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Defecography
X.-M. Yang, K. Partanen, P. Farin & S. Soimakallio
To cite this article: X.-M. Yang, K. Partanen, P. Farin & S. Soimakallio (1995) Defecography, ActaRadiologica, 36:5, 460-468
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Acra Radiologica
36 1995)
460 468
Printed in Denmark
.
All rights reserved
Copyrighi Acru R er l i~ i log im1995
A C T A R A
D I O L O G
C A
ISSN 0248-1851
Review
Article
DEFECOGRAPHY
X.-M. YANG,K . PARTANEN,? FARINnd S. SOIMAKALLIO
Depar tment
of
Clinical Radiology, Kuo pio University Hospital, Ku opio, Finla nd.
Abstract
Defecography, a dynamic imaging modality, plays an imp ortan t role in the
diagnosis of functional and morphologic abnormalities of the anorectal re-
gion. We have here summarized the principle and techniques as well as obser-
vations
of
defecography, with special emphasis on morphologic measure-
ments, clinical relevance, and limitations. Th e application of M R imaging in
examination of anorectal function has also been addressed.
Defecography is a dynamic radiologic investiga-
tion performed during voluntary evacuation of the
rectum. Some authors have called it “evacuation
proctography”
26),
“dynamic proctography” 1
3),
and “voiding proctography” (
1).
This modality
was originally described by WALLDENn 1952, who
investigated the significance of an abnormally deep
pouch of Douglas in disturbed defecation
55).
During the
1960s,
only
a
few additional papers
were published on this topic
6-8).
Since
1984,
im-
provements and refinements in proctologic surgical
techniques brought about new interest in defecog-
raphy 10,23, 30, 32). Today, defecography is wide-
ly used as a routine imaging examination of the
anorectal function.
Anatomy and physiology of anorectum
The rectum is approximately 12 cm long and fol-
lows the curvature of the sacrum and coccyx. The
rectum usually extends
3
cm beyond the coccyx,
turning posteroinferiorly to form the anal canal of
2
to
4
c m h length
34).
Studies of fecal evacuation are based on func-
Key words: Anus, defecography; MR
imaging; pelvis; rectum.
Correspondence: Xiao-Ming Yang,
Clinical Radiology, Kuopio Univer-
sity Hospital, FIN -702 10 Kuopio,
Finland. FAX *358-71-17 33 41.
Accepted for publication 15 December
1994.
tion of the pelvic floor muscles surrounding the
rectum and anal canal and attached to the bony
pelvis
10, 19).
The levator ani muscle, consisting
of the ileococcygeus and pubococcygeus as well as
puborectalis muscles, is an important component
of the pelvic floor. It anchors the rectum in the
middle third of the pelvis
37).
The puborectalis
and the deep portion of the external sphincter
muscle are fused together. Both muscles originate
from the back of the symphysis pubis, proceed
backward and downward along the upper part of
the anal canal, forming a U-shaped loop termed
the “puborectalis sling” behind the anorectal junc-
tion 12,
50 .
The puborectalis sling creates the
anorectal angle by pulling the anorectal verge
anteriorly, resulting in an anorectal angulation of
80
to
90”
at rest
12, 17, 57).
Any increase of
in-
traabdominal pressure forces the anterior rectal
wall against the upper anal canal, thereby effec-
tively occluding it, as a flap valve effect (21). The
rectosphincteric reflex, including both the internal
and external sphincters, is mediated through spinal
reflex pathways via the pudendal nerve and
branches of
S3
and
S4.
The external sphincter is
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DEFECOGRAPHY
believed to be more important than the puborec-
talis sling in maintaining fecal continence (1 1, 12).
The anatomic features correlate closely with de-
fecographic findings. During straining, laxity of
the levator ani muscle is seen as a descent of the
anorectal junction (10). The relaxation of the pu-
borectalis muscle can be observed as an increase in
the anorectal angle (1 8). The sphincter relaxation
widens the anal canal. The “opening” function of
these muscles converts the anorectum into a fun-
nel-shaped structure which enables the passage of
stool in combination with an increased intraabdo-
minal pressure (17).
