel or colonic atresia usually is accompanied by a mesenteric defect, as the etiology is an in utero mesenteric vascular accident; when there is a sizable gap in the mesentery, the intestine distal to the obstruction obtains its blood supply from the ileocecal vessels by retrograde flow, and the intestine winds about the marginal vessels in a peculiar arrangement resembling a “Christmas tree” or an “Apple peel”; with this anatomic arrangement, the apex of the deformity may twist and infarct
Congenital bands can compress and obstruct the intestine, including Ladd bands and Meckel bands
Ladd bands in malrotation: These peritoneal attachments normally fix the duodenal jejunal junction at the ligament of Treitz or attach the ascending and descending colon to the retroperitoneum
Meckel diverticulum bands: These remnants of the omphalomesenteric duct can act as a fulcrum around which a loop of intestine flips, causing a “closed-loop” obstruction involving both its efferent and afferent limbs
Fluid-filled intestinal duplications: Like bulky ovarian cysts, the duplications may 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
Obstructed distal intestine: Affected babies 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 consisting of multiple loops of dilated small intestine 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 its intraluminal contents (inspissated or thick, sticky meconium)
Rectum: A shelf-like partition may develop just above a normal-appearing anal canal; other anorectal anomalies are readily diagnosed by inspection of the baby’s perineum. In babies whose anus is imperforate, the rectum tapers, ending as a fistula to the bladder, urethra, or scrotum in males and vagina or perineum in females
Aganglionic megacolon, or 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 appears normal. Before the etiology of the disease was understood, surgeons removed the dilated (abnormal-appearing) 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 (see the image below). The alimentary tube is divided into 3 sections on the basis of its blood supply: foregut, midgut, and hindgut.
The esophagus, stomach, and duodenum are vascularized by multiple sources, including the following:
Superior mesenteric vessels
The jejunum, ileum, and ascending and proximal transverse colon are vascularized by the superior mesenteric vascular pedicle.
The distal transverse colon, the descending and sigmoid colon are supplied by the inferior mesenteric vessels.
The rectum is supplied by the internal iliac vessels.
Duodenal atresia results from defective canalization of the solid duodenal anlage, wherein vacuoles form and coalesce, creating a lumen. This process occurs during the eighth week of gestation. There are multiple presentations, such as the following  :
There may be a membranous obstruction, which is usually located near the ampulla of Vater; the dilated proximal duodenum and diminutive distal duodenum are in continuity. Mucosal webs may be fenestrated, creating a partial obstruction
Occasionally, the obstructing web protrudes into the distal lumen like a “wind sock”; the etiology of the obstruction may not be immediately apparent to the surgeon when the duodenum is opened through the transition point. It may be necessary to pass a tube from the stomach into the duodenum to find the obstructing membrane
There may be discontinuity, with a gap of varying lengths, between the dilated proximal duodenum and the hypoplastic distal duodenum; occasionally, repair by duodenojejunostomy is technically simpler than duodenoduodenostomy.
An annular pancreas may denote the site of the obstruction without being the actual cause of the obstruction; it is corrected by an anastomosis of proximal-to-distal duodenum (not by cutting the encircling ring of pancreas)
In malrotation, the proximal and distal ends of the midgut, the duodenum and the cecum, are bound to one another around the superior mesenteric vessels by peritoneum, termed “Ladd bands,” in honor of the surgeon who devised the operative technique used to correct this anomaly.  These peritoneal bands normally form the ligament of Treitz, securing the duodenojejunal junction to the retroperitoneum in the left upper quadrant and the ascending colon to the retroperitoneum along the right lateral aspect of the peritoneal cavity. In malrotation, their ectopic course partially obstructs the duodenum and creates a mesentery with a narrow base, which allows volvulus of the midgut to occur during peristalsis. 
Jejunoileal atresia is an accident of fetal development and not a preprogrammed embryonic anomaly. In their classic work on fetal dogs, Louw and Barnard elucidated the pathophysiology of jejunoileal atresia.  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 proximal tributaries of the superior mesenteric vasculature results in a proximal atresia; the distal intestine survives because of retrograde blood flow from the ileocolic vessels. Other in utero events such as gastroschisis or intussusception may be associated with intestinal atresia from attendant vascular compromise. 
Meconium ileus is associated with 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 the newborns with cystic fibrosis, 10-20% present with meconium ileus, an association first described by Landsteiner in 1905. [10, 11]
Meconium plug syndrome refers to inspissated meconium that obstructs the colon; it may signal Hirschsprung disease or cystic fibrosis. Conditions that predispose to dysmotility of the neonatal bowel (maternal preeclampsia, maternal diabetes mellitus, maternal ingestion 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.
