Intestinal Obstruction in the Newborn

Overview of Intestinal Obstruction

Anatomic location

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.

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Esophageal atresia. Intraoperative view of proximal esophageal atresia and distal tracheoesophageal fistula.

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Pyloric stenosis. Intraoperative view of the hypertrophied pylorus prior to a pyloromyotomy incision.

Etiology

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)

Mechanism

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.

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Intraoperative view showing an intraluminal web, which will be excised; the longitudinal enterotomy will then be closed transversely.

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Discontinued intestinal atresia. Intraoperative view of the bulbous obstructed proximal bowel and the diminutive distal intestine.

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Midgut volvulus. Intraoperative view of the twisting of the terminal ileum and cecum around the base of the mesentery.

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Incarcerated inguinal hernia. Intestinal obstruction caused by an incarcerated inguinal hernia; the viability of the testicle is also at risk.

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Meconium ileus. Intraluminal intestinal obstruction from thick, tenaceous meconium.

Complete or incomplete

Bowel obstruction may be complete (atresia) or incomplete (stenosis, fenestrated web). Other considerations include the following:

• Malrotation and/or volvulus
• Hirschsprung disease

Associated conditions

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:

• See the image below.
• Small left colon syndrome (infants of diabetic mothers) may simulate Hirschsprung disease.
</ul>See the image below.

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Colonic atresia. This huge, dilated colon will never function satisfactorily and therefore must be resected.

Background

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^[1] :

• History of maternal polyhydramnios
• Feeding intolerance
• Bilious emesis
• Delayed passage of meconium
• Failure to pass transitional stools
• Abdominal distention

Successful management of neonatal intestinal obstruction demands timely diagnosis and appropriate intervention.^{[2, 3]}

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^[4] ; 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^[5]
• 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

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Anatomy

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.

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Omphalomesenteric duct (Meckel diverticulum) attached to the umbilicus.

Foregut

The esophagus, stomach, and duodenum are vascularized by multiple sources, including the following:

• Thyrocervical
• Intercostal
• Celiac axis
• Superior mesenteric vessels

Midgut

The jejunum, ileum, and ascending and proximal transverse colon are vascularized by the superior mesenteric vascular pedicle.

Hindgut

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.

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Pathophysiology

Foregut anomalies

Duodenal atresia

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^[4] :

• 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)

Midgut anomalies

Malrotation

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.^[6] 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.^[7]

Jejunoileal atresia

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.^[8] 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.^[9]

Meconium ileus

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.

Hirschsprung disease

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).

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Colon pull-through for Hirschsprung disease.

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Etiology

Genetic factors

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).^[10] 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.

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Epidemiology

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.^[12]

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.^[13]  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.

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Imperforate anus.

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Prognosis

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.^[14]

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.

Mortality/morbidity

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.

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Malrotation with volvulus of proximal small intestine coiled around the superior mesenteric vessels.

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Midgut volvulus. Necrosis of the midgut is the the most feared complication of malrotation/volvulus.

The Ladd procedure corrects the partial duodenal obstruction and prevents midgut volvulus, but duodenal dysmotility, delayed emptying, may persist.

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History and Physical Examination

The signs and symptoms of intestinal obstruction in a newborn may be subtle and nonspecific; hence, a detailed history and a thorough physical examination are important.

Bilious gastric aspirates or emesis indicate that the obstruction is distal to the ampulla of Vater. An infant with bilious vomiting should be considered to have malrotation and midgut volvulus until proven otherwise (with upper gastrointestinal (GI) contrast study).^[4]

Although bilious emesis is an acknowledged medical emergency, a survey of 175 pediatric and neonatal physicians, nurses, midwives, and parents reported that almost 75% of participants did not properly identify green as the color of bilious emesis; yellow was the color most often selected.^[15]

With a bulbous, dilated obstructed loop of intestine, there may be abdominal distention. Peristalsis may be palpable, particularly if the bowel is filled with fluid. Bowel sounds may be absent, normal, or hyperactive. If perfusion of the intestine is compromised, the infant may have tenderness and signs of shock, including pallor, prolonged capillary refill time, and poor perfusion. There may be hematochezia or evidence of thrombocytopenia or coagulopathy.

Infants with distal intestinal obstruction generally present with diffuse abdominal distention and delayed passage of meconium and absent transitional stools. Bowel sounds may be hypoactive or absent if the obstruction is chronic.

