Pyloric Stenosis vs Intussusception

Pediatrics · Gastrointestinal / Nutrition·Updated 2026-10-28

What it is

Hypertrophic pyloric stenosis is thickening of the pyloric sphincter that blocks gastric emptying in young infants. Vomiting of stomach contents removes hydrogen and chloride ions, producing hypochloremic, hypokalemic metabolic alkalosis and dehydration, which are corrected before a pyloromyotomy. Intussusception is the telescoping of one bowel segment into the next, most often the ileum into the colon at the ileocecal valve. The trapped segment obstructs the bowel and compresses its blood supply, so blood and mucus enter the stool and the bowel can become ischemic and perforate.

What the NCLEX focuses on

Pyloric stenosis: projectile, nonbilious vomiting after feedings; the infant is hungry right after vomiting; visible left-to-right peristaltic waves; a firm olive-shaped mass in the epigastrium right of the midline.
Weight loss, fewer wet diapers, a sunken fontanel and lethargy show dehydration; ultrasound confirms the thickened pylorus.
Intussusception: sudden episodes of severe colicky pain with screaming and knees drawn to the chest, vomiting, lethargy between episodes and a sausage-shaped mass in the right upper quadrant.
Currant jelly stools (blood and mucus) are a late sign; do not wait for them to suspect intussusception.
An air or hydrostatic (saline or contrast) enema under imaging both diagnoses and reduces most intussusceptions; surgery is needed for failure or perforation.
A normal brown stool before the enema suggests spontaneous reduction; report it at once because the plan changes.
Fever, a rigid abdomen, tachycardia and falling blood pressure signal perforation and peritonitis.

Priority nursing actions

Assess hydration: weight, wet diapers, fontanel, mucous membranes, capillary refill and heart rate.
Keep the infant NPO as prescribed and insert a nasogastric tube for decompression if prescribed.
Give prescribed IV fluids and electrolytes; add potassium only after urine output is confirmed.
Monitor vomitus and stools, and report a normal brown stool or signs of peritonitis immediately.
Prepare the child and family for pyloromyotomy or enema reduction, then advance feedings gradually as prescribed and assess the incision.

Numbers to know

Feature	Pyloric stenosis	Intussusception
Typical age	Usually 2 to 8 weeks	Most often 3 months to 3 years
Vomiting	Projectile, nonbilious, after feedings	Present; becomes bile-stained as obstruction progresses
Pain	Minimal; infant hungry and irritable	Episodic severe colicky pain with knees drawn up
Stools	Fewer and smaller	Currant jelly stools (late sign)
Mass	Olive-shaped, epigastric, right of midline	Sausage-shaped, right upper quadrant
Key findings	Hypochloremic, hypokalemic metabolic alkalosis; ultrasound	Ultrasound; the enema diagnoses and treats
Treatment	Correct fluids and electrolytes, then pyloromyotomy	Air or hydrostatic enema; surgery if it fails

Common exam traps

Choosing to add potassium chloride to the IV before the infant voids: wrong because hyperkalemia results if the kidneys are not producing urine.
Choosing emergency surgery before alkalosis and dehydration are corrected: wrong because pyloric stenosis is not a surgical emergency and uncorrected alkalosis raises anesthesia risk, including postoperative apnea.
Choosing gastroesophageal reflux for projectile vomiting with weight loss: wrong because reflux spitting is effortless and the infant keeps gaining weight.
Choosing colic or gastroenteritis for episodic screaming with knees drawn up and lethargy between episodes: wrong because this pattern signals intussusception.
Choosing to continue enema preparation without reporting a normal brown stool: wrong because spontaneous reduction changes the plan.

What to teach

After pyloromyotomy, give small, frequent feedings advanced as prescribed; a little vomiting in the first 24 hours is common, but persistent vomiting, fever or incision redness is reported.
Count wet diapers and report fewer than usual, no tears or a sunken fontanel.
Intussusception can recur after enema reduction; report renewed colicky pain, vomiting or bloody stools at once.

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Question 1 · QID F551DAFC

A parent brings an infant to the clinic reporting episodes of inconsolable crying with the infant drawing the legs up toward the abdomen, followed by a period of lethargy. The parent also mentions a recent stool that looked like it contained blood and mucus. Which condition should the nurse suspect?

Select the best answer.

A. Constipation causing intermittent abdominal cramping and straining after a recent change in feeding pattern
B. Intussusception
C. Viral gastroenteritis causing abdominal cramping, transient lethargy, and mucus-streaked stools during an acute intestinal infection
D. Infant colic causing recurrent episodes of intense crying with leg flexion followed by periods of exhaustion and sleep

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Sources

Hockenberry MJ, Duffy EA, Gibbs KD. Wong's Nursing Care of Infants and Children. 12th ed. Elsevier; 2024.
Kliegman RM, St Geme JW, Blum NJ, et al. Nelson Textbook of Pediatrics. 22nd ed. Elsevier; 2024.

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