Pyloric stenosis pathophysiology

The pathogenesis of infantile hypertrophic pyloric stenosis is not completely understood^[1]. However, infantile hypertrophic pyloric stenosis may result from abnormal innervation of the pyloric smooth muscle.^[1] The chloride loss due persistent vomiting results in hypochloremia which impairs the kidney‘s ability to excrete bicarbonate. This factor significantly prevents correction of the alkalosis. The secondary hyperaldosteronism develops due to the hypovolaemia. The body’s compensatory response to the metabolic alkalosis is hypoventilation resulting in an elevated arterial pCO₂. In relatives of probands of infantile hypertrophic pyloric stenosis patients and monozygotic co-twins the recurrence pattern did not depict a single major inheritance.

The pathogenesis of infantile hypertrophic pyloric stenosis is not completely understood.

• However, infantile hypertrophic pyloric stenosis (IHPS) may result from abnormal innervation of the pyloric smooth muscle.^[1]
• Evidence of increased collagen production and abnormal amounts of extracellular matrix proteins has also been observed in patients with hypertrophic pyloric muscle.^[1]
• 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 is projectile in nature. The vomited material does not contain bile because the pyloric obstruction 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 factor significantly prevents correction of the alkalosis.^[2]

• A secondary hyperaldosteronism develops due to the hypovolaemia. The high aldosterone levels causes the kidneys to:^[3]
  • 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.^[4]

In relatives of probands of infantile hypertrophic pyloric stenosis patients and monozygotic co-twins the recurrence pattern did not depict a single major inheritance.^[5]

Various conditions associated with infantile pyloric stenosis include:^[6]

• Neuromuscular disorders
• Connective tissue disorders
• Metabolic disorders
• Intracellular signalling pathway disturbances
• Intercellular communication disturbances
• Ciliopathies
• DNA-repair abnormalities
• Transcription regulation disorders
• MAPK-pathway abnormalities
• Lymphatic abnormalities
• Environmental factors

On gross pathology, characteristic findings of pyloric stenosis include:

• Hypertrophic muscularis mucosa
• Protrusion of gastric mucosa into the smooth muscle layer^[7]

The following observations may be seen in pyloric stenosis:^[8]

• Smooth muscle cells are in a proliferative phase and there is very few gap junctions between smooth muscle cells in pyloric stenosis.
• The circular muscle layer is characterized by very few large granular vesicle-containing nerve fibers.
• The number of nerve cell bodies in the myenteric plexus, and the total number of ganglia is lower than normal.
• Interstitial cells of Cajal are almost completely absent.

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