Extrinsic Compression

Because the bowel is a flexible organ, anything that compresses it externally can decrease the intraluminal diameter and precipitate obstruction. For example, adhesions are fibrous bands of tissue that spontaneously arise within the peritoneum in reaction to insults, such as peritonitis or abdominal surgery, and can encircle and constrict loops of bowel. They are relatively common after surgery, with up to a 25% 5-year readmission rate caused by adhesions, depending on the type of operation.

Intraabdominal masses, such as Wilms’ tumor, can compress and obstruct bowel by their sheer size (“mass effect”). Annular pancreas is an anatomic variant in which a ring of pancreatic tissue encircles and can cause duodenal obstruction. Superior mesenteric artery (SMA) syndrome results from compression of the third duodenal segment by the artery against the aorta. It is sometimes seen in patients who have had precipitous weight loss with resultant loss of the mesenteric fat pad that protects the duodenum from compression; external body cast application; or after intestinal or orthopedic surgery that results in traction upon the SMA, pulling it down upon the duodenum. Another example is closed loop obstruction (internal hernia), in which a loop of bowel passes through a mesenteric defect or similar orifice (e.g., inguinal hernia) and becomes lodged within it, resulting in occlusion of both the proximal and distal ends of the loop.

Intrinsic Decrease in Lumen Caliber

Acquired Defects

Chronic bowel inflammation can, over time, lead to narrowing of the lumen. An important example is Crohn’s disease, in which there is discontinuous full-thickness bowel inflammation anywhere from the mouth to the anus (see Chapter 110). Over time, inflamed areas may stricture and obstruct. Another example of this is eosinophilic esophagitis, an entity that lies within the spectrum of food allergies and atopic disease. Because of persistent eosinophilic inflammation in the presence of the offending antigen, the esophagus can eventually stricture over time, leading to dysphagia and the need for esophageal dilatation to relieve the obstruction. Malignancy, although relatively uncommon in children compared with adults, is another important cause of decreased lumen caliber. For example, the GI tract is the most common extranodal site affected in non-Hodgkin’s lymphoma. Infiltration of the bowel wall by tumor leads to decreased effective luminal diameter and a higher risk of obstruction. Achalasia causes functional esophageal obstruction caused by aperistalsis and inadequate lower esophageal sphincter relaxation. An example of gastric outlet obstruction caused by decreased diameter is hypertrophic pyloric stenosis, a disease primarily affecting infants in the first few months of life in which smooth muscle hypertrophy leads to occlusion of the pylorus (Figure 109-3).

Figure 109-3 Hypertrophic, pyloric stenosis.

Internal Blockage

A wide variety of etiologies may be associated with internal blockage of the GI tract. Areas that are inherently narrow relative to the rest of the GI tract (upper esophageal sphincter, esophagus adjacent to the carina, lower esophageal sphincter, pylorus, ileocecal valve) are at more risk of becoming obstructed by large foreign bodies. In a special example of this, bezoars are accumulations of indigestible material (e.g., hair, fiber from vegetables) that become trapped in the GI tract (typically the stomach) and can cause obstruction when they grow large enough. Injury to the wall of the small intestine from blunt abdominal trauma, as can occur when bicycle handlebars injure a child’s duodenum, may instigate a hematoma, which can obstruct the small intestine because of its small caliber.

In neonates, meconium ileus is a cause of distal GI obstruction shortly after birth. Meconium is a conglomeration of sloughed intestinal mucosa, bile salts, and other debris that accumulates during fetal development. It is normally passed within the first day of life, but when it is exceedingly inspissated, as occurs in cystic fibrosis, patients may be unable to expel it, leading to obstructive symptoms. In young children, intussusception is an example in which the bowel obstructs itself because of telescoping of one portion of bowel into the adjacent region of bowel.

