Pyloric stenosis, IHPS, duodenal stenosis

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Infantile Hypertrophic Pyloric Stenosis (IHPS) and Duodenal Stenosis

PART 1: Infantile Hypertrophic Pyloric Stenosis (IHPS)

Epidemiology

Incidence: ~1 in 300-900 live births; the most common surgical cause of vomiting in infants
M:F ratio = 4-5:1 (boys far more commonly affected)
Presents between 3rd and 6th weeks of life (range 2-10 weeks); rare after 12 weeks
Associated with: first-born children, prematurity, young maternal age, monozygotic twins (high concordance)
Risk increased in siblings (~6% vs ~0.2% general population)
Associated syndromes: Turner syndrome, trisomy 18
Erythromycin or azithromycin exposure (orally or via breast milk) in the first 2 weeks of life increases risk

Pathology

Hypertrophy and hyperplasia of the pyloric muscularis propria (circular > longitudinal muscles) causes progressive gastric outlet obstruction. This is NOT a congenital anomaly - the muscle grows after birth. Mucosal and submucosal edema and inflammation may also contribute. The hypertrophied pylorus forms a firm, palpable "olive."

Clinical Features

Feature	Details
Vomiting	Forceful, projectile, non-bilious (proximal to bile duct entry)
Timing	Typically starts ~3-6 weeks; worsens progressively
Feeding	Infant remains hungry after vomiting ("hungry vomiter")
Peristaltic waves	Visible left-to-right waves across upper abdomen just before vomiting
Palpable mass	Firm, olive-shaped, 1-2 cm epigastric mass - nearly pathognomonic; found in up to 90% if stomach decompressed first (now found in <30% in contemporary practice due to early presentation)
Dehydration	Sunken fontanelles, dry mucous membranes, decreased urine output

Metabolic Derangement

Persistent vomiting of gastric acid leads to:

Hypochloremic, hypokalemic metabolic alkalosis

Loss of HCl → low Cl⁻, elevated HCO₃⁻
Paradoxical aciduria (kidneys preferentially retain Na⁺ over H⁺ in severe alkalosis)
Bicarbonate > 30 mEq/L = respiratory depression risk → must be corrected before anesthesia

Diagnosis

Ultrasound is the gold standard (sensitivity and specificity up to 98-100%):

Ultrasound Criterion	Threshold
Pyloric muscle thickness	≥ 4 mm
Pyloric canal length	≥ 15-17 mm
Other signs	Shoulder sign (muscle bulging into antrum), nipple sign (hyperechoic mucosa protrudes into stomach), cervix sign

IHPS - Ultrasound (pyloric muscle thickness, canal length) and contrast study showing narrowed pylorus (arrow) with distended fundus (F)

A: Ultrasound - pyloric muscle wall thickness >4mm. B: Pyloric channel length >14mm. C: Contrast study showing narrowed pyloric canal (arrow) with markedly distended fundus (F). From The Developing Human - Clinically Oriented Embryology.

Upper GI contrast series (UGI) is used when ultrasound is equivocal (can show elongated "string sign" of narrowed pyloric channel) and to evaluate for other causes (GERD, malrotation, antroduodenal webs).

Preoperative Resuscitation

Surgery is NEVER a true emergency. Resuscitate first:

One to two boluses of normal saline 20 mL/kg
D5/NS at 1.5x maintenance with electrolytes
Check electrolytes every 6-12 hours

Endpoints for readiness for surgery:

Wet diapers (adequate urine output)
Chloride ≥ 90-100 mEq/L
Bicarbonate ≤ 30 mEq/L

Do NOT proceed to anesthesia with bicarbonate > 30 mEq/L (risk of postoperative apnea/respiratory arrest).

Surgical Treatment: Fredet-Ramstedt Pyloromyotomy

The operation of choice - open (umbilical or RUQ incision) or laparoscopic (now standard at most children's hospitals):

Ramstedt pyloromyotomy diagram: A single longitudinal incision divides the hypertrophied circular muscle to the level of the submucosa. The inset shows the submucosa herniating into the myotomy site.

Ramstedt pyloromyotomy. The hypertrophied pyloric muscle is incised longitudinally. The inset shows submucosal herniation into the myotomy site, confirming adequate division. From Mulholland & Greenfield's Surgery.

A single longitudinal incision through the anterior wall of the pyloric canal, from stomach to duodenal junction
Muscle is spread until submucosa bulges up freely = complete myotomy
A leak test (30-60 mL air via orogastric tube) confirms no mucosal perforation
Laparoscopic approach: 3 ports (umbilical + two 3-mm stab incisions)

Complications:

Incomplete myotomy - ongoing projectile vomiting; requires return to OR
Mucosal perforation - repair + buttress with omentum, or rotate pylorus 180° and re-myotomize
Both are rare; mortality is distinctly unusual

Postoperative feeding: Start at 6-8 hours; ad lib with 60-mL limit; discharge usually within 24-36 hours.

