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Pediatric Abdominal Pain
In pediatrics, one of the most common presenting symptoms to the pediatrician or emergency department is abdominal pain. It is a source of much consternation for parents and is often an extrapolated symptom by the parent based on how the child is behaving. Nearly one-fourth of patients younger than 15 years will have seen a physician for this problem. Abdominal pain may be defined as any discomfort that may be acute or chronic, constant or intermittent, or sudden or insidious. These variables, along with the patient’s age and accompanying symptoms or signs, play a role in the subsequent work-up of the problem and help determine the path that is most appropriate for diagnosis and treatment. The differential diagnosis is broad ( Table 5.1 ); therefore any signs, symptoms, or laboratory data that may narrow the differential are helpful. The history is crucial to arrive at a tailored diagnosis.
TABLE 5.1
Limited Age-Based Table of Common Etiologies for Abdominal Pain in Children With Secondary Associated Symptom Differential Diagnosis
| 2 Months to 2 Years | 2–5 Years | >5 Years |
|---|---|---|
With Fever:
With Vomiting:
Bloody Stool:
Other:
|
With Fever:
With Vomiting:
Bloody Stool:
Other:
|
With Fever:
With Vomiting:
Bloody Stool:
Other:
|
NAT , Nonaccidental trauma.
Scientifically, abdominal pain results from stimulation of nociceptive receptors and afferent sympathetic stretch receptors. Visceral pain is triggered by nociceptors of a hollow viscera as experienced in intestinal obstruction, appendiceal inflammation, and renal or biliary stones. Visceral pain is often referred and therefore not well localized. Parietal pain is associated with direct noxious stimuli to the parietal peritoneum, as demonstrated by tenderness at McBurney point or pain from irritation of the diaphragm. Alternatively, abdominal pain can be induced or psychosomatic in etiology, presenting as a manifestation of a psychosocial problem that may be rooted in the home or at school. These cases are the most difficult to sort out, and radiology is rarely helpful other than to exclude other demonstrable causes.
What Is the Role of Imaging in Abdominal Pain?
Imaging of the abdomen can help guide the clinician toward a surgical or nonsurgical approach and expedite the appropriate care of the child. The etiology for pain can be benign or gravely serious requiring immediate attention, which is part of the challenge to approaching these patients for the clinician. Unfortunately for the clinician, the spectrum of symptoms produced by these conditions can often be vague and nonspecific, and for this reason imaging plays a prominent role in the evaluation of these patients. A complete history and physical examination are necessary to direct the imaging workup. Often a screening radiograph of the abdomen is most useful to assess the need for further imaging or to determine the need for immediate surgical intervention ( Table 5.2 ). The decision to image or not often depends on the acuity of the presenting symptom; therefore to direct the imaging most logically, an algorithm may help direct the workup where the initial distinction is acute versus chronic. After this, the age of the patient, along with the presence or absence of fever, might mark the next branch point in the decision tree. Associated symptoms and signs will lead down directed pathways to finally arrive at a concise differential diagnosis. When the starting symptom is as broad as abdominal pain, even a directed algorithm will still result in a differential diagnosis rather than a single final answer.
TABLE 5.2
Primary Indications for Abdominal Radiography
Adapted from the ACR-SPR Practice Parameter for the Performance of Abdominal Radiography.
|
How to Approach the Abdominal Radiograph in Pediatrics
There are many approaches to interpreting abdominal plain film, some of which are guided by catchy mnemonics. All of these have in common the goal of being systematic so as not to neglect any one aspect of the film. This can happen when there is a positive finding, the so-called satisfaction of search. Although ordering a plain radiograph is frequently a knee-jerk reflex for the clinician, it is important to understand the limitations of the examination. Not surprisingly, the plain abdominal radiograph is often as nonspecific as the presenting complaint. There is broad variability in the interpretation and agreement among radiologists. Thus the final interpretation of a “nonspecific bowel gas pattern” is often considered a nondiagnostic examination (see Box 5.1 ).
BOX 5.1
Mnemonics
Inside-out, outside-in
Gas, mass, bones, stones
CBA (chest, bones, abdomen)
A-A-I-I-M-M:
- ▪
Adhesions
- ▪
Appendicitis
- ▪
Intussusception
- ▪
Inguinal hernia
- ▪
Malrotation
- ▪
Miscellaneous (Meckel, tumor, duplication, etc.)
How to Describe the Overall Gas Pattern
Many terms are used in the radiology lexicon to describe both specific and nonspecific gas patterns. Radiologists should be familiar with the various descriptions, their implied meanings, and the interpreted meaning by the referring doctor.
Normal Gas Pattern
When evaluating the bowel by radiograph, we are looking at the gas pattern, because the air interface with the adjacent tissue is really what is being imaged. Normal position of the bowel is the first assessment. The stomach typically contains air and is located in the left upper quadrant. The small bowel is often central and should be relatively uniform where it is air filled ( Fig. 5.1 ). One should be careful in using adult criteria for bowel obstruction, such as dilation of bowel loops longer than 3 cm, because this may lead to underdiagnosis in children. Average bowel diameter in infants is approximately 1.2 cm at 6 months of age, increasing to 2.1 cm by 8 years of age, and reaching average adult diameter by 15 years. One should be able to see the valvulae conniventes traversing the small bowel loop in older patients, but in the young toddler and infant, these may not yet be visible. Large bowel is typically located on the periphery, and the haustral markings can be seen more widely spaced apart and partially indenting the gas-filled looped on either side ( Fig. 5.2 ). In younger children, haustra may not be present. Depending on the timing of imaging, a variable amount of formed stool may be seen in the colon. The delayed development of haustral markings and visibility of small bowel plicae can make bowel evaluation and localization of the problem in the youngest patients more difficult.