Imperforate anus and other anorectal anomalies are readily diagnosed by inspection of the perineum.

Duodenal atresia

Vomiting and upper abdominal fullness are consistent findings with duodenal atresia. An infant with duodenal atresia may present with emesis of gastric contents or with bilious vomiting, depending upon the location of the obstruction with respect to the ampulla of Vater. In 85% of patients with duodenal atresia, the obstruction lies distal to the ampulla, and these patients have bilious vomiting.

The abdomen is usually distended by the dilated stomach and proximal duodenum but becomes scaphoid when the contents of the distended stomach and duodenum are aspirated. Patients with duodenal atresia should be evaluated for trisomy 21 (Down syndrome).

Malrotation with volvulus

The initial presentation of a newborn with volvulus of the midgut is often bilious vomiting. Immediately after acute volvulus of the midgut, the abdomen is soft and scaphoid and may or may not be tender. As blood flow in the superior mesenteric pedicle is compromised, the bowel becomes ischemic and dilates, and the baby’s abdomen becomes increasingly distended and firm. Hypotension and shock may develop from sequestration of fluid within the obstructed bowel. Passage of frank blood per rectum may also occur. Prompt surgical intervention is required.

Jejunal atresia

Infants with Jejunal atresia usually present with bilious vomiting. If the atretic proximal intestine is dilated and bulbous, the baby may also have abdominal distension.

Ileal atresia

With distal obstruction, babies present with more generalized abdominal distention and obstipation; vomiting occurs late, and it is usually feculent. Intestinal duplications may cause obstruction by impingement upon the intestine’s lumen or by volvulus.

Meconium ileus and plug syndrome

Meconium ileus usually presents with abdominal distention and obstipation. Meconium plug syndrome is a relatively benign condition, usually occurring in healthy-appearing term infants. Abdominal distention and failure to pass meconium within the first 24 hours of life are the presenting signs.

Hirschsprung disease

Babies with Hirschsprung’s disease either fail to pass meconium in the first 24 hours of life, or are intolerant of feedings, or develop abdominal distended and refractory constipation after discharge from the nursery. One must be vigilant to carefully follow infants who have delayed passage of meconium.^[16] Failure to recognize Hirschsprung’s disease in a timely fashion may eventuate in toxic megacolon and death.^[17]

Imperforate anus

Routine inspection of a newborn perineum should include notation of the position and patency of the anus. Anorectal malformations range from anterior displacement of the anal opening to a completely imperforate anus (see the image below). Many infants with imperforate anus have an abnormal sacral progression (seen on pelvic radiographs), as well as a fistula between the rectum and the genitourinary tract, demonstrated by finding meconium in the urine.

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Imperforate anus.

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Approach Considerations

Imaging is a mainstay of the diagnosis of intra-abdominal pathology and should be readily performed in an infant with suspected intestinal obstruction. Noninvasive techniques, such as plain radiography and ultrasonography, can be performed at the bedside and can yield valuable information. A Gastrografin (diatrizoate) enema may be both diagnostic and therapeutic; however, clinicians not only must ensure the infant is well hydrated prior to the enema study but also must avoid excess hydrostatic pressure so as not to cause intestinal perforation.

Imperforate anus may occur as part of the VACTERL (vertebral, anal, cardiac, tracheal, esophageal, renal, and limb) association of congenital anomalies. Anorectal malformations are considered midline defects and require investigation for other midline anomalies. Ultrasonography and radiography of the heart, central nervous system (CNS), kidneys, and the sacral vertebrae and radii are recommended.

Computed tomography (CT) scans may be useful in the diagnosis of malrotation/volvulus. Normally, the superior mesenteric artery lies to the left of the superior mesenteric vein. Reversal of this spatial relationship suggests malrotation with midgut volvulus.

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Ultrasonography

Polyhydramnios is present in 50% of fetuses with duodenal obstruction. The stomach and proximal duodenum are fluid-filled and dilated. The image on fetal ultrasonography is similar to that of the “double-bubble sign” observed on radiography of the infant after birth (ie, air fills the dilated stomach and duodenum).

Prenatal ultrasonography may detect small bowel obstruction due to jejunal atresia (which may also lead to polyhydramnios). This may be detected on prenatal ultrasonography.

