Nursing care
Pyloric stenosis vs intussusception: vomiting, pain, stools and the infant's age
Written and reviewed by Dana Whitfield, RN, MSN · 4 min read · Updated October 2026
Short answer
Pyloric stenosis typically appears at three to six weeks with projectile, non-bilious vomiting after feeds in a hungry infant, sometimes with an olive-shaped upper abdominal mass. Intussusception usually affects older infants and toddlers with sudden episodes of colicky pain, drawing up the legs, vomiting and later bloody, mucus-filled stools. Both can progress to dehydration and need prompt escalation.
The first cue: feeding pattern or pain pattern
The most useful split is what the infant is doing between episodes. With pyloric stenosis the baby vomits forcefully soon after feeding and then wants to feed again, often appearing otherwise well. With intussusception the child has sudden bouts of severe, crampy pain, cries and pulls the knees to the chest, then may seem calm or drowsy until the next bout.
Age supports the pattern. Pyloric stenosis symptoms usually begin between about three and six weeks of life. Intussusception is most common from around six months to three years. An exam stem describing a three-week-old who is hungry after vomiting points one way; a ten-month-old with recurrent screaming episodes points the other.
What the vomit and the stools tell you
In pyloric stenosis the thickened pylorus blocks the stomach outlet before bile enters the gut, so vomiting is non-bilious. The infant fails to gain weight and becomes dehydrated, and visible waves of gastric peristalsis may cross the upper abdomen after a feed. Stools may become scant simply because little is getting through.
In intussusception one segment of bowel telescopes into the next, obstructing it and eventually compromising blood supply. Vomiting is common, and stools mixed with blood and mucus, the so-called red currant jelly stool, can follow. MSD notes this stool is a late finding, so its absence should not delay escalation of a child with typical pain episodes.
Examination and imaging overlap
Both conditions can produce a palpable mass, which is why the mass alone needs context. Pyloric stenosis may give a small, firm, movable olive-shaped mass in the upper abdomen; intussusception may give a sausage-shaped mass. Ultrasound is the usual first imaging study for both, showing a thickened pylorus in one and a target appearance in the other.
Neither diagnosis should be assumed from one sign. Dehydration, lethargy and vomiting occur in many infant illnesses, including gastroenteritis. The combination of age, feeding behaviour, pain pattern and stool findings is what makes one condition more likely, and the prescriber confirms it with imaging.
Nursing priorities for each
For pyloric stenosis, surgery is not an emergency in the first minutes; correcting fluid and electrolyte problems comes first. Monitor intake and output, weight, mucous membranes, fontanelle and laboratory trends, keep the infant nil by mouth as ordered and support the parents. After pyloromyotomy, feeds usually restart within about a day according to the surgical plan.
Intussusception is time-sensitive because the trapped bowel can become ischaemic and perforate. Report it promptly, monitor for continuous pain, rigidity, fever, pallor, rising heart rate or lethargy suggesting peritonitis or shock, and prepare for fluids, gastric decompression and air enema as ordered. Passage of a normal stool after reduction is a reassuring sign to report; recurrence is possible.
Worked study scenario
Picture a hypothetical eight-month-old with three hours of sudden screaming episodes every fifteen to twenty minutes, legs drawn up, vomiting twice, and quiet drowsiness between bouts. Stools are normal so far. Options include giving an oral rehydration trial and reassessing in the morning, documenting colic, or reporting suspected intussusception urgently. Urgent reporting is the strongest answer.
Colic does not explain the age and the lethargy between bouts, and waiting for bloody stool waits for a late sign. Pyloric stenosis is a poor fit because the child is too old and the vomiting is not described as projectile after feeds. Exam reasoning here is pattern recognition; actual imaging and reduction follow the team's protocol.
Sources and further reading
MSD Manual Professional: Hypertrophic pyloric stenosis. Onset at three to six weeks, projectile non-bilious vomiting, olive mass, ultrasound, fluid correction before pyloromyotomy, feeding after surgery.
MSD Manual Professional: Intussusception. Age range, recurrent colicky pain, currant jelly stool as a late sign, sausage mass, target sign, air enema and its contraindications.
MedlinePlus: Intussusception in children. Sudden crying with knees drawn up, bloody mucus stool, signs of shock, recurrence risk and emergency status.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our pediatrics practice questions are the closest set to what this page covers.
Common questions
Is vomiting in pyloric stenosis bilious?
Typically not. The obstruction is at the stomach outlet, above where bile enters, so the vomit is usually milk or formula without green bile. Green vomiting in an infant suggests obstruction further down and needs urgent review.
Does every child with intussusception pass a currant jelly stool?
No. Bloody, mucus-filled stool is a late finding and many children do not have it at presentation. Recurrent colicky pain with lethargy between episodes should be escalated without waiting for it.
Why is surgery for pyloric stenosis delayed until fluids are corrected?
Repeated vomiting causes dehydration and electrolyte and acid-base disturbance. MSD describes fluid resuscitation and electrolyte correction as the first step before pyloromyotomy, which makes anaesthesia safer.