Disclosure
Bowel obstruction in the newborn is one of the most common and potentially dire newborn surgical emergencies. Successful management of a newborn with a bowel obstruction depends upon both timely diagnosis and prompt therapy. Many causes of bowel obstruction in the newborn can be readily diagnosed with physical examination and simple radiographic examinations. Crucial to the management of most newborn bowel emergencies is effective nasogastric or orogastric decompression. Early consideration of the need for surgical intervention may mean the difference between intestinal salvage and catastrophe. Have a high index of suspicion; often, a surgeon's approach to a newborn with a potential bowel obstruction is to rule out the worst possibility first. Important signs to identify are stools containing occult blood, hypotension, metabolic acidosis, progressive respiratory failure, and thrombocytopenia. A delay in diagnosis of a newborn bowel obstruction may exacerbate the compromise of dilated bowel upstream of the obstruction; result in clinical deterioration with dehydration, fever, and unconjugated hyperbilirubinemia; and predispose the child to complications such as aspiration pneumonia. For example, a child with bilious emesis must be considered to have malrotation with volvulus until proven otherwise. A few hours may make the difference between full recovery and massive bowel necrosis. If a newborn in distress demonstrates evidence of a high-grade proximal small-bowel obstruction with some air past the duodenum, suspect volvulus and urgently consider an exploratory laparotomy. Signs and symptoms of a newborn bowel obstruction may be subtle and nonspecific. Bilious gastric aspirates or emesis suggests an obstruction distal to the ampulla of Vater, usually in the proximal small bowel, and demands an immediate evaluation. As a rule, consider any infant or child with bilious vomiting to have a bowel obstruction until proven otherwise; emergent assessment is mandatory. Abdominal distention or tenderness is a less-specific finding and may indicate bowel obstruction or bowel compromise from other causes, such as septic ileus or necrotizing enterocolitis. An abnormal gas pattern visualized on abdominal radiography often leads to the diagnosis of bowel obstruction. The importance of a thorough physical examination cannot be overstated. Inspection and palpation of the infant's abdomen and perineum often suggest a diagnosis. An incarcerated hernia, an anterior ectopic anus, or imperforate anus can be identified with careful perineal inspection. Inability to pass a nasogastric tube may be diagnostic of esophageal atresia. Diagnostic modalities, such as simple abdominal radiography, radiographic contrast studies, and abdominal ultrasonography, can be extremely helpful in identifying the cause of a neonatal bowel obstruction. A more detailed discussion of the causes of bowel obstruction in the newborn can be divided into proximal bowel obstruction and distal bowel obstruction. Patients with proximal obstruction often present with different clinical scenarios than patients with distal obstruction, and different diagnostic approaches are indicated. Understanding the causes and evolution of neonatal bowel obstruction is enhanced by careful prenatal imaging and diagnosis. Once a newborn presents with evidence of bowel obstruction, dividing the differential diagnoses into categories of surgical versus nonsurgical etiologies is useful.
Prenatal imaging, especially with ultrasonography, can be extremely effective in detecting of bowel obstruction. A fetus with proximal bowel obstruction may present with polyhydramnios that occurs when the normally large volume of amniotic fluid swallowed by the fetus remains in the amniotic sac. Approximately 50% of newborns with duodenal atresia have polyhydramnios. Polyhydramnios increases the risk of premature birth. The high resolution of fetal ultrasonography and fetal magnetic resonance imaging (MRI) frequently enables identification of abnormal features of the bowel in the fetus. Both studies readily identify a dilated loop of bowel and are good predictors of a proximal bowel obstruction such as atresia or volvulus. In some situations, fetal diagnosis of a proximal bowel atresia may prompt amniocentesis because a strong relationship exists between some types of bowel obstruction and some chromosomal anomalies. For example, children with duodenal atresia have a higher incidence of trisomy 21. Thus, prenatal imaging of a bowel obstruction may complement other modalities of prenatal counseling for parents. Ultrasonography is useful for identification of abnormal loops of bowel in the fetus. Unlike in the newborn, the fetal bowel is gasless, without swallowed air that distorts the image. As mentioned above, a dilated loop of small bowel may suggest an atresia or volvulus. A whirlpool appearance to the bowel and bowel mesentery may indicate malrotation with volvulus. Echogenic bowel suggests bowel compromise. In approximately one third of fetuses with echogenic bowel on prenatal ultrasonography, a malformation of the GI tract is later confirmed. Some prenatal ultrasonographic or MRI features are associated with specific abnormalities in the fetus. A dilated proximal esophagus is often observed with esophageal atresia. Bowel within the thoracic cavity confirms a congenital diaphragmatic hernia. More subtle signs can be observed as well. Flecks of calcification throughout the peritoneal cavity suggest meconium peritonitis from prenatal bowel compromise and perforation and strongly suggest cystic fibrosis. Finally, the nonspecific finding of ascites can suggest compromised bowel in the fetus. Other nonsurgical causes of postnatal bowel dysfunction, such as hydrocephalus or renal disease, may also be observed on prenatal imaging studies. The prenatal diagnosis of a bowel obstruction may directly improve postnatal outcome by expediting its surgical management. Immediate surgical intervention may be needed in patients with congenital diaphragmatic hernia, esophageal atresia, or malrotation with volvulus. Many children with a prenatal diagnosis of bowel obstruction are referred for delivery in a center where pediatric surgeons are readily available. In situations where prenatal imaging has been used to diagnose an anatomic cause of bowel obstruction, focused resuscitation in the delivery room may facilitate preoperative stabilization. If positive pressure respiratory support is needed, rapid intubation without prolonged bag-mask ventilation may minimize bowel distention and improve outcome. A child born with a possible bowel obstruction should undergo immediate nasogastric decompression because progressive bowel distention from swallowed air may cause further compromise. Fluid sequestration in a dilated loop of obstructed bowel may require aggressive parenteral fluid administration to maintain the patient's hemodynamic stability. Preoperative laboratory studies, antibiotics, and vitamin K may also be an appropriate part of the delivery room resuscitation.
