Mobility of the Rectosigmoid

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Abstract
While the rectosigmoid is one of the most frequent sites of disease of the alimentary tract, it is the most difficult to examine roentgenographically. Newer technics (1) have been of considerable assistance in revealing the anatomy of the rectum as well as various pathological conditions not shown by routine methods. Any additional light that can be thrown on the presence or extent of disease in this region should be helpful to both the roentgenologist and the surgeon. It is unfortunate that lateral roentgenograms of the colon before and after evacuation of a barium enema are too infrequently employed, for in our experience they have often given more information than could be obtained from the postero-anterior films. The sigmoid colon begins at the pelvic brim as a continuation of the descending colon and ends at its junction with the rectum at the level of the third sacral vertebra. The rectum extends from the third sacral vertebra to the pelvic diaphragm, where it becomes continuous with the anal canal. The sigmoid is suspended by its mesentery, one end of which is attached to the left side and posterior surface of the sigmoid and upper rectal ampulla, and the other to the left side and front of the prevertebral fascia. Cunningham (2) states that “the sigmoid mesentery (or pelvic mesocolon) is a fan-shaped fold in the form of an inverted V and is shorter in its middle portion than at its lateral extremities. Its root is attached along an inverted V-shaped line, one limb of which runs close to the medial border of the left psoas major muscle as high as the bifurcation of the common iliac artery; there, it bends at an acute angle and the second limb bends over the front of the sacrum to the middle of the third piece, where the mesentery ceases. When the pelvic colon ascends into the abdomen proper, the mesentery is doubled upon itself, the side which was naturally posterior becoming anterior.” From this description, it may be seen that the sigmoid mesentery is redundant to allow for varying degrees of distention and pressure within the related segment of the large bowel. The rectum is suspended between two points—the upper being its continuity with the sigmoid; the lower, the pelvic diaphragm. The lower attachment of the rectum is securely fixed by the levator ani muscle, some fibers of which blend with the intrinsic musculature of the rectum. The upper attachment is a movable point. Posteriorly, the rectum is in contact with fibro-areolar and fatty tissue which acts as a cushion between the bowel and the bony pelvis. Anteriorly, the rectum is separated by similar tissue from the vagina and urethra in the female and the prostate and urethra in the male. The fine dissections of Curtis, Anson, and Beaton (3) have shown that “of the three pelvic organs, the rectum is the least firmly fixed to its peritoneal covering, a clear separation being easily effected between the latter and the rectal collar of the endopelvic fascia ….

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