Defects in Bowel Arrangement

Malrotation is an important entity that clinicians must be aware of when evaluating intestinal obstruction of unknown etiology. Malrotation is a congenital defect typically involving both the small and large intestines that occurs when the bowel assumes an abnormal spatial arrangement within the abdomen. Intestinal development is a complex, continuous process spanning the fourth fetal week to birth that takes the primitive gut, which begins as a short, straight tube, and transforms it into a long, highly specialized organ. As part of this process, the intestinal tract, after rotating 270 degrees, becomes fixed in a specific arrangement such that the duodenum ends at the ligament of Treitz in the left upper quadrant and the cecum is found in the right lower quadrant. When this final arrangement fails to take place properly, the bowel is malrotated. Although this may not result in any clinical symptoms in mild cases, the most feared complication is volvulus, a surgical emergency in which the bowel, as a result of its inappropriate positioning and lack of usual support, twists upon its mesenteric stalk, causing not only intestinal obstruction but also ischemia (Figure 109-4). Ladd’s bands, intraperitoneal fibrous bands that can encircle and obstruct the duodenum, are also associated with malrotation.

Figure 109-4 Malrotation and volvulus.

Motility Failure

Even when there is not an occlusive obstruction of the intestine, failure of appropriate peristalsis can nonetheless create obstructive symptoms. A common example is postinfectious ileus, which is an interruption in normal intestinal motility and forward propulsion of contents without physical occlusion that most often occurs after viral gastroenteritis. It is usually mild and self-limited, but in rare instances, it can result in severe and prolonged gastroparesis, feeding intolerance, and the need for postpyloric nasogastric enteral feeding until it resolves. Intestinal surgery can cause postoperative ileus, a temporary disruption of normal motility, particularly when combined with narcotics, which have intrinsic antimotility effects.

Another important consideration is intestinal pseudoobstruction, which is a spectrum of congenital and acquired disorders involving the small or large bowel (or both) that ultimately results from failure of either the enteric nervous system or the intestinal smooth muscle to coordinate appropriate peristalsis. Examples of factors that can trigger pseudoobstruction are trauma, electrolyte abnormalities, sepsis, orthopedic and cardiovascular surgery, and pregnancy.

What Is the Age of the Patient?

Although many etiologies cross age lines, the age of a patient can raise the level of suspicion for particular problems. The neonatal period is when many congenital disorders, such as atresias and webs, become evident. Although malrotation can present at any point in life, most are diagnosed within the first year in patients with recurrent or bilious vomiting. Meconium ileus becomes evident within the first few days of life and prompts concern for cystic fibrosis. Hypertrophic pyloric stenosis presents within the first few months of life as nonbilious “projectile” vomiting. Intussusception most often presents within the first few years of life as recurrent bouts of vomiting associated with intense pain that both completely resolve between episodes.

Is the Patient Ill Appearing?

One of the first priorities of the physician is to determine the severity of the patient’s illness. Although any patient who has comorbid conditions or who has had prolonged obstruction may be ill appearing (e.g., pallor, lethargy, diaphoresis, restlessness), the ill appearance itself should prompt concern that the patient has a complication of the obstruction. In this regard, an important way of classifying an obstruction is whether it is simple or strangulated. Whereas simple obstruction implies preserved blood flow to the bowel in the setting of obstruction, a strangulated obstruction denotes an obstructive process complicated by bowel ischemia. Certain etiologies, such as volvulus and internal hernia, have a high risk of strangulation. Strangulated obstruction is an emergency that requires prompt attention and surgical evaluation.

What Is the Character of the Vomitus?

Obstruction can occur anywhere from the esophagus to the anus, with the location being an important influence on the symptom pattern that the patient experiences. If the obstruction is in the esophagus, the patient may experience dysphagia (difficulty swallowing) or outright inability to intake orally. Low-grade esophageal obstruction can hinder the swallowing of solids, and high-grade obstruction can also interfere with the ingestion of liquids, which results in drooling and frequent spitting. Gastric outlet obstruction, as in pyloric stenosis, causes nonbilious vomiting because bile is secreted by the liver into the duodenum at the ampulla of Vater beyond the point of obstruction.

