The so-called small intestine is a long 'floppy' tube, up to 6 metres (20 feet) in length, which is similar in width and consistency to the inner tyre of a bicycle. The wall of the intestine is composed largely of muscle which, by alternately squeezing and relaxing, mixes the contents. In addition, prolonged contractions which move forwards, propel the contents along the intestine, like the action used to squeeze toothpaste out of its tube.
The loops of intestine lie loosely piled on top of one another and fill the central part of the abdominal cavity (below the stomach). The inner surface of the abdominal wall and the surface of the intestine are covered with a continuous slippery "lubricated" film, so that the many loops of intestine can move freely and independently of each other.
When the abdominal cavity is opened during a surgical operation, especially if a procedure has to be performed on the intestine, a raw surface in the covering membrane can occur in one or more places. During the healing process, raw areas may 'stick' to one another. These 'adhesions' usually cause no trouble and their presence is unknown. However, an adhesion can restrict the movement of the intestine because the floppy tube becomes kinked, twisted or restricted by an external band of scar tissue. As a result, passage of intestinal contents may be blocked at that point. This can lead to episodes of colicky pain, as the intestinal muscle contracts more strongly than usual to propel the contents through the narrowed segment. Other symptoms may be a sense of distension, nausea or vomiting, and an altered bowel habit. The blockage is usually partial but can be complete, in which case symptoms are more severe and admission to hospital is needed.
The presence of adhesions is difficult to detect. An X-ray of the abdomen may suggest the presence of obstruction to the passage of intestinal contents because the intestine is shown to be widened and contains more fluid and gas than normal. Even X-rays which follow the progress of a substance such as barium through the bowel are often normal because they are performed when the intestine is empty. The only certain way of detecting adhesions is to look inside the abdominal cavity, either with a viewing instrument (laparoscope) or at operation.
Abdominal pain and altered bowel habit may be caused by many conditions, especially irritable bowel syndrome. Caution and investigation is needed before such symptoms are attributed to adhesions, and particularly before contemplating further surgery.
As most adhesions cause no trouble operation is not necessary. Division of adhesions at operation can relieve obstructive symptoms. However, new raw areas on the inside of the abdominal cavity or surface of the intestine can again become adherent to one another during healing so that new adhesions may form. Complex operations to prevent the intestine kinking are sometimes performed but such procedures do not always relieve symptoms and are reserved for particularly troublesome and extensive adhesions.