Pathophysiology
of
anorectum
The anorectal angle and the degree of perineal de-
scent during defecation straining are the most fre-
quently used indicators of physiologic status of the
pelvic floor muscles.
A
reduction of the anorectal
angle and/or a decrease of the perineal descent
during straining may be evidence of an inability to
relax the pelvic floor muscles due to the spastic
pelvic floor syndrome or paradoxical reaction (25).
This inability of relaxing pelvic floor muscles leads
to obstructed defecation, i.e., constipation and ob-
stipation (15, 31, 54, 56). In this condition, pa-
tients must strain heavily to defecate, causing
further anorectal disturbances, such as rectal intus-
susception, rectocele, and anterior mucosal pro-
lapse (18, 25). The latter may cause ischemia and
ulceration of the rectum (18).
The presence of an obtuse anorectal angle at rest
and an excessive perineal descent during straining,
“descending perineum
.
syndrome”, suggests
weakening and increased laxity of the pelvic floor
muscles due to a long period of excessive straining
at fecal evacuation. This condition leads to incon-
tinence. During defecation, the force of abdominal
straining is mainly transmitted through the an-
terior rectal wall, easily causing temporary mu-
cosal prolapse into the anal canal. In most cases,
this is readily corrected by contraction of the pelvic
floor muscles. When these muscles are weakened,
as in the descending perineum syndrome, the an-
terior rectal wall continues to bulge into the anal
canal and then rectal prolapse may develop (19,
21, 44).
Procedur es at defecography
Preexamination approaches.
To show the small
bowel loops in the pelvis, the patient is given 500
ml barium contrast medium (BaS04 suspension)
orally 1 ,hour before defecography. Opacification
of the pelvic small bowel is considered complete
when some barium is fluoroscopically identified in
the right colon (10, 26). The purpose of showing
the pelvic bowel loops is to detect enterocele. In
women, a tampon soaked with contrast medium
is placed in the posterior fornix of the vagina for
localizing the vagina (10, 26). However, it has been
suggested that the tampon can interfere with nor-
mal pelvic floor movements during defecography
and thus obscure diagnostic information (1, 34).
A
water-soluble contrast medium gel has been for-
mulated, composed of equal parts of a sterile, low-
pH gel intended for vaginal use and high-density
water-soluble iodine contrast medium (1). The gel-
contrast combination is easier to administer, even
in elderly patients, and is more physiologic (34).
The patient should be asked to void before defeco-
graphic examination to prevent compression of the
rectum by a full bladder (27).
Techniques of defecography
With the patient in the left decubitus position, a
thick barium paste (a stool-like semisolid contrast
medium) is injected into the rectum using a plastic
syringe connected to a catheter (9,
47,
53), or a
caulking gun (10).
GOEI
t al. (18) used 300 ml
thick barium paste, prepared by adding 50
g
of a
suspending carbopol agent into 5 liters of barium
sulfate, and then mixed gradually with 340 ml of
sodium hydroxide until a thick paste of pH 7 was
formed.
TING
t al. (53) injected 150 ml thick bar-
ium paste, prepared by mixing 200 ml of potato
starch with 250 ml of warm water, followed by
adding 50 ml of
a
commercially available barium
suspension. In order to attain fecal viscosity and a
specific gravity of 1.2 g/cm3, KRUYT t al. (28)
made their thick barium paste by adding Metamu-
cil to BaS04 contrast medium in a ratio of 1:30.
Before radiography, the position of the anal
verge is indicated by attaching a metal marker to
the skin with micropore tape (42). Then, the pa-
tient sits on a specifically designed toilet seat or
commode, mounted on the footboard of a remote-
control fluoroscopy stand in an upright position
(12). Because of the great differences in radio-
lucency between the pelvic soft tissue and the air
below the buttocks, the placement of a filter device
is necessary to absorb the unwanted radiation
from the region of the anal canal (5, 14, 53). Dif-
ferent defecographic seats or commodes have been
constructed of various materials, such as wood (5),
Plexiglas (14,45), lead (53) or a water-filled rubber
ring (12, 17).
