Twenty-one cases of small bowel intussusception: the pathophysiology of idiopathic intussusception and the concept of benign small bowel intussusception.

Ultrasonography (US) was used to study intussusceptions prospectively at Kiyama Hospital in 1999 and 2000 under the classification of small bowel intussusception (SBI) and large bowel or ileo-ileo-colic intussusception (LBI). The clinical features, management, outcome and etiology were analyzed. All LBIs and SBIs with ischemic symptoms and SBIs complicated by LBI were treated by enema reduction, whereas SBIs considered to be nonischemic were observed. SBI was seen in 21 patients with a mean age of 62.6+/-31.2 months. Four cases (19.0%) were diagnosed during the course of LBI. US showed mesenteric lymphoid hyperplasia in 15 (71.4%). Hydrostatic enema reduction was successful in 9/9, and SBI reduced naturally in the other 12 (benign SBI). LBI occurred in 38 patients with a mean age of 27.8+/-21.2 months. Mesenteric lymphoid hyperplasia was observed in 29 (76.3%). Hydrostatic enema reduction was successful in 37/38. SBI occurs more frequently and in a wider age group than previously considered. Many SBIs reduced naturally, suggesting that they were only transient invagination phenomena and should be called benign SBI. The frequent association of SBI with LBI and also the frequent association of mesenteric lymphoid hyperplasia with both SBI and LBI seem the key to the pathophysiology of intussusception.