Etiology And Pathogenesis
Abdominal pain falls into three
clinical categories: visceral, parietal (somatic), and referred pain. A general
understanding of these is helpful in determining the cause of abdominal pain.
Visceral pain is poorly localized and is often described as
dull and aching. It is caused by stretching, distension, or ischemia of the
viscera. Parietal (somatic) pain is well localized, discrete, and often
described as sharp and intense in character. Pain is stimulated by stretching,
inflammation, or ischemia of the parietal peritoneum. The pattern of pain in
appendicitis has features of both visceral and parietal pain. Initially, the
pain is visceral in nature: vague, poorly localized, and periumbilical. As the
peritoneum becomes inflamed over the ensuing 12 to 48 hours, the pain migrates
to and localizes in the right lower quadrant (RLQ).
Referred pain is often perceived at sites distant from the
affected organ and may be described either as sharp and localized or as a vague
aching sensation (Figure 5-1). Examples include irritation of the parietal
pleura of the lung perceived as abdominal wall pain and inflammation of the gallbladder
perceived as scapular pain.
It is helpful to classify the cause
of acute abdominal pain by age (Table 5-1). There are many potential causes of
abdominal pain, including infectious, anatomic, traumatic, inflammatory,
functional, and oncologic.
Clinical Presentation
Differential Diagnosis
The differential diagnosis for
abdominal pain in children is very broad, and it can be approached in different
ways (Figure 5-2). Certain conditions occur more commonly at specific ages and
therefore it may be useful to classify causes of acute abdominal pain based on
age. ain may also be classified as surgical or medical
(Table 5-1).
Across all ages, gastroenteritis and
appendicitis are the most common medical and surgical causes of acute abdominal
pain, respectively. Malrotation with midgut volvulus is the single most
devastating abdominal surgical emergency of childhood (see Chapter 109).
Life-threatening causes of abdominal
pain include those related to trauma, intestinal obstruction, and peritoneal
irritation. Examples of processes that present with intestinal obstruction are
intussusception, midgut volvulus, and extrinsic obstruction caused by adhesions
from prior surgery. Peritoneal irritation may be secondary to inflammation or
perforated viscus; examples include necrotizing enterocolitis in a neonate,
acute appendicitis, and ruptured ectopic pregnancy.
Abdominal pain can also be
classified based on the location of the pain. A classic approach is by dividing
the abdomen into four quadrants (Figure 5-3). This can help the practitioner
direct the workup to rule in or out the most common diagnoses based on the
location of symptoms. For example, hepatic and gallbladder disease usually
present with right upper quadrant pain (see Chapter 115). Appendicitis
classically presents with migration of pain to the RLQ. Gastritis or peptic
ulcer disease may present with left upper quadrant pain (see Chapter 108).
History
The initial evaluation of acute
abdominal pain is particularly challenging in pediatrics because children often
cannot describe, articulate, or localize their symptoms. This is often
exacerbated by anxiety, making it harder for the clinician to examine and
identify positive findings.
Pain Character
Acute abdominal pain caused by a
medical or surgical emergency typically increases in intensity over time, may
awaken the child at night, and likely interferes with activity. In addition to
the age of patient and the location of the pain, other important features of
the history include the onset, frequency and duration, pattern, associated
symptoms, and pertinent medical history.
Infants and young children can
seldom localize their pain, and parents often describe an inconsolable child
who lies with his or her legs drawn up to the chest. Asking the parents if they
think the child is in pain can be helpful to distinguish pain from fussiness or
irritability. Pain that is intermittent, with paroxysms of cramping
inconsolable pain alternating with return to normal state, is characteristic of
intussusception (Figure 5-4). Peritoneal irritation is suggested by pain that
is worse with movements that change the tension of the abdominal wall, such as
a bumpy car ride or walking. Pain that improves after vomiting or a bowel
movement reflects a small bowel or large bowel cause, respectively.
The pain of acute appendicitis is
progressive in character without intermittent relief. The initial pain of early
evolving appendicitis is classically periumbilical. As the inflammatory process progresses to affect the
surrounding abdominal wall structures, the pain shifts to the RLQ (Figure 5-5).
This progression is very helpful if obtained on history. Patients may describe
a sudden temporary decrease in pain, which often coincides with perforation and
temporary relief of intraluminal pressure.
Associated Symptoms
Certain infectious processes are
associated with abdominal pain: fever, headache, and sore throat suggest
streptococcal pharyngitis (see Chapter 35); dysuria and vomiting may be attributable to a urinary tract infection (see
Chapter 93); tachypnea and cough point to a lower lobar pneumonia (see Chapter
91). An associated rash may suggest a vasculitis such as Henoch- Schönlein
purpura as the cause of the abdominal pain (see Chapter 28). Whereas nonbloody
diarrhea suggests gastroenteritis, bloody diarrhea could also signal hemolytic
uremic syndrome, inflammatory bowel disease, or bacterial enteritis. Abdominal
pain that is accompanied by vomiting but without diarrhea should prompt a more
careful evaluation for potentially life-threatening conditions such as
intussusception, midgut volvulus, adhesive small bowel obstruction, or
pancreatitis.
