Intestinal Obstruction in the Newborn

Neonatal intestinal obstruction comprises many conditions, as obstruction may occur at any point in the gastrointestinal tract.[1, 2, 3] Even when restricting one's focus to a single location, several variations of obstruction are possible. The general principles involved in managing intestinal obstruction are the same regardless of the patient population, from the newborn to the geriatric.

The following image depicts malrotation/volvulus.

 

Intestinal obstruction occurs in approximately 1 in 2000 births[4] ; hence, it is a frequent reason for pediatric surgical consultation.[5] Neonatal intestinal obstruction is suggested by the following features[1] :

• Maternal polyhydramnios
• Feeding intolerance
• Bilious emesis
• Abdominal distention
• Delayed passage of meconium
• Absent transitional stools

Classic clinical signs of neonatal intestinal obstruction are vomiting, abdominal distention, and failure to pass meconium.[5] However, the infant's clinical presentation is dependent on the anatomic level of the obstruction, as follows:

• Foregut obstruction: Infants with foregut obstructions have difficulty swallowing, or they regurgitate or vomit gastric contents. Their abdominal examination may show localized distention, as in the left upper quadrant bulge that is typical of pyloric stenosis. Prolonged vomiting produces a characteristic electrolyte disturbance (hypokalemic metabolic alkalosis).

• High (jejunal) obstruction: Babies with high (jejunal) obstructions vomit bilious succus entericus. Their abdominal evaluation reveals a scaphoid abdomen; however, a mass (distended bowel) may be palpable. Nasogastric output is generally voluminous, and characteristic electrolyte abnormalities (hyperkalemic metabolic acidosis) are present.

• Distal small bowel or colonic obstruction: Babies with obstruction at these anatomic levels present with feeding intolerance and abdominal distention. If the diagnosis is delayed, feculent emesis may occur. Abdominal palpation may reveal a mass (intestinal duplication or intussusception). Plain radiographs show multiple dilated loops of bowel.

It is important to exercise clinical acumen. Conduct the following:

• Obtain an accurate history.
• Perform a careful, thorough physical examination.
• Obtain radiographs that corroborate or refute the "working diagnosis."

Once the correct diagnosis is ascertained, the surgeon can decide upon an appropriate intervention. Fortunately, the outlook for babies with intestinal obstruction is generally excellent.[6, 7]

Intestinal obstruction in a patient with peritonitis constitutes a surgical emergency; the presence of pain generally denotes ischemia. A loop of bowel may be twisted, creating a "closed loop" obstruction (see the image below). Because both limbs (loops) (afferent and efferent) are obstructed, there is no outlet and the bowel becomes massively distended. If the intraluminal pressure exceeds the blood pressure, perfusion ceases and the bowel dies. In "strangulation" obstruction, the mesentery is kinked and blood flow is impaired, causing ischemia and, ultimately, gangrene.

 

A patient with an incomplete or partial small bowel obstruction (SBO) may be treated expectantly; however, if the obstruction is complete (distended small bowel and collapsed colon), and the patient complains of abdominal pain, intestinal viability is threatened. Hence the adage, "Never let the sun set on a patient with intestinal obstruction!"

 

Embryology

The gastrointestinal (GI) tract arises from the yolk sac. At 3-4 weeks' GA (gestational age), it becomes a distinct entity.

The vitellin or omphalomesenteric duct connects the developing midgut to the yolk sac; it may persist as a Meckel diverticulum (see the image below). The alimentary tube is divided into foregut, midgut, and hindgut. Although there is some overlap, each division has a separate "named" blood supply.

 

Foregut

The esophagus, stomach, and duodenum are vascularized by multiple sources, including the thyrocervical trunk, intercostal vessels, and celiac axis.

Midgut

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

Hindgut

The distal transverse colon and the descending and sigmoid colon are supplied by the inferior mesenteric vessels.

The rectum is supplied by the internal iliac vessels.

Sites and causes of obstruction

Obstruction may occur anywhere in the GI tract:

Esophagus

Esophageal atresia (see the image below) is usually associated with tracheoesophageal fistula. Esophageal webs may also cause obstruction

 

Stomach

An antral atresia or mucosal web may occur, but it is exceedingly rare (see the next image). Hypertrophic pyloric stenosis is an acquired disorder and termed "congenital" to distinguish it from cicatricial stenosis caused by peptic ulcer disease (see the second image below). Gastric volvulus may also cause obstruction.

Duodenum

Duodenal atresia or stenosis is caused by a developmental error, incomplete canalization, by coalescence of vacuoles within the solid tubular anlage.[8] Duodenal obstruction is frequently associated with Down syndrome. It may also result from malrotation and/or volvulus (see the image below). When malrotation occurs, the tissue that normally creates the duodenal C loop (around the pancreas) overlies and compresses the duodenum; this tissue forms "Ladd bands," named in honor of the surgeon who devised the operation used to prevent midgut volvulus.

 

Small intestine

Jejunal or ileal atresia may have continuity in the bowel and mesentery, or there may be a gap of varying distance (see the first two images below). If a thromboembolic event destroyed the proximal mesentery, blood from the ileocecal vessels may flow retrograde into the proximal intestine; as the bowel winds around these vessels, it resembles an "apple peel” or "Christmas tree" (see the third image below). Rarely, there may be multiple obstructions, giving the bowel a "string of sausages" appearance (see the fourth image below).

 

Meconium ileus (see the next image) or an incarcerated inguinal hernia may also cause small intestinal obstruction.

 

Omphalomesenteric (or Meckel) bands may entrap a loop of small intestine or cause it to flip, creating a “closed-loop” obstruction, in which there is no egress; this leads to massive dilatation and ischemia (La Place law).

In the same manner that bulky ovarian cysts cause torsion, a bulbous loop of intestine or an enteric duplication may precipitate torsion. Prompt surgical intervention is necessary to salvage the intestine. Fortunately, these events occur infrequently.

 

Colon

Causes of colon obstruction include colonic atresia, meconium plug, small left colon syndrome, and Hirschsprung disease. Hirschsprung disease (aganglionic megacolon) may present during the newborn period or later. Faulty innervation (absence of ganglion cells) interrupts peristalsis, both contraction and relaxation. Agangionic bowel is unable to relax, and this nixes propulsion. (Before the etiology of Hirschsprung disease was understood, surgeons removed the dilated intestine, assuming that it was flaccid and unable to contract; however, the correct etiology was the exact opposite.)

Rectum

In rectal atresia, an obstruction is noted inside a normal-appearing anal canal.

Anus

Imperforate anus may cause obstruction. Anorectal anomalies are immediately apparent by inspection of the perineum (see the following image); however, accurate diagnosis may require radiographic studies, endoscopy, or laparoscopy. In high imperforate anus, the rectum ends as a fistula in the urinary tract in males and in the vagina in females.

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[8] :

• There may be a membranous obstruction, which usually is 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 is redundant and may protrude into the distal bowel like a “wind sock”. If the obstructing membrane is not apparent when the duodenum is opened, manipulating a tube from the stomach into the duodenum will help identify the obstruction.

• There may be discontinuity, with a gap of varying lengths, between the dilated proximal duodenum and the hypoplastic distal duodenum. If the gap is long, repair by duodenojejunostomy may be more feasible than duodenoduodenostomy.

• An annular pancreas marks the site of the obstruction, without actually being the cause of the obstruction. Duodenal atresia is corrected by anastomosing the proximal dilated duodenum to the distal duodenum.

Midgut anomalies

Malrotation

The peritoneum normally attaches the duodenum and the ascending colon to the retroperitoneum, creating the ligament of Treitz in the left upper quadrant of the abdomen and the right lateral paracolic gutter, the "white line of Toldt." Normally the two ends of the midgut are spread wide apart, and the base of the mesentery is wide. In malrotation, however, the proximal and distal ends of the midgut, the duodenum, and the cecum, are bound together by peritoneum (Ladd bands) as well as bound to and overlie their blood supply (superior mesenteric vessels). Thus, in malrotation the base of the mesentery is narrow and may become a fulcrum about which the entire midgut may twist. This is termed, midgut vovulus, and its occurrence is potentially catastrophic because the blood supply to the entire small intestine and half of the colon may be compromised.[9]  (As noted earlier, William E Ladd is the surgeon whose operative procedure is used to prevent midgut volvulus in a patient with malrotation.[10] ) 

Jejunoileal atresia

Jejunoileal atresia is caused by a vascular accident rather than a defect in embryogenesis. In their classic work on fetal dogs, Louw and Barnard showed that the extent of intestinal loss varied according to the timing and the extent of the disruption of the mesenteric blood supply.[11]

Atresias may be proximal or distal, single or multiple; there may be minimal or massive loss of intestinal length, depending upon the extent of the mesenteric vasculature disruption. The distal intestine may survive via retrograde blood flow from the ileocolic vessels. In these cases, the tiny (unused) intestine coils around the ileocecal vessels and looks like an "apple peel" or "Christmas Tree." Other in utero events such as gastroschisis or intussusception may also be associated with intestinal atresia.[12]

Meconium ileus

Meconium ileus is associated with cystic fibrosis, an autosomal recessive condition that diminishes membrane transport of chloride and water; this increases the viscosity of mucus and impairs transport by beating cilia, which is vital to tracheobronchial toilet. An estimated 10%-20% of newborns with cystic fibrosis present with meconium ileus, an association first described by Landsteiner in 1905.[13, 14]

Meconium plug syndrome may be considered as neonatal constipation. The infant's meconium is thick and difficult to evacuate. A water-soluble contrast enema confirms the diagnosis and, when followed by an evacuation, it is therapeutic. If the baby continues to have problems stooling, Hirschsprung disease should be considered and a rectal biopsy performed.

The following conditions may predispose to meconium plug syndrome or small left colon syndrome:

• Maternal preeclampsia
• Maternal diabetes mellitus
• Maternal ingestion of magnesium sulfate
• Prematurity
• Sepsis
• Hypothyroidism

Hirschsprung disease

Harold Hirschsprung, a Danish pediatrician, was puzzled by the death of two infants with refractory constipation. Autopsy showed dilatation and hypertrophy of the sigmoid colon and a normal-appearing rectum. In 1886, he reported this bizarre association and postulated a congenital etiology. Even after the absence of ganglion cells was identified as the determinant factor, it took time for surgeons to devise an effective operation, so convinced were they that the dilated, hypertrophied bowel was abnormal. In fact, the inability of the normal-appearing rectum to relax was the critical factor.

Peristalsis requires sequential contraction and relaxation, mediated by the neuroenteric system. During embryologic development, neural crest cells migrate along the bowel mesentry (cranial to caudal), differentiate, and populate the submucosa and muscular layers as ganglion cells. Normally, the rectum is reached by the tenth week following gestation. In Hirschsprung disease, the embryonic migration of ganglion cells is arrested proximal to the rectum—usually the sigmoid colon. The transition (± ganglion cells) is determined by the "leveling biopsy"; the most distal bowel with ganglion cells is "pulled through" the pelvis to become the "neorectum."

Mechanisms of obstruction

The mechanism by which intestinal obstruction may be caused include intrinsic (developmental) defects or extrinsic factors (kinks, twists), or the obstruction may be intraluminal, as follows:

• Intrinsic factors: The obstructed bowel may be in continuity, partitioned by a web (duodenal atresia), or the two ends may be entirely separate with a gaping mesentery, or there may be a functional abnormality (aganglionosis).

• Extrinsic factors: Bands (Ladd or Meckel) may cause compression; a bulbous duplication cyst may cause volvulus; or a knuckle of bowel may become incarcerated in an inguinal (or Morgagni) hernia.

• Intraluminal: Obstruction may be caused by inspissated meconium (meconium ileus or meconium plug syndrome).

Faulty embryogenesis leading to the development of neonatal intestinal obstruction may result from the following:

• Genetic factors: Duodenal atresia is associated with trisomy 21 in 30% of cases.[4]

• Environmental exposure in utero may lead to VACTERL syndrome: Vertebral anomalies, imperforate Anus, congenital Cardiac disease, Tracheoesophageal fistula, Esophageal atresia, Renal anomalies, and Limb anomalies (radius)

• Placental thromboembolic event(s) may cause fetal mesenteric vascular accidents and damage the developing intestine (atresia, stenosis).

Genetic factors

A single genetic abnormality may be associated with multiple anomalies.

• Babies with trisomy 21 may have imperforate anus, congenital heart disease, duodenal atresia, or Hirschsprung disease.

• Genetic abnormalities are rare in babies with jejunoileal atresia.

The gene for cystic fibrosis is carried by 4% of Ashkenazi Jews and 1% of Asians.

• In 1988, the genetic mutation causing cystic fibrosis was identified on the q31.2 locus on chromosome 7.

• Since then, over 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).[13]

• 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 and, given the poor motility of immature intestine, may lead to intraluminal obstruction, meconium ileus. Contrast enema will show an unused microcolon.

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, which is encoded by the gene EDNRB, 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, 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.

Malrotation

The incidence of malrotation is 1 in 6000 newborns.

• Obstructive symptoms usually occur during the first month of life (50% of cases)
• 90% of cases present during the first year of life.
• The diagnosis, however, may be delayed until adulthood. ^[15]
• One in 1000 newborns have an asymptomatic anomaly of intestinal rotation and fixation.
• Malrotation is associated with congenital diaphragmatic hernia, gastroschisis, and omphalocele.

Duodenal obstruction

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.
• Jejunoileal atresia occurs more frequently, 1 in 1,500 births.

Cystic fibrosis

Cystic fibrosis occurs in 1 in 3000 live births.

• This condition is the most common genetic disease in people of European origin.
• It is present in 10%-20% of babies with meconium ileus. ^[14]

Hirschsprung disease 

Hirschsprung disease affects 1 in 4,500-7,000 newborns.

• This condition is more common in white individuals.
• Males are affected four times as frequently as females.
• A family history of Hirschsprung disease is present in approximately 12.5% of patients.
• These patients typically have more extensive involvement (total colonic aganglionosis).

Imperforate anus

The incidence of imperforate anus is 3 per 10,000 births

• There is a female predominance
• Administration of folic acid during pregnancy reduces the incidence to 1 in 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.

Bowel dysmotility issues (refractory constipation and episodes of enterocolitis) such as the following may continue to plague patients with Hirschsprung disease, even after removing the aganglionic colon and rectum:

• Disordered motility in the proximal colon (elucidated by manometry)
• Internal anal sphincter achalasia (treated with Botox or sphincterotomy)
• Functional megacolon with stool retention (usually responds to bowel management program) ^[16]

The outlook in patients with anorectal anomalies is complex and is influenced by factors other than the operative procedure.

• If the sacrum is normal, usually the pelvic musculature and its innervation are intact.
• Colonic motility, in most patients with anorectal abnormalities, is sluggish, and the patients are constipated.
• A minority of patients, however, have hypermotility; these patients have diarrhea.
• Continence is far easier to achieve in patients with anorectal who have constipation.
• Bowel management programs, enemas, cathartics, and antispasmotics are all utilized, as indicated.

Morbidity/mortality

The morbidity and mortality from malrotation/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.[17]

Infants with intestinal obstruction are unable to feed; hence, their problem is immediately apparent.

Infants with pyloric stenosis vomit gastric content: milk or mucus. If there is associated gastritis, the emesis may be rust colored.

Bilious (green) gastric aspirate or emesis indicates that the intestines are obstructed below the ampulla of Vater.

An infant who was eating well but who suddenly vomits bile (green fluid) has malrotation/volvulus until proven otherwise by upper gastrointestinal (GI) studies.[8]

Surprisingly, a survey of 175 knowledgeable people (pediatricians, neonatologists, nurses, midwives, and parents) determined that most respondants (75%) did not know that the color of "bilious emesis" is green.[18]

Important observations to make in examining an infant with intestinal obstruction include the following:

• Is the baby's abdomen scaphoid or distended?
• Is there a palpable mass (usually the obstructed loop of intestine)?
• Does the abdomen have rippled appearance? Do the waves feel ropey (dilated intestine)?
• Are bowel sounds present or absent or hyperactive?
• Is the abdomen tender?

Peritonitis is an ominous sign, suggesting bowel ischemia or necrosis, sepsis, and multisystem organ failure. Closely monitor for the following signs:

• Hypotension and tachycardia
• Prolonged capillary filling and pallor
• Hematochezia (intussusception, necrotizing enterocolitis)
• Thrombocytopenia and Coagulopathy
• Respiratory failure

Duodenal atresia/stenosis

Vomiting and right upper quadrant fullness complement the radiologic "double-bubble sign" in duodenal atresia. This fullness may disappear upon placement of an orogastric tube. In 85% of patients, the obstruction is distal to the ampulla of Vater, and these patients have bilious vomiting. Patients with duodenal atresia should be evaluated for trisomy 21.

Malrotation/volvulus

Babies with malrotation/volvulus present with sudden onset of bilious vomiting. Initially, the abdomen is scaphoid. Midgut volvulus begins as an incomplete closed-loop obstruction; however, with the passage of time, the obstruction becomes complete and the baby's abdomen becomes increasingly distended. Obtain an urgent upper GI onstrast study.

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 distention and a palpable mass.

Ileal atresia

Infants with distal bowel obstruction present with abdominal distention, delayed passage of meconium, and absent transitional stools. Bowel sounds may be hypoactive or absent (fatigue in chronic obstructions).

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 disease usually have distended abdomens and are intolerant of feedings; often, passage of meconium is delayed. A contrast enema study may be diagnostic (delay digital rectal examination until after the radiologic study) and therapeutic (initiating a bowel movement). Some neonates with Hirschsprung disease may be managed with rectal dilatation and irrigations and undergoing a primary pull-through procedure. Infants with enterocolitis, however, should be treated with diversion (a "leveling colostomy").

Strangely, some babies with Hirschsprung disease present later in life, perhaps because breast milk has so little residue. Later, when additional foods are added to the baby's diet, symptoms of constipation develop.[19]

Imperforate anus

A diagnosis of imperforate anus is imediately obvious upon inspection of the newborn's perineum. Anorectal malformations range from anterior displacement of the anal opening to an absent patent anus. Infants with imperforate anus (see the following image) may have abnormalities of the sacrum; boys with high imperforate anus will have a rectourinary tract fistula, which may be demonstrated by the presence of meconium in the urine.

When considering intestinal obstruction in the newborn, useful information may be gleaned from plain x-rays and ultrasonography, which can be performed in the nursery. Water-soluble contrast enemas may be both diagnostic and therapeutic (meconium plug syndrome). Ensure the infant is well hydrated and kept warm during the contrast enema, and remind the radiologist to be gentle during instillation of the contrast material, because the colon may be tiny and unused.

Complete or incomplete intestinal obstruction

"Atresia" denotes a complete obstruction, whereas "stenosis" implies a partial obstruction, usually from a fenestrated web.

Malrotation/volvulus may simulate the double-bubble radiographic appearance of duodenal atresia, but the initial radiographs in malrotation/volvulus usually show air in the distal intestine, whereas duodenal atresia does not. These considerations may be helpful in determining the urgency of surgical intervention.

Paradoxically, infants with distal small bowel obstruction may pass meconium stools. Whereas stooling usually indicates a partial obstruction, the obstructing event (mesenteric vascular accident or volvulus) may have occurred after meconium reached the colon. Babies must pass transitional stools (digested milk and meconium) to demonstrate intestinal continuity (patency).

Rectal stimulation in babies with Hirschsprung disease usually elicits an evacuation, because aganglionosis causes spastic contraction of the rectum (± the distal sigmoid colon). It may occur in conjunction with the meconium plug syndrome, which is typically relieved following administration of a water-soluble contrast enema.

Imperforate anus

Imperforate anus occurs in conjunction with the VACTERL association (vertebral, anal, cardiac, tracheal, esophageal, renal, and radius anomalies). The following investigations for concurrent anomalies are indicated:

• Ultrasonography of the kidneys and central nervous system (CNS)
• Echocardiography
• Plain radiographs of the vertebral column and forearm (radius)

Malrotation/volvulus

An upper gastrointestinal study usually suffices to diagnose malrotation/volvulus (see the image below), but computed tomography (CT) scanning may have been ordered prior to consultation.

 

Normally, the superior mesenteric artery lies to the left of the superior mesenteric vein. Reversal of this spatial relationship suggests malrotation with midgut volvulus (see the CT scan below).

Polyhydramnios occurs in 50% of pregnancies in which the fetus has duodenal obstruction. The dilated stomach and duodenum may be visualized with fetal ultrasonography, and the image is similar to the double-bubble appearance of the plain radiographs obtained after birth. Prenatal ultrasonography may also detect jejunoileal atresia. Polyhydramnios occurs with proximal intestinal atresia, but usually not when the obstruction is distal.

A complication of meconium ileus is in utero perforation, which ocurs proximal to an obstruction. Meconum escapes from the intestine and is then contained by adjacent loops of intestine, creating a pseudocyst. Intense inflammation follows, giving this condition its appellation “meconium peritonitis.”

Distinctive ultrasonographic features of meconium peritonitis include the following:

• Meconium pseudocyst (an echogenic mass)
• Abdominal calcifications
• Ascites
• Intestinal obstruction

If the perforation seals and only a small amount of meconium escapes, scattered calcifications will be seen on abdominal radiographs because extraluminal meconium calcifies.[21]

Duodenal obstruction

Plain x-rays of the abdomen show the classic “double-bubble sign” of duodenal atresia. Air is an excellent contrast medium and may be introduced into the baby’s stomach via a nasogastric tube if duodenal obstruction is suspected. Incomplete duodenal obstruction mandates contrast radiography to differentiate duodenal atresia from malrotation/volvulus. Significant dilatation of the duodenum indicates chronicity, whereas minimal dilatation suggest an acute event.

Malrotation/volvulus

If malrotation/volvulus is suspected, an upper gastrointestinal (GI) series should be obtained as soon as possible.[22, 23]

Corroborative radiographic findings include the following:

• Incomplete obstruction of the duodenum may occur from Ladd bands in the absence of volvulus (indicated by the spiral below the obstruction).
• The ligament of Treitz (duodenojejunal junction) is located to the right of the vertebral column (directly below the pylorus).

If a baby presents with abdominal distention and tenderness, with or without hematochezia, a barium enema is a more definitive study, because it helps to differentiate malrotation/volvulus from Hirschsprung enterocolitis.

Contrast enema signs of malrotation include the following:

• Absence of the splenic and hepatic flexures
• Incomplete descent of the cecum (it remains subhepatic)
• Impeded flow of contrast medium through the colon
• Volvulus: A "closed loop" obstruction; it involves the proximal and distal limbs of the intestinal loop

Jejunal atresia

In 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 small bowel obstruction

Typically, plain radiographs of distal small bowel obstruction reveal 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.

Hirschsprung disease

In babies with Hirschsprung disease, a contrast enema shows a transition zone, which is an abrupt change in the diameter of the narrow aganglionic rectum and the proximal obstructed colon. Failure to evacuate the contrast medium within 24 hours also suggests 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 and helps to differentiate high from low imperforate anus. This radiographic study is best performed 12-24 hours after birth to allow swallowed air to reach the rectum.

Newborns with a low imperforate anus have a perineal fistula; in babies with a high imperforate anus, the rectal fistula ends in the genitourinary system (the bladder, urethra, or vagina). Low imperforate anus may be repaired during the newborn period by perineal anoplasty. In newborns with high imperforate anus, a safer option is a temporary colostomy (3-6 months) followed by posterior sagital anorectoplasty.

Anal manometry

Anal manometry is utilized in patients with Hirschsprung disease to measure the pressure of the muscles of the anal sphincter. A balloon is inserted into the rectum and inflated. Normally, this elicits initial resistance, followed by relaxation. In Hirschsprung disease, the initial resistance (high pressure) never abates; the rectum never relaxes, following distention. Obviously, the study is not possible to perform in uncooperative children.

Rectal biopsy

If the contrast enema suggests Hirschsprung disease, a confirmatory suction rectal biopsy is performed.

• The instrument looks like a pencil with a side opening. It is inserted into the rectum (>2 cm) with the opening pressed against the posterior rectal wall.
• Suction is applied to pull a bit of rectal mucosa into the instrument.
• A trigger is pulled, amputating this bit of mucosa, which is submitted to pathology for examination.
• If ganglion cells are found, the baby is normal. If ganglion cells are not identified, a larger specimen is provided to the pathologist to ensure that the absence of ganglion cells was not because the specimen was inadequate. 

Pathologic examination of the rectal mucosa is facilitated by use of acetylcholinesterase, which stains the hypertrophic nerve fibers in Hirschsprung disease.[24]

Intestinal obstruction causes fluid and electrolyte losses from vomiting in proximal obstructions and from sequestration of fluid (within the intestines) in distal obstructions. To minimize morbidity and mortality, these deficits must be corrected while obtaining appropriate diagnostic studies. In addition, the clinician must perform the following:

• Decompress the intestinal tract (orogastric tube)
• Provide respiratory and cardiovascular support, as needed
• Administer intravenous antibiotics, in anticipation of surgery

Consultations

Treatment of neonatal intestinal obstruction requires collaboration between the neonatologist and pediatric surgeon to ascertain the correct diagnosis and proceed with appropriate treatment. When the acute problem is associated with another chronic disease, such as cystic fibrosis, early and ongoing consultation between these specialists is appropriate and appreciated.

Distal small bowel obstruction

A Gastrografin (diatrizoate) enema study should be obtained in babies with distal small bowel obstruction. Contrast enemas are diagnostic and may be therapeutic, because Gastrografin acts as a detergent, loosening the sticky meconium and promoting evacuation (>50% success rate).

Multiple enemas may be required in babies with meconium plug syndrome. If the previous enema elicited an evacuation but the baby is still obstructed, another enema may be tried. However, if the previous enema was ineffective, it may be time to consider surgery. Before success is declared, the enema fluid must reach the terminal ileum. Diatrizoate and N-acetylcysteine may also be instilled via a nasogastric tube. Hyperosmolar solutions suck fluid into the bowel and soften the thick meconium; however, their use entails a slight risk of perforation (3%-10%).

Intussusception

Air insufflation has supplanted hydrostatic reduction in intussusception. Findings from a meta-analysis of 32,451 children with intussusception (ages 1 day to 22 years) found the following[25] :

• Air insufflation success: 83%
• Hydrostatic success: 70%
• Similar rates of perforation (0.39% air vs 0.43% hydrostatic reduction) and recurrence (6% vs 7.3%) between the two groups
• Higher morbidity of perforation in hydrostatic reduction group (spillage of contrast into the peritoneal cavity)

​Esophageal atresia (EA) and tracheoesophageal fistula (TEF)

Traditionally, infants with EA/TEF have been segregated according to the following features:

• Maturity (term vs premature)
• Weight (appropriate for gestational age or small for gestational age)
• Associated lung disease (hyaline membrane disease [HMD])
• Accompanying congenital heart disease and other anomalies

The lungs of term babies with EA/TEF are in optimal condition at birth, whereas premature infants suffer from HMD.

Delay (in both groups) risks antegrade passage of air through the TEF into the stomach, and positive pressure in the stomach facilitates reflux of gastric secretions (acid) into the lungs. As general rule, the body can withstand one insult with minimal sequelae but not repeated insults.

Positive-pressure ventilation exacerbates the above dynamics. The lungs in HMD are noncompliant; surfactant is given to expand the alveoli. Positive-pressure ventilation forces air through the TEF into the gastrointestinal tract, which increases intra-abdominal pressure, thereby elevating the diaphragm and increasing the amount of pressure required to inflate the lungs.

HMD tends to improve over time, as long as the baby’s lungs are not injured by ventilator-induced barotrauma (excessive pressure) or high oxygen concentration. Neonatologists carefully avoid excess pressure and oxygen, and ventilators that are specially designed for premature infants are available.

Definitive repair of EA/TEF may be performed soon after birth in term babies, but for premature babies, it is desireable to wait until their lungs recover—but how is that possible, given the following dynamics?

• Positive-pressure ventilation causes air to pass through the TEF into the stomach.
• Distention of the stomach and intestines increases the intra-abdominal pressure.
• Greater pressure is required to expand the lungs.
• More air passes through the fistula into the stomach and intestines.
• A vicious cycle ensues.
• Gastric rupture has even occurred from excessive ventilatory pressures.

Insertion of a gastrostomy tube breaks the vicious cycle and allows the definitive operation to be postponed until the baby's lungs are in optimal condition.[26]

 

If the lungs are so stiff that too much of the inspired gas escapes through the gastrostomy tube, the tube may be placed to “underwater seal drainage,” and the depth of the water level may be altered to resist the escape of inspired gas (through the gastrostomy tube) that is meant to inflate the lungs.[27]

Or a Fogarty embolectomy catheter can be inserted through the gastrostomy tube into the esophagus to the origin of the TEF (utilizing fluoroscopy); inflating the balloon at the tip of the catheter occludes the fistula.[28]

Note: Routine placement of gastrostomy tubes in babies with EA/TEF is not currently practiced for the following reasons:

• Gastrostomy tubes tether the stomach to the anterior abdominal wall, making the intrathoracic esophageal anastomosis more difficult.
• These tubes increase the incidence of gastroesophageal reflux and, therefore, the necessity for medications and surgery to correct this problem.

Despite these negative considerations, insertion of gastrostomy tubes (in selected cases) may allow the baby's lungs to recover sufficiently for the definitive operation to be performed safely.

Duodenal atresia

Babies with duodenal obstruction require fluid and electrolyte restoration and nasogastric tube decompression. These infants should also 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 radiography.

Malrotation/volvulus

If malrotation/volvulus is suspected, expeditious diagnostic studies must be obtained, followed by urgent relief of the (strangulation) 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. Administer broad-spectrum antibiotics because ischemic or necrotic bowel may be encountered. Delay in treating malrotation/volvulus may lead to catastrophic loss of intestine.

Jejunal atresia

In patients with jejunal atresia, nasogastric suction decompresses the proximal atretic bowel. Intravenous (IV) fluids are given for maintenance and replacement of fluid losses. A contrast enema corroborates the diagnosis and excludes a second, more distal obstruction. Postoperative parenteral nutrition as well as respiratory, cardiovascular, and/or hemodynamic support may be necessary.

Meconium ileus

In cases of meconium ileus, nasogastric decompression, IV fluids, and antibiotics are administered. A diatrizoate enema may be effective in loosening the meconium impaction. The volume of enema fluid must be carefully proportioned in premature infants.[29] Diatrizoate diluted with N-acetylcysteine may also be administered by nasogastric tube. By sucking fluid into the lumen of the bowel, hyperosmolar solutions (10% acetylcysteine) loosen meconium, but they also exacerbate electrolyte disturbances and hypovolemia. Use of hyperosmolar enemas also entails a small risk of perforation and sepsis.

Pyloric stenosis

Surgical intervention (pyloromyotomy) is the treatment for pyloric stenosis. This procedure divides the muscles of the pylorus are  to open up the gastric outlet.

Duodenal atresia

Correction of duodenal atresia requires identifying the cause of the obstruction (ie, atresia, annular pancreas, or web), approximating the duodenum above and below the obstruction, and determining how best to retore continuity.

Malrotation/volvulus

Malrotation/volvulus is a surgical emergency. Delay in diagnosis may result in catastrophic necrosis of the twisted midgut. If the entire midgut is lost, the patient will be dependent upon parenteral nutrition while awaiting an intestinal transplant.

The initial step in correcting malrotation/volvulus is to eviscerate all of the intestines and then look at the retroperitoneum; the colon will be found wrapped transversely around the base of the mesentery. The volvulus is reduced by twisting the entire midgut in a counter-clockwise direction; this maneuver unwinds the colon and restores blood flow to the midgut. Bands attaching the duodenum to the colon are divided, and the proximal and distal limbs of the midgut are separated as widely as possible. The intestines are returned to the abdomen: duodenum to the right, colon to the left; this spreads apart the superior mesenteric vessels, which fuse to the retroperitoneum, and prevents further twisting.

 

Whereas normally the mesentery spreads from the ligament of Treitz in the left upper quadrant to the cecum in the right lower quadrant, the ”Ladd procedure” reverses the orientation: The duodenojejunal junction is moved to the right lower quadrant and the cecum to the left upper quadrant. The mesentery becomes adherent to the retroperitoneum, and this prevents recurrent volvulus. The appendix is removed, because in its new location, diagnosing appendicitis would be chalenging.

Jejunoileal atresia

Surgical treatment of jejunoileal atresia involves resection and anastomosis of the proximal and distal segments of intestine. A diverting enterostomy is generally avoided. Similar to duodenal atresia, tapering the proximal, dilated segment may be necessary to improve peristalsis. The ileocecal valve is preserved, as this structure prevents egress of bacteria from the colon into the small intestine, causing bacterial overgrowth and malabsorption.

Meconium ileus

Calcifications seen on plain x-rays indicate that an intestinal perforation occurred in utero and spontaneously sealed. Alternatively, the extruded meconium may be walled off by adjacent loops of intestine, creating a pseudocyst. Affected babies have "meconium peritonitis"; their appearance is unmistakable: a distended, erythematous abdomen. Laparotomy is undertaken to drain the meconium pseudocyst and identify the site of the perforation, which is converted to an enterostomy. In uncomplicated meconium ileus, an enterotomy (or appendicostomy) with irrigation and evacuation of the obstructing meconium relieves the intraluminal obstruction. Alternatively, an ostomy for diversion and access for distal instillation of N-acetylcysteine may be necessary.

Meconium plug syndrome

Operative intervention is indicated in infants with meconium plug syndrome, if contrast enemas are unsuccessful in loosening the meconium obstruction and prompting evacuation.

Hirschsprung disease

Treatment of Hirschsprung enterocolitis entails rectal irrigations, antibiotics, and fluid resuscitation. A colostomy may be necessary to decompress the colon and allow the infant to resume feedings expeditiously.

In the absence of enterocolitis, a pull-through procedure may be performed during the neonatal period; however, some surgeons open a "leveling colostomy" (at the transition zone) and perform the pull-through procedure (bring the colostomy to the anus) when the baby is 3-6 months old.

Innovations in the treatment of Hirschsprung disease include transanal and laparoscopic pull-through procedures.

 

Imperforate anus

Low imperforate anus (perianal or perineal fistula) may be repaired during the neonatal period (perineal anoplasty). In babies with high imperforate anus, a colostomy is performed, and the definitive repair (posterior sagittal anorectoplasty) is performed when the baby is 3-6 months old.[30] The ultimate outcome depends upon the precision of the surgery, the presence or absence of normally innervated musculature, and the degree of colonic dysmotility.

In the postoperative period, fluid and electrolyte imbalance, altered glucose metabolism, and need for ventilatory assistance may occur. Patients may have third-space fluid sequestration, causing their intravenous (IV) fluid requirements to be increased 1.5-2 times normal.

Heart rate, blood pressure, capillary refill, and urine output reflect the adequacy of fluid resuscitation. Closely monitor electrolyte levels; third-space fluid sequestration may be replaced with half normal saline (0.45%) or normal saline (0.9%).

Nasogastric tube decompression “puts the injured part at rest” and provides time for healing. The duration and depth of the anesthetic reflect the length and complexity of the surgical procedure; the analgesic requirement relates to respiratory depression and the duration of postoperative ileus. Abdominal distention impairs diaphragmatic excursion and increases the necessity of respiratory support.

The duration of antibiotic therapy depends on how much contamination occurred during the operative procedure.

Total parental nutrition (TPN) may be advisable until bowel function returns. Even after resumption of peristalsis, enteral feedings may not be tolerated. The intestinal mucosa must regenerate following ischemic or infectious injury before it is able to absorb nutrients. Trophic feedings stimulate adaptation, and predigested or elemental formulas may be tolerated more readily. If the terminal ileum is resected, anticipate derangements in folate metabolism and in enterohepatic circulation of bile salts.

Cardiovascular and coagulation complications, shock, and disseminated intravascular coagulation may occur in patients with intestinal ischemia or necrosis. Management of these issues may challenge even the most experienced clinicians.

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

General complications

General complications of intestinal obstruction include the following:

• Intestinal obstruction from strictures and adhesions
• Prolonged ileus because of impaired gut motility
• Malabsorption caused by massive resection or intestinal injury from ischemia or infection
• Inadequate venous access, including catheter sepsis

Percutaneously inserted catheters (PIC) are increasingly used, but the caliber of these catheters is small and infusion of blood products may require alternative routes.

Complications of total parenteral nutrition (TPN) include cholestatic liver disease, nutritional deficiencies, and problems related to venous access. Meticulous attention to the composition of TPN solutions and strict protocols regarding insertion and maintenance of central venous catheters may minimize complications. Fish-oil lipid emulsion has proved to be less toxic to the liver than soybean oil lipid formulations.[31]

Normal oropharyngeal activities (eg, sucking) should be encouraged and the skills of occupational therapists employed to overcome oral aversion.

Development of adhesions is always worrisome, as are anastomotic strictures. In 1,541 children who had intestinal surgery, approximately 10% developed adhesions proximate to the operative site, and 5% occurred remotely.[32]

Handling the bowel gently, limiting contamination of the peritoneal cavity, and employing meticulous technique may limit anastomotic strictures and postoperative adhesions.

Decreased gut motility may occur following intestinal resection. Dilatated intestine above an obstruction may be slow to recover normal caliber and function. Interruption of vagal neuroenteric pathways by an atresia or by resection and anastomosis may contribute to abnormal intestinal motility.

Two promotility pharmacologic agents are useful: metoclopramide and erythromycin. Note the following:

• Randomized controlled trials of these drugs yield varied results relative to placebos.
• Both drugs have side effects that may limit their usefulness.
• Their effectiveness is substantiated by anecdotal reports and personal experience, rather than evidence-based medicine.

The length of small bowel in a normal term infant is approximately 250 cm. In adults, it is 600-800 cm. The minimum length for normal function in a term infant is estimated to be 75 cm. Resection of more than 60% of the small bowel or resection of crucial anatomic areas (eg, the ileocecal valve) may cause malabsorption and failure to thrive. Bacterial overgrowth also may contribute to malabsorption.

Short-gut syndrome occurs when the intestine cannot absorb enough nutrients for normal growth and development. Note the following:

• Children with short-gut syndrome require supplemental parenteral nutrition or elemental formulas.
• Pharmacologic agents are used to slow motility.
• Probiotics have been shown to normalize bowel flora and improve absorption of nutrients.
• Bowel-lengthening procedures require dilated bowel, which may be surgically created by intraluminal valves.
• Pharmacologic manipulations, including nutritional and hormonal treatments, may assist in weaning children from dependence upon parenteral nutrition.
• Techniques such as the serial transverse enteroplasty (STEP) procedure may offer improved bowel function and length in some patients.

Patients with infarction of the midgut or multiple intestinal atresias may lack enough intestine to survive. Whether or not life support should be continued is a difficult ethical decision, and communication with insightful colleagues is advisable. Small-bowel transplantation, with or without other viscera such as the liver and pancreas, is performed in select centers in the United States, with varying results.

Complications associated with specific conditions

Malrotation

With malrotation, complications depend upon 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 volvulus and the Ladd procedure, followed in 24 hours by a "second look" procedure, may permit salvage of intestine that initially appeared nonviable. If a large amount of intestine is removed and a proximal jejunostomy created, large volumes of fluid and electrolytes will be lost, making the formulation of parenteral nutrition solutions extremely challenging. After the jejunostomy is closed, the colon will absorb fluid and electrolytes and simplify the patient’s management; however, severe diarrhea and its attendant complications may occur (at least temporarily).

Duodenal atresia

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

Jejunoileal atresia

In uncomplicated intestinal atresia, complications are not common. The obstruction resulted from an in utero event injuring a segment of intestine. If the bowel is in good condition, primary repair is possible. Small bowel atresia may occur in conjunction with gastroschisis; however, the exposed bowel may be inflamed and not amenable to performing an anastomosis. Also, it may be difficult to differentiate dilatation from an in utero kink to that from an actual atresia. A correct assessment may not be possible until the inflammation has subsided.

Abnormal bowel motility and function longer than 4 weeks postoperatively should be evaluated by a contrast study, to look for a mechanical obstruction from extrinsic bands, or an atresia or ischemic stricture.

Meconium ileus and meconium plug syndrome

Complications in treating babies with meconium plug syndrome are 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, characterized by abdominal distention and explosive diarrhea, especially following dilation of the anal sphincter (by digital examination).

Sepsis (enteric organisms) may result from bacterial overgrowth in dilated, poorly motile bowel. The mechanism is bacterial mucosal translocation and invasion of the mesenteric vasculature.

Management includes intravenous (IV) fluids and antibiotics, and rectal irrigation with a tube inserted through the anus. Stool should be tested for Clostridium difficile toxin; if positive, oral vancomycin or metronidazole is indicated. A diverting colostomy may be necessary, if rectal irrigations and Botulinum toxin and anal internal sphincterotomy all fail in preventing episodes of enterocolitis.

Imperforate anus

Babies with 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 may occur if 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 mucosal prolapse through the neoanus are readily repaired. Dr Alberto Pena has devised a bowel-training program that is helpful in managing anorectal patients with constipation or incontinence.[30]

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

Class Summary

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

Diatrizoate enema (Hypaque Sodium)

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).

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.

Metoclopramide (Metozolv)

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

Erythromycin (E.E.S., Erythrocin)

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.

Class Summary

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

Vancomycin

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. Vancomycin 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.

Metronidazole (Flagyl)

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.