Pyloric stenosis is a childhood condition wherein an infant's small intestine opening, or pylorus, is too narrow because the pylorus muscles are thickened, according to MedlinePlus. Pyloric stenosis most often impacts infants under 6 months old, not adults. The condition affects more boys than girls.
The pylorus connects the small intestine and stomach, explains WebMD. When the pylorus is too thick, food is blocked from passing into the intestine. Symptoms of pyloric stenosis include a distended stomach after feeding and vomiting soon after eating. The vomiting may begin gradually and increase in force and frequency as the pylorus tightens.
Signs of pyloric stenosis that require a doctor's attention include weight loss, dehydration, projectile vomiting, lethargy and fussiness in the child, notes Mayo Clinic. Environmental and genetic factors may play a part in the cause of pyloric stenosis, which typically presents shortly after birth.
Risk factors include the child's sex and race, as well as premature birth, family history and smoking during pregnancy, advises Mayo Clinic. Antibiotic use, either in the infant shortly after birth or with the mother late in the pregnancy, is also a risk factor. Bottle feeding may also contribute to the development of pyloric stenosis, although it is not clear if it is the formula or the bottle that creates the risk.