weeks Infants will present with progressive, projectile nonbilious emesis, and in advanced cases, severe dehydration, electrolyte imbalances, and hypoglycemia Some infants may tolerate clear fluids, such as Pedialyte, but will vomit with milk Early exposure to macrolides has been associated with the development of hypertrophic pyloric stenosis Diagnosis can be confirmed by clinical examination of a palpable mass in the epigastrium that is roughly the size and shape of an olive In the absence of a palpable mass, diagnosis can be made by US, which would reveal increased diameter, thickness and length of the pylorus Definitive treatment remains surgical pyloromyotomy As hypertrophic pyloric stenosis is not a surgical emergency, the infant should be fully stabilized and resuscitated with adequate fluids and any electrolyte disturbances corrected prior to surgical repair (see Chapter 12 Abdominal Distention ) Preterm infants with hypertrophic pyloric stenosis are not affected by corrected gestational age at presentation, however are more likely to have a higher complication rate and longer length of stay compared to term infants Meconium Syndromes Meconium syndromes can result in intestinal obstruction due to thick, inspissated meconium Meconium ileus occurs in up to 20% of infants with cystic fibrosis and is often the first manifestation of the disease Abnormal mucosal cell secretion in this population results in thickened meconium throughout the small intestines and into the colon It often presents with failure to pass meconium within 48 hours, progressive abdominal distention, eventual feeding intolerance, and clinical signs of bowel obstruction, including bilious vomiting Abdominal radiography may reveal distended bowel loops typical of obstruction, as well as a granular appearance of the retained meconium within the bowel Complications of meconium ileus include volvulus, necrosis, or perforation—which can also occur prenatally Contrast enema will often demonstrate microcolon, but can also be therapeutic if the contrast can reflux into the ileum and the retained meconium is washed out The infant must be well hydrated to compensate for fluid shifts associated with the hyperosmolar enema, and care must be taken to avoid perforation or enterocolitis If the enema is incomplete or the patient has complicated meconium ileus, management typically requires surgical intervention to irrigate the bowel and evacuate the meconium, as well as address any associated atresia, necrosis, perforation, or volvulus Meconium peritonitis can occur from in utero bowel necrosis and perforation with subsequent leak of meconium into the peritoneal cavity Meconium in the peritoneum is often accompanied by inflammatory changes that may result in peritoneal calcifications