In contrast to visceral pain, somatic pain results when overlying body structures are injured. Somatic structures include the parietal peritoneum, fascia, muscles, and skin of the abdominal wall. In contrast to pain emanating from visceral injury, somatic nociceptive fibers are myelinated and are capable of rapid transmission of well-localized painful stimuli. When intra-abdominal processes cause inflammation or injury to the parietal peritoneum or abdominal wall structures, poorly localized visceral pain becomes well-localized somatic pain. For example, in acute appendicitis, the initial activation of visceral nociceptive fibers yields poorly localized discomfort in the mid-abdomen. When the inflammatory process extends to the overlying parietal peritoneum, the pain becomes severe and localizes to the right lower quadrant. This is called somatoparietal pain.
Referred pain is a painful sensation in a body region distant from the true source of pain. The location of referred pain is predictable based on the locus of visceral injury. Stomach pain is referred to the epigastric and retrosternal regions, and liver and pancreas pain is referred to the epigastric region. Gallbladder pain often is referred to the region below the right scapula. Somatic pathways stimulated by small bowel visceral afferents affect the periumbilical area, and colonic injury results in infraumbilical referred pain.
Acute abdominal pain can signal the presence of a dangerous intra-abdominal process (e.g., appendicitis or bowel obstruction) or may originate from extraintestinal sources (e.g., lower lobe pneumonia or urinary tract stone). Not all episodes of acute abdominal pain require emergency intervention. Appendicitis and volvulus, for example, must be ruled out as quickly as possible. Few patients presenting with acute abdominal pain actually have a surgical emergency, but they must beseparated from cases that can be managed conservatively.
Table 126-1 lists a diagnostic approach to acute abdominal painin children. Events that occur with a discrete, abrupt onset, suchas passage of a stone, perforation of a viscus, or infarction, resultin a sudden onset of pain. Gradual onset of pain is common withinfectious or inflammatory causes, such as appendicitis and IBD.
A standard group of laboratory tests usually is performed for acute abdominal pain (see Table 126-1). An abdominal x-ray series evaluates for bowel obstruction or nephrolithiasis. Ultrasound or computed tomography (CT) can visualize the appendix if appendicitis is suspected but the diagnosis remains in doubt. If the initial evaluation suggests intussusception, a barium or pneumatic (air) enema may be used to diagnose and treat this condition (see Chapter 129).
Table 126-2 lists the differential diagnosis of acute abdominal pain in children. The urgent task of the clinician is to rule out surgical emergencies. In young children, malrotation with volvulus, incarcerated hernia, congenital anomalies, and intussusception are common concerns. In older children and teenagers, appendicitis is more common. An acute surgical abdomen is characterized by signs of peritonitis, including tenderness, abdominal wall rigidity, guarding, and absent or diminished bowel sounds. Helpful characteristics of onset, location, referral, and quality of pain are noted in Table 126-3.
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Recurrent abdominal pain is a common problem, affecting more than 10% of all children. The peak incidence occurs between ages 7 and 12 years. Although the differential diagnosis of recurrent abdominal pain is fairly extensive (Table 126-4),most children do not have a serious (or even identifiable) underlying illness causing the pain.
Onset Sudden or gradual, prior episodes, association with meals, history of injury
Nature Sharp versus dull, colicky or constant, burning
Location Epigastric, periumbilical, generalized, right or left lower quadrant, change in location over time