# Pediatric Abdominal Emergencies: Appendicitis, Intussusception, and Pyloric Stenosis

## Pediatric Appendicitis

### Epidemiology

Appendicitis is the most common surgical emergency in children, with a peak incidence at 10 to 12 years and a lifetime risk of 7 to 8 percent. It is rare in children under 2 years, but when it does occur in very young children, it is much more likely to perforate. The overall perforation rate in children is 30 to 40 percent, rising to 80 to 100 percent in children under 5 years because of atypical presentations and delayed diagnosis.

### Pathophysiology

The process begins with luminal obstruction, which may be caused by a fecalith, lymphoid hyperplasia, or a foreign body. Obstruction leads to increased intraluminal pressure, followed by venous congestion, bacterial invasion, necrosis, and ultimately perforation. The risk of perforation increases significantly after 36 to 48 hours of symptoms.

### Clinical Presentation

The classic presentation is periumbilical pain that migrates to the right lower quadrant as the inflammation progresses from visceral to parietal peritoneal irritation, accompanied by anorexia, nausea, vomiting, and low-grade fever. In children under 5 years, atypical presentations are the rule rather than the exception, with diffuse abdominal pain, irritability, diarrhea, and vomiting, and peritoneal signs that are unreliable. Examination findings include right lower quadrant tenderness, guarding, and rebound at McBurney's point, along with Rovsing sign, psoas sign, and obturator sign. The hop test and cough test are positive when hopping or coughing reproduces the pain, indicating peritoneal irritation.

### Scoring Systems

The Pediatric Appendicitis Score (PAS), validated for ages 4 to 15, incorporates migration of pain, anorexia, nausea and vomiting, RLQ tenderness, cough/hop/percussion tenderness, fever, leukocytosis, and neutrophilia. A score of 3 or below indicates low risk (less than 3 percent), a score of 4 to 6 is equivocal and warrants imaging, and a score of 7 or above indicates high risk (greater than 90 percent). The Alvarado Score is widely used but less well validated in the pediatric population.

### Imaging

Ultrasound is the first-line imaging study in pediatric appendicitis because it avoids radiation. Findings include a non-compressible, blind-ending tubular structure greater than 6 mm in diameter, an appendicolith, and periappendiceal fluid or fat stranding. Sensitivity is 88 to 94 percent but is operator dependent, with limitations including retrocecal appendix, obesity, and obscuring bowel gas. When ultrasound is equivocal or the appendix is not visualized but clinical concern persists, CT or MRI should be obtained.

CT has a sensitivity exceeding 95 percent and is the most accurate imaging modality, but radiation exposure is the primary concern in children, and ALARA principles should be followed. Low-dose CT protocols reduce radiation while maintaining diagnostic accuracy. MRI has no radiation and is increasingly used for pediatric appendicitis, with sensitivity comparable to CT at 96 to 97 percent, though it is limited by availability, the need for sedation in young children, and longer acquisition times.

### Management

Uncomplicated appendicitis is treated with appendectomy, with the laparoscopic approach preferred. Non-operative management with antibiotics first is an active area of investigation, with multiple randomized controlled trials showing approximately 70 to 75 percent success rates, though recurrence rates of 15 to 30 percent at one year persist. Perforated appendicitis is managed with antibiotics first (piperacillin-tazobactam or ceftriaxone plus metronidazole) and fluid resuscitation, with the choice between interval appendectomy and early appendectomy still debated. An appendiceal abscess is treated with antibiotics and percutaneous drainage if large, followed by interval appendectomy 6 to 8 weeks later.

## Intussusception

### Epidemiology

Intussusception is the most common cause of intestinal obstruction in children between 6 months and 3 years, with a peak at 5 to 9 months and a male predominance of 3 to 2. Most cases are ileocolic, where the ileum telescopes into the colon. In children under 3 years, the cause is usually idiopathic, likely related to lymphoid hyperplasia and often following a viral illness. In children over 3 years or with recurrent intussusception, a pathologic lead point should be considered, such as a Meckel diverticulum, lymphoma, polyp, or Henoch-Schonlein purpura.

### Clinical Presentation

The classic triad is colicky intermittent abdominal pain, vomiting, and currant jelly stool, though this triad is present in only about 20 percent of cases. Episodes of severe pain with drawing up of the legs alternate with periods of calm or lethargy. A sausage-shaped mass may be palpable in the right upper quadrant (Dance sign refers to the empty RLQ resulting from cecal displacement). Lethargy or altered mental status can be the presenting finding in 25 percent of cases and is easily mistaken for sepsis or a neurologic emergency. Bloody stool is a late sign indicating mucosal ischemia, and bilious vomiting suggests obstruction.