Fetal ultrasonography may not be able to detect distal intestinal obstruction. Dilated loops of small bowel may be mistakenly identified as colon as parturition approaches.

One of the complications of meconium ileus is in utero perforation; the extruded meconium is contained by adjacent loops of intestine, creating a pseudocyst. This causes intense inflammation of the overlying abdominal wall, termed “meconium peritonitis.” Distintincive ultrasonographic features of meconium peritonitis include meconium pseudocyst, echogenic mass, abdominal calcifications, ascites, polyhydramnios, and dilated bowel or intestinal obstruction.^[19]  In other instances, the perforation may seal after releasing only a small amount of meconium. Extraluminal meconium calcifies, and these scattered calcifications may be seen with fetal ultrasonography and abdominal radiography.

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Radiography

Duodenal atresia

Plain x-rays of the abdomen show the classic “double-bubble sign.” Air is an excellent contrast medium and may be introduced into the baby’s stomach through a nasogastric tube, if duodenal obstruction is suspected. Incomplete duodenal obstruction mandates urgent radiographic imaging, laparotomy, or both to differentiate duodenal atresia from malrotation/volvulus.

Malrotation with volvulus

When a baby, in whom midgut volvulus is suspected, presents with bilious vomiting, obtain an upper gastrointestinal (GI) series.^{[20, 21]} Findings that corroborate this diagnosis include incomplete obstruction of the duodenum caused Ladd bands or volvulus. The ligament of Treitz may be located to the right of the vertebral column, directly below the pylorus.

If the presentation is abdominal distention and tenderness and, possibly, hematochezia, a barium enema is more definitive, because it differentiates malrotation/volvulus from Hirschsprung enterocolitis. Radiographic signs of malrotation include absence of the splenic and hepatic flexures, and the cecum is in the right upper quadrant. With midgut volvulus, there is obstruction to the flow of contrast medium through the distal colon.

See the images below.

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Malrotation volvulus. Note the partial duodenal obstruction. The distal duodenum does not cross the midline (over the vertebral column) and the "curly....

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Duodenal atresia. Note the double-bubble sign and narrowing in the second portion of the duodenum. There is partial obstruction, the duodenum does cro....

Jejunal atresia

Plain radiography of the abdomen reveals distention of the stomach and small bowel proximal to the obstruction. In 12% of newborns with jejunoileal atresia, intra-abdominal calcifications, which represent extraluminal meconium, are observed on plain radiography. This association occurs because interruption of blood flow to the atretic bowel is followed by sterile necrosis and perforation of the intestine with extrusion of meconium.

Occasionally, in proximal atresias with large mesenteric defects, the distal bowel obtains its blood supply by retrograde flow from the ileocecal vessels. The tiny, unused intestine spirals around these vessels, simulating an “apple peel” or “Christmas tree” appearance. The tip of the “Christmas tree” (the proximal end of the preserved distal intestine) may twist and obstruct its rather precarious blood supply, adding urgency to the evaluation and surgical correction of this condition, because the length of the intestine is already shortened by the atresia.

Distal obstruction

Typically, plain radiography reveals multiple dilated loops of intestine, air fluid levels, and absence of air in the rectum. A diatrizoate (Gastrografin) enema is indicated and demonstrates “microcolon.” In patients with meconium plug, the diatrizoate enema is both diagnostic and therapeutic.

Meconium ileus

Bowel loops with varying diameters are seen on plain radiography, as well as a “soap bubble” or “ground glass” appearance from the sticky, inspissated meconium. Scattered calcifications suggest in utero perforation.

Meconium plug syndrome

A contrast enema should be performed in all infants with distal intestinal obstruction. It is diagnostic of meconium plug syndrome—a normal colon laden with meconium filling defects—as well as therapeutic, facilitating evacuation of a meconium plug. Hirschsprung disease may be associated with meconium plug syndrome in 4% of patients; therefore, some clinicians perform a rectal biopsy in patients presenting with meconium plug syndrome.

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Gastrografin enema. Note the tiny, unused colon and the dilated (by swallowed air) proximal, obstructed intestine.

Hirschsprung disease

Hirschsprung disease may be diagnosed by finding a “transition zone” on contrast radiography, which is defined by an abrupt change in diameter between the narrow aganglionic rectum and distal colon, and the dilated, more proximal, normally innervated bowel. Failure to evacuate contrast medium within 24 hours of the enema is another finding characteristic of Hirschsprung disease.

