Acute Abdominal Pain in Infants and Children

1. THE 2-MINUTE PHYSIOLOGY (Rapid Pathophysiology)

• The Obstructive vs. Inflammatory Paradigm: Pediatric abdominal pain frequently stems from mechanical obstruction or hollow viscus inflammation. In appendicitis, luminal obstruction of the blind-ending cecal appendage leads to increased intraluminal pressure, venous engorgement, ischemia, and bacterial translocation. The risk of appendiceal perforation is exceedingly high (up to 30%) and greatest in children under 4 years old, largely due to their inability to articulate localized symptoms before rupture occurs.
• The Ischemic Cascade (Volvulus & Intussusception): In malrotation with midgut volvulus, an embryologic failure of gut rotation results in a narrow mesenteric base, predisposing the bowel to twist around the superior mesenteric artery, causing catastrophic, rapid midgut necrosis. In intussusception, a proximal segment of bowel telescopes into a distal segment, causing lymphatic and venous congestion that progresses to bowel ischemia and the sloughing of necrotic mucosa (yielding the classic "currant jelly" stool).
• The Metabolic Mimic: In Diabetic Ketoacidosis (DKA), profound metabolic acidosis, ketonemia, and osmotic diuresis precipitate severe delayed gastric emptying and pseudo-peritonitis, presenting as acute abdominal pain that perfectly mimics a surgical abdomen.

2. THE BEDSIDE ACTION PLAN (Rapid ER Management)

• Immediate Stabilization: Assess the Pediatric Assessment Triangle (Appearance, Work of Breathing, Circulation). Children with an acute abdomen may present atypically with lethargy, isolated fever, or irritability rather than focal pain.
• NPO & Resuscitation: Make the patient strictly nil per os (NPO). Establish IV access. If the child shows signs of hypovolemia or hemorrhagic shock from a GI bleed, administer a 20 mL/kg bolus of isotonic crystalloids or Packed Red Blood Cells (PRBCs).
• Pharmacotherapy:
• Analgesia: Administer IV opioids (e.g., Fentanyl 1 mcg/kg or Morphine 0.1 mg/kg); the classic surgical dogma that analgesia masks pediatric abdominal pathology is obsolete.
• Antibiotic Stewardship: Do NOT rush to give empiric antibiotics to children presenting with bloody diarrhea. Premature antibiotic administration in Shiga toxin-producing E. coli 0157:H7 can precipitate Hemolytic Uremic Syndrome (HUS).
• Serial Examinations: In cases of blunt abdominal trauma or equivocal pediatric abdominal pain, serial abdominal exams by the same provider are an essential monitoring parameter to detect delayed viscus perforation or evolving peritonitis.

3. THE DIAGNOSTIC GRID (Differential Diagnosis & Workup)

• Top "Can't-Miss" Hidden Pathologies:
• Testicular Torsion: 31% of torsion cases present exclusively as abdominal pain, not testicular pain.
• Malrotation with Midgut Volvulus: Must be ruled out in any neonate/infant with bilious emesis.
• Intussusception: Suspect in children 6 to 36 months presenting with intermittent severe crampy pain, drawing legs up, vomiting, or isolated unexplained lethargy/altered mental status.
• Meckel Diverticulum: The leading cause of painless lower GI bleeding in toddlers.
• Prioritized Diagnostic Workup:
• Tier 1 (Bedside/Clinical): Perform a full Genitourinary (GU) exam to rule out torsion. Obtain a point-of-care blood glucose to rule out DKA.
• Tier 2 (Ultrasound First): Point-of-Care Ultrasound (POCUS) or formal abdominal US is the initial modality of choice to evaluate for appendicitis, intussusception, and hypertrophic pyloric stenosis, sparing the child ionizing radiation.
• Tier 3 (Advanced Imaging): An Upper GI series with contrast is the gold standard for malrotation/volvulus. If CT is required for appendicitis or undifferentiated pain, order it with IV contrast only; oral and rectal contrast add zero diagnostic yield, cause unnecessary delays, and traumatize the child.

4. THE VISUAL BOARD (ECG / POCUS / Imaging)

• Intussusception (Ultrasound): The definitive finding is the "Target" sign or "Bullseye" sign in the transverse plane, representing the layers of the telescoped bowel.
• Appendicitis (Ultrasound): Look for a non-compressible, blind-ending tubular structure with an outer diameter > 6 mm. Color Doppler will often show a "ring of fire" denoting hyperemic inflammation.
• Necrotizing Enterocolitis (NEC) (Plain Film): In an infant presenting with abdominal distension and bloody stools, scrutinize the abdominal X-ray for pneumatosis intestinalis (air within the bowel wall), pneumoperitoneum, or hepatobiliary gas.
• Malrotation/Volvulus (Upper GI Series): Look for the classic "corkscrew" appearance of the duodenum and a misplaced ligament of Treitz.