Small bowel obstruction leads to abdominal distension, cramping discomfort in the middle or upper abdomen, and repeated episodes of bilious vomiting. Symptoms often have a rapid onset after the obstructive process has begun. If there is total obstruction, patients eventually become obstipated (i.e., cease to pass stool). Fluid and electrolyte disturbances are relatively common. Abdominal pain raises concerns for bowel ischemia. Large bowel obstruction, on the other hand, tends to have symptoms that are milder and slower in onset compared with small bowel obstruction. Vomiting does not invariably occur, although the bowel does become distended. Patients may have lower abdominal cramping. On rectal examination, if the obstruction is high in the colon, the rectum will be devoid of stool, but hard stool in the rectum may be present if the patient has fecal impaction. Explosive stooling may be precipitated by rectal examination in a patient with Hirschsprung’s disease. Fluid and electrolyte disturbances do not tend to develop as precipitously as in small bowel obstruction.

Are the Symptoms Constant or Intermittent?

Partial obstruction occurs when the effective intraluminal diameter through which intestinal contents may pass is narrowed to the point of reducing, but not eliminating, flow. In these cases, patients may experience waxing and waning symptoms, and older patients who have repeated episodes of partial small bowel obstruction, such as those with a Crohn’s disease–associated stricture, may even adapt themselves by limiting oral intake at the moment they detect characteristic symptoms. Complete obstruction results from a total inability of the bowel to propel its load forward past the blockage point. When such a process has begun, symptoms typically continue until the patient has been mechanically decompressed and the obstruction has been relieved.

Has the Patient Had a Chronic History of Severe Reflux or Abdominal Pain?

If a patient has had a long-standing history of severe reflux or abdominal pain, it raises suspicion for malrotation, as well as mild forms of other congenital anomalies such as webs.

Has the Patient Had Previous Abdominal Surgery (or other Peritoneal Insults)?

In any patient with obstructive symptoms who has had previous abdominal surgery, the clinician should suspect the presence of adhesions. Such concern should also arise in patients who have had other forms of peritoneal injury. For example, patients with advanced liver disease and associated ascites are at risk for spontaneous bacterial peritonitis. Repeated episodes may lead to the formation of adhesions. In patients who have had peritoneal dialysis for renal failure, there have been rare cases of a disorder called sclerosing encapsulating peritonitis in which the entire bowel becomes progressively encased in fibrotic tissue.

Does the Child Have Other Historical or Physical Examination Abnormalities?

The presence of other abnormalities may raise suspicion for particular etiologies. Trisomy 21 is one of many congenital disorders that can be associated with intestinal atresia and other anomalies such as malrotation (see Chapter 117). Heterotaxy is associated with malrotation, which can lead to Ladd’s bands and volvulus. Patients who have recently had Henoch-Schönlein purpura, an acquired form of vasculitis, are at risk for intussusception, as are those with polyps and duplication cysts (see Chapter 28). Crohn’s disease is a common cause of intestinal stenosis (see Chapter 110).

Initial Care in the Emergency Department

Patients reporting symptoms concerning for obstruction should be directed to emergency care. The goal of the initial evaluation in the emergency department is to determine the acuity and severity of the child’s illness. The clinician should rapidly obtain a general sense of the patient’s predicament through the general appearance, ascertaining clinical signs such as lethargy, diaphoresis, pallor, and restlessness. The first pass on physical examination should quickly acquire information regarding the patient’s critical features, beginning with the ABCs (airway, breathing, and circulation). Vital signs should be evaluated for fever (in the setting of obstruction, concerning for ischemia), tachycardia, hypotension (worrisome for decompensated shock), and low-normal blood pressure with widened pulse pressure (concerning for compensated shock). On the second pass, the clinician should perform a thorough but expedient head-to-toe examination that includes assessments of mental status, level of dehydration, signs of trauma, and stigmata of disease. The abdominal examination must assess for distension (and whether it is caused by gas or fluid), bowel sounds (early obstruction results in hyperactive sounds, but ischemic bowel will be silent), the presence of masses, and the presence and location of pain. If peritoneal signs are present (involuntary guarding, rebound tenderness to palpation, exquisite sensitivity to movement), there should be immediate concern for perforation. In addition, the assessment should include a rectal examination to check stool for the presence of blood via stool guaiac testing and to screen for low-lying pathologies such as distal intussusception, Hirschsprung’s disease, fecal impaction, and pelvic masses.

