# Pediatric Abdominal Emergencies

## Introduction

Pediatric abdominal emergencies present unique diagnostic challenges because the differential diagnosis is heavily influenced by the **age of the child**. Imaging plays a critical role in rapid diagnosis and surgical planning. Ultrasound is the preferred initial modality in most cases to minimize radiation exposure, with CT reserved for complex or equivocal scenarios.

### Age-Based Differential Diagnosis

| Age Group | Key Emergencies |
|-----------|----------------|
| Neonate (0-28 days) | NEC, malrotation with volvulus, meconium ileus, duodenal atresia |
| Infant (1-12 months) | Hypertrophic pyloric stenosis, intussusception, malrotation |
| Toddler (1-5 years) | Intussusception, appendicitis, Meckel diverticulum |
| Older child (>5 years) | Appendicitis, ovarian torsion, Meckel diverticulum |

## Neonatal Emergencies

### Necrotizing Enterocolitis (NEC)

NEC is the most common gastrointestinal emergency in **premature neonates**. The radiographic hallmark is **pneumatosis intestinalis**, which appears as linear or bubbly lucencies within the bowel wall representing intramural gas. **Portal venous gas** indicates severe disease and carries a worse prognosis. **Pneumoperitoneum** indicates bowel perforation and constitutes a surgical emergency. Serial abdominal radiographs every 6-8 hours are used to monitor progression, and a persistently dilated, unchanging loop of bowel (the **sentinel loop**) suggests necrosis.

### Malrotation with Midgut Volvulus

Malrotation with midgut volvulus is a **true surgical emergency** requiring immediate diagnosis and intervention. It results from failure of normal counterclockwise rotation of the midgut during embryologic development. The **upper GI series** is the gold standard, demonstrating an abnormal position of the **duodenojejunal junction (ligament of Treitz)** to the right of the left pedicle and below the duodenal bulb. A **corkscrew appearance** of the distal duodenum and proximal jejunum indicates volvulus. Ultrasound may show the **whirlpool sign**, representing swirling of the SMV and mesentery around the SMA. An abnormal relationship of the SMA and SMV on ultrasound (SMV to the left of or anterior to the SMA) is suggestive but not diagnostic in isolation.

### Meconium Ileus

Meconium ileus is strongly associated with **cystic fibrosis** and is nearly pathognomonic. Inspissated meconium causes distal ileal obstruction. Radiographs show dilated bowel loops without air-fluid levels (because the thick meconium prevents layering). The **Neuhauser sign** is a bubbly or granular appearance of meconium mixed with air in the right lower quadrant. A water-soluble contrast enema can be both diagnostic and therapeutic, revealing a microcolon distally.

## Infant and Toddler Emergencies

### Hypertrophic Pyloric Stenosis (HPS)

HPS classically presents with **projectile, non-bilious vomiting** in a 2-6 week old infant. Ultrasound is diagnostic and relies on specific measurements: **pyloric muscle thickness greater than 3 mm** and **pyloric channel length greater than 15 mm**. The **target sign** on transverse view shows the hypertrophied muscle surrounding the echogenic mucosa. The **antral nipple sign** represents redundant mucosa prolapsing into the antrum.

### Intussusception

Intussusception has a peak incidence at **6-36 months** of age, and **ileocolic intussusception** is the most common type in children. Ultrasound is the imaging modality of choice, showing the **target sign** or **doughnut sign** on transverse view and the **pseudokidney sign** on longitudinal view. Pathologic lead points (Meckel diverticulum, polyp, lymphoma) are more common in children over 5 years. **Air or hydrostatic enema reduction** is therapeutic but is contraindicated if there is pneumoperitoneum or peritonitis. The **rule of 3s** permits 3 attempts at reduction, each lasting up to 3 minutes.

### Meckel Diverticulum

Meckel diverticulum is the **most common congenital anomaly of the GI tract**, remembered by the rule of 2s: 2% of the population, 2 feet from the ileocecal valve, 2 inches long, and 2 types of ectopic tissue. It contains ectopic **gastric mucosa** in approximately 50% of symptomatic cases. The **technetium-99m pertechnetate scan (Meckel scan)** detects this ectopic gastric mucosa. It typically presents with painless rectal bleeding in children.

## Older Child Emergencies

### Appendicitis

Appendicitis is the most common surgical emergency in **children over 2 years**. Ultrasound is the first-line imaging modality, using the **graded compression technique**. The diagnostic criteria are a **non-compressible, aperistaltic, blind-ending tubular structure greater than 6 mm in diameter**. Secondary signs include periappendiceal fat stranding, free fluid, and appendicoliths. CT is used when ultrasound is equivocal or the appendix is not visualized. **Perforation** is more common in younger children due to delayed diagnosis.

### Ovarian Torsion

Ovarian torsion has a peak incidence in **adolescent girls**. Ultrasound with Doppler is the primary modality, revealing an enlarged, edematous ovary with peripheral follicles (the **string of pearls sign**). Arterial and venous flow may be absent or decreased on Doppler, but the **presence of flow does not exclude torsion**. The **whirlpool sign** may be seen at the twisted vascular pedicle.

## Clinical Pearls

**Age is the most important factor** in determining the differential diagnosis for pediatric abdominal emergencies. Malrotation with midgut volvulus is a time-critical diagnosis, and an upper GI series should be performed emergently when suspected. Ultrasound is the preferred first-line modality for most pediatric abdominal emergencies to minimize radiation. In intussusception, the presence of color Doppler flow within the intussusceptum is a favorable prognostic sign for successful reduction.

## References

1. ACR Appropriateness Criteria: Suspected Appendicitis in Children. *J Am Coll Radiol*. 2019;16(5S):S252-S263.
2. Imaging of Pediatric Abdominal Emergencies. *Radiographics*. 2017;37(6):1748-1766.
3. Pediatric Intussusception: Clinical Practice and Evidence-Based Imaging. *Pediatr Radiol*. 2020;50(11):1582-1595.
4. Malrotation and Midgut Volvulus: A Systematic Approach to Diagnosis. *Radiology*. 2018;288(1):18-27.