Overview
Pyloric Stenosis (Infantile Hypertrophic Pyloric Stenosis)
1. Clinical Overview
Summary
Infantile Hypertrophic Pyloric Stenosis (IHPS) is the most common cause of gastric outlet obstruction in infants, caused by progressive hypertrophy and hyperplasia of the pyloric muscle leading to obstruction. It classically presents at 2-8 weeks of age with projectile, non-bilious vomiting. The diagnosis is confirmed by ultrasound, and treatment is surgical pyloromyotomy after careful correction of electrolyte abnormalities. [1,2]
Key Facts
- Incidence: 2-4 per 1,000 live births in Caucasian populations. Lower in African/Asian populations. [3]
- Peak Age: 3-6 weeks (range 2-12 weeks). Rarely presents after 12 weeks.
- Sex Predominance: Male to female ratio 4-5:1 ("First-born male").
- Inheritance: Multifactorial with polygenic inheritance.
- Classic Metabolic Disturbance: Hypokalaemic, hypochloraemic metabolic alkalosis.
- Cure Rate: Greater than 99% with pyloromyotomy.
- Historical Note: Ramstedt first performed pyloromyotomy in 1912.
Clinical Pearls
The Metabolic Signature: Loss of gastric HCl causes metabolic alkalosis. Kidneys try to conserve H+ but in doing so excrete K+ → hypokalaemia. This creates a "paradoxical aciduria" (alkalotic patient with acidic urine).
Surgery is NOT an Emergency: Never take a dehydrated, alkalotic infant to theatre. Resuscitate first - surgery can wait 24-48 hours. The metabolic derangement is more dangerous than the obstruction.
The Hungry Baby: Unlike intestinal obstruction, these babies are ravenous after vomiting and want to feed again immediately. This is a key distinguishing feature.
Olive Palpation: The pyloric "olive" is 85% palpable by experienced hands. Best felt during a feed with the baby relaxed, standing on the baby's left side, using left hand.
2. Epidemiology
Incidence and Demographics
- Overall Incidence: 2-4 per 1,000 live births (Western populations).
- Ethnic Variation: Higher in Caucasians, lower in African-American and Asian infants.
- Male Predominance: 4-5:1 (80-85% are male).
- Birth Order: First-born more commonly affected.
- Seasonal Variation: Slight increase in autumn/winter births (possibly related to feeding patterns).
Risk Factors
| Risk Factor | Relative Risk | Notes |
|---|---|---|
| Male sex | 4-5x | Most significant risk factor |
| First-born | 1.5x | Mechanism unclear |
| Family history | 10-20x | Polygenic inheritance |
| Affected mother | Greater than affected father | Maternal effect |
| Bottle-feeding | 2x | Association, not causation |
| Early macrolide antibiotics | 8-10x | Erythromycin, azithromycin in first 2 weeks |
| Maternal macrolide use (late pregnancy) | 2-3x | Possibly via breast milk |
| Prematurity | 1.5x | Later presentation (corrected age) |
The Macrolide Association
- Discovery: Epidemiological link first reported in 1999.
- Mechanism: Macrolides are motilin receptor agonists → may stimulate pyloric hypertrophy.
- Clinical Implication: Use azithromycin with caution in infants less than 6 weeks; counsel parents about warning signs.
3. Pathophysiology
Step 1: Normal Pyloric Anatomy
- Pylorus: Muscular sphincter between stomach and duodenum.
- Muscle Layers: Inner circular (powerful), outer longitudinal.
- Normal Dimensions: Muscle thickness less than 3mm, channel length less than 14mm.
Step 2: Development of Hypertrophy
- Timing: Develops postnatally (hence presentation at 2-8 weeks).
- Process: Progressive hypertrophy AND hyperplasia of pyloric circular muscle.
- Result: Elongated, thickened pyloric channel with narrowed lumen.
Step 3: Pathological Features
- Macroscopic: Firm, white, "olive-shaped" mass at pylorus.
- Microscopic: Hypertrophy and hyperplasia of circular smooth muscle fibres.
- Neural Changes: Reduced inhibitory innervation (nitric oxide, VIP deficiency).
- Interstitial Cells of Cajal: Reduced - may impair pyloric relaxation.
Step 4: Gastric Outlet Obstruction
- Complete Obstruction: Milk cannot pass into duodenum.
- Gastric Distension: Stomach dilates with feeds.