After the patient’s status has been determined, initial interventions should be initiated without delay while the workup continues. Patients with vomiting should receive nothing by mouth (NPO) and should have an intravenous (IV) line started for maintenance fluids. If there are signs of dehydration, isotonic fluid boluses are appropriate until the patient is hemodynamically stable. Patients with repeated emesis should also receive a nasogastric tube using a sump-type catheter (which is more rigid, larger in caliber, and less likely to collapse than a feeding tube), which can then be placed on low intermittent suction. If the sump aspirates large volumes, it is important to replace those losses via IV fluid administration. Indeed, without decompression, even when a patient is NPO, vomiting may continue because of the significant volume of fluid that the GI tract produces in the form of secretions. If the patient is ill appearing or has fever in the context of suspected obstruction, the physician should strongly consider initiating IV antibiotic therapy with adequate coverage for common gut flora (gram-negative and anaerobic organisms) after obtaining a blood culture. Early in this process, the team should contact a surgeon to evaluate the need for operative intervention. If patients are determined in the course of their workup to have partial small bowel obstruction, they may be admitted for observation and continued decompression before further evaluation and management. Those with complete obstruction or other complications, such as ischemia and perforation, require surgical management.

It is essential to keep in mind that many illnesses can initially present with a constellation of signs and symptoms resembling obstruction. This can make the assessment of the vomiting child challenging. On the more benign end of the spectrum, viral gastroenteritis is an example of a disorder that can cause repeated vomiting. What distinguishes this from obstruction is that there is typically a history of ill contact, the vomiting is nonbilious (or perhaps “highlighter” green after repeated vomiting episodes, as opposed to the “spinach green” color of truly bilious emesis in obstructed patients), diarrhea is present, and the patient’s abdomen is not distended. On the other end of the spectrum are several pitfalls that are important for the physician not to miss:

Using the clinical questions presented in the previous section, the clinician can begin to localize and characterize the nature of the symptoms to construct a differential diagnosis based on data that addresses those questions.

Laboratory Tests

Although clinical suspicion should ultimately determine the full set of laboratory tests ordered, initial laboratory studies should generally include a complete chemistry panel (with blood urea nitrogen and creatinine), glucose, hepatic function panel (to screen for metabolic abnormalities), amylase and lipase (to screen for pancreatic involvement, although an isolated amylase elevation could be attributable to bowel injury from ischemia), complete blood count (to ensure tachycardia is not attributable to anemia and to assess for leukocytosis), and urinalysis (to check for evidence of urinary tract infection or hematuria as evidence of stones). If there is concern for drug ingestion, appropriate drug testing should be considered. In postmenarchal women, pregnancy testing should be included. If the patient is ill appearing and has a fever, a blood culture should be done before administration of antibiotics. In a deteriorating patient, blood gas measurement may also be helpful in determining whether there is a metabolic acidosis, which would heighten concern for bowel ischemia.

Radiologic Tests

All patients with signs consistent with obstruction should have initial flat and upright abdominal radiographs to assess the bowel gas pattern and to screen for other pathologies, such as intraabdominal free air, foreign bodies, volvulus, and masses. Air-fluid levels denote stasis of intraluminal contents, either from obstruction or ileus. Obstruction is generally associated with significant proximal intestinal distension, either with fluid or air, and the portions of bowel that are distended may help locate the obstruction. For example, an image that shows gas in the stomach but not in any distal regions suggests gastric outlet obstruction or, less likely, gastric volvulus. The “double-bubble” sign, in which air is seen both in the stomach and in the proximal duodenum but not distally, is suggestive of duodenal atresia.