Imperforate anus

A cross-table lateral x-ray, with the baby in prone “jack-knife” position, reveals the position of the rectum relative to the levator muscle complex. This study helps clinicians to determine whether an anoplasty or a colostomy is appropriate as the initial operative procedure. This radiologic study should be performed 12-24 hours after birth to allow for swallowed air to reach the rectum.

Newborns with a low imperforate anus have a fistula to the skin; in those with a high imperforate anus, the fistula ends in the genitourinary system (the bladder, urethra, or vagina). Low lesions may be primarily repaired by perineal anoplasty. In newborns with high imperforate anus, a temporary colostomy is the safer option.

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Other Tests

Anal manometry

Anal manometry is utilized in patients with Hirschsprung disease. A positive study demonstrates failure of the rectum to relax following inflation of the balloon; however, the study is impossible to perform in uncooperative children.

Rectal biopsy

If the contrast study suggests Hirschsprung disease, it should be followed by a confirmatory rectal biopsy. Suction rectal biopsy may be performed at the bedside with a specially designed instrument inserted through the baby’s anus. Suction is applied through a side hole, and a knife amputates a small piece of rectal mucosa and muscularis mucosa. The specimen is examined for ganglion cells, which, if present, effectively eliminates Hirschsprung disease from further diagnostic consideration.

Acetylcholinesterase staining of the submucosa may reveal abnormal hypertrophic nerve fibers characteristic of Hirschsprung disease. False positives may occur,^[22] because an absence of ganglion cells may simply reflect inadequacy of the tissue sample; hence, full-thickness rectal biopsy should be performed to corroborate the negative finding of “absent ganglion cells,” before concluding that the diagnosis of Hirschsprung disease is definitive.

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Approach Considerations

Intestinal obstruction generally causes fluid loss and an electrolyte imbalance, either from vomiting, in cases of proximal obstruction, or third-space sequestration of fluid within the intestine’s lumen, in more distal obstructions. To minimize mortality and morbidity, clinicians must treat these life-threatening consequences of the obstruction, while simultaneously identifying and treating the underlying cause.

Perform gastric intubation and decompression. Provide respiratory and cardiovascular support to maintain hemodynamic stability. Administer intravenous antibiotics, because as the bowel distends in response to increased intraluminal pressure, perfusion to the intestine diminishes (ie, Law of Laplace); consequently, its resistance to bacterial invasion diminishes. In addition, bacterial overgrowth occurs in association with intestinal obstruction.

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Enemas

A diatrizoate (Gastrografin) enema should be performed in cases of distal intestinal obstruction. Distal contrast radiography is diagnostic, and the diatrizoate enema has remarkable efficacy in loosening the sticky meconium and facilitating evacuation (>50% success rate).

Multiple enemas may be required in meconium plug syndrome. The enema fluid must be refluxed into the terminal ileum for successful relief of the obstruction. Diatrizoate and N-acetylcysteine may be administered antegrade by nasogastric tube to help loosen the impacted meconium. Hyperosmolar solutions (10% acetylcysteine) draw fluid into the lumen of the bowel and enhance their efficacy in evacuating thick meconium; however, this may also increase the risk of perforation, which reportedly occurs in 3-10% of cases.

In children with intussusception air enema may be superior relative to liquid enema for intussusception reduction.^[23] In a meta-analysis of 102 articles comprising results for 32,451 children (age range, 1 day to 22 y), Sadigh et al found an 82.7% combined estimate of success rate for air enema in 44 studies (n = 16,187), whereas it was 69.6% for liquid enema in 52 studies (n = 15,752).^[23] However, the combined estimates of perforation rate (0.39% vs 0.43%) and rate of first intussusception recurrence (6% vs 7.3%) were similar between air and liquid enema, respectively.

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Preparation for Operation

Duodenal atresia

Preoperative measures for duodenal atresia include fluid resuscitation and nasogastric decompression. The baby should be evaluated for trisomy 21.

Duodenal atresia is considered a “midline embryologic defect,” and evaluation for associated anomalies should include echocardiography, head and renal ultrasonography, and vertebral skeletal radiography.