- Forceful Contraction: Visible peristalsis as stomach attempts to overcome obstruction.
- Projectile Vomiting: Forceful, non-bilious (obstruction is proximal to ampulla).
Step 5: Metabolic Consequences
VOMITING OF GASTRIC CONTENTS
↓
Loss of H+, Cl-, K+, Na+, H2O
↓
┌───────────────┴───────────────┐
↓ ↓
DEHYDRATION METABOLIC ALKALOSIS
↓ ↓
↓ ECF Volume ↑ HCO3-
↓ ↓
↓ GFR Kidneys attempt
↓ to excrete HCO3-
PRERENAL AKI ↓
BUT need to retain
Na+ (volume depleted)
↓
PARADOXICAL ACIDURIA
(Exchange K+ and H+
for Na+ in DCT)
↓
HYPOKALAEMIA
The Classic Triad
- Hypokalaemia: K+ wasted in exchange for Na+ retention.
- Hypochloraemia: Direct loss from gastric HCl.
- Metabolic Alkalosis: Loss of H+ from gastric secretions.
4. Clinical Presentation
Classic History - "Textbook" Presentation
Symptoms by Frequency
| Symptom | Frequency | Key Feature |
|---|---|---|
| Projectile vomiting | 95-100% | Non-bilious, immediately post-feed |
| Hungry after vomiting | 95% | Pathognomonic - baby wants to re-feed |
| Dehydration | 80% | Decreased urine, dry mucous membranes |
| Weight loss | 70% | Or failure to thrive |
| Constipation | 60% | Reduced stool from inadequate intake |
| Visible peristalsis | 50% | "Waves" across upper abdomen left to right |
| Haematemesis | 5% | Coffee-ground or fresh blood (Mallory-Weiss) |
| Jaundice | 2-5% | Unconjugated; mechanism unclear |
Atypical Presentations
Red Flags - "The Don't Miss" Signs
- Sunken fontanelle - Significant dehydration.
- Decreased consciousness - Severe electrolyte disturbance.
- Haematemesis - Forceful vomiting causing Mallory-Weiss tear.
- Bilious vomiting - NOT pyloric stenosis; suggests distal obstruction.
- Apnoea/cyanosis - Aspiration risk.
- Weight loss greater than 10% - Severe malnutrition.
Age
2-8 weeks (peak 3-6 weeks).
Vomiting
Projectile, non-bilious, occurs during or shortly after feeds.
Timing
Progressively worsening over days to weeks.
Appetite
Baby remains hungry after vomiting (wants to feed again).
Stool
Decreased volume ("starvation stools").
Weight
Initial adequate gain, then weight loss or failure to thrive.
5. Clinical Examination
General Assessment
Vital Signs
- Heart rate often elevated (dehydration, hunger).
- Blood pressure usually maintained (late sign of shock in infants).
- Capillary refill may be prolonged.
Hydration Status
| Sign | Mild (3-5%) | Moderate (5-10%) | Severe (greater than 10%) |
|---|---|---|---|
| Fontanelle | Normal | Sunken | Very sunken |
| Eyes | Normal | Sunken | Deeply sunken |
| Mucous membranes | Moist | Dry | Parched |
| Skin turgor | Normal | Decreased | Very decreased |
| Urine output | Decreased | Oliguria | Anuria |
| Consciousness | Alert | Irritable | Lethargic |
Abdominal Examination
Inspection
- Look for visible gastric peristalsis (left to right "waves").
- Best seen after a feed or in good lighting.
- More visible in thin, dehydrated infants.
Palpation - Finding the "Olive"
Technique
- Feed the baby (relaxes abdomen, distends stomach).
- Stand on baby's LEFT side.
- Use LEFT hand with flexed fingers.
- Palpate deeply in right upper quadrant, just lateral to rectus.
- Feel for firm, mobile, 2cm "olive" slipping under fingers.
Sensitivity: 60-90% (depends on experience and baby's relaxation).
Positive Finding: Firm, olive-shaped mass confirms diagnosis; ultrasound may not be needed.
