Barium findings in retrograde intussusception.

Four instances of antiperistaltic intussusception are presented. These serve to depict the varied roentgen appearances in both types of intussusception on barium study and emphasize two simple interpretational principles: (1) when contrast material is administered orad to an antegrade or caudad to a retrograde intussusception, it must first enter the intussusceptum; and (2) when barium is administered orad to a retrograde or caudad to an antegrade intussusception, it must first enter the intussuscipiens. Attention is also directed to tube related intussusceptions and to potential difficulty in their identification.