Infants with an air- and liquid-filled stomach often have a gastric outlet that is pushed beyond midline to the right side of the abdomen, and often the pylorus dives posteriorly In this setting, rotating the infant to the right decubitus position can improve visualization Allowing the child to feed clear fluids during the examination facilitates identification of the pylorus by providing an excellent acoustic window If available, warm gel will improve probe contact as infants are particularly intolerant of cold gel FIGURE 131.20 Longitudinal view of pylorus The “A” calipers measure the muscle thickness and the “B” calipers measure the channel length Intussusception Anatomy Intussusception occurs when a loop of bowel, the intussusceptum, advances distally and, through peristalsis, becomes trapped in the distal bowel lumen, the intussuscipiens The bowel wall becomes edematous and intestinal obstruction ensues The most common site of intussusception is the ileocolic region of the bowel Mesentery, vascular supply, and lymph tissue accompany the invaginated loop and, as entrapment persists, ischemia develops and the bowel is at risk of perforation Small bowel intussusceptions can occur but are typically selfresolving