Aetiology

No single aetiology is causative of pyloric stenosis. Hyperacidity as a result of antral distention with feeding and hypertrophy of the pylorus from repeated contraction is believed to be a cause.[25] Additionally, poor pyloric muscle neuronal innervation is believed to play a role.[26][27] The lack of intestinal-pacemaker cells of Cajal is postulated to be another mechanism leading to pyloric stenosis.[28] Nitric oxide synthase deficiency is also implicated as a biochemical cause, by decreasing smooth muscle relaxation.[29][30][31] However, none of these aetiologies have been definitively confirmed.

Several risk factors have been associated with an increased incidence of disease. For example, the incidence of pyloric stenosis has been noted to vary depending on geography and ethnic background. Specifically the incidence of pyloric stenosis is reported to be almost four times less in Chinese and Southeast Asian populations than in those with Western heritage.[32] Although there is no clear genetic basis for pyloric stenosis, it has been noted to run in some families and there are several genetic syndromes, including Cornelia de Lange, that have been associated with it.[17][19][33][34] Male sex, prematurity and birth order (first born) have also been described as risk factors.[17][19][22][24][33][35] Certain medications have been associated with pyloric stenosis, including erythromycin.[36][37] However, there are limited data in the literature as to the strength of this association. Similarly, some data exist for the role of prostaglandins or maternal macrolides as a cause of pyloric stenosis, however, these associations remain conflicted and ill defined.[37][38][39][40]

Pathophysiology

With prolonged vomiting, electrolyte and water loss leads to hypochloraemic, hypokalaemic metabolic alkalosis. Hypovolaemia results in an increase in aldosterone and subsequent renal absorption of sodium and water. This phenomenon results in a paradoxical loss of hydrogen ions. This alkalosis is worsened by renal absorption of bicarbonate. Potassium ion fluctuations are also seen; both hypokalaemia and hyperkalaemia (which may be related to haemolysis) have been described.[41] The severity of hypovolaemia and electrolyte abnormalities is directly proportional to the length of the symptoms prior to presentation. Indirect hyperbilirubinaemia is seen in a small proportion of infants due to a deficit in glucuronyl transferase activity.

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