Malrotation with volvulus

Preoperative treatment of malrotation and volvulus is focused on urgent relief of the intestinal obstruction. In addition to nasogastric decompression and fluid resuscitation, these infants may require intubation and mechanical ventilation as well as vasopressor agents for cardiovascular support. Broad-spectrum antibiotics should be administered because of the likelihood of ischemic or gangrenous bowel. A delay in diagnosis of malrotation/volvulus may lead to catastrophic loss of intestine.

Jejunal atresia

In patients with jejunal atresia, immediate preoperative nasogastric decompression limits distention of the proximal atretic bowel. Appropriate intravenous (IV) fluids should be started. A contrast enema corroborates the diagnosis and is useful in excluding a second, more distal obstruction. Postopoerative parenteral nutrition, as well as respiratory, cardiovascular, and hemodynamic support, may be necessary.

Meconium ileus

In cases of meconium ileus, nasogastric decompression and IV fluids and antibiotics are initially administered. A diatrizoate enema may be effective in loosening the meconium impaction, but the enema fluid must be refluxed into the terminal ileum. The volume of the instilled fluid must be carefully regulated in premature infants.^[24] Diatrizoate diluted with N-acetylcysteine may be administered by nasogastric tube from above to further loosen the meconium. By drawing fluid into the lumen of the bowel, hyperosmolar solutions (10% acetylcysteine) have enhanced efficacy; however, this may cause electrolyte disturbances due to intracellular and extracellular fluid shifts, with the attendant risk of hypovolemic shock. Hyperosmolar enemas may increase the risk of perforation and sepsis with enteric bacteremia.

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Surgical Relief of Obstruction

Duodenal atresia

Correction of duodenal atresia requires identifying the cause of the obstruction (ie, atresia, annular pancreas, or web), locating the duodenum above and below the obstruction, and determining how best to bring the two lumens into continuity.

Malrotation with volvulus

Malrotation with midgut volvulus is a true surgical emergency. Delay in diagnosis may result in catastrophic loss of the bowel and death. In patients with irreversible ischemia, the entire midgut is forfeit, and the child cannot survive without an intestinal transplant.

Surgery for malrotation/volvulus involves evisceration of the small intestine. The base of the mesentery is examined; and if volvulus is present, the colon will be wrapped around the mesentery. Volvulus is reduced by twisting the mesentery counterclockwise, thereby unraveling the colon. This maneuver restores blood flow to the midgut. The duodenum is then located and followed; bands attaching it to the colon are divided, and these two structures, duodenum and colon, are separated as widely as possible. The superior mesenteric vessels are seen as the leaves of the mesentery are separated like opening the pages of a book. The bowel is returned to the abdomen—duodenum to the right, colon to the left, midgut in the center—so as to spread out the small bowel mesentery. (See the images below.)

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Midgut volvulus. The bowel is eviscerated and the entire midgut is twisted counterclockwise, effecting reduction of the volvulus.

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The midgut volvulus is reduced.

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The peritoneal bands (Ladd bands) tethering the duodenum to the colon are divided, exposing the superior mesenteric vessels.

Whereas, before, the mesentery extended from the ligament of Treitz in the left upper quadrant to the cecum in the right lower quadrant, the ”Ladd procedure” reverses the position of the duodenojejunal junction to the right lower quadrant and the cecum to the left upper quadrant. The mesentery is draped over the retroperitoneum, where it becomes adherent, and this prevents recurrent volvulus. The appendix is removed, because its new location is the left upper quadrant, where a future diagnosis of appendicitis would be problematic.

Jejunoileal atresia

Surgical treatment of jejunoileal atresia involves resection and primary anastomosis of the proximal and distal segments of the intestine. A diverting enterostomy is avoided. As with surgery for duodenal atresia, resection or tapering of the proximal dilated segment is occasionally necessary to limit the dysmotility that occurs in grossly dilated bowel. The ileocecal valve is preserved if possible, because this prevents egress of bacteria from the colon into the small intestine and the resultant bacterial overgrowth and malabsorption.

Meconium ileus

Calcification on scout radiography indicates that an intestinal perforation occurred in utero and spontaneously sealed; if not, the extruded meconium is walled off by adjacent intestine to form a pseudocyst. Affected babies have meconium peritonitis and their appearance is unmistakable: The baby is born with a distended, erythematous abdomen. Laparotomy is undertaken with drainage of the meconium pseudocyst and identification of the site of the perforation, which is converted to an enterostomy. In uncomplicated meconium ileus, an enterotomy with irrigation and evacuation of the obstructing meconium may successfully relieve the intraluminal obstruction. In other patients, an ostomy for diversion and access for proximal and distal irrigation with N-acetylcysteine may be necessary.