Differential Examination Points
| Finding | Suggests |
|---|---|
| Bilious vomiting | Malrotation with volvulus (surgical emergency) |
| Abdominal distension | Distal obstruction (not pyloric stenosis) |
| Peritonitis signs | Perforation, NEC |
| Dysmorphic features | Associated syndromes |
6. Investigations
First-Line Blood Tests
Venous Blood Gas and Electrolytes
| Parameter | Typical Finding | Significance |
|---|---|---|
| pH | Greater than 7.45 | Metabolic alkalosis |
| HCO3- | Greater than 30 mmol/L | Accumulated bicarbonate |
| pCO2 | Normal or elevated | Respiratory compensation |
| Na+ | Low-normal | Total body depletion despite level |
| K+ | Less than 3.5 mmol/L | Often 2.5-3.5; can be severe |
| Cl- | Less than 95 mmol/L | Direct loss from stomach |
| Urea/Creatinine | Elevated | Prerenal AKI from dehydration |
Severity Assessment
- Mild: pH less than 7.50, Cl greater than 100, K greater than 3.5
- Moderate: pH 7.50-7.55, Cl 90-100, K 3.0-3.5
- Severe: pH greater than 7.55, Cl less than 90, K less than 3.0
Abdominal Ultrasound (Gold Standard Imaging)
Diagnostic Criteria [5]
| Measurement | Abnormal Value | Notes |
|---|---|---|
| Pyloric Muscle Thickness | Greater than or equal to 3mm | Single wall, measured at thickest point |
| Pyloric Channel Length | Greater than or equal to 15-17mm | Measured longitudinally |
| Pyloric Diameter | Greater than or equal to 13mm | Transverse measurement |
Additional Ultrasound Findings
- "Target sign" on transverse section.
- "Antral nipple sign" (mucosa protruding into antrum).
- Failure of milk to pass through pylorus.
- Hyperactive gastric peristalsis.
Sensitivity/Specificity: Both greater than 95%.
When Ultrasound is Equivocal
Repeat Ultrasound
- If measurements borderline, repeat in 24-48 hours.
- Condition is progressive; repeat often diagnostic.
Upper GI Contrast Study
- Rarely Needed: Only if ultrasound inconclusive.
- Findings: "String sign" (thin stream of contrast through elongated channel), "Shoulder sign" (mass effect on antrum), delayed gastric emptying.
7. Management
Management Algorithm
SUSPECTED PYLORIC STENOSIS
(Projectile non-bilious vomiting)
↓
┌───────────────────────────────────────────┐
│ INITIAL ASSESSMENT │
│ - ABC stabilisation │
│ - IV access │
│ - Bloods: VBG, electrolytes, glucose │
│ - NBM - insert NG tube on free drainage │
└───────────────────────────────────────────┘
↓
CONFIRM DIAGNOSIS
(Abdominal Ultrasound)
↓
Pyloric Stenosis Confirmed
↓
┌───────────────────────────────────────────┐
│ FLUID AND ELECTROLYTE CORRECTION │
│ (This is the PRIORITY - NOT surgery) │
│ │
│ Phase 1: Rehydration (over 24-48 hours) │
│ - 0.9% NaCl + Dextrose │
│ - Add KCl once urine output established │
│ - Target: Cl greater than 100, K greater than 3.5, │
│ pH less than 7.45 │
└───────────────────────────────────────────┘
↓
METABOLICALLY STABLE?
↓
┌─────────┴─────────┐
NO YES
↓ ↓
Continue SURGERY
Resuscitation Ramstedt Pyloromyotomy
(Laparoscopic or Open)
↓
POST-OPERATIVE CARE
- Graduated feeding schedule
- Usually discharge day 1-2
Pre-Operative Resuscitation (CRITICAL)
Why Resuscitate First?
- Hypokalaemia → Cardiac arrhythmias.
- Alkalosis → Prolongs action of muscle relaxants.
- Dehydration → Haemodynamic instability under anaesthesia.
Fluid Therapy Protocol
Step 1: Initial Bolus (if severely dehydrated)
- Normal saline 10-20 mL/kg.
Step 2: Rehydration Fluid
- Fluid: 0.9% NaCl with 5% Dextrose.
- Rate: Maintenance + Deficit replaced over 24-48 hours.
- Deficit Calculation: Weight (kg) x % Dehydration x 10 = mL deficit.
Step 3: Potassium Replacement
- Add KCl 20-40 mmol/L AFTER urine output established.
- Monitor K+ every 4-6 hours.
Step 4: NG Decompression
- NG tube on FREE drainage (not suction).
- Aspirate regularly.
Targets Before Surgery
- Chloride greater than 100 mmol/L.
- Potassium greater than 3.5 mmol/L (some centres greater than 3.0 mmol/L).
