 The phenomenon is caused by a weak section of fascial supports of the vagina (the uterosacral cardinal ligament
complex and rectal vaginal septum), which allows a section of peritoneum containing the sigmoid colon to prolapse out of normal position and fall between the rectum and the vagina.It is not possible to differentiate between a rectocele and a sigmoidocele on vaginal examination.Defecating proctography will demonstrate a sigmoidocele during straining.