The diagnostic evaluation of a neonatal bowel obstruction must be expeditious because some causes of bowel obstruction rapidly cause ischemia leading to necrosis and bowel death. Bilious vomiting is perhaps the most common symptom that initiates an emergent workup for bowel obstruction. Physical signs, such as abdominal distention or tenderness, abdominal wall erythema, a palpable mass, or visible loop of bowel, also demand further investigation. In some situations, an exploratory laparotomy is the best diagnostic test. Most infants pass meconium in the first 12-24 hours after birth. No newborn should be discharged from the hospital before passing meconium. The pattern of bowel gas on plain radiography can be used to differentiate between proximal and distal bowel obstruction. Duodenal atresia, a common cause of proximal small-bowel obstruction, often creates a double bubble sign on plain radiographic examination. A dilated stomach and obstructed duodenum, indented at the waist by the pylorus, produces this characteristic appearance. Plain radiography revealing malrotation with midgut volvulus may show a bowel gas pattern in the duodenum with an abrupt cutoff in the distal duodenum. A bird's beak sign may be observed. Radiography of jejunal atresia may also show a few dilated proximal loops of bowel with no distal bowel gas. If many nondilated loops of bowel are gas-filled but no air is observed in the rectum, a more distal cause of bowel obstruction is suggested. Ultrasonography can be helpful in making the diagnosis in newborns with a palpable abdominal mass. Tumors, intestinal duplication, mesenteric cysts, ovarian masses, or cystic lymphatic malformations may be identified by ultrasonography. A mass in the inguinal region may represent an incarcerated inguinal hernia. The use of upper GI series, ultrasonography, and contrast enema are discussed below in the context of each specific cause of bowel obstruction. An ileus, or functional bowel obstruction, may result from causes other than those requiring surgical intervention. Premature infants frequently demonstrate abdominal distention because of small amounts of subcutaneous fat making the abdominal wall more distensible and because of immature peristaltic function. Abdominal distention may also be the first sign of necrotizing enterocolitis, a particularly ominous disease process that can cause death in a neonate. Ileus can also be a symptom of neonatal sepsis, as well as a result of a central nervous system (CNS) lesion such as hydrocephalus or a subdural hematoma. Polycystic kidney disease may mechanically obstruct the bowel as well as predispose to an ileus. Metabolic disorders, such as hypothyroidism, are rare causes of chronic neonatal ileus that can masquerade as bowel obstruction for several months before the definitive diagnosis is made. Hirschsprung disease, the absence of ganglion cells in the distal bowel, can also cause chronic obstructive signs until the definitive diagnosis is finally made by rectal biopsy. |
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Most babies with a proximal bowel obstruction present with vomiting. Depending on the level of obstruction, abdominal distention may also be a feature. If the obstruction is distal to the drainage of the common bile duct at the ampulla of Vater in the second portion of the duodenum, the vomitus is likely to be bilious. The differential diagnosis for proximal bowel obstruction includes atresias, both duodenal and jejunoileal, as well as malrotation with volvulus. Responsibility rests with the clinician to expeditiously exclude the diagnosis of volvulus. Plain radiography of proximal bowel obstruction may demonstrate little gas beyond the proximal duodenum. Placement of a nasogastric tube may be both diagnostic and therapeutic. An upper GI contrast study through the nasogastric tube may be helpful. Malrotation and volvulusBecause of the potential for midgut volvulus and loss of the entire small bowel, malrotation represents perhaps the most feared cause for proximal small-bowel obstruction. Midgut volvulus from malrotation is a life-threatening surgical emergency in the newborn. Remember that malrotation is not synonymous with volvulus. Malrotation occurs in approximately 1 in 6000 newborns; rotational abnormalities may be present in as many as 1% of the population. Volvulus represents the acute twisting of the intestines upon their mesentery and can occur in a patient with malrotation due to the lack of normal fixation of the bowel to the retroperitoneum. Patients who develop obstructive symptoms of malrotation usually present in the first month of life. Of those who are eventually symptomatic, 90% present in the first year of life. Associated anomalies include duodenal or jejunoileal atresia, Hirschsprung disease, and, rarely, mesenteric cysts. Malrotation results from a failure of the GI tract to complete its normal rotation as it returns to the abdominal cavity at 8-10 weeks' gestation. The bowel develops outside of the abdominal cavity as a single long loop of bowel based on the pedicle of the superior mesenteric vessels. As the bowel returns to the abdomen, the proximal small bowel returns first and the duodenum rotates underneath the superior mesenteric vessels to assume a retroperitoneal position. Rotation continues as the large bowel returns to the peritoneal cavity, rotating over the