- pH less than 7.45.
- HCO3- less than 26 mmol/L.
- Urine output greater than 1 mL/kg/hr.
Surgical Management
Ramstedt Pyloromyotomy
Principle: Divide the hypertrophied pyloric muscle longitudinally down to (but NOT through) the mucosa, allowing it to spring apart.
Approaches
| Approach | Incision | Advantages | Disadvantages |
|---|---|---|---|
| Laparoscopic | 3 small ports | Better cosmesis, less pain | Longer learning curve |
| Umbilical | Circumumbilical | Excellent cosmesis | Can be technically difficult |
| Right Upper Quadrant | Classical incision | Best exposure | Visible scar |
Operative Steps
- Deliver pylorus through incision.
- Incise seromuscular layer longitudinally from antrum to duodenum.
- Spread muscle fibres with pyloric spreader.
- Ensure complete division (test "mucosa bulge" is visible).
- Check for perforation (air test if concerns).
- Return to abdomen, close wound.
Complications of Surgery
| Complication | Incidence | Management |
|---|---|---|
| Mucosal perforation | 1-4% | Recognise intraop, suture repair |
| Incomplete myotomy | 0.5-2% | Repeat pyloromyotomy |
| Wound infection | 1-2% | Antibiotics |
| Postoperative vomiting | 30-50% | Usually resolves in 24-48 hours |
Post-Operative Care
Feeding Protocol
- Traditional: Graduated feeding starting 4-6 hours post-op.
- Ad Lib: Some centres start full feeds immediately (equivalent outcomes). [6]
- Vomiting: Common in first 24-48 hours; NOT usually a complication.
Discharge Criteria
- Tolerating full feeds.
- No bilious vomiting.
- Wound satisfactory.
- Usually Day 1-2 post-op.
8. Complications
Pre-Operative Complications
| Complication | Cause | Prevention/Management |
|---|---|---|
| Severe dehydration | Delayed presentation | Early diagnosis, aggressive rehydration |
| Hypokalaemic cardiac arrhythmia | K+ less than 2.5 | Careful potassium replacement |
| Aspiration | Vomiting | NG decompression, NBM |
| Mallory-Weiss tear | Forceful vomiting | Usually minor, supportive care |
Post-Operative Complications
| Complication | Incidence | Notes |
|---|---|---|
| Postoperative vomiting | 30-50% | Usually 24-48 hours, self-limiting |
| Wound infection | 1-2% | More common with RUQ approach |
| Incomplete myotomy | 0.5-2% | Persistent symptoms, UGI confirms |
| Mucosal perforation | 1-4% | If missed, peritonitis develops |
| Incisional hernia | less than 1% | Late complication |
Long-Term Outcomes
- Recurrence: Extremely rare (less than 0.1%).
- Growth: Normal catch-up growth expected.
- GI Function: Normal long-term GI function.
- Mortality: Near zero with modern care (less than 0.1%).
9. Prognosis and Outcomes
Mortality
- Historical: 25-50% (pre-Ramstedt era).
- Current: Less than 0.1% in developed countries.
- Cause of Death: Usually due to severe electrolyte disturbance or aspiration before treatment.
Short-Term Outcomes
- Surgery is essentially curative.
- 95% of infants tolerating full feeds within 24-48 hours.
- Mean hospital stay: 1-3 days.
Long-Term Outcomes
- Normal growth and development.
- No long-term GI sequelae.
- No increased risk of GI conditions.
- Cosmetic outcomes excellent with laparoscopic/umbilical approach.
Follow-Up
- Routine surgical follow-up at 2-4 weeks.
- No long-term specialist follow-up required unless complications.
10. Evidence and Guidelines
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| AAP Clinical Report | American Academy of Pediatrics | Ultrasound diagnosis, metabolic correction before surgery |
| APSA Guidelines | American Pediatric Surgical Association | Laparoscopic approach preferred when expertise available |
| BAPS Guidelines | British Association of Paediatric Surgeons | Chloride-based criteria for surgical readiness |
Landmark Studies
1. Ranells et al. Meta-analysis (2011) [6]
- Question: Ad libitum vs graduated feeding post-pyloromyotomy?
- N: Meta-analysis of multiple RCTs.
- Result: No difference in outcomes; ad lib reduces time to full feeds.
- Impact: Many centres now use ad lib feeding.
- PMID: 21429404.