Under fluoroscopy in the right lateral projec-
tion, the anorectal function is studied by either re-
cording the defecation procedure on a videotape
(53), or photographing the various stages of def-
ecation with a 100-mm camera a t a frame rate of
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X. - M. YANG
ET AL.
1 frameh or 1 frame12 s (17, 19).The images of the
anorectal region are obtained 1) during squeezing,
whereby the patient exerts maximal contraction of
the pelvic floor muscles; 2) at rest, when the patient
is asked to completely relax the pelvic floor
muscles; and 3) during straining with complete
evacuation of the rectal contents (16,
19).
The de-
fecographic measurements should be corrected by
Fig. 3. After several minutes of straining, an enterocele (E) is
detected between the space of the vagina (V) and rectum
(+).
AR=anterior rectocele.
the incorporation of a midline radiopaque cent-
imeter ruler into the commode
(19,
51).
Fig. ] .’A large anterio r rectocele
(AR)
associated with a rectal
prolapse
(+).
V=vagina.
Qualitative evaluation rnorphologic changes of
anorecturn
The pathologic findings at defecography include
anterior rectocele, perineal herniation (posterior
rectocele), enterocele or sigmoidocele, anterior or
posterior mucosal prolapse, intussusception, and
rectal prolapse.
An anterior rectocele is a more than 2 cm bulg-
ing of the rectum into the posterior wall of the
vagina during defecation straining (26, 34) (Fig.
1).
The cause of anterior rectocele is considered to
be an anatomic weakness of the anterior wall of
the rectum that allows expansion in the form of a
pouch (33, 43). Patients with paradoxic reaction
are frequently affected by this morphologic dis-
order because they must strain heavily to defecate.
A perineal herniation, also termed “posterior
rectocele”, is an abnormal prolapse1herniation of
the posterior rectal wall or whole rectum through
a levator ani defect during straining (43) (Fig. 2).
An enterocele is defined as a cul-de-sac filled
with small bowel or omentum herniating down-
ward between the vagina and rectum (26) (Fig. 3).
A sigmoidocele is a herniated cul-de-sac filled with
sigmoid colon. Clear-cut differentiation between
an enterocele and a sigmoidocele is difficult in de-
fecography. The causes of enterocele or sig-
terectomy, urethropexy, or ventral suspension of
Fig.
2.
A small perineal herniation or posterior rectocele
(+)
moidocele may be prior pelvic surgery, such as hYs-
associated with a mild enterocele (E).
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DEFECOGRAPHY
uterus or vagina. These procedures change the nor-
mal horizontal vaginal axis and pull the vagina
more anteriorly, which exposes the cul-de-sac and
leaves it vulnerable to the subsequent development
of an enterocele. Chronically increased intraabdo-
minal pressure from any cause and mesenteric
lengthening may facilitate enterocele formation.
Some authors placed rectocele and enterocele as
well as sigmoidocele in the group of posterior com-
partment pelvic prolapse (26). Unlike a rectocele,
which is usually most evident during evacuation,
enteroceles are sometimes confirmed only with re-
peated straining for several minutes after evacu-
ation. It is important, therefore, to instruct the pa-
tient to continue straining after evacuation for fa-
cilitating detection of enteroceles (10, 26).
Anterior mucosal prolapse, also termed “inter-
nal prolapse of the anterior rectal wall”, is defined
as an invagination of the anterior rectal wall into
the rectal lumen or anal canal (45, 53) (Fig. 4).
Posterior mucosal prolapse is rare (Fig. 5). Some
authors also named a small perineal hernia as a
posterior mucosal prolapse (43). The defecograph-
ic differentiation of