# Acute Abdomen: Surgical Decision-Making in Children and Adults

## Introduction

The acute abdomen is a common clinical scenario requiring rapid assessment and decision-making. The differential diagnosis varies significantly by age, and the med-peds physician must recognize **age-specific surgical emergencies** while avoiding unnecessary interventions. This lecture covers the systematic approach to abdominal pain from infancy through adulthood with emphasis on surgical versus medical management.

## Age-Specific Differential Diagnosis

### Neonates (0-28 days)
**Necrotizing enterocolitis (NEC)**: Primarily in premature infants; feeding intolerance, bloody stools, pneumatosis intestinalis. **Malrotation with midgut volvulus**: Bilious emesis is a surgical emergency until proven otherwise. Hirschsprung disease: Failure to pass meconium in first 48 hours. Intestinal atresia.

### Infants (1-12 months)
**Intussusception**: Colicky pain, currant jelly stools, sausage-shaped mass; peak 6-36 months. Incarcerated inguinal hernia. Pyloric stenosis: Projectile nonbilious vomiting at 3-6 weeks.

### Children (1-12 years)
**Appendicitis**: Most common surgical emergency in children. Meckel diverticulum: Painless rectal bleeding, or may present like appendicitis; Mesenteric lymphadenitis; Constipation (most common cause of abdominal pain in children).

### Adolescents and Adults
**Appendicitis**: Remains most common surgical emergency. Cholecystitis and cholelithiasis; Small bowel obstruction (adhesive disease, hernias); Perforated peptic ulcer; Diverticulitis (typically age >40); Ovarian torsion, ectopic pregnancy (reproductive-age females); Mesenteric ischemia (elderly; "pain out of proportion to exam").

![Diagram of age-specific causes of acute abdomen](images/acute-abdomen-by-age.jpg)

## Clinical Assessment

### History
Onset, location, character, radiation, severity of pain; Associated symptoms: vomiting (bilious vs. nonbilious), fever, diarrhea, anorexia. Last bowel movement, urinary symptoms; Menstrual history and pregnancy status in reproductive-age females; Surgical history (adhesive obstruction risk).

### Physical Examination
**Inspection**: Distension, visible peristalsis, surgical scars. **Auscultation**: Absent bowel sounds (ileus/peritonitis), high-pitched tinkling (obstruction) **Palpation**: Rebound tenderness, guarding, rigidity (peritoneal signs) **Special signs**: McBurney point tenderness, Rovsing sign, psoas sign, obturator sign (appendicitis); Murphy sign (cholecystitis) **Pediatric considerations**: Exam may be unreliable in young children; observe gait, positioning, and facial expressions.

### Red Flags Requiring Urgent Surgical Consultation
**Bilious vomiting in a neonate** (malrotation until proven otherwise); Peritoneal signs (rigid abdomen, rebound, guarding); Hemodynamic instability with abdominal pain; Evidence of bowel ischemia or perforation on imaging; Signs of incarcerated hernia.

## Diagnostic Workup

### Laboratory Studies
CBC with differential, CRP; BMP, lipase, liver function tests; Urinalysis (rule out UTI, nephrolithiasis); **Beta-hCG** in all reproductive-age females; Lactate if mesenteric ischemia or sepsis is suspected; Type and screen if surgical intervention anticipated.

### Imaging

| Modality | Pediatric Indications | Adult Indications |
|---|---|---|
| **Ultrasound** | First-line for appendicitis, intussusception, pyloric stenosis, ovarian pathology | Cholecystitis, appendicitis (initial), ovarian torsion |
| **CT abdomen/pelvis** | Used if US equivocal; limit radiation exposure | Gold standard for appendicitis, diverticulitis, SBO, perforation |
| **X-ray (KUB)** | Free air, obstruction, NEC (pneumatosis) | Free air, obstruction pattern, foreign body |
| **MRI** | Appendicitis in pregnancy; complex cases | Appendicitis in pregnancy; equivocal cases |

**Pediatric principle**: Ultrasound first to minimize radiation (ALARA principle) **Adult principle**: CT with IV contrast is the workhorse for acute abdominal imaging.

![Imaging algorithm for suspected appendicitis in children vs adults](images/appendicitis-imaging-algorithm.jpg)

## Appendicitis: The Prototype Surgical Emergency

### Pediatric Appendicitis
Perforation rate higher in young children (up to 80% in children <5 years) Atypical presentations common in young children. **Pediatric Appendicitis Score (PAS)** or **Alvarado Score** for risk stratification. Ultrasound first; CT if US is equivocal. Appendectomy (laparoscopic) is standard treatment. Non-operative management with antibiotics is an emerging option for uncomplicated cases.

### Adult Appendicitis
Classic presentation: periumbilical pain migrating to RLQ, anorexia, fever. Alvarado score or AIR score for risk stratification. CT abdomen/pelvis with IV contrast is the primary imaging modality. Laparoscopic appendectomy remains standard of care. **CODA trial**: Antibiotics alone are a reasonable alternative for uncomplicated appendicitis in adults.

## Surgical Decision-Making Principles

**Operate early** when clinical and imaging findings are clear. **Observe and reassess** when diagnosis is uncertain; serial abdominal exams are valuable. Avoid unnecessary surgery in conditions managed medically (mesenteric lymphadenitis, constipation, pancreatitis) Understand the role of **interventional radiology** for percutaneous drainage of abscesses. Multidisciplinary communication between surgery, radiology, and primary team is essential.

## Clinical Pearls

Bilious vomiting in a neonate is malrotation with volvulus until proven otherwise; this is a true surgical emergency. Ultrasound is the first-line imaging modality for pediatric abdominal pain; limit CT use to minimize radiation exposure. Always obtain a pregnancy test in reproductive-age females with abdominal pain before any imaging or intervention. Perforated appendicitis rates are highest in the very young and the elderly due to delayed or atypical presentations. The med-peds physician should maintain a low threshold for surgical consultation when peritoneal signs are present, regardless of age.

![Flowchart for acute abdomen management decision pathway](images/acute-abdomen-flowchart.jpg)

## References

1. CODA Collaborative. A randomized trial comparing antibiotics with appendectomy for appendicitis. *N Engl J Med*. 2020;383(20):1907-1919.
2. Kharbanda AB, Vazquez-Benitez G, Ballard DW, et al. Development and validation of a novel pediatric appendicitis risk calculator (pARC). *Pediatrics*. 2018;141(4):e20172699.
3. Di Saverio S, Podda M, De Simone B, et al. Diagnosis and treatment of acute appendicitis: 2020 update of the WSES Jerusalem guidelines. *World J Emerg Surg*. 2020;15(1):27.
4. Leung AK, Sigalet DL. Acute abdominal pain in children. *Am Fam Physician*. 2003;67(11):2321-2326.