Real-time fluoroscopic contrast studies greatly enhance the radiologic ability to discern anatomic features of the bowel and thus are of considerable value in determining the region of obstruction in stable patients. Furthermore, fluoroscopy provides dynamic information about the function of the bowel. Historically, the contrast agent has been barium, but in the setting of evaluating obstruction, it is more appropriate to use a water-soluble contrast agent. This is because barium that extravasates into the peritoneum through a perforation can create severe peritonitis, and stagnant barium that becomes trapped at the obstruction will solidify over time, potentially creating further complications. When a patient is medically unstable, fluoroscopic contrast studies are inadvisable given that they involve introduction of a foreign substance into the GI tract, and they do not provide enough information about extraintestinal pathology that may be contributing to the clinical picture.

If the individual has primarily esophageal symptoms, an esophagram can delineate the site and nature of defect, as well as evaluate esophageal function (see Chapter 107). In a stable patient with small bowel obstructive symptoms, the study of choice is the upper GI series, in which the contrast is followed to the ligament of Treitz. This study assesses for malrotation or volvulus in addition to a host of other anatomic defects. It is essential that any child younger than 1 year of age with bilious vomiting must be assessed for malrotation and volvulus. A variant on the upper GI series is the upper GI with small bowel follow-through, in which the radiologist assesses the bowel to the terminal ileum. This study is inappropriate for the acute setting given the length of time required to perform the study and the need to use barium, which is required because endogenous secretions dilute water-soluble contrast as it passes through the GI tract, making it ineffective for delineating the distal small bowel. However, this is a valuable tool when the suspicion is that a defect beyond the ligament of Treitz may be causing partial small bowel obstruction.

In limited settings, contrast enemas help to delineate causes of colonic obstruction. For example, the unprepped barium enema is an essential tool in the workup of Hirschsprung’s disease. In the rare case of colonic tumors (a far more common problem in adults), it is also helpful. It is unnecessary in the evaluation of fecal impaction, which can be diagnosed by clinical assessment. A special case is the air-contrast enema study, which is used in the setting of suspected intussusception. In this situation, air is the contrast agent used to diagnose the area involved. After the radiologist identifies the intussusception, this modality becomes useful as a therapeutic tool because the air then serves as a means to reduce the intussusception.

In patients who are medically unstable, who have a history of trauma, or who have a suspected perforation, the study of choice is the CT scan because of its rapid throughput and ability to provide the clinical team with large amounts of information about the intestinal anatomy as well as extraintestinal pathologies. The drawback to CT is its radiation burden, which is equal to many plain radiographs and is at least twice that of an upper GI series with small bowel follow-through. However, this consideration is outweighed by its benefits in the acute setting, and newer pediatric protocols have reduced the radiation load significantly.

In limited situations, ultrasound is a useful tool when specific etiologies are suspected. For example, it is widely used in the assessment of pyloric stenosis and intussusception. Because it does not create a radiation burden, it is also finding use at some centers in the form of small bowel evaluation of strictures that may cause partial small bowel obstruction, as can occur in Crohn’s disease.

Additional Evaluation

Although it is not indicated in the acute setting, GI endoscopy is a useful tool for diagnosing mucosal disorders that may not be obvious on radiologic imaging, and it offers the advantage of allowing therapeutic intervention in some cases. Endoscopy involves a gastroenterologist inserting an endoscope into either the mouth or anus, depending on the region of interest. The instrument allows direct visualization of the mucosa and provides the ability to sample the tissue for histologic diagnosis. For example, an older patient who has had a long-standing history of intermittent abdominal pain and poor weight gain and is found to have small bowel strictures causing partial small bowel obstruction could have Crohn’s disease, which requires mucosal biopsies for definitive diagnosis. In progressive esophageal strictures, eosinophilic esophagitis is an important consideration; this also requires histologic diagnosis from biopsies.

Surgical evaluation is critical at all stages of the assessment of children with obstruction. After enough clinical information is available to determine whether the child should go to the operating room, the surgical team will proceed with exploratory laparotomy or, at some centers, laparoscopy. Although the most invasive of all diagnostic modalities, it provides definitive diagnosis of the obstruction, and it is lifesaving and absolutely indicated in patients with complete obstruction and who have evidence of bowel ischemia or perforation.