History and exam

Key diagnostic factors

common

first-born male infant

Considered a key risk factor. The incidence is approximately four times greater in male infants than in female infants.[19]

Usually affects the first-born male.[17][19][22]

nonbilious projectile vomiting

Occurs soon after feeding.

2 to 12 weeks old

Most infants present between 2 and 3 weeks of age. Typically, diagnosed in term infants.[2]​[3]​[4]​ It may be more difficult to diagnose in premature infants, who may have atypical symptoms or ultrasound findings. 

upper abdominal mass

Confirms the diagnosis if present on examination. Also known as an "olive".

uncommon

peristaltic waves

Waves traveling from left to right across the abdomen. Due to the stomach attempting to force its contents past the narrowed pyloric outlet.

Other diagnostic factors

common

family history of pyloric stenosis

Considered a risk factor. Non-Mendelian familial pattern has been well described.[17][19][33]

multiple formula changes

Early symptoms may be vague and confused with intolerance to certain formulas.

tachycardia

Delayed presentation can lead to severe volume depletion.

decreased wet diapers

Delayed presentation can lead to severe volume depletion.

dry mucous membranes

Delayed presentation can lead to severe volume depletion.

flat or depressed fontanelles

Delayed presentation can lead to severe volume depletion.

constipation

Can be seen with delay in diagnosis; due to volume depletion and poor oral intake.

poor weight gain

Can be seen with delay in diagnosis.

irritability

Usually the infant is not calm, and is crying. This is because the infant is extremely hungry.

Risk factors

strong

first-born male infant

Male sex represents the strongest epidemiologic factor.[33]

The incidence is approximately four times greater in male infants than in female infants.[19] Usually affects the first-born male.[17][19][22][33]

family history of pyloric stenosis

Non-Mendelian familial pattern has been well described.[17][19][33]

weak

prematurity

Pyloric stenosis is associated with preterm delivery.[24][35]

Premature infants present at a later chronological age (40 days vs. 33 days in full-term infants), but at an earlier postmenstrual age (42 weeks vs. 45 weeks in full-term infants), than full-term infants.[24] A greater degree of prematurity is associated with older chronological age at presentation.[42]

early exposure to erythromycin

Exposure to oral erythromycin, especially during the first 2 weeks of life, appears to increase the risk of developing pyloric stenosis.[36][37] This is thought to be due to increased gastric and pyloric contractions, that ultimately lead to pyloric hypertrophy. However, the association between prenatal erythromycin exposure and pyloric stenosis has not been consistently demonstrated.[37][38]

exposure to prostaglandins

There are conflicting data potentially linking prostaglandins with an increased risk of pyloric stenosis. The presence of high levels of prostaglandins in patients with pyloric stenosis is the basis of this association.[40] Also, the therapeutic use of exogenous prostaglandins, for example in the treatment of congenital heart conditions, may lead to antral hyperplasia and emesis, which appear clinically similar to pyloric stenosis.

maternal exposure to macrolides

The association between exposure to prenatal erythromycin or non-erythromycin macrolides, and the development of pyloric stenosis, has not been consistently demonstrated.[37][38][39]

geographic location/ethnic background

In limited studies the incidence of pyloric stenosis is reported to be approximately four times less in Chinese and Southeast Asian populations than in those with Western heritage.[32]

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