vascular pedicle to place the ileocecal valve in the right lower quadrant and establishing the hepatic and splenic flexures. Fixation points develop in the peritoneum at the duodenum, ligament of Treitz, ileocecal valve, and right and left paracolic gutters. This arrangement results in a broad fixed base of the small-bowel mesentery by 10 weeks' gestation. If the rotation of the bowel is incomplete or does not occur, normal mesenteric attachments are absent and abnormal peritoneal bands may develop. These bands may obstruct the duodenum and are known as Ladd bands. Most worrisome in malrotation is the lack of peritoneal attachments of the bowel. The unfixed bowel may twist around itself and compromise the blood supply of the superior mesenteric pedicle. The initial presentation of a newborn with volvulus of the midgut may be bilious vomiting. The abdomen is initially soft and scaphoid and may or may not be tender on physical examination. As the obstruction progresses, the volvulus compromises flow in the superior mesenteric pedicle and the ischemic bowel becomes dilated, distended, and firm. The child may become hypotensive from sequestration of fluid within the obstructed bowel; peritonitis and shock may develop. Metabolic acidosis on laboratory evaluation may indicate bowel compromise. Prompt surgical intervention is required. Some patients with malrotation present with a more indolent course of long-standing partial obstructive symptoms, constipation, and associated intestinal dysmotility. A history of chronic intermittent abdominal pain may also be associated with malrotation, presumably from intermittent partial volvulus. Radiographic imaging that exhibits a characteristic pattern can confirm a diagnosis of malrotation in a stable patient. An upper GI series usually shows incomplete obstruction with extrinsic compression of the duodenum and torsion of the small bowel. The ligament of Treitz may be found in an abnormal position to the right of the midline or below the level of the pylorus. Obstructive bands may partially block the duodenum. The position of the splenic and hepatic flexure as well as the cecum may not demonstrate the normal fixation pattern to the right and left paracolic gutters. Ultrasonography may also be helpful in confirming the diagnosis. Normally, the superior mesenteric artery (SMA) lies to the left of the superior mesenteric vein (SMV). An SMA that lies to the right or anterior to the SMV suggests malrotation. Contrast enema may demonstrate the abnormal position of the cecum but is no longer considered the best study to establish the diagnosis of malrotation. Malrotation with midgut volvulus is a true surgical emergency in the newborn. Delay in operation may result in catastrophic loss of a large portion of the small bowel. In patients with severe midgut volvulus, the entire midgut is necrotic and the child cannot survive. Surgical treatment for malrotation is the Ladd procedure. A Ladd procedure includes evisceration of the midgut and immediate counterclockwise derotation of the gut to release the volvulus and reestablish flow of blood to the bowel. Obstructing Ladd bands from the colon to the duodenum are released. The position of the mesentery does not allow the bowel to be placed in a normal position within the abdomen; therefore, the bowel is returned to the abdomen in a manner that spreads out the mesentery as much as possible. The duodenum and small bowel are placed on the right side of the abdomen, and the colon is placed on the left, with the cecum in the left lower quadrant. Because the ileocecal valve now is on the left side of the abdomen, the appendix is removed. Development of new postoperative adhesions may secure the bowel in this new configuration to avoid recurrent volvulus. Morbidity and mortality from malrotation and volvulus are directly related to the extent of bowel necrosis. The mortality rate may be as high as 65% if more than 75% of the small bowel is necrotic at the time of laparotomy. Survivors may develop short bowel syndrome, with its associated complications of malabsorption and malnutrition. The Ladd procedure does not address the intestinal dysmotility associated with malrotation but rather prevents the risk of midgut volvulus. Thus, patients with constipation and motility problems from malrotation may not note improvement in their symptoms following the Ladd procedure. Duodenal atresiaDuodenal obstruction from atresia or web affects as many as 1 in 6,000-10,000 infants. Polyhydramnios is present in as many as 50% of fetuses with duodenal obstruction and frequently leads to prenatal diagnosis of duodenal atresia. This polyhydramnios may lead to fetal distress and premature delivery in one third of patients. Vomiting, abdominal distention, and a dilated loop of bowel on plain radiography are consistent features of duodenal atresia or web. Some atresias may be obstructing incompletely; in these situations, a small amount of distal bowel gas may be observed on plain radiography. Duodenal atresia is believed to occur from a failure of revacuolization of the lumen of the duodenum at 8-10 weeks' gestation. At earlier phases in fetal development, the lumen of the duodenum is obliterated by the proliferation of the layers of duodenal wall. Beginning at 8 weeks' gestation, a lumen is regenerated in the previously solid duodenum. If this process is incomplete, an