I find it difficult to classify Intussusception as obstruction due to a problem in the lumen of the bowel, the wall of the bowel or outside the bowel as it is a combination of all.
There may be a polyp or hypertrophy of lymphatics (is this the wall or the lumen?). The bowel that invaginates is in the lumen and it is the wall. In addition the obstruction is due to the bit invaginating and the bowel into which it has invaginated (is this the wall or the outside?). Another consideration is that a full intussusception can only occur when there is a mobile partly malrotated caecum and terminal ileum.
The classical intussusception is mainly a disease of the young, it is the main cause of intestinal obstruction in those aged 6 to 18 months. Adults may also get an intussusception, but this is rare.