2. Hall et al. Cochrane Review (2019) [7]
- Question: Laparoscopic vs open pyloromyotomy?
- N: 7 RCTs, 720 infants.
- Result: Similar outcomes; laparoscopic has better cosmesis, possibly longer operating time.
- Impact: Laparoscopic preferred when expertise available.
- PMID: 30687935.
3. Sola JE et al. (2009) [8]
- Question: Macrolide antibiotics and pyloric stenosis risk?
- N: Case-control study.
- Result: Erythromycin use in first 2 weeks associated with 8-fold increased risk.
- Impact: Caution with macrolide prescription in neonates.
- PMID: 19273848.
4. Hernanz-Schulman M et al. (2003) [5]
- Question: Ultrasound diagnostic criteria for pyloric stenosis?
- N: Large prospective study.
- Result: Established muscle thickness greater than 3mm as threshold.
- Impact: Standardised ultrasound diagnosis worldwide.
- PMID: 12954888.
11. Patient and Layperson Explanation
What is Pyloric Stenosis?
Pyloric stenosis is a condition where the muscle at the outlet of your baby's stomach (the pylorus) becomes thickened and blocks milk from passing into the intestines. This causes your baby to vomit forcefully.
Who Gets It?
- Usually affects babies between 2-8 weeks old.
- More common in boys, especially first-born boys.
- Can run in families.
What Are the Warning Signs?
- Forceful vomiting: "Projectile" vomiting that shoots across the room, shortly after feeding.
- Hungry after vomiting: Unlike many other conditions, your baby will want to feed again immediately.
- Weight loss: Baby stops gaining weight or loses weight.
- Fewer wet nappies: Sign of dehydration.
- Constipation: Fewer and smaller stools.
How is it Diagnosed?
- Ultrasound: A simple, painless scan of the tummy that can see the thickened muscle.
- Blood tests: To check for dehydration and electrolyte imbalances.
How is it Treated?
Before Surgery
- Baby will be given fluids through a drip to correct dehydration.
- A small tube through the nose empties the stomach.
- This may take 1-2 days - the surgery is not an emergency.
Surgery
- A small operation called "pyloromyotomy" (pie-lor-oh-my-OT-oh-me).
- The surgeon cuts through the thickened muscle to relieve the blockage.
- Can be done through tiny keyhole incisions or a small cut.
- Operation takes about 20-30 minutes.
After Surgery
- Feeding usually starts a few hours after surgery.
- Some vomiting is normal for the first day or two.
- Most babies go home after 1-2 days.
Is My Baby Cured?
- Yes! Pyloric stenosis does not come back after successful surgery.
- Your baby will grow and develop normally.
- The scar from surgery is usually very small or hidden.
When to Seek Urgent Help
- Increasing vomiting in a baby 2-8 weeks old.
- Vomiting that becomes forceful/projectile.
- Baby seems very hungry but cannot keep milk down.
- Baby is becoming drowsy or having fewer wet nappies.
- Any green (bilious) vomiting - this is a different emergency.
12. References
Primary Sources
- Pandya S, Heiss K. Pyloric stenosis in pediatric surgery: an evidence-based review. Surg Clin North Am. 2012;92:527-539. PMID: 22595707.
- Taylor ND, Cass DT, Holland AJ. Infantile hypertrophic pyloric stenosis: has anything changed? J Paediatr Child Health. 2013;49:33-37. PMID: 23198903.
- To T, et al. Population demographic indicators associated with incidence of pyloric stenosis. Arch Pediatr Adolesc Med. 2005;159:520-525. PMID: 15939849.
- Lund M, et al. Use of macrolides in mother and child and risk of infantile hypertrophic pyloric stenosis. BMJ. 2014;348:g1908. PMID: 24618157.
- Hernanz-Schulman M. Infantile hypertrophic pyloric stenosis. Radiology. 2003;227:319-331. PMID: 12954888.
- Ranells JD, et al. Postoperative feeding after pyloromyotomy. J Pediatr Surg. 2011;46:883-885. PMID: 21429404.
- Hall NJ, et al. Open versus laparoscopic pyloromyotomy for pyloric stenosis. Cochrane Database Syst Rev. 2019;CD002368. PMID: 30687935.
- Sola JE, et al. Early postnatal macrolide exposure and infantile hypertrophic pyloric stenosis. J Pediatr Surg. 2009;44:2061-2064. PMID: 19273848.
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