### Diagnosis

Ultrasound is the study of choice, with sensitivity and specificity exceeding 95 percent. The target sign on transverse view shows concentric rings of hypoechoic and hyperechoic layers, and the pseudokidney sign is seen on longitudinal view. Plain X-ray may show a soft tissue mass, paucity of bowel gas in the RLQ, or signs of obstruction, but a normal X-ray does not exclude intussusception. CT is rarely needed but may show a target sign and can be useful when a lead point is suspected in older children.

### Management

Air-enema reduction (pneumatic reduction) is the first-line treatment, performed by a radiologist under fluoroscopy. Air is insufflated into the rectum, and the pressure pushes the intussusceptum back. The success rate is 80 to 95 percent. Contraindications include peritonitis, perforation, shock, and significant clinical deterioration. Risks include perforation (less than 1 percent) and recurrence (5 to 10 percent within 72 hours). Hydrostatic reduction using saline or barium under fluoroscopic or ultrasound guidance is an alternative. Surgical reduction is indicated when air-enema fails after 2 to 3 attempts or when peritonitis, perforation, or shock is present. After reduction, patients should be observed for 12 to 24 hours with return precautions given for recurrence symptoms. If intussusception recurs, a repeat air-enema is often successful, but multiple recurrences should prompt workup for a pathologic lead point.

## Pyloric Stenosis (Hypertrophic Pyloric Stenosis)

### Epidemiology

Pyloric stenosis occurs at a rate of 2 to 3 per 1,000 live births, with a male-to-female ratio of 4 to 1, most commonly affecting firstborn males. It typically presents between 2 and 8 weeks of age, rarely before 2 weeks or after 12 weeks. Risk factors include male sex, firstborn status, family history, and macrolide exposure (erythromycin or azithromycin) in the first 2 weeks of life.

### Pathophysiology

Hypertrophy and hyperplasia of the pyloric circular muscle cause gastric outlet obstruction. The cause is unknown and likely multifactorial.

### Clinical Presentation

The hallmark is projectile, non-bilious vomiting that worsens over days to weeks and occurs shortly after feeding. The infant is characteristically hungry and eager to feed immediately after vomiting, giving rise to the term "hungry vomiter." Dehydration of varying degrees develops depending on the duration before presentation, along with weight loss or failure to thrive. On examination, a firm, mobile, 1 to 2 cm "olive" mass may be palpable in the right upper quadrant or epigastrium, found in 60 to 80 percent of cases by an experienced examiner and best felt after vomiting or with NG decompression. Visible gastric peristaltic waves may be seen traveling left to right across the upper abdomen.

### Key Differentiating Features of Infant Vomiting Emergencies

| Feature | Pyloric Stenosis | Malrotation/Volvulus | Intussusception |
|---------|-----------------|---------------------|-----------------|
| Age | 2–8 weeks | Any (especially neonate) | 6–36 months |
| Vomiting | Non-bilious, projectile | Bilious (GREEN) | Intermittent, may be bilious |
| Key finding | "Olive" mass, hungry vomiter | Bilious vomiting = volvulus until proven otherwise | Colicky pain, currant jelly stool (late) |
| Diagnosis | Ultrasound (pyloric thickness > 3 mm) | Upper GI series | Ultrasound (target sign) |
| Urgency | Medical then surgical | Emergent surgical | Air-enema reduction |
| Labs | Hypochloremic, hypokalemic metabolic alkalosis | May have lactate elevation | Usually normal |

### Metabolic Derangements

The classic electrolyte pattern is a hypochloremic, hypokalemic metabolic alkalosis. The mechanism is loss of hydrochloric acid from vomiting, leading to chloride depletion. The kidneys respond by retaining hydrogen ions and excreting potassium in an attempt to conserve sodium, producing a paradoxical aciduria. The BMP shows low chloride, low potassium, elevated bicarbonate, and elevated pH. Dehydration may also cause pre-renal azotemia. It is essential to correct these metabolic derangements before surgery, because pyloric stenosis is a medical emergency (requiring fluid and electrolyte correction) before it becomes a surgical emergency.

### Diagnosis

Abdominal ultrasound is the study of choice, with sensitivity and specificity exceeding 95 percent. Diagnostic criteria include a pyloric muscle thickness greater than 3 mm (single wall) and a pyloric channel length greater than 15 to 17 mm. If ultrasound is equivocal, an upper GI series can be obtained, which shows a "string sign" (elongated pyloric channel) and a "shoulder sign" (pyloric mass indenting the antrum).

### Management

Fluid resuscitation begins with a normal saline bolus of 20 mL/kg, followed by D5 NS with potassium chloride for maintenance, correcting the hypokalemia and alkalosis. The patient is kept NPO with NG decompression if there is significant distension. The definitive treatment is Ramstedt pyloromyotomy, performed laparoscopically when possible, which involves a longitudinal incision through the hypertrophied muscle down to the submucosa. It is curative with an excellent prognosis. Importantly, surgery is not emergent; the metabolic derangements should be corrected first, which may take 24 to 48 hours.

