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Defecography
Defecography
can show both the functional aspects
of defecation, and defects in ano-rectal
anatomy. The rectum is filled with radio-opaque
contrast medium, after which the patient
expels the medium under cineradiological
screening (Burhenne,
1964). The technique allows the
recognition of the importance of the
anorectal angle in successful defecation.
Normally this angle, formed by the lines
of the rectal ampulla and the anal canal,
is about 90o and in defecation
it increases to around 135o .
This increase reflects the relaxation
of the puborectalis muscle. Failure
of puborectalis to relax, or even a
contraction during attempted defecation,
is indicated by maintenance or decrease
of the anorectal angle, and constitutes
a functional outlet obstruction. This
has been termed the spastic pelvic floor
syndrome, or paradoxical puborectalis
contraction (Kuijpers
and Strijk, 1984). However, even
in normal subjects puborectalis contraction
has been described during straining
and so this alone is not a clear indication
of pathological defecation.
On
the other hand, defecography gives an indication of the speed
and effectiveness of the act of defecation. It also shows up anatomic
variations, such as rectocele, enterocele or intussusception,
that may contribute to difficulty in defecation.
Figure
6.1 Megarectum
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| Radiograph
of severe constipation, showing loaded colon and megarectum.
Courtesy of Dr. John Yiannakou. |
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Figure
6.2 Rectocele
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| Barium
enema series in a patient with chronic idiopathic constipation,
with evidence of a rectocele. Courtesy of Dr. John
Yiannakou. |
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