Rectosigmoid sphincter of O'Beirne.

In the early 19th century, James O'Beirne proposed that a physiologically important sphincter existed at the rectosigmoid junction. Interest in the rectosigmoid junction had been stirred by a common affliction of the time: spasmodic constriction of the rectum. It was believed that many patients suffered from chronic constipation because of rectosigmoid spasms. O'Beirne proposed that a sphincter at the rectosigmoid junction governed the passage of stool from the sigmoid into the rectum. Further, he maintained that spasmodic constriction of the rectum resulted from dysfunction of this rectosigmoid sphincter. His views, however, conflicted with those of such contemporaries as Houston, who emphasized the role of rectal valves in producing spasmodic constriction. Anatomic studies in the early 20th century found at least a rudimentary sphincter at the rectosigmoid junction in 40 percent of the normal population. Motility studies in the last 35 years have demonstrated unique intraluminal pressure patterns as well as the propagation of retroperistaltic waves in this area. The rectosigmoid in patients with constipation shows an increased activity, as if this area is causing a physiologic obstruction to the passage of stool into the rectum. In contrast, the rectosigmoid in patients with diarrhea demonstrates markedly decreased activity, thereby providing unobstructed access of the feces to the rectum. These studies support O'Beirne's hypothesis that a sphincter governs the passage of stool from the sigmoid colon into the rectum.