5. THE SCORING MATRIX (Risk Stratification & Guidelines)

• PECARN Blunt Abdominal Trauma Tool: Used to identify children at very low risk for intra-abdominal injury (IAI) to safely avoid CT radiation. A patient is very low risk if they lack ALL of the following 7 variables:

1. No evidence of abdominal wall trauma or seatbelt sign.

2. Gcs > 13.

1. No abdominal tenderness.
2. No evidence of thoracic wall trauma.
3. No complaints of abdominal pain.
4. No decreased breath sounds.
5. No vomiting.

• Pediatric Appendicitis Risk Calculator (pARC) & Pediatric Appendicitis Score (PAS): Validated scoring tools used to stratify the likelihood of acute appendicitis and guide the need for surgical consultation vs. ultrasound vs. discharge.

6. THE DANGER ZONE (Pitfalls & Critical Actions)

• Pitfall - The Testicular Miss: Failing to fully expose a crying toddler and examine the genitals. Critical Action: You must perform and document a genitourinary exam in every male child presenting with abdominal pain to rule out testicular torsion.
• Pitfall - The Iodine Allergy Myth: Withholding IV contrast for a pediatric abdominal CT because the parents report a "shellfish allergy." Critical Action: Shellfish allergy is driven by the protein tropomyosin, not iodine. It is not a contraindication to IV contrast. Do not delay imaging or mandate steroid premedication for this myth.
• Pitfall - The Oral Contrast Delay: Ordering oral or rectal contrast for an acute abdominal CT. Critical Action: Routine use of oral/rectal contrast in nontraumatic pediatric abdominal pain (NTPAP) increases length of stay without improving diagnostic yield; it should be abandoned in the ED.
• Pitfall - Ignoring Bilious Emesis: Attributing green/yellow vomit in a neonate to gastroenteritis. Critical Action: Bilious emesis in an infant is a surgical emergency (malrotation with volvulus) until proven otherwise and requires an immediate surgical consult and imaging.

7. MCQ MASTERCLASS (Written Exam Tips)

• Buzzwords: "Intermittent episodes of crying with legs drawn up," "sausage-shaped abdominal mass," "currant jelly stool," or simply "isolated severe lethargy" in a toddler. Diagnosis: Intussusception.
• Buzzwords: "Painless rectal bleeding" in a 2-year-old child (Rule of 2s: 2 years old, 2% of population, 2 inches long, within 2 feet of the ileocecal valve). Diagnosis: Meckel Diverticulum.
• Common Distractor: A 4-year-old presents with bloody diarrhea and abdominal cramping. An option suggests: "Discharge with oral Cefdinir or Azithromycin." Differentiate: This is a lethal trap. Antibiotics in the setting of Shiga toxin-producing E. coli 0157:H7 can precipitate Hemolytic Uremic Syndrome (HUS). Provide supportive care and IV hydration.
• Common Distractor: A 14-year-old male presents with acute lower abdominal pain. An option suggests "Immediate CT Abdomen/Pelvis." Differentiate: The highest priority action before radiation is performing a genitourinary examination to rule out testicular torsion, which presents as abdominal pain in nearly a third of cases.

8. THE BOARDROOM SCRIPT (OSCE & Oral Board Tips)

• The Opening Salvo: "My primary priority is the pediatric ABCs. Because emergent surgical conditions in children can present atypically with isolated lethargy, vomiting, or fever, I will fully expose the patient. I am explicitly performing a genitourinary examination to rule out testicular torsion and ordering a point-of-care glucose to rule out DKA."
• Addressing High-Risk Symptoms: "The mother reports the neonate had bilious emesis. This is a red-flag symptom. I am immediately making the infant NPO, starting IV fluid resuscitation, and placing an emergent consult to Pediatric Surgery for suspected malrotation with midgut volvulus while I order an Upper GI series."
• Articulating Diagnostic Stewardship: "To evaluate this toddler's intermittent, severe, crampy abdominal pain, I suspect intussusception. I will order a targeted abdominal ultrasound to look for a 'target sign,' explicitly avoiding a CT scan to spare the child unnecessary ionizing radiation. If intussusception is found, I will consult radiology for a therapeutic air or hydrostatic enema."
• Defending Contrast Use: "If ultrasound is equivocal and a CT is required for appendicitis, I will order a CT of the abdomen and pelvis with IV contrast only. I will not order oral or rectal contrast, as the literature shows it delays care without increasing diagnostic yield, and a reported shellfish allergy is not a true contraindication to iodine-based IV contrast."