atresia or web may occur. Duodenal web results from an obstructive band of mucosa that stretches across the duodenal lumen. These webs may be incomplete, or a web may stretch out distally in the lumen of the duodenum like a windsock. Duodenal atresia may also occur from an improper rotation of the pancreas to the right of the duodenum and may be associated with an annular pancreas. Development of duodenal atresia follows a different embryologic pattern from that of jejunoileal atresias. Unlike jejunoileal atresias, which are believed to result from a mesenteric accident, in patients with duodenal atresia, the mesentery of the duodenum is intact. The finding of duodenal atresia suggests an early error in development, and duodenal atresia may be associated with other congenital anomalies in as many as 50% of patients. Associated disease processes include trisomy 21 (40% of patients), imperforate anus, and congenital cardiac disease. An infant with duodenal atresia may present with bilious or nonbilious vomiting. If a complete duodenal atresia or web lies upstream of the ampulla of Vater, the vomiting is nonbilious. In 85% of patients with duodenal atresia, the obstruction lies distal to the ampulla or is incomplete. In these situations, vomiting is bilious. The abdomen is usually distended by the dilated duodenal loop but may be scaphoid if the obstruction is incomplete. Preoperative treatment for these patients includes fluid resuscitation and nasogastric decompression. Consultation with a cardiologist and echocardiography may be helpful because of the high incidence of associated anomalies. If the obstruction is incomplete as evidenced by some distal gas on plain radiography, urgent laparotomy may be necessary to differentiate duodenal atresia from malrotation with volvulus. Surgery involves resection or bypass of the atretic segment. A web must be identified and completely resected to the degree that it no longer obstructs the distal lumen. Many pediatric surgeons bypass rather than resect the atretic segment to avoid injury to the ampulla or to the pancreatic blood supply that usually is nearby. A severely dilated duodenum may require a tapering duodenoplasty to mitigate the poor long-term duodenal motility that can be observed in these dilated proximal segments. A nasoenteric feeding tube is often placed across the duodenal anastomosis for early decompression and late feeding. Jejunoileal atresiaAtresia of the jejunum or ileum is more common than duodenal atresia, occurring in 1 in 1500 births. Small-bowel obstruction from jejunoileal atresia may also lead to polyhydramnios. Premature delivery is observed in one third of patients with intestinal atresia. In contrast to duodenal atresia, jejunoileal atresia is widely considered to be a condition acquired during development, rather than a preprogrammed anomaly. In classic work on fetal dogs in 1955, Louw and Barnard demonstrated the pathophysiology by which intrauterine mesenteric vascular accidents produce atresia in the segment of intestine that is devascularized. The extent of atresia and the appearance of the atretic intestinal segment vary according to the timing and degree of the disruption of the mesenteric blood supply. Atresias may be focal or multiple throughout the small bowel. Interruption of the main superior mesenteric blood supply can result in atresia of most of the jejunum and ileum. Other abdominal conditions, such as gastroschisis or intrauterine intussusception, may be associated with intestinal atresia, presumably from kinking, stretching, or otherwise disrupting the blood supply to the fetal bowel. Chromosomal anomalies are rare (<1%) in children with jejunoileal atresia. Infants with jejunoileal atresia may present with distention and vomiting. Thumb-sized loops of bowel with air-fluid levels can be observed on plain radiography. As many as 12% of newborns with jejunoileal atresia may have intra-abdominal calcifications observed on plain radiography. These calcifications are consistent with meconium peritonitis, resulting from necrosis and perforation of a devascularized loop of bowel. Blood flow to the segments immediately proximal and distal to the atresia may be compromised. For this reason, preoperative nasogastric decompression is vital to limit distention of the intestine proximal to the atresia. A delay in diagnosis or operation may distend and compromise the poorly vascularized, dilated, often bulbous bowel. Some surgeons insist on a contrast enema to exclude colonic atresia, while others examine the colon intraoperatively to ensure patency of the distal bowel. Surgery for jejunoileal atresia involves resection and primary anastomosis of the atretic segments. Diverting ostomies are avoided if possible. As with surgery for duodenal atresia, tapering of the proximal dilated segment occasionally is necessary to limit the motility problems observed with dilated proximal bowel. If at all possible, the ileocecal valve is preserved. Long-term outcomes are generally excellent if sufficient bowel is present for absorption and growth. Other causes of proximal bowel obstructionEsophageal atresia and tracheoesophageal fistula Esophageal atresia is a foregut malformation resulting from an error in separation of the esophagus from the respiratory tree. Newborn infants with esophageal atresia are unable to swallow their secretions and present with