Evacuation proctography: an investigation of rectal expulsion in 20 subjects without defecatory disturbance.

Evacuation proctography is a dynamic investigation of rectal expulsion that records the voluntary evacuation of thick barium paste on videotape. Evacuation is a passive phenomenon in a defined zone of the rectum, associated with pelvic floor descent of 3 cm from a resting position of the anorectal junction less than 2 cm above the plane of the ischial tuberosities. The anal canal does not open immediately; it takes about 4.5 sec to open to a maximum diameter of 1.5 cm, with rectal emptying in 11 sec. Anterior rectoceles commonly invert over the anal canal as the rectum collapses in at the end of evacuation.