All are false except one in case of hypertrophic pyloric stenosis -
Hypertrophic Pyloric Stenosis (HPS) 

The musculature of the pylorus and adjacent antrum is grossly hypertrophied, the hypertrophy being maximum in the pylorus itself.
It occurs in approximately 3 in 1000 live birth and is the most common surgical cause of vomiting in infancy.
M> F (4 : 1)*
Characteristically the first born male child is affected.


The condition is most commonly seen at 4 wks after birth ranging from the 3rd wk to on rare occasion, the 7th. However, 20% of infants are symptomatic from birth, and most are symptomatic within the first 2 months after birth.


Non-bilious vomiting, becoming increasingly projectile, occurs over several days to weeks. Eventually the infant will develop a nearly complete obstruction by the second to fourth week of life and will not be able to hold down even clear liquids. This invariably proceeds to severe dehydration if not t/t.
These infants develop a metabolic alkalosis with severe depletion of potassium and chloride ions.
" The diagnosis of pyloric stenosis usually can be made on physical examination by palpation of the typical 'olive' in the right upper quadrant and the presence of visible gastric waves on the abdomen.
When the olive cannot be palpated, ultrasound in experienced hands will diagnose the condition accurately in 95 percent of pts." - Schwartz.

Treatment

Pyloric stenosis is never a surgical emergency although dehydration and electrolyte abnormalities may present a medical emergency
Fluid resuscitation and correction of electrolyte, abnormalities and metabolic alkalosis is essential before surgery.

-     Surgery : Fredet-Ramstedtpy/oromyotomy. (In it the pyloric mass is split without cutting the mucosa)
Also know

Administration of erythromycin in early infancy has been linked to the subsequent development of HPS.
Jaundice may be seen in HPS, although cause is not clear.
Symptomatic within one week
Lump is always clinically palpable
T/t of choice is Finney's pyloroplasty
Ultrasonography is diagnostic test