respiratory distress or an inability to nurse. Inability to pass a nasogastric tube is diagnostic of esophageal atresia. The common association of a distal tracheoesophageal fistula predisposes a newborn to aspiration of acidic gastric contents and respiratory distress. Preoperative management must take into account the danger of respiratory collapse with positive pressure ventilation because ventilated breaths may preferentially shunt through the tracheoesophageal fistula into the stomach. Repair of esophageal atresia involves ligation of the tracheoesophageal fistula and anastomosis of the proximal and distal ends of the esophagus, if possible. Occasionally, esophageal replacement with bowel or stomach is necessary. Anastomotic stricture, gastroesophageal reflux, and poor esophageal motility affect long-term outcome. Hypertrophic pyloric stenosis Gastric outlet obstruction from pyloric stenosis results from hypertrophy of the pylorus. This condition is acquired, although its etiology is not fully characterized. Hypertrophy of the pylorus is associated with reduced nitric oxide levels in the pyloric muscle tissue. Nitric oxide generally mediates relaxation of gastrointestinal smooth muscle so that pyloric obstruction may be related to a local reduction of nitric oxide levels in the pyloric muscle. Most children with pyloric stenosis present with nonbilious vomiting and dehydration at 4-6 weeks, although hypertrophic pyloric stenosis can be observed in babies younger than 1 week. The thickened pylorus muscle is often palpable; ultrasonography and contrast studies may be helpful in diagnosis. Operative pyloromyotomy is curative.
In contrast to obstruction in the duodenum or proximal small bowel, patients with a distal bowel or colonic obstruction often present in the newborn period with subacute clinical and radiographic features characterized by distention. In most patients with distal obstruction, the bowel is not immediately in danger of compromise, thus time is available for appropriate workup and diagnostic studies. Distention, rather than vomiting, is frequently the dominant clinical feature. Imperforate anus and other anorectal anomalies may be readily diagnosed on inspection of the perineum. Plain radiographic findings often suggest a distal obstruction with a pattern of proximal air-filled dilated small-bowel loops but no distal air. In these patients, a contrast enema may be both diagnostic and therapeutic. A contrast enema, usually with hyperosmolar Gastrografin (diatrizoate), can help differentiate causes of distal bowel obstruction. The colonic and distal small-bowel lumen may be obstructed with thick meconium in patients with meconium ileus. Colon dilated proximal to a thick obstructing mass of meconium suggests meconium plug syndrome. A contrast enema may demonstrate a transition zone between small-caliber distal colon and more dilated proximal colon in patients with Hirschsprung disease. More proximal obstructions can produce a contrast enema picture of a small-caliber colon, termed congenital microcolon or small left colon syndrome. Meconium ileus Meconium ileus is the term used to describe neonatal presentation of distal small-bowel obstruction from thickened meconium in patients with cystic fibrosis. Meconium ileus is the earliest manifestation of cystic fibrosis in the newborn period. Cystic fibrosis is 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. Incidence of cystic fibrosis is 1 case per 3000 live births. Of newborns with cystic fibrosis, 10-20% present with meconium ileus. The gene for cystic fibrosis is carried by 3.3% of whites. Identified in 1985, the cystic fibrosis gene localized to the DF508 locus on chromosome 7 codes for a protein that acts as a cystic fibrosis transmembrane conductance regulator (CFTCR). Abnormalities in the CFTCR disrupt membrane function. In the GI mucosa of the newborn, this defect manifests as poor motility. Meconium may build up and obstruct the lumen of the distal small bowel and colon. Because meconium does not pass readily into the distal GI tract, distal small-bowel obstruction may develop in utero. The involved segment of bowel may dilate and even perforate. A pseudocyst may wall off around the perforation. Prenatal ultrasonography or neonatal plain radiography may identify a soap bubble or ground glass appearance of inspissated meconium. Adhesions may develop from the perforation. The functional picture of tenacious thick meconium that does not pass is termed meconium ileus. Segmental obstruction of the small bowel from meconium ileus can also precipitate volvulus of the bowel upstream from the obstruction. Treatment of meconium ileus involves evacuation of the meconium. In more than 50% of patients, nonsurgical management relieves the obstruction successfully. A contrast enema may be both diagnostic and therapeutic. For the enema to evacuate the meconium, fluid must be refluxed into the terminal ileum. Multiple enemas may be administered. Dilute Gastrografin with N-acetylcysteine may be administered by nasogastric tube from above to help loosen the meconium. Hyperosmolar solutions (1% acylcysteine) may be effective in drawing more fluid into the lumen of the bowel, thereby enhancing the ability to loosen the thick meconium. Hyperosmolar enemas may increase the risk of perforation. The risk of perforation reportedly is 3-10%. Calcification on scout