## Other Pediatric Abdominal Emergencies

### Malrotation with Midgut Volvulus

Malrotation with midgut volvulus is a true surgical emergency, and any delay leads to midgut necrosis. The key presentation is bilious vomiting in a neonate or infant, and any bilious vomiting in a neonate should be considered midgut volvulus until proven otherwise. Diagnosis is made by an upper GI series showing an abnormal position of the ligament of Treitz, with the duodenojejunal junction failing to cross the midline to the left of the spine. On ultrasound, the "whirlpool sign" represents a twisted SMA/SMV relationship. Treatment is an emergent Ladd procedure consisting of surgical detorsion, lysis of Ladd bands, broadening of the mesentery, and appendectomy.

### Meckel's Diverticulum

Meckel's diverticulum follows the "rule of 2s": it occurs in 2 percent of the population, is located 2 feet from the ileocecal valve, is 2 inches long, contains 2 types of ectopic tissue (gastric and pancreatic), and typically presents at 2 years of age. The most common pediatric presentation is painless rectal bleeding, but it can also cause obstruction, inflammation mimicking appendicitis (Meckelitis), or serve as a lead point for intussusception. Diagnosis is made with a Meckel scan (technetium-99m pertechnetate scan) that detects ectopic gastric mucosa. Treatment is surgical resection by diverticulectomy or segmental bowel resection.

### Incarcerated Inguinal Hernia

Incarcerated inguinal hernia is more common in premature infants and males. It presents as an irreducible, firm inguinal mass with pain, irritability, and vomiting. It must be differentiated from a hydrocele (which transilluminates, is non-tender, and is reducible) and a retractile testis. Management begins with an attempt at manual reduction using gentle, sustained pressure. Emergent surgery is indicated if the hernia is irreducible or there are signs of strangulation (erythema, edema, tenderness, systemic toxicity).

<image>A three-panel ultrasound image set for pediatric abdominal emergencies. Panel 1: Pyloric stenosis — longitudinal and transverse ultrasound views of the pylorus showing a thickened pyloric muscle wall (greater than 3 mm) and elongated pyloric channel (greater than 15 mm), with measurement calipers shown. Panel 2: Intussusception — transverse ultrasound showing the "target sign" or "donut sign" with concentric rings of bowel wall layers. Panel 3: Appendicitis — ultrasound showing a non-compressible, fluid-filled tubular structure greater than 6 mm in diameter with surrounding echogenic inflamed fat. Each image is labeled with key diagnostic measurements and findings.</image>

<image>A clinical comparison diagram of vomiting patterns in infants. Three columns comparing: pyloric stenosis (non-bilious projectile vomiting, age 2-8 weeks, hungry after vomiting, olive mass, hypochloremic hypokalemic metabolic alkalosis), malrotation with volvulus (bilious vomiting, any age but especially neonates, surgical emergency, UGI series diagnostic), and intussusception (intermittent colicky pain with vomiting, age 6-36 months, currant jelly stool late, target sign on US). Each column includes a key clinical image or finding, the urgency level, and the definitive management approach.</image>

## Clinical Pearls

Ultrasound is the first-line imaging for pediatric appendicitis, and CT radiation should be avoided whenever possible, with MRI serving as a radiation-free alternative. Children under 5 years with appendicitis present atypically and have very high perforation rates of up to 80 percent, requiring a high index of suspicion. Lethargy can be the presenting symptom of intussusception and should not be assumed to represent sepsis or a neurologic cause without first considering this diagnosis. A normal plain X-ray does not exclude intussusception, and ultrasound is required. Air-enema reduction for intussusception has an 80 to 95 percent success rate and is first-line, with surgical reduction reserved for failure or complications. In pyloric stenosis, the metabolic derangements (hypochloremic, hypokalemic metabolic alkalosis) must be corrected before surgery because this is a medical emergency first. Bilious vomiting in a neonate is midgut volvulus until proven otherwise and represents a true surgical emergency requiring emergent upper GI series and surgical consultation. The classic triad of intussusception (pain, vomiting, currant jelly stool) is present in only 20 percent of cases, and clinicians should not wait for the complete triad before pursuing the diagnosis.

## References

- Bachur RG, et al. Effect of reduction in the use of computed tomography on clinical outcomes of appendicitis. *JAMA Pediatr*. 2015;169:755-760.
- Georgiou R, et al. A meta-analysis of non-operative versus surgical management of uncomplicated appendicitis in children. *J Pediatr Surg*. 2017;52:1219-1227.
- Daneman A, Navarro O. Intussusception: diagnosis and management. *Radiol Clin North Am*. 2004;42:445-461.
- Olive AP, Endom EE. Infantile hypertrophic pyloric stenosis. *UpToDate*. 2023.
- Sola JE, Neville HL. Laparoscopic vs open pyloromyotomy: a systematic review and meta-analysis. *J Pediatr Surg*. 2009;44:1631-1637.