Appendicitis is classically
accompanied by anorexia before the onset of pain, although this is not always
the case. Fever is variable, and vomiting usually occurs after the pain has
migrated to the RLQ. Diarrhea is occasionally seen with appendicitis, often
caused by pelvic irritation after perforation. The diagnosis of appendicitis
can be difficult in children because classic symptoms are often not present,
especially in infants and very young children.
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Figure 5-2 The acute abdomen.
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Pertinent Medical History
Certain chronic medical conditions
are associated with abdominal complications. Patients with sickle cell disease
are predisposed to cholecystitis, splenic sequestration, and abdominal
vasocclusive crises (see Chapter 53). Patients with diabetic ketoacidosis often present with accompanying
abdominal pain (see Chapter 4). Patients with Hirschsprung’s disease are at
risk for enterocolitis and toxic megacolon, and those with nephrotic syndrome
may develop primary bacterial peritonitis. Patients with a history of abdominal
surgery are predisposed to adhesions, which may cause obstruction.
Physical Examination
Clinicians can gain considerable
information from the patient’s general appearance even as observed from afar. A
child in severe pain may prefer to be curled up in a position that shortens the
rectus muscles and protects the abdomen. Patients with peritonitis often appear
acutely ill and prefer to lie still. Intussusception should always be
considered in a young child with altered mental
status. Clinicians should pay attention to vital signs, specifically for the
presence of fever, tachycardia, or hypotension. Signs of poor perfusion may be
seen with peritonitis or hypovolemia.
The abdominal examination is
optimally performed when the child is quiet, calm, and cooperative. Clinician
should consider examining young patients in the parent’s lap, if possible.
Start in the area away from reported pain. Evaluate for distension and the
presence or absence of bowel sounds. Palpate while paying close attention to
presence of masses or focal tenderness. A mass may be indicative of neoplasm,
intussusception, or stool. Reproducible focal tenderness points to an
intraabdominal inflammatory process. Patients with peritoneal irritation
present with percussion pain, involuntary guarding, or rebound tenderness.
Rebound is elicited by deep palpation followed by a sudden release. Pay
attention to the child’s face when attempting these maneuvers because they may
not always be able to express localization. The rectal examination is sometimes
useful in helping to narrow the differential diagnosis: note the presence of
hard stool in the rectal vault (constipation), blood (intussusception,
inflammatory bowel disease, infection, milk-protein allergy), or an inflamed
retrocecal appendix.
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Figure 5-3 Quadrants of the abdomen.
Signs on examination that suggest an
acute surgical cause include marked abdominal distension, severe tenderness,
rigidity, involuntary guarding, and rebound tenderness. Classic presentations
of acute surgical conditions include a neonate with bilious vomiting (midgut
volvulus), colicky abdominal pain (intussusception), and RLQ pain
(appendicitis). Surgical subspecialists should be alerted early when a surgical
cause is suspected. A delay in the diagnosis of appendicitis is associated with
rupture and associated complications, especially in young children younger the
age of 2 years. A delay in diagnosis increases risk of perforation and
postoperative complications to as high as 39%. Overall, the cause is less
likely to be serious in an otherwise healthy child who has a nonfocal
examination, is without obvious discomfort to deep palpation, and is without
constitutional or extraabdominal findings.
Figure 5-4 Intussusception.
Evaluation And Management
The clinician’s first priority is to
stabilize patients who are critically ill, focusing on identifying and
addressing abnormalities in airway, breathing, and circulation. Next, the
clinician must identify potential acutely life-threatening processes requiring
emergent surgical intervention (Table 5-1). Typically, these are distinguished
based on the patient’s history and physical examination, as discussed
previously. Laboratory testing and imaging studies may be useful adjuncts in
identifying the diagnosis.
Laboratory Testing
Testing should be tailored to the
pertinent findings during the history and physical exam in order to come to a
timely diagnosis. In most children older than 5 years of age with abdominal
pain, tests are needed only to confirm a diagnosis that is suspected
clinically. Radiographic studies can be useful and diagnostic in many
instances.
In the presence of clinical evidence
of obstruction, peritonitis, or a mass, a complete blood count (CBC) with
differential is indicated to evaluate for anemia or
thrombocytopenia. When the diagnosis is uncertain, a CBC can help point towards
or away from an inflammatory process. Note that in acute appendicitis before
rupture, white blood cell count may only be minimally elevated or even normal.
C-reactive protein (CRP) has gained favor as an early inflammatory marker, and
many investigators are exploring its clinical utility in the pediatric
emergency department.
A urinalysis to evaluate hydration
status and the presence of infection is
useful. Serum electrolytes should also be obtained in ill patients to assess
fluid and electrolyte balance, as well as acidosis. However, checking routine
serum electrolytes is not necessary in the face of acute gastroenteritis.
Additional laboratory tests that may be helpful are hepatic function panel,
amylase, lipase, and inflammatory markers.
A qualitative urine pregnancy test
must always be sent in any postpubertal female patient with abdominal pain.
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