radiography suggests intrauterine perforation. Do not administer therapeutic contrast enemas in the presence of bowel perforation or compromise. A pseudocyst may develop around a bowel perforation during development. In these patients or in those who underwent unsuccessful initial management with enemas, postnatal laparotomy is indicated. An enterotomy with irrigation of the bowel contents may move the meconium through successfully. In some patients, an ostomy for diversion and access for proximal irrigation may be necessary. Long-term outcome depends upon management of the underlying cystic fibrosis. Meconium plug syndrome Some newborns present with bowel obstruction from plugs of meconium isolated to the colon. Most of these newborns are otherwise healthy babies, but all should undergo a contrast enema, which almost always is diagnostic (no pathology) as well as therapeutic (successful in loosening the meconium plug and resolving the obstruction). A plug of meconium isolated to the colon is usually unrelated to cystic fibrosis. Conditions that predispose to dysmotility of the neonatal bowel, such as maternal preeclampsia, maternal diabetes mellitus, maternal administration of magnesium sulfate, prematurity, sepsis, and hypothyroidism, may be responsible for the formation of the meconium plug. In each of these conditions, the colon distal to the obstruction is narrowed and small in caliber. Because of the frequent association between maternal diabetes mellitus and colonic obstruction with a small left colon, this association is termed small left colon syndrome. As with meconium ileus, a nonoperative approach with administration of enemas is favored to relieve the obstruction. The enemas can also serve to dilate the small-caliber distal colon. A need for laparotomy to evacuate the meconium suggests a diagnosis other than simple meconium plug syndrome. Hirschsprung disease can be associated with meconium plug syndrome in 4% of patients; therefore, a suction rectal biopsy may be indicated. Hirschsprung disease Hirschsprung disease is a disorder of the neuroenteric pathways within the distal large bowel that prevents bowel relaxation, resulting in a functional distal bowel obstruction. Hirschsprung disease is not an acquired disease as the name suggests, but rather is a congenital absence of neuroganglion cells from the distal intestine that affects 1 in 4500-7000 newborns. Hirschsprung disease is more common in white infants and affects males 4 times more frequently than females. In approximately 12.5% of patients, Hirschsprung disease may be familial, especially when the entire colon is affected, which is termed total colonic aganglionosis. Functional bowel obstruction in Hirschsprung disease results from an inability of the colon to relax during peristalsis. The relaxation phase of peristalsis usually occurs as a reflex to the antegrade peristaltic wave. In Hirschsprung disease, the affected bowel cannot relax and, therefore, remains contracted. The relaxation phase reflex is controlled by neuroenteric ganglion cells, which are present in the submucosa layer of the intestine. Normally, at 7-12 weeks' development, neuroenteric ganglion cells migrate from the neural crest along the bowel distally to reach the distal rectum. If these ganglion cells are not present, the peristaltic relaxation phase is not conducted to the affected distal segment of the bowel. The affected distal colon does not relax appropriately, and a functional obstruction develops. Because of the migration pattern of these ganglion cells, Hirschsprung disease usually affects a continuous segment of bowel extending from the rectum proximally to the level of normal ganglionated bowel. The extent of the aganglionic segment varies with each patient. The genetic defect responsible for Hirschsprung disease has been linked to the ret protooncogene, located on the long arm of chromosome 10. Current understanding of the influence of the ret protooncogene on migration of the ganglion cells is evolving. Hirschsprung disease may also be linked to other disorders of bowel motility. Diagnosis of Hirschsprung disease is suggested by contrast enema and confirmed by rectal biopsy. If Hirschsprung disease is suggested, perform a contrast enema. Older children with Hirschsprung disease show a characteristic transition zone between narrow-caliber aganglionic bowel and dilated upstream normally ganglionated bowel. A distinct transition zone is often difficult to observe in newborns. Failure to evacuate the contrast in 24 hours following the contrast enema may be diagnostic for Hirschsprung disease. Anal manometry may also suggest a diagnosis of Hirschsprung disease but is difficult to perform in the newborn period. The criterion standard to confirm Hirschsprung disease is rectal biopsy. Rectal biopsy may be readily performed at the bedside in newborns with a specially designed rectal biopsy tool. This instrument suctions the rectal mucosa and submucosa into the tool and amputates the specimen without perforating the serosa of the rectum. Collection of the specimen via suction is replacing the more conventional open biopsy method of obtaining tissue for histopathologic examination. The specimen is examined for the presence of ganglion cells in the submucosal layer. In addition, acetylcholinesterase staining of the submucosa identifies abnormal hypertrophic nerve fibers in