Pathophysiology
The most frequent type of intussusception is one in which the ileum enters the cecum, however other types are known to occur, such as when a part of the ileum or jejunum prolapses into itself. Almost all intussusceptions occur with the intussusceptum having been located proximally to the intussuscipiens. The reason for this is that 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 which protrudes into the bowel lumen) is present in approximately 10% of intussusceptions.
As the trapped section of bowel may have its blood supply cut off, there is resultant 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 which 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.
Read more about this topic: Intussusception (medical Disorder)