A 10-month-old boy has recently been weaned and placed on solid food. He develops colicky abdominal pain with vomiting. Examination of the abdomen shows emptiness in the right iliac fossa and a mass in the epigastrium. Intussusception is suspected. Following adequate hydration, this condition should be treated by which of the following?

Treatment in infants is by controlled radiologic reduction initially, with surgery reserved for cases in which ischemia is expected or reduction is unsuccessful. The leading part of the intussusception is the apex. The outer sheath is the intussuscipiens, which receives the inner intussusceptum. The outer intussuscipiens elicits peristalsis, which forces the intussusceptum to extend distally.