The
transit of the stool through the colon may be at normal
speed but when the stool reaches the rectum there is failure
to progress.
Typically the patient is called to stool at least daily but only small amounts of stool are passed with a sense of incomplete evacuation.
The mechanism of blockage
Failure to evacuate the rectum is commonly due to a
mechanical blockage of the anal outlet.
Mechanical blockage of the anal outlet may occur in a number
of ways. The muscles and connective tissue supporting the
rectum can become weakened and unsupportive.
There
will then be a failure to “lift” and straighten the rectum
and tension the fascial sheaths that surround the bowel and
separate the pelvic organs when defecation is attempted. The
result may be a baggy rectum which bulges into the vaginal
space (rectocoele).
Often, no stool can be evacuated unless the patient manually
lifts the perineum and places a finger into the vagina or
the rectum to reduce the 'bulge'
The passage of odd shaped stool is commonly noted.