Functional radiology of the ano-rectal region.
Chronic constipation is probably the most common symptom resulting in a referral of patients for a dynamic radiologic investigation of the GI tract. The primary usefulness of defecography in chronic constipation is to provide details about the dynamic phenomenon of evacuation which cannot be elicited by any other medical technique. It is employed to demonstrate or rule out the presence of an anatomical deformity (prolapse, rectocele, intussusception) and/or a localized dysfunction (outlet obstruction, rectal inertia) of the distal GI tract. Defecography can distinguish between a grossly obstructed pattern and an overtly normal one, but a definitive diagnosis is made by manometry and electromyographic studies. On the other hand, it should be noted that a failure to show abnormalities by defecography does not necessarily imply a normal anorectal function. A better understanding of anorectal physiology is expected in the future from combined video-pressure studies, which will provide the exact timing between the pressure drop and barium passage through the distal colon.