Pyloric Stenosis

Pyloric stenosis is progressive hypertrophy of the circular muscle layer of the pylorus, producing gradual gastric outlet obstruction. It is one of the commonest surgical conditions of infancy.

It typically presents between two and eight weeks of age with progressive, non-bilious projectile vomiting in an otherwise hungry, avidly feeding infant. There is a notable male predominance and increased risk with a positive family history.

Prompt recognition of the characteristic pattern is the clinical priority. Correcting the metabolic derangement takes management priority over surgery. Definitive, generally curative surgery follows.

Pathophysiology and epidemiology

• Progressive hypertrophy and hyperplasia of the circular smooth muscle of the pylorus gradually narrow and elongate the pyloric canal.
• The mechanism is believed to combine genetic susceptibility with, in some studies, certain environmental exposures. The complete aetiology remains incompletely characterised.
• Risk is substantially increased in infants with an affected parent or sibling. Male predominance has a ratio of approximately four to one.
• The condition is not present at birth. The pyloric muscle hypertrophy increases progressively over the first weeks of life. A well infant at birth therefore develops worsening symptoms over several weeks as gastric outlet obstruction gradually becomes significant.
• The characteristic metabolic derangement is hypochloraemic, hypokalaemic metabolic alkalosis. It results from persistent loss of hydrochloric acid and, secondarily, potassium through recurrent vomiting.
• The renal compensatory response initially conserves sodium and hydrogen ion at the expense of potassium excretion. As hypokalaemia develops, a paradoxical aciduria appears despite the systemic alkalosis, because the kidney prioritises sodium conservation over acid-base balance in significant volume depletion.
• This biochemical pattern is relevant to diagnosis and to the fluid and electrolyte correction required before surgery.

• The classic, defining symptom is progressive, non-bilious vomiting that becomes projectile (forceful vomiting travelling a significant distance from the infant), typically developing over the second to eighth week of life.
• The infant remains hungry and eager to feed again immediately after vomiting. This reflects the gradual, mechanical nature of the obstruction rather than illness or loss of appetite.
• Non-bilious vomiting is an essential diagnostic feature. It reflects the pre-ampullary location of the obstruction, proximal to where bile enters the duodenum.
• Bilious vomiting warrants urgent consideration of a more distal obstruction, including malrotation with volvulus, a more immediately life-threatening surgical emergency.
• Persistent vomiting causes progressive dehydration. If unrecognised and untreated, faltering weight gain or frank weight loss develops.
• The infant becomes progressively more unwell and lethargic, with reduced urine output and other signs of significant dehydration.
• On examination, visible gastric peristaltic waves may traverse the upper abdomen from left to right, particularly immediately before or during a feed.
• A palpable, firm, mobile, olive-shaped mass, the hypertrophied pylorus, may be felt on careful palpation, classically in the right upper quadrant or epigastrium.
• This finding is highly specific when present but is identified on examination alone in only a proportion of cases. Its absence does not exclude the diagnosis where the history is strongly suggestive.

• Abdominal ultrasound is the diagnostic investigation of choice. It is highly sensitive and specific, directly visualising and measuring the hypertrophied pyloric muscle. Established thresholds for pyloric muscle wall thickness and pyloric channel length confirm the diagnosis.
• Venous blood gas analysis and serum electrolytes are essential in every suspected case. They confirm and quantify the hypochloraemic, hypokalaemic metabolic alkalosis.
• The severity of the metabolic derangement determines the intensity and duration of the preoperative fluid and electrolyte correction.
• Take a detailed feeding and vomiting history. Characterise the non-bilious, projectile vomiting and the infant's continued hunger and eagerness to feed between episodes.
• Examine for the classical palpable pyloric mass. Palpation is best with the infant calm and, where feasible, immediately after a test feed.
• Clinical assessment supports the diagnosis alongside confirmatory ultrasound.
• If the presentation is atypical, or there is any suggestion of bilious vomiting, urgent investigation to exclude malrotation with volvulus or another cause of neonatal or infant obstruction takes priority. This alternative diagnosis is substantially more urgent and potentially catastrophic.

• Correcting the fluid and electrolyte derangement is the essential, immediate priority and takes clear precedence over surgery.
• Anaesthesia and surgery in a significantly dehydrated, alkalotic, hypokalaemic infant carry significant risk. This includes arrhythmia from the electrolyte disturbance and postoperative apnoea.
• Intravenous rehydration uses an isotonic or near-isotonic solution, with potassium added once adequate urine output is confirmed. It is titrated to the degree of dehydration and the electrolyte derangement.
• Fluid composition and rate are individualised to clinical status and serial biochemical reassessment. Adequate correction before surgery generally takes one to two days, sometimes longer in more severely affected infants.
• Place a nasogastric tube on free drainage or intermittent aspiration. It decompresses the stomach, helps prevent further vomiting and aspiration during resuscitation, and measures ongoing gastric losses to guide fluid replacement.
• Pyloromyotomy (the Ramstedt procedure) is the definitive, curative treatment. It is a longitudinal incision of the hypertrophied pyloric muscle down to, but not through, the mucosa. This relieves the obstruction while preserving mucosal integrity.
• It is performed once adequate fluid and electrolyte correction is achieved. The approach is open or, increasingly commonly, laparoscopic, according to local expertise and preference. Both give excellent, comparable outcomes.
• Postoperative feeding is typically reintroduced gradually over the first day or so.
• Some infants have transient postoperative vomiting from gastric dysmotility or oedema at the pyloromyotomy site, not inadequate relief of obstruction. It generally resolves with gradual feeding advancement.
• Prognosis after successful pyloromyotomy is excellent. The great majority of infants achieve complete, durable resolution of symptoms and normal growth and development.
• Educate and reassure parents about the excellent prognosis. Postoperative follow up confirms feeding is established and symptoms have resolved.