Hypertrophic Pyloric Stenosis

DEFINITION

Acquired condition characterized by progressive idiopathic hypertrophy of pyloric circular muscle.
Causes narrowing and elongation of pyloric channel leading to gastric outlet obstruction.
Not present at birth; develops postnatally.

Factor	Details
Incidence	2-5 per 1000 live births.
Demographics	Caucasian/Northern European predominance.
Sex	Males affected 4-6 times more than females.
Birth Order	Firstborn males most commonly affected.
Genetics	High heritability (87%). Offspring of affected mother at highest risk (20% males, 10% females). Monozygotic twin concordance high. Linked to NOS1 gene variant.
Environmental	Bottle-feeding (formula milk). Macrolide antibiotics (erythromycin) exposure in first 2 weeks of life. Maternal smoking.

Nitric Oxide Deficiency: Reduced Neuronal Nitric Oxide Synthase (NOS) prevents smooth muscle relaxation. Compensatory hyperperistalsis leads to hypertrophy.
Histology: Degeneration of intramuscular ganglion cells in Auerbach’s plexus.
Hormonal: Formula feeding increases gastrin and decreases vasoactive intestinal peptide (VIP), promoting contraction.

Onset: Typically between 3 to 6 weeks of age. Rare >6 months.
Vomiting: Non-bilious, projectile emesis immediately following feeds. Progressively worsens.
Appetite: Infant remains ravenously hungry post-emesis (“hungry vomiter”).
Stools: Small “starvation stools”.
Signs of Dehydration: Weight loss, lethargy, decreased urine output.
Icteropyloric Syndrome: Unconjugated hyperbilirubinemia seen in ~5% cases; resolves post-pyloromyotomy. Linked to UGT1A1 (Gilbert syndrome) variant.

Gastric Peristalsis: Visible peristaltic waves moving left to right across epigastrium during/after feeding.
Pyloric “Olive”: Palpable firm, olive-shaped mass in mid-epigastrium/right upper quadrant. Best palpated during test feed or post-emesis.

Classic Triad: Hypochloremic, hypokalemic metabolic alkalosis.
Mechanism: Loss of gastric HCl triggers alkalosis. Kidneys compensate by retaining H+ at the expense of K+ and Na+.
Paradoxical Aciduria: Occurs in severe, prolonged dehydration. Kidneys preferentially reabsorb Na+ in exchange for H+ to maintain intravascular volume, resulting in acidic urine despite systemic alkalosis.

Modality	Diagnostic Criteria / Findings
Ultrasound	Test of Choice. High sensitivity/specificity (~100%).- Muscle wall thickness >3-4 mm (average 5 mm).- Pyloric channel length >14-16 mm.- Total pyloric diameter >12-14 mm.
Upper GI Contrast (Barium)	Reserved for equivocal ultrasound or ruling out malrotation.- String sign: Elongated, narrow pyloric channel.- Shoulder sign: Hypertrophied muscle bulging into antrum.- Mushroom sign: Indentation into duodenum.- Double tract sign: Parallel streaks of barium in channel.

Gastroesophageal Reflux (GERD): Effortless regurgitation, self-limiting.
Malrotation with Volvulus: Emesis is typically bilious; requires emergent surgery.
Metabolic Errors (e.g., CAH, Urea Cycle Defects): Associated with acidosis/alkalosis, lethargy, or seizures.
Infection/Sepsis: Gastroenteritis, UTI, meningitis. Usually accompanied by fever/diarrhea.

Status: Not a surgical emergency. Must correct metabolic/fluid derangements first.
Airway/GI: NPO. Nasogastric/orogastric tube for decompression.
Fluid Therapy: Initial resuscitation with Normal Saline bolus. Maintenance with 5% Dextrose + 0.45% NS.
Electrolytes: Add Potassium (KCl) only after urine output is established.
Surgical Readiness: Surgery contraindicated until alkalosis resolves. General anesthesia during severe alkalosis depresses respiratory drive, risking post-operative apnea. Target Serum Chloride > mid-90s mEq/L prior to surgery.

Procedure: Ramstedt Pyloromyotomy. Longitudinal incision and blunt splitting of the hypertrophied circular muscle down to, but sparing, the submucosa.
Approaches:
- Open (Right upper quadrant transverse or Bianchi transumbilical approach).
- Laparoscopic (Decreased hospital stay, rapid full feed tolerance).
- Endoscopic (G-POEM): Gastric peroral endoscopic myotomy (emerging technique).

Reserved for patients unfit for general anesthesia/surgery.
Pharmacotherapy: Intravenous followed by oral Atropine sulfate (muscle relaxant). Lower success rate (80.8% vs 100%) and longer hospital stay compared to surgery.

Incomplete Myotomy: Suspected if vomiting persists long-term. May require endoscopic balloon dilatation.
Mucosal Perforation: Unnoticed intraoperative duodenal perforation risks catastrophic peritonitis.
Post-operative Vomiting: Common (up to 50%). Usually self-limiting, secondary to localized edema at incision site.
Post-operative Apnea: Secondary to inadequately corrected metabolic alkalosis.