Defecographic functional evaluation of rectal akinesia
Defecation is a complex and still incompletely understood phenomenon related to several integrated mechanisms. However, improvements over the past few years in our understanding of the process of defecation, along with the increasing use of radiological and anorectal physiology studies, have led to improved treatment results. Segmental and propagated contractions deliver colonic content into the rectum, where sensory mechanisms relay the sense of rectal filling sensation, stimulating rectal emptying. As stool passes through the colon, it is stored in the sigmoid colon until a mass movement empties it into the rectum. Rectosigmoid contractions develop an expulsive force vector directed toward the rectum and the anal canal. A vector is a mathematical representation of a magnitude of force and the direction in which the force is applied. The movement of stool through the colon and rectum can be analyzed by examining the pressure vectors that act upon the stool. When the concept of vector analysis is applied to bowel continence, two major categories of opposing forces appear. Propulsive forces (peristalsis, Valsalva, gravity) are those factors with a pressure vector that would result in the elimination of the stool from the body. Resistive forces are factors that slow or prevent elimination of stools from the body. Resistive forces could be defined as active (primary muscles: puborectalis, internal and external anal sphincter) or passive (including strictures, angulation of the bowel, decreased compliance, poor fixation or the rectosigmoid colon). Moreover, it has been suggested that the anterior and posterior rectal walls appeared to be stretched during defecation: The anorectal angle moved significantly downward and began to open; the diameter of the anus enlarged to at least twice its resting size; and the anterior wall of the anus was pulled forward along with the distal part of the urethra. These changes in anorectal position during defecation can be resolved as three muscle vectors. The anterior wall of the anus was pulled forward; the posterior wall of the rectum was pulled backward, opening the posterior anorectal angle and approximately doubling its resting diameter; and the anterior edge of the levator plate and coccyx was angulated downward [1]. In the first video [video 1], the normal rectal emptying is well documented by the presence of an air–fluid level (yellow arrow) which makes it possible to follow the progressive expulsion, according to the force vector direction (green arrow). At the end of the evacuation, the rectal walls were collapsed. Some patients with impaired defecation, for which none of the usually known causes (including anismus, dyssynergia, intussusception, rectal prolapse, enterocele, rectocele) could be demonstrated, were functionally characterized by the absence or the reduction of the propulsion and the wall contractions, with an altered ampullar motility [2]. This condition could be defined as idiopathic rectal akinesia [3]. In patients with this condition, cinedefecography shows the absence of an expulsive force vector and the presence of vicarious rectal movements. As shown in the second video [video 2], no force vector could be documented, with fixed air–fluid level (yellow arrow) and failed barium expulsion. Electronic supplementary material The online version of this article (doi:10.1007/s10151-015-1310-9) contains supplementary material, which is available to authorized users.