59. Pyloric stenosis

1. Definition

• Pyloric stenosis (gastric outlet obstruction) → narrowing of the pylorus or first part of the duodenum that blocks gastric emptying
• Infantile hypertrophic pyloric stenosis (IHPS) → thickening of the circular pyloric muscle in the first weeks of life
• Adult pyloric stenosis → acquired narrowing from scarring of a peptic ulcer or from cancer (antrum, pancreatic head, duodenum)

2. Epidemiology

• IHPS:
  • About 2–3 per 1,000 live births (1 in 300–900)
  • Boys : girls about 4 : 1; first-born boys
  • Onset 2–8 weeks of age (peak 3–6 weeks)
  • Family history → higher risk in children of affected mothers
• Adult:
  • Benign ulcer stricture → fallen with H. pylori eradication and PPIs
  • Today malignancy is the commonest cause of gastric outlet obstruction in adults in the West (over half)

3. Aetiology and risk factors

Infantile

• Cause unknown; multifactorial
• Lack of nitric oxide synthase in pyloric muscle → failure to relax
• Genetic factors, family history
• Erythromycin (or azithromycin) in the first 2 weeks of life (motilin agonist)
• Bottle feeding, maternal smoking, prematurity

Adult

• Chronic duodenal or pyloric channel ulcer → fibrosis and scarring
• Gastric antral cancer
• Pancreatic cancer, duodenal or ampullary tumours, lymphoma
• Chronic pancreatitis, Crohn's disease, caustic stricture
• Adult form of hypertrophic pyloric stenosis (rare)

4. Pathogenesis

Infantile

1. Pyloric circular muscle thickens → "olive" tumour
2. Lumen narrows → milk cannot leave the stomach
3. Stomach dilates; strong peristalsis visible
4. Projectile vomiting of gastric contents (no bile)

Metabolic changes (both forms)

1. Loss of gastric acid (H⁺ and Cl⁻) → hypochloraemic metabolic alkalosis
2. Loss of fluid → dehydration → kidneys hold sodium via aldosterone
3. Sodium kept in exchange for potassium and H⁺ → hypokalaemia
4. Paradoxical aciduria → acid urine despite systemic alkalosis (late sign)
5. Alkalosis lowers ionised calcium → tetany in adults
6. Infants → risk of postoperative apnoea if alkalosis is not corrected (alkalosis depresses breathing)

5. Classification

• Infantile hypertrophic (congenital, acquired in the first weeks)
• Adult:
  • Benign → peptic ulcer, caustic, Crohn's
  • Malignant → gastric, pancreatic, duodenal
• Adult by stage (classic):
  • Compensated → stomach still pushes against the block; strong peristalsis
  • Decompensated → large, atonic stomach; stasis; metabolic changes

6. Clinical picture

Symptoms

• Infant:
  • Non-bilious, projectile vomiting after feeds, from 2–8 weeks
  • Hungry baby that feeds again straight after vomiting
  • Weight loss, fewer wet nappies, constipation
  • Late → lethargy, jaundice (unconjugated)
• Adult:
  • Vomiting of large volumes of undigested food eaten many hours or days before; foul, no bile
  • Early fullness, epigastric bloating, weight loss
  • Long history of ulcer pain (benign) or short history with weight loss and anaemia (cancer)

Signs

• Infant:
  • Palpable "olive" in the right upper quadrant or epigastrium during a test feed (positive predictive value about 99%)
  • Visible gastric peristalsis from left to right
  • Dehydration → sunken fontanelle, dry mouth
• Adult:
  • Succussion splash more than 4 hours after a meal
  • Visible peristalsis, epigastric distension
  • Wasting, dehydration
  • Epigastric mass, Virchow's (Troisier's) node in cancer

7. Diagnosis

Infant

• Ultrasound → test of choice:
  • Pyloric muscle thickness > 3 mm
  • Pyloric channel length > 15–16 mm
  • No passage of fluid through the pylorus
• Blood gas → hypochloraemic, hypokalaemic metabolic alkalosis
• U&E, glucose
• Contrast meal → only if ultrasound is not available or unclear ("string sign", "shoulder sign")

Adult

• Bloods → U&E, chloride, bicarbonate, FBC, albumin
• Nasogastric aspiration → large volume of old food and fluid (saline load test: over 400 mL left after 30 minutes)
• Gastroscopy (after washouts) → cause; biopsy every case to rule out cancer
• CT → staging of cancer, pancreatic mass
• Barium meal → large stomach, delayed emptying, narrow pylorus
• Endoscopic ultrasound → small tumours

8. Differential diagnosis

• Infant:
  • Gastro-oesophageal reflux (not projectile, baby thrives)
  • Overfeeding, milk allergy
  • Bilious vomiting → malrotation with volvulus (surgical emergency)
  • Infection (UTI, sepsis, meningitis), raised intracranial pressure
  • Congenital adrenal hyperplasia (salt-losing: low sodium, high potassium, acidosis)
• Adult:
  • Gastroparesis (diabetes, after vagotomy)
  • Gastric or pancreatic cancer
  • Superior mesenteric artery syndrome
  • Gastric volvulus, bezoar

9. Treatment

Conservative

• IHPS is not an emergency operation; it is a medical emergency:
  1. Stop feeds; NG tube if vomiting
  2. IV fluids → 0.9% saline with 5% (or 10%) glucose, add potassium chloride once urine is passed
  3. Correct the alkalosis before surgery → chloride > 100 mmol/L and bicarbonate < 28 mmol/L (unit targets vary)
• Adult:
  1. NG decompression and gastric washouts
  2. IV 0.9% saline with potassium → corrects alkalosis
  3. Nutrition → parenteral or nasojejunal
  4. IV proton pump inhibitor; treat H. pylori
  5. Benign stricture → endoscopic balloon dilatation (repeat sessions; good results in many)
  6. Malignant, unfit or advanced → endoscopic duodenal stent (self-expanding metal stent)

Surgical: infant

• Ramstedt pyloromyotomy → open (right upper quadrant or supraumbilical incision) or laparoscopic:
  1. Deliver the pylorus
  2. Longitudinal incision through the serosa and muscle from the pyloric vein of Mayo to the gastric antrum
  3. Spread the muscle until the mucosa bulges through
  4. Do not breach the mucosa at the duodenal end (thin, where the duodenal fornix lies)
  5. Check for leaks with air through the NG tube
• Feeds restart within 4–6 hours; discharge in 1–2 days

Surgical: adult

• Benign:
  • Failed dilatation → gastrojejunostomy (laparoscopic) or antrectomy; vagotomy now rarely needed with PPIs
  • Pyloroplasty (Heineke-Mikulicz, Finney) if the duodenum is soft
• Malignant:
  • Resectable gastric cancer → distal gastrectomy with D2 lymphadenectomy
  • Unresectable → gastrojejunostomy or endoscopic stent; EUS-guided gastroenterostomy (newer)
• Stent → quick relief, short life expectancy; bypass → more lasting, longer life expectancy (over 2 months)

10. Complications

• Disease → dehydration, metabolic alkalosis, hypokalaemia, tetany, aspiration pneumonia, malnutrition
• Pyloromyotomy:
  • Mucosal perforation (1–2%; repair and delay feeds)
  • Incomplete pyloromyotomy (persistent vomiting over 5 days)
  • Wound infection, incisional hernia
  • Postoperative apnoea (uncorrected alkalosis)
• Adult surgery → anastomotic leak, delayed gastric emptying, dumping, stent migration or blockage