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Complicated meconium ileus. Volvulus of the dilated, meconium-ladened loop of intestine.

Meconium plug syndrome

Operative intervention is indicated in infants with meconium plug syndrome only if diatrizoate enemas are unsuccessful in loosening the whitish meconium plug, thereby permitting the baby to evacuate the black and tarry meconium.

Hirschsprung disease

Treatment of Hirschsprung enterocolitis includes bowel irrigations and decompression, administration of antibiotics, and fluid resuscitation. Colostomies expeditiously decompress the bowel and allow affected babies to resume feedings with minimal delay. Pull-through procedures are usually performed at age 3-6 months.

If there is no history of enterocolitis, pull-through procedures are performed during the newborn period, with excellent results.

Innovations in the treatment of Hirschsprung disease include minimally invasive techniques, such as the transanal laparoscopic pull-through procedures.

Imperforate anus

If an imperforate anus is low, with a perianal or perineal fistula, it can be repaired primarily by means of a perineal anoplasty. If the distal rectum is high above the anus, or if a fistula runs from the rectum to the vagina or urethra, or to the urinary bladder, the imperforate anus is classified as high, and the infant should undergo a colostomy.

Definitive repair of the imperforate anus is accomplished by means of posterior sagittal anorectoplasty, in which the rectum is situated within the striated muscle complex (levator sling) and anal sphincter. This procedure allows the muscles of continence to function properly.^[25] The ultimate outcome depends on the precision of the surgery, the presence or absence of normally innervated sacroperineal musculature, and the degree of colonic dysmotility.

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Postoperative Care

In the postoperative period, derangements in fluid balance, glucose metabolism, and respiratory status may occur. Many infants following laparotomy have third-space fluid sequestration, and their intravenous (IV) fluid requirements are increased 1.5 to 2 times normal.

By checking the patient’s heart rate and blood pressure, peripheral perfusion (capillary refill), and urine output, the adequacy of fluid resuscitation can be determined. Serum electrolyte levels should be closely monitored, because fluid shifts between the intravascular and extravascular spaces are common and require prompt responses. Replacement of fluid lost through third-space fluid sequestration should consist of 0.5% to normal (0.9%) saline.

Gastric decompression “puts the injured part at rest” and facilitates healing of an intestinal anastomosis. The duration and depth of anesthesia reflect the length and complexity of the surgical procedure, which relates to the analgesic requirement and resultant respiratory depression as well as the duration of postoperative ileus, which impairs normal movement of the diaphragm and increases the requirement for respiratory support. 

The duration of antibiotic therapy depends on whether there was contamination of the peritoneal cavity. Total parental nutrition (TPN) is indicated until return of bowel function permits delivery of adequate enteral nutrition. Even when peristalsis has resumed, these infants may not tolerate enteral feedings, because their intestinal mucosa must regenerate before it is able to absorb nutrients. A period of trophic feeding may stimulate mucosal regeneration, and a predigested or elemental formula may be better tolerated. If the terminal ileum is resected, derangements in folate metabolism and in the enterohepatic circulation may occur.

Cardiovascular and coagulation complications, such as shock and disseminated intravascular coagulation, may occur with intestinal ischemia or necrosis. Management of these issues may also challenge the clinician during the postoperative period.

Wound care is usually straightforward; antibiotics are not generally required beyond the immediate preoperative period.

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Complications

General complications

General complications include postoperative strictures and adhesions, prolonged ileus because of impaired gut motility, and malabsorption, usually related to inadequate gut length or intestinal injury from ischemia or infection; there are also complications related to prolonged use of total parenteral nutrition (TPN), including problems in obtaining central venous access and catheter complications, such as sepsis.

Percutaneously inserted catheters (PIC) are utilized successfully in this population, but the caliber of these catheters is small and infusion of blood products may require alternative routes. Problems caused by the TPN solution include cholestasis, liver damage, and nutritional deficiencies. Meticulous attention to the composition of TPN solutions may minimize these long-term complications.

