[1] Babies with this condition usually present any time in the first weeks to 6 months of life with progressively worsening vomiting.

Dehydration may occur which causes a baby to cry without having tears and to produce less wet or dirty diapers due to not urinating for hours or for a few days.

While the exact cause of the hypertrophy remains unknown, one study suggested that neonatal hyperacidity may be involved in the pathogenesis.

[10] This physiological explanation for the development of clinical pyloric stenosis at around 4 weeks and its spontaneous long term cure without surgery if treated conservatively, has recently been further reviewed.

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

Rarely, there are peristaltic waves that may be felt or seen (video on NEJM) due to the stomach trying to force its contents past the narrowed pyloric outlet.

[citation needed] Most cases of pyloric stenosis are diagnosed/confirmed with ultrasound, if available, showing the thickened pylorus and non-passage of gastric contents into the proximal duodenum.

Gastric contents should not be seen passing through the pylorus because if it does, pyloric stenosis should be excluded and other differential diagnoses such as pylorospasm should be considered.

[citation needed] Infantile pyloric stenosis is typically managed with surgery;[18] very few cases are mild enough to be treated medically.

Therefore, the baby must be initially stabilized by correcting the dehydration and the abnormally high blood pH seen in combination with low chloride levels with IV fluids.

It has a success rate of 85–89% compared to nearly 100% for pyloromyotomy, however it requires prolonged hospitalization, skilled nursing and careful follow up during treatment.

[citation needed] The definitive treatment of pyloric stenosis is with surgical pyloromyotomy known as Ramstedt's procedure (dividing the muscle of the pylorus to open up the gastric outlet).

[20] Today, the laparoscopic technique has largely supplanted the traditional open repairs which involved either a tiny circular incision around the navel or the Ramstedt procedure.

Compared to the older open techniques, the complication rate is equivalent, except for a markedly lower risk of wound infection.

Rarely, the myotomy procedure performed is incomplete and projectile vomiting continues, requiring repeat surgery.