Rectosigmoid junction

The rectosigmoid junction, formerly the rectosigmoid sphincter or sphincter of O'Beirne, is the junction of the sigmoid colon and the rectum.^[1]

Hypothesized sphincter

The rectosigmoid sphincter, also known as the sphincter of O'Beirne, was hypothesized as an anatomical structure located between the sigmoid colon and rectum.^[1] The structure was first proposed by the 19th-century Irish surgeon James O'Beirne. Its existence, structure and function has been a matter of long-standing medical controversy.^[1][2] The Latin names sphincter ani tertius and pylorus sigmoidrectalis also been used.^[3][4]

As of 2025^[update], the existence of some form of distinct contractile anatomical structure at the rectosigmoid junction, if not an actual sphincter, in many people is acknowledged in numerous articles in the medical literature.^{[3][1][5][6][7][8][9][10]}

Molecular signature of rectosigmoid junction cancer

A 2023 study suggested that cancers of the rectosigmoid junction exhibit different chemical signatures from either cancers of the colon or cancers of the rectum.^[11]