An invagination of a part of the intestines is followed by a constriction of mesenteric vessels. This compromises the venous flow first, and then, increasing because of the edema, the arterial blood flow. This causes necroses of the affected part of the intestines and a subsequent peritonitis.
The symptoms are to be deciphered with the help of the young age of the patient and by attentive gatheric and evaluation of the clinical symptoms.
In invaginations, peritoneal symptoms start suddenly with muscular defense. Often, there is reflective vomiting. Affected children frequently scream incessantly and look haggard (pale-greyish skin). The abdomen is shrunken, but it can appear swollen later because of the obstruction. In a posture of relief, the legs frequently are kept in flexion.
A valuable diagnostic sign can be found out by the anamnesis of the mother/father. Frequently, the invagination symptoms are preceded by 3 to 8 hours by a discharge of red, jelly-like stool ("raspberry jelly").
Source: Ultraschall im Netz