Infantile hypertrophic pyloric stenosis
Summary
Hypertrophy of the pyloric circular muscle → fixed gastric outlet obstruction in young infants (classically the “hungry vomiter” 2–8 weeks old). Ultrasound is diagnostic; treatment is pyloromyotomy after correcting dehydration and metabolic alkalosis.
Epidemiology
- Onset: typically 3–5 weeks of life (range ~2–12 weeks)
- Male predominance (~4:1)
- More common in firstborn infants
- ↑ incidence in preterm infants
- Overall frequency: ~1–2 per 1000 live births
Risk factors
- Feeding / perinatal
- Bottle feeding
- Preterm birth
- Caesarean section
- Maternal
- Maternal smoking in pregnancy
- Neonatal
- Macrolide antibiotics in the first weeks of life (e.g. erythromycin, azithromycin)
- Genetic / familial
- Positive family history (siblings or parents with IHPS)
Pathophysiology
- Hypertrophy and hyperplasia of the pyloric circular muscle with mucosal oedema
- Narrow, elongated, non-relaxing pyloric canal → progressive gastric outlet obstruction
- Result: increasingly forceful gastric peristalsis against a fixed obstruction
Clinical presentation
- Initially well infant, then:
- Onset of symptoms at 3–5 weeks
- Non-bilious, projectile vomiting shortly after feeds
- Often still hungry after vomiting (“hungry vomiter”)
- With time:
- Poor weight gain / weight loss, constipation
- Signs of dehydration
- Examination:
- Epigastric fullness and sometimes visible peristaltic waves (L→R)
- Palpable “olive”: firm, mobile mass in the right upper quadrant / epigastrium
- Biochemistry (after prolonged vomiting):
- Hypochloraemic, hypokalaemic metabolic alkalosis
- ± paradoxical aciduria in more advanced cases
Imaging
Imaging of choice – Ultrasound
- First-line, essentially replaces routine contrast studies
- Advantages: no radiation, quick, highly sensitive/specific when done well
- Technique:
- High-frequency linear probe
- Supine or right lateral decubitus / right posterior oblique
- Feed a small amount of fluid during scan to assess dynamic passage through pylorus
Key sonographic appearances
All of these are supportive evidence (adjunctive to measurement diagnostic criteria)
- Transverse plane
- “Target / doughnut sign”: hypoechoic hypertrophied muscle as a ring around echogenic mucosa
- Longitudinal plane
- “Cervix sign”: elongated pyloric canal and hypertrophied muscle resembling a uterine cervix
- “Antral nipple sign”: redundant pyloric mucosa protruding into the antrum
- "Double track sign": two parallel echogenic lines within the pyloric canal, with a thin hypoechoic/anechoic stripe between them.
- Dynamic
- Little or no passage of gastric contents through the pylorus into the duodenum despite persistent gastric peristalsis
Ultrasound diagnostic criteria
Most commonly used abnormal thresholds (infants <3 months):
- Pyloric muscle thickness
- > 3 mm = abnormal / highly suspicious for IHPS
- 2–3 mm = equivocal → repeat scan, consider clinical course and Pylorospasm
- Pyloric canal length
- ≥ 15–16 mm = abnormal
- < 12 mm usually normal; 12–15 mm = grey zone (correlate clinically, repeat)
- Transverse pyloric diameter (optional but nice to know)
- > 11–12 mm supportive of IHPS
- Always integrate:
- Measurements + non-passage of gastric contents + compatible clinical picture
Tip
Exam-safe: “Muscle thickness >3 mm and canal length ≥15–16 mm in a vomiting infant, with no gastric contents traversing the pylorus, is diagnostic of IHPS on ultrasound.”
Other imaging
- Plain abdominal radiograph
- Distended, air-filled stomach
- Paucity of distal bowel gas
- “Caterpillar stomach”: prominent gastric peristaltic waves indenting the greater curvature
- Upper GI contrast study (if US equivocal or unavailable)
- “String sign”: thin streak of contrast through narrowed pyloric canal
- “Shoulder / tit signs”: impression of hypertrophied pylorus on antrum / lesser curve
- These are now more viva/MCQ material than real-world first-line tests.
Treatment
- Initial
- Correct dehydration and electrolyte disturbances (especially Cl⁻, K⁺, H⁺)
- Normalise acid–base status before surgery
- Definitive
- Ramstedt pyloromyotomy (open or laparoscopic): excision of muscular layer, no mucosal breach.
- Excellent prognosis when treated
- Post-op:
- Vomiting may persist transiently for 24–48 h but should improve
- Recurrence is rare
Exam nuggets
- “2–8 week old firstborn boy with projectile non-bilious vomiting, still hungry, with a palpable olive and visible gastric peristalsis.”
- Biochemistry buzzword: hypochloraemic hypokalaemic metabolic alkalosis
- Ultrasound: muscle ≥3 mm, length ≥15–16 mm, no passage of stomach contents
- Management phrase: “Resuscitate and correct electrolytes first, then Ramstedt pyloromyotomy.”
