Pyloric stenosis

Infantile pyloric stenosis is a not uncommon pediatric condition where there is a congenital narrowing of the pylorus (the opening at the lower end of the stomach). Males are more commonly affected than females, and there is increased predominance in children of affected parents. It is uncertain whether there is a real congenital narrowing or whether there is a functional hypertrophy of the muscle which develops in the first few weeks of life.

(Note: Pyloric stenosis also occurs in adults where the cause is usually a narrowed pylorus due to scarring from chronic peptic ulceration. This is a different condition from infantile hypertrophic pyloric stenosis.)

Symptoms

Babies with this condition usually present within the first few weeks (usually between 2nd and 3rd) of life with poor feeding, weight loss and progressively worsening vomiting leading ultimately to projectile non-bilious vomiting.

Diagnosis

Diagnosis is via a careful history and physical examination. Palpation of the abdomen during a test feed may reveal a mass in the epigastrium consisting of the enlarged pylorus (pyloric tumour) with palpable peristaltic waves consisting of the stomach trying to force its contents past the narrowed pylorus.

Blood tests will reveal hypochloremic alkalosis secondary to loss of acidic gastric secretions due to persistent vomiting.

A pediatric surgeon would typically be able to palpate a pyloric tumour in about 80% of cases. Such a tumour is often not detected by less experienced medical staff. If no tumour is palpated despite a significant clinical suspicion, an imaging study should be performed.

Ultrasound examination will show hypertrophied pyloric musculature, sometimes greater than 4 mm. A barium meal may be useful in cases which ultrasound is not readily available.

Pathophysiology

The gastric outlet obstruction due to the hypertrophic pylorus impairs emptying of gastric contents into the duodenum. As a consequence all ingested food and gastric secretions can only exit via vomiting which can be of a projectile nature. The vomited material does not contain bile because the pyloric onstruction prevents entry of duodenal contents (containing bile) into the stomach.

This results in loss of gastric acid (hydrochloric acid). The chloride loss results in hypochloremia which impairs the kidney's ability to excrete bicarbonate. This is the significant factor that prevents correction of the alkalosis. ^*.

A secondary hyperaldosteronism develops due to the hypovolaemia. The high aldosterone levels causes the kidneys to:

avidly retain Na⁺ (to correct the intravascular volume depletion)
excrete increased amounts of K⁺ into the urine (resulting in hypokalaemia).

The body's compensatory response to the metabolic alkalosis is hypoventilation resulting in an elevated arterial pCO2.

Treatment

Infantile pyloric stenosis is not a surgical emergency, but if not surgically corrected, the infant will die of malnutrition and dehydration.

Initially the baby's condition must be improved by correcting the dehydration and hypochloremic alkalosis with IV fluids. This can usually be accomplished in about 24-48 hours.

Definitive treatment of pyloric stenosis is with surgical pyloromyotomy - dividing of the muscle layer of the pylorus to open up the gastric outlet (distal opening of the stomach). Once the stomach can empty into the duodenum feeding can commence.

Reference

Hulka F, Campbell TJ, Campbell JR, Harrison MW. Evolution in the recognition of infantile hypertrophic pyloric stenosis. Pediatrics 1997;100(2):E9. Fulltext. PMID 9233980.

External links

Surgery