About 90% of cases of intussusception in children arise from an unknown cause. They can include infections, anatomical factors, and altered motility. Meckel's diverticulum Polyp Duplication Appendix Hyperplasia of Peyer's patches Idiopathic While an earlier version of the rotavirus vaccine was linked to intussusception, the current versions are not. Pathophysiology In the most frequent type of intussusception, the ileum enters the cecum. However, other types occur, such as when a part of the ileum or jejunum prolapses into itself. The part that prolapses into the other is called the intussusceptum, and the part that receives it is called the intussuscipiens. Almost all intussusceptions occur with the intussusceptum having been located proximally to the intussuscipiens. This is because peristaltic action of the intestine pulls the proximal segment into the distal segment. There are, however, rare reports of the opposite being true. An anatomic lead point (that is, a piece of intestinal tissue that protrudes into the bowel lumen) is present in approximately 10% of intussusceptions. The lead point (best exemplified by a polyp) serves as a focal area of traction, which the peristaltic action pulls into the distal bowel, thus invaginating the attached bowel segment. The trapped section of bowel may have its blood supply cut off, which causes ischemia (lack of oxygen in the tissues). The mucosa (gut lining) is very sensitive to ischemia, and responds by sloughing off into the gut. This creates the classically described "red currant jelly" stool, which is a mixture of sloughed mucosa, blood, and mucus. A study reported that in actuality, only a minority of children with intussusception had stools that could be described as "red currant jelly", and hence intussusception should be considered in the differential diagnosis of children passing any type of bloody stool. Diagnosis An intussusception is often suspected based on history and physical exam, including observation of Dance's sign. A digital rectal examination is particularly helpful in children, as part of the intussusceptum may be felt by the finger. A definite diagnosis often requires confirmation by diagnostic imaging modalities. Ultrasound is the imaging modality of choice for diagnosis and exclusion of intussusception, due to its high accuracy and lack of radiation. The appearance of target sign (also called "doughnut sign" on a sonograph, usually around 3 cm in diameter, confirms the diagnosis. The image seen on transverse sonography or computed tomography is that of a doughnut shape, created by the