Acquired Pyloric Stenosis (Adults)

Occurs due to antral gastritis, peptic ulcers near the pylorus, or carcinoma of the distal stomach/pancreas causing fibrosis or malignant infiltration.

PART 2: Duodenal Stenosis (and Atresia)

Embryology & Etiology

The duodenum develops in the 4th week. During weeks 5-6, luminal obliteration occurs due to mucosal proliferation, followed by gradual recanalisation over subsequent weeks. Duodenal atresia (DA) and stenosis result from failure of this recanalisation process.

Forms of obstruction:

Complete membrane obstructing the lumen (most common)
Blind-ending pouch with fibrous cord to distal duodenum
Blind-ending pouch with no connection
Perforate membranes / webs (cause partial stenosis)
Extrinsic compression: annular pancreas or preduodenal portal vein

Location: In 80% of cases, obstruction is just distal to the ampulla of Vater → bilious vomiting

Pre-ampullary obstruction (15-20%) → non-bilious vomiting

Incidence & Associated Anomalies

~1 per 200,000 live births (combined atresia, stenosis, web); slight female preponderance
Associated anomalies present in >50% of patients:

Association	Frequency
Down syndrome (Trisomy 21)	25-30% (some series >50%)
Congenital heart disease	~20%
Malrotation	20-30%
VACTERL (incl. esophageal atresia)	OA in ~10%
Renal anomalies, imperforate anus, CNS lesions	Variable

Any infant with Trisomy 21 and bilious vomiting must be evaluated for duodenal stenosis/atresia.

Clinical Features

Prenatal:

Dilated stomach + duodenal cap on US (double bubble in utero)
Polyhydramnios in 33-50% (fetus cannot swallow/absorb amniotic fluid)
IUGR, prematurity

Postnatal:

Early bilious vomiting (first day of life in atresia; may be delayed months to years in partial stenosis/web)
Upper abdominal distension
Duodenal stenosis/partial membrane may present at any age depending on degree - can even go undiagnosed until adulthood

Diagnosis

Plain X-ray - "Double Bubble" sign:

Classic double-bubble sign on plain abdominal X-ray: two air-filled spaces representing the distended stomach and first part of duodenum, with no distal gas - pathognomonic for duodenal atresia

Classic "double-bubble" sign. Two dilated gas-filled structures (stomach + first part of duodenum). No distal gas confirms complete atresia. From Grainger & Allison's Diagnostic Radiology.

Two air bubbles = dilated stomach + dilated proximal duodenum
No distal gas = complete atresia; classic double bubble in a stable child does not require further imaging before surgery
If distal gas is present = partial obstruction (stenosis, web) - warrants upper GI contrast study

Upper GI contrast study (for partial obstruction):

Duodenal stenosis: narrowing in the second part of duodenum
Duodenal web: thin filling defect extending across lumen with pre-stenotic dilatation

Ultrasound: Can demonstrate duodenal obstruction, especially with clear fluids given first to distend proximal gut.

Treatment

Surgical correction after stabilization:

Duodenoduodenostomy (anastomosis of proximal to distal duodenum) - operation of choice for atresia
Web excision / duodenoplasty for membranous obstruction
Must evaluate for and address malrotation intraoperatively (present in 20-30%)

Comparison at a Glance

Feature	IHPS	Duodenal Stenosis/Atresia
Cause	Post-natal muscle hypertrophy	Failed recanalisation of duodenum (failure of vacuolisation, 8-10 wks)
Onset	3-6 weeks after birth	Day 1 (atresia) or any age (stenosis)
Vomiting	Non-bilious, projectile	Bilious (80%) or non-bilious (20% if pre-ampullary)
Key X-ray sign	Normal (US is gold standard)	Double bubble on plain film
Key US finding	Pyloric muscle ≥4 mm, length ≥15-17 mm	Dilated stomach + duodenum
Associated anomalies	Erythromycin exposure; rarely Turner/T18	Down syndrome (25-50%), VACTERL
Metabolic disturbance	Hypochloremic hypokalemic alkalosis	Dehydration ± alkalosis (less specific)
Surgery	Fredet-Ramstedt pyloromyotomy	Duodenoduodenostomy
Emergency?	No - resuscitate first	No - stabilize first

Sources: Current Surgical Therapy 14e; Robbins & Cotran Pathologic Basis of Disease; The Developing Human - Clinically Oriented Embryology; Grainger & Allison's Diagnostic Radiology; Mulholland & Greenfield's Surgery 7e; Sleisenger & Fordtran's Gastrointestinal and Liver Disease.

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