meconium ileus, obstruction of the small intestine in the newborn caused by impaction of thick, dry, tenacious meconium, usually at or near the ileocecal valve. Symptoms include abdominal distension, vomiting, failure to pass meconium within the first 24 to 48 hours after birth, and rapid dehydration with associated electrolyte imbalance. The condition results from a deficiency in pancreatic enzymes and is the earliest manifestation of cystic fibrosis. In uncomplicated cases in which perforation, volvulus, or atresia does not occur, the obstruction may be relieved by giving enemas with a contrast medium, such as a hypertonic solution of meglumine diatrizoate and sodium diatrizoate, under fluoroscopy. Fluid is replaced intravenously to prevent dehydration. If two or three enemas do not dislodge the obstruction, surgery is necessary. See also meconium plug syndrome.
