This is a condition of frequent occurrence, but one which is perhaps too little borne in mind as a cause of obstruction. It" occurs in the great majority of cases at the Sigmoid flexure of the colon. The descending colon above the flexure, and the rectum below it, have virtually no mesentery, being fixed to the abdominal wall. The flexure therefore is fixed at its two extremities and these are near one another, while the loop forming the flexure is movable. It is as if the loop were attached by its two ends to a fixed point, and it is easy to understand how it should sometimes twist round this as an axis. The twist is, as it were, in two half turns (see Fig. 394), and it is usually the upper limb of the loop which turns round the lower, at its neck.

The twisting causes some obstruction of the intestine, but this is not usually complete. Faeces still pass into the flexure, and they may accumulate in enormous quantity. This partial obstruction with accumulation of faeces may persist for months and lead to extreme dilatation of the flexure, so that it may fill the abdomen and reach up to the diaphragm. The walls of the intestine in these prolonged cases may be greatly thickened, especially the muscular coat. In some cases twisting may exist without any obstruction of consequence.

While twisting is most common in the' sigmoid flexure, it is liable to occur also when other parts of the intestine assume similar relations, that is to say, when a free loop of small intestine becomes fixed at its extremities, and these extremities are near each other. This happens most frequently when one extremity is normally fixed, as is the case at the upper and lower ends of the small intestine where on the one hand the duodenum, and on the other the colon, is fixed to the abdominal wall and holds the intestine down. If, by inflammation or otherwise, an abnormal adhesion is acquired so that the gut is fixed at a point near the situation of the natural fixation, then twisting is apt to occur, and probably more readily here than in the sigmoid flexure, as the small intestine is naturally more mobile.

The author has recorded a case in which a peritonitis had fixed the small intestine about a foot above the ileo-ca?cal valve, so as to bring about the conditions named, and twisting occurred in consequence. A fixation may also be brought about by a Meckel's diverticulum which has retained its connection with the umbilicus (Coupland's case).

Literature

Coats, Glasg. Med. Jour., xiii., 1880, p. 445; Coupland, Path, trans., xxxi., 1880, p. 144.