Harold Hirschsprung, a Danish pediatrician, attended two infants who had died from refractory constipation. The autopsies showed hypertrophy and dilatation of the colon that Hirschsprung correctly believed was congenital. He described the disease that bears his name in 1886. The actual cause of this congenital anomaly, an absence of ganglion cells, was determined later in the twentieth century. Aganglionic intestine is unable to relax; it assumes a state of tonic contraction.
Propagation of peristaltic waves through the intestine requires sequential contraction and relaxation, which is mediated by neuroenteric ganglion cells located in the submucosa. Neural crest cells migrate caudally along the mesentery and reach the rectum around the tenth gestational week. The embryonic migration of ganglion cells is arrested proximal to the rectum in Hirschsprung disease—usually the sigmoid colon. The “transition point” is determined by biopsy and ultimately becomes the “pull-through” segment, the neorectum, when the definitive operation is performed (see the image below).
Congenital anomalies, such as trisomy 21 (40% of patients), imperforate anus, and congenital heart 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 Asians. The genetic mutation that causes cystic fibrosis was localized to the q31.2 locus on chromosome 7 in 1988. Since then, more than 1400 mutations have been identified in this gene, which contains 230,000 base pairs and codes for the protein, cystic fibrosis transmembrane conductance regulator (CFTCR).  Abnormalities in CFTCR disrupt the ingress and egress of sodium and chloride ions through cellular membranes. 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 shows microcolon, which results from the proximal obstruction.
Hirschsprung disease is associated with multiple genetic defects, a phenomenon termed oligogenic inheritance. As such, it may serve as a model for understanding other disorders of bowel motility.
The RET proto-oncogene, located at chromosome 10q11.21 interacts with a protein, EDNRB, encoded by the gene, EDNRB, which is located on chromosome 13. Mutations in RET and related signaling pathways and modifier genes on 3p21, 9q31, and 19q12 lead to failure of migration of the enteric neural crest cells during fetal development.
Syndromic cases of Hirschsprung disease (associated with other defects of the autonomic nervous system) are associated with mutations in the homeobox gene, PHOX2B.
Six other genes are associated with Hirschsprung disease; these include 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.
The incidence of malrotation of the midgut is 1 case per 6000 newborns. Obstructive symptoms usually occur during the first month of the life (50% of cases); 90% of cases present during the first year of life. The diagnosis, however, may delayed until adulthood. 
As many as 1 in 1000 newborns have an asymptomatic anomaly of intestinal rotation and fixation, which also occurs with congenital diaphragmatic hernia, gastroschisis, and omphalocele.
Duodenal obstruction affects as many as 1 in 6,000-10,000 infants. Duodenal atresia is present in 4% of infants with trisomy 21, who frequently have associated congenital heart disease.
Atresia of the jejunum or ileum occurs more frequently (1 case per 1500 births).
Cystic fibrosis occurs in 1 infant per 3000 live births; it is reported in 10-20% of babies with meconium ileus.  This 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 populations and affects males four times as frequently as females. A family history of Hirschsprung disease is present in approximately 12.5% of patients; this subset of patients typically may have involvement of the entire colon (total colonic aganglionosis).
Imperforate anus (see the following image) has an incidence of 1-3 cases per 10,000 births; there is a female predominance. Administration of folic acid during pregnancy has been shown to reduce the incidence of imperforate anus to 1 case per 10,000 births.
The prognosis for duodenal and jejunoileal atresia is similar: relatively normal bowel function can be expected except in cases of short-gut syndrome.
The long-term outlook for a patient with meconium ileus is determined by the severity of the cystic fibrosis and the effectiveness of its management.
Most patients with meconium plug syndrome have an excellent outcome after relief of the obstruction, and no further intervention is required.
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.
Disordered motility in the proximal colon, internal anal sphincter achalasia, or functional megacolon (associated with stool-holding behavior) may persist following a successful pull-through procedure and require complex interdisciplinary care to ensure an adequate quality of life. 
The outlook in patients with anorectal anomalies is complex; it depends upon the precision of the surgery, the adequacy of the sacral and perineal musculature, and the degree of colonic dysmotility.
The morbidity and mortality from malrotation and midgut volvulus (see the images below) are related to the loss of intestine. The mortality may be as high as 65%, if more than 75% of the small bowel is 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 duodenal dysmotility, delayed emptying, may persist.
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