A fish-oil lipid emulsion appears to minimize the liver toxicity that is seen with traditional soybean oil lipid formulations.^[26]

Normal oropharyngeal activities (eg, sucking) should be encouraged or oral aversion may develop.

Postoperative adhesions may occur between loops of intestine or between the intestine and the peritoneum. Anastomotic strictures may develop. In a study of 1541 children who had intestinal surgery, approximately 10% had adhesions at the operative site, and 5% occurred in areas that were away from the site of surgery.^[27] Gentle manipulation of the bowel, limiting contamination of the peritoneal cavity, and meticulous anastomotic technique may limit postoperative strictures and adhesions.

Decreased gut motility is often observed after bowel resection for intestinal obstruction. Chronic dilatation of the intestine proximal to the obstruction may alter normal peristalsis across that segment of bowel, even after the obstruction has been relieved. Interruption of vagal neuroenteric pathways by an atresia or a surgical anastomosis may also contribute to abnormal intestinal motility.

Two promotility pharmacologic agents are used in this age group: metoclopramide and erythromycin. Randomized controlled trials of these agents have produced variable results compared with placebo; and each drug has side effects that may be unacceptable. Utilization is frequently based upon anecdotal reports or personal experience, rather than” evidence-based medicine”.

The normal length of the small bowel in a term infant is approximately 250 cm; in adults, it is 600-800 cm. The estimated minimum length for adequate intestinal function in a term infant is 75 cm. Resection of more than 60% of the small bowel or resection that removes crucial anatomic segments (eg, the ileocecal valve) predisposes the infant to malabsorption, which may cause failure to thrive, in which the infants do not grow and develop normally. Bacterial overgrowth also contributes to malabsorption. Accordingly, every effort to preserve bowel length is imperative.

Short-gut syndrome results when the remaining intestine cannot sustain normal absorption of nutrients. Children with short-gut syndrome may survive with parenteral nutrition supplementation, predigested formulas, and pharmacologic agents used to slow motility. Probiotics have been shown to normalize bowel flora and improve absorption of nutrients.

Bowel-lengthening procedures abetted by the creation of intraluminal valves, and pharmacologic manipulation of bowel recovery with nutritional and hormonal treatments assist in weaning children with short-gut syndrome from dependence on parenteral nutrition. Newer techniques, such as the serial transverse enteroplasty (STEP) procedure, may offer improved bowel function and length in some patients.

Patients with volvulus and infarction of the entire midgut or who have multiple intestinal atresias may not have enough intestine to survive. A difficult ethical decision is whether to proceed with intestinal resection and whether to continue life support. Small-bowel transplantation, with or without other viscera such as the liver and pancreas, is being performed in select centers in the United States, with varying results.

Complications associated with specific conditions

Complications may also be particularly associated with one or another of the various conditions that cause bowel obstruction in the newborn.

Malrotation

With malrotation, complications depend on the condition of the bowel at the time of presentation and surgical treatment. The most feared complication is necrosis of the entire midgut.

Reduction of the volvulus, performing a Ladd procedure, and planning a second-look procedure 24 hours later may allow salvage of intestine that initially appeared nonviable. If a massive small bowel resection is performed, a high jejunostomy is created, which results in the loss of large volumes of fluid and electrolytes and makes formulation of TPN solutions more complex.

In time, the ostomy can be closed. The remaining colon absorbs fluid and electrolytes and may simplify the baby’s management; however, severe diarrhea and the attendant complications may occur.

Duodenal atresia

The most frequent complication of a duodenal anastomosis is delayed emptying. Patience is required, because the anastomosis will usually function by the third postoperative week. Revising an anastomosis is rarely necessary.

Jejunoileal atresia

In uncomplicated cases of intestinal atresia, complications are very uncommon. The obstruction resulted from an in utero event leading to ischemia or necrosis of a segment of intestine. If the bowel is in good condition at birth, a primary repair is possible. Small bowel atresia may occur in conjunction with gastroschisis, however, and the exposed bowel may be inflamed, thickened, and matted together. In such cases, it may take time to differentiate the mechanical obstruction, the atresia, from the dysfunction associated with injury from exposure to the amniotic fluid. The atresia may not be diagnosed for several weeks after surgical repair of the abdominal wall defect.

Failure of normal bowel motility and function 4 weeks following repair should prompt a contrast medium study to look for evidence of mechanical obstruction, such as extrinsic compression (associated Ladd bands), atresia, or postinflammatory adhesions.