Ileus
Ileus is typically adynamic. Adynamic ileus refers to a functional or nonanatomic etiology for the obstruction of gas in the small bowel, or a functional paralysis of the bowel. Because there is no anatomic obstruction, there is no disproportionate dilation of upstream bowel. Therefore the bowel loops are either uniformly dilated or uniformly without any gas ( Fig. 5.3 ). These patients may present asymptomatically or with signs and symptoms of an anatomic obstruction. Typical clinical settings include sepsis, trauma, and metabolic disturbances (see Box 5.2 ).
BOX 5.2
When to Suspect Ileus
Clinical findings: Abdominal distention with or without obstructive symptoms (i.e., vomiting)
Imaging findings:
- ▪
Uniform air-filled distention of nondilated bowel
- ▪
Localized: sentinel dilated loop
- ▪
Presence of distal colonic gas
Obstruction
A mechanical blockage, either intrinsic or extrinsic, to the passage of air or fecal content in the bowel results in obstruction. The radiographic appearance is specific with dilated bowel loops proximal to the point of obstruction and decompressed bowel distal to that point. Conversely, in later obstruction the bowel may be fluid filled and dilation difficult to assess, thus the importance of an orthogonal view. There are often cases where variation in timing of the obstruction leads to anomalies in the gas pattern. Some experts describe the appearance of obstructed bowel loops as “sad sausages” ( Fig. 5.4 ) in reference to their smooth, featureless appearance, in contrast with “happy polygons” (see Fig. 5.1 ), which describes the normal wall variability seen in nonobstructed bowel. The “string of pearls” or “string of beads” sign refers to the appearance of trapped air between the valvulae conniventes in a predominantly fluid-filled small bowel loop. These gas bubbles may appear stacked or side by side in a string. Alternatively, there may be a “stepladder” configuration of small air–fluid levels in the obstructed small bowel ( Fig. 5.5 ; see also Box 5.3 ).
BOX 5.3
When to Suspect Obstruction
Clinical findings: Abdominal distention, pain, and vomiting
Imaging findings:
- ▪
Dilated bowel loops upstream of the transition
- ▪
Decompressed distal loops
- ▪
Air–fluid levels
- ▪
“String of pearls” sign in late obstruction
- ▪
“Sad sausages”
Age-Based Differential Considerations
The broad range of etiologies that may cause acute-onset abdominal pain in children overlaps across age groups, although some may be more typical than others in each age group. We will discuss each of these entities in detail, but keep in mind, many of these diagnoses may be seen in all age groups. In most cases, when a child presents with acute abdominal pain, the most pressing question is whether the child needs an operation, or can surgery be prevented in the near future by intervening/acting on an important finding.
Infants Beyond the Neonatal Period
The etiology of abdominal pain in infants between 2 months and 2 years of age may be difficult to diagnose because symptoms are largely interpreted based on physical signs. Mechanical causes for pain are the most important to exclude, most commonly, intussusception and volvulus. Less common causes of acute abdominal pain in this age group include appendicitis, sepsis, and obstruction as a result of adhesions. Although the most common causes for abdominal pain may be non-life-threatening, such as colic or enteritis, the clinician needs to maintain a high level of suspicion for less common but possibly life-threatening causes for pain in this age group, such as nonaccidental trauma.
Toddlers and School-Age Children
Abdominal pain in toddlers and young school-age children is a common problem. According to Centers for Disease Control and Prevention statistics, the incidence of children aged 0 to 4 years presenting to either the outpatient setting or the emergency department with abdominal pain was approximately 268 per 10,000 as of 2010. The causes of abdominal pain in this age group can range from the annoying but relatively benign (constipation, gastroenteritis) to life-threatening (appendicitis, intussusception). Unfortunately for the clinician, the spectrum of symptoms produced by these conditions can often be vague and nonspecific, and for this reason imaging plays an important role in the evaluation of these patients.
Right lower quadrant pain in toddlers and young children is a frequent presenting complaint, the etiologies of which range from the emergent, such as appendicitis and intussusception, to the self-limited, such as mesenteric adenitis. Evaluation often begins with radiographs, due to widespread availability, rapidity of the exam, and lack of need for patient prep or sedation. Findings on radiographs are frequently nonspecific, however, which may prompt a need for more advanced imaging, such as ultrasound, computed tomography (CT), or magnetic resonance imaging (MRI). The availability of these more advanced imaging modalities varies with the facility to which the patient presents, and transfer to higher-level facilities may be needed to accomplish this imaging.
Bowel obstruction on plain radiographs can be one of the quickest methods to distinguish serious from benign conditions. Causes of bowel obstruction in young children are generally going to be those potentially requiring surgical intervention, such as appendicitis, intussusception, or Meckel diverticulum. The AAIIMM mnemonic (appendicitis, adhesions, intussusception, inguinal hernia, Meckel, malrotation) can be a helpful reminder of some of the conditions producing bowel obstructions in children.
Patient age and clinical symptoms are important to narrow the differential diagnosis when a bowel obstruction is recognized. Intussusception typically occurs in patients 3 months to 3 years of age and is typically accompanied by crampy abdominal pain, fussiness, lethargy, and, possibly, bloody stools (“currant jelly stool”). Appendicitis is seen more frequently in older pediatric patients (10–19 years old) and is associated with fever, leukocytosis, nausea/vomiting, and anorexia. In toddlers and younger children who may not be able to verbalize their symptoms, the diagnosis of appendicitis is more likely to be delayed and present with appendiceal perforation. In these patients, symptoms may include vague abdominal pain and distention, fussiness, or lethargy, in addition to fever and vomiting.
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