This section is from the book "Diseases Of The Intestines", by Max Einhorn. Also available from Amazon: Diseases Of The Intestines A Text-Book For Practitioners And Students Of Medicine.
The lesions which are encountered in acute ileus, no matter what be its origin, are the following: The intestinal coils above the occluded part of the bowels present a quite different appearance from those below. The former are distended, filled with gas and ill-smelling feculent contents; and this ectatic condition is the more pronounced the nearer they are situated to the occluded part. If the occlusion lies in the jejunum or ileum, the distention will involve the entire upper portion of the small intestine and also the stomach. If, however, the stoppage is situated within the colon, the dilatation will at first occupy that portion of the colon situated between the ileocaecal valve and the obtruded spot, while the small intestine may remain unchanged, the ileocaecal valve acting in its usual way and thus preventing an overflow of the contents of the colon into the small intestine. Under such circumstances the dilated portion of the colon may attain considerable size, resembling almost the stomach. After the condition has lasted a few days, however, the ileocaecal valve ceases to functionate and now the contents of the colon overflow the small intestine and the stomach and these organs become also overfilled and distended.
The portion of the intestine situated below the occlusion is empty and contracted.
1 Treves: "Intestinal Obstruction," p. 211.
The intestinal coils above the occluded spot are usually engaged in very active peristaltic movements, which represent an attempt of nature to overcome the obstacle. After these peristaltic motions have lasted a few days, a paralytic state of the intestines supervenes.
The intestinal mucosa situated near the occlusion is subjected to great mechanical and chemical irritations due to the constant presence of considerable amounts of decomposed material, and thus grows intensely inflamed. Often ulcers develop which may penetrate the wall of the bowel and cause fatal peritonitis. In rare instances after such a perforation, adhesion to neighboring intestinal coils may occur and give rise to fecal abscesses and abnormal communications between different intestinal segments. By means of a similar process an opening may be established between the intestine and the abdominal walls in such a manner that the fecal matter finds an exit here (anus praeternaturalis).
Localized or general peritonitis is thus often present in cases of intestinal obstruction. Serous, bloody, or purulent exudation is frequently found in the abdominal cavity. The anatomical lesions are most pronounced in the immediate vicinity of the occluded intestine. This is due not only to the stoppage of the intestinal contents but also to interference with the circulation of the gut produced by the same factors which have caused the obstruction. Numerous large and small mesenteric veins become compressed, thus causing congestion and hemorrhages. The intestinal walls appear infiltrated with blood, showing ec-chymoses at various places, and may even appear dark red. In the neighborhood of the occlusion the intestine may be covered with black curdled blood in the form of a membrane. Its walls become brittle and gangrenous.