Meconium ileus and plug syndrome

Complications in treating babies with meconium plug syndrome are extremely rare. Babies with meconium ileus and cystic fibrosis may require enzyme replacement, although predigested or elemental formulas may be sufficient during the neonatal period.

Hirschsprung disease

Infants with Hirschsprung disease may present with enterocolitis, which is suggested by abdominal distention and explosive diarrhea, especially following a rectal examination and dilation of the anal sphincter. Sepsis (enteric organisms) may result from compromise of the integrity of the massively dilated proximal bowel, which allows bacterial mucosal translocation and invasion into the intestinal vascular supply.

Management includes intravenous (IV) fluids and antibiotics, along with irrigation of the distal colon using a rectal tube inserted through the anus. Stool studies may be positive for the Clostridium difficile toxin, mandating the use of oral vancomycin or metronidazole. A diverting colostomy may be necessary, if rectal irrigations fail to control recurrent episodes.

Imperforate anus

Babies who have low imperforate anus typically suffer from constipation, although the anus is widely patent. The major complication in babies with high imperforate anus is incontinence, which occurs either because the rectum is improperly situated within the striated muscle complex or because the muscle complex is defective. Constipation or diarrhea may occur, depending on the motility of the colon.

Other minor complications, such as prolapse of rectal mucosa through the neoanus, are easily repaired surgically. Pena has devised a bowel-training program that is extremely helpful in the management of these patients.^[25]

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Consultations

In all of these conditions in volving bowel obstruction in the newborn, the neonatologist and pediatric surgeon work together, so that the diagnosis can be quickly established and appropriate therapy rapidly implemented. In conditions that are associated with systemic disease, such as duodenal atresia (trisomy 21) and meconium ileus (cystic fibrosis), appropriate consultation should be obtained early, and with the continued involvement of appropriate specialists long after the baby has recovered from the initial hospitalization.

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Medication Summary

The goals of pharmacotherapy are to facilitate evacuation, reduce morbidity, and prevent complications.

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Diatrizoate enema (Hypaque Sodium)

Clinical Context:  An enema with a high osmolality solution should be performed to facilitate evacuation. Diatrizoate enema has the advantage of acting as an osmotic laxative, which may aid in the evacuation of the colonic contents. Contrast radiography is diagnostic, and the diatrizoate enema has remarkable efficacy in loosening the sticky meconium and facilitating evacuation (>50% success rate).

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Class Summary

An enema with a high osmolality solution should be performed to facilitate evacuation.

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Metoclopramide (Metozolv)

• Dosing, Interactions, etc.

Clinical Context:  Metoclopramide is a dopamine antagonist that stimulates acetylcholine release in the myenteric plexus. Metoclopramide enhances gastrointestinal motility and accelerates gastric emptying time.

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Erythromycin (E.E.S., Erythrocin)

• Dosing, Interactions, etc.

Clinical Context:  Erythromycin has a prokinetic effect on the GI tract at a dose that is about a quarter less of the antibiotic dose, which may be mediated by stimulating cholinergic neurons. High doses may directly stimulate a motilin muscular receptor in the GI tract.

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Class Summary

Two promotility pharmacologic agents are useful: metoclopramide and erythromycin. Randomized controlled trials of these agents have produced variable results compared with placebo, and each has adverse effects that may render them unacceptable. Many clinicians justify the use of these medications with anecdotal reports or by personal experience, rather than according to “evidence-based medicine.”

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Vancomycin

• Dosing, Interactions, etc.

Clinical Context:  Vancomycin is a potent antibiotic directed against gram-positive organisms; in addition, it is active against Enterococcus species. It is useful in the treatment of gram-positive septicemia and soft-tissue infections. It is indicated for patients who are allergic to penicillin or cephalosporin, or whose infections have not responded to these agents. Creatinine clearance may be used to adjust the dosage in patients with renal impairment.

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Metronidazole (Flagyl)

• Dosing, Interactions, etc.

Clinical Context:  Metronidazole causes a chemical reduction reaction in anaerobic bacteria and sensitive protozoa. It is readily absorbed and permeates all tissues, including cerebrospinal fluid (CSF), breast milk, and alveolar bone. It is metabolized and excreted in the liver and kidneys. 

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Class Summary

Empiric antimicrobial therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting.

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