Hirschsprung tissue. All children with delayed passage of meconium with a suspicious finding on contrast enema should undergo rectal biopsy prior to discharge. Constipation of varying severity is a feature of all patients with Hirschsprung disease. The length of the aganglionic segment greatly influences bowel dysmotility. Aganglionosis confined to a short segment of distal rectum may cause only mild constipation, while patients with longer segments of aganglionic bowel may present with complete functional obstruction in the newborn period. Infants with Hirschsprung disease frequently present with enterocolitis. A child may exhibit explosive diarrhea, sepsis, and abdominal distention. The mucosal integrity of the massively dilated proximal bowel may be compromised, allowing bacterial invasion of the epithelium. Management of Hirschsprung enterocolitis includes aggressive washout of the distal segment to decompress the bowel. Intravenous antibiotics are administered. A diverting colostomy has been traditionally performed to aid with this process. Treatment of Hirschsprung disease is surgical. Several different surgical approaches have been described that pull ganglionated bowel down to the rectum. Most pediatric surgeons have performed a colostomy to allow for decompression of the bowel. Most recently, a minimally invasive pull-through technique with a transanal approach but without formal laparotomy has gained acceptance. For many surgeons, newer laparoscopic techniques greatly facilitate performance of the transanal approach. This primary pull-through technique avoids both a formal laparotomy and a diverting ostomy and may be appropriate for newborns with Hirschsprung disease who have no evidence of enterocolitis. Long-term complications of Hirschsprung disease include a continued risk for chronic constipation and enterocolitis, even after successful pull-through. Bowel dysmotility may persist in many patients despite successful removal of aganglionic bowel. Outcome for patients with Hirschsprung disease who have undergone a pull-through procedure is generally good in terms of both continence and stool frequency. Colonic atresia Colonic atresia is a rare condition usually associated with genitourinary anomalies or abdominal wall defects. Pathophysiology of colonic atresia parallels that of jejunoileal atresia in that it results from an intrauterine mesenteric vascular accident. Its rarity may result from better protection of the colon from segmental ischemia afforded by the well-developed vascular arcade that runs immediately adjacent to it. This provides a more generous collateral blood supply between the network of colonic arteries than that from the more radial blood supply of the small bowel. Diagnosis of colonic atresia may be made by contrast enema. Diverting colostomy may be necessary if the proximal colon is extremely dilated. Volvulus of the dilated colon proximal to an atretic colonic segment has been observed. Imperforate anus Routine inspection of a newborn should note the position and patency of the anus. Anorectal malformations range from slight anterior displacement of the anal opening to a completely imperforate anus. Many children with imperforate anus have an abnormal sacral progression as well as internal fistulas between the rectum and the genitourinary structures. All children with an anorectal malformation are predisposed to constipation. A newborn with imperforate anus should undergo plain radiography 12-24 hours after birth to assess the distal extent of bowel gas. Preoperative workup for imperforate anus is focused on the proximity of the distal rectum to the anal skin and sphincter complex. Lateral radiography with the child in a prone position, invertography, may be helpful in classifying the imperforate anus. Many newborns with imperforate anus have a fistulous tract to the skin or genitourinary system. Low lesions that have a fistulous connection between perianal or perineal body skin and rectum may be primarily repaired with a perineal anoplasty. If the distal rectum is several centimeters above the anal skin or has a fistula to the vagina or urinary bladder, the imperforate anus is classified as intermediate or high. In intermediate or high imperforate anus, colostomy is performed in the newborn period. Following colostomy for intermediate or high imperforate anus, the infant undergoes a staged repair of the imperforate anus to pull down the rectum into the center of the anal sphincter complex. Continence has been achieved with both anterior and posterior approaches. Currently, the most widely performed procedure is a posterior sagittal anorectoplasty as described by Pena in 1998. Outcome is dependent upon the precision of the surgery, the severity of the sacral and perineal musculature anomaly, and the degree of colonic dysmotility. Anorectal malformations are part of the VACTERL (vertebral, anal, cardiac, tracheal, esophageal, renal, limb) association of congenital anomalies. Diagnosis of an anorectal malformation requires an investigation for other associated midline anomalies. Cardiac echocardiography, renal and sacral ultrasonography, and plain radiography of the vertebrae and radii are recommended. Because esophageal atresia with tracheoesophageal fistula is part of the VACTERL spectrum, any infant with imperforate anus and respiratory distress should undergo full airway evaluation.
Although laparotomy in the newborn period poses a significant stress to the patient, most infants recover well following successful surgical correction of the cause of the bowel obstruction. In the initial postoperative period, derangements in fluid balance, glucose metabolism, and respiratory status are common. Most infants have some third-space fluid sequestration following laparotomy and may require additional fluids in the postoperative period. Maintenance IV fluid requirements are initially at least 1.5 times normal. Nasogastric decompression until normal bowel function is established aids in the decompression of proximal bowel and facilitates healing of a bowel anastomosis. Following surgery for bowel obstruction, a transient ileus is invariably present. If postoperative bowel function is not expected to rapidly return, parenteral nutrition support is indicated. Patience before feeding a child may avoid anastomotic breakdown or postoperative obstruction. Once bowel motility is reestablished, an infant frequently demonstrates intolerance to lactose and other complex carbohydrates. A predigested or lactose-free formula may initially aid in absorption. If the terminal ileum is resected, derangements in folate metabolism and the enterohepatic circulation may be observed. Wound care is usually straightforward, and empiric antibiotics are not generally recommended after the perioperative period.
In general, most infants with bowel obstruction who are expeditiously identified and treated have an excellent outcome. Survival usually depends on comorbidities, such as degree of prematurity, associated cardiac anomalies, and the presence of peritonitis or bowel compromise at the time of surgery. The survival rate for duodenal atresia is greater than 90%. Long-term survival in patients with volvulus and jejunoileal atresia depends upon the amount of bowel remaining after resection, but an 80-90% survival rate is expected. The rate of leaking anastomoses following repair of newborns with jejunoileal atresia is approximately 15%. Total parenteral nutrition and better methods for central IV access have greatly improved outcomes for neonates who undergo surgery for bowel obstruction. Often, bowel function is not established for a prolonged interval postoperatively. While total parenteral nutrition can support an infant through this period, both long- and short-term complications are observed. Short-term complications from parenteral nutrition include catheter sepsis, respiratory insufficiency, and problems related to securing central venous access. Long-term problems include cholestasis, nutritional deficiencies, and development of oral aversion. As with any laparotomy, postoperative adhesions may develop. Operative technique that avoids unnecessary manipulation of the bowel and spillage of enteric contents is perhaps the best prevention against the development of intraperitoneal scar tissue. Poor motility is often observed following bowel resection for obstruction. Chronic dilation of the intestinal segment proximal to the obstruction may alter normal peristalsis across that segment of bowel. For example, persistent constipation and delayed intestinal transit may not resolve after relief of chronic partial volvulus via Ladd procedure. Interruption of vagal neuroenteric pathways by an atresia or surgical anastomosis may also contribute to abnormal intestinal motility. Short bowel syndrome deserves special mention. Short bowel syndrome results when the remaining length of intestine cannot sustain normal absorptive functions. Normal length of the small bowel in a term infant is approximately 250 cm and in an adult is 600-800 cm. The estimated minimum jejunoileal length for sufficient bowel function in a term infant is 75 cm. Resection of more than 60% of the small bowel predisposes the child to malabsorption, resulting in failure to grow and develop normally. Every effort is made intraoperatively to preserve bowel length. Some children with short bowel syndrome manage to survive with the aid of parenteral nutrition. Bowel lengthening procedures, creation of intraluminal valves, and manipulation of bowel recovery with nutritional and hormonal treatments can help wean the patient with short gut syndrome from dependence on parenteral nutrition. In patients with severe volvulus with infarction of the entire midgut or multiple intestinal atresias, the child may clearly not have enough bowel length to survive. A difficult ethical decision must be made at the time of operation whether to proceed with resection.
Bowel obstruction in the newborn can be a true surgical emergency. Urgent surgical consultation is appropriate in most patients with neonatal bowel obstruction, and catastrophic causes of both proximal and distal bowel obstruction must be excluded without delay. Prompt recognition and treatment of the source of obstruction can prevent complications ranging from gangrene and septic peritonitis to catastrophic bowel loss. Bilious vomiting in a newborn should trigger an immediate suspicion of malrotation with midgut volvulus and initiate an immediate workup or even exploratory laparotomy. The importance of radiographic imaging modalities, especially contrast studies and ultrasonography, cannot be overemphasized. Quick recognition and expeditious treatment usually results in successful resolution of neonatal bowel obstruction, with resultant favorable short- and long-term outcomes for the patient. For excellent patient education resources, visit eMedicine's Esophagus, Stomach, and Intestine Center. Also, see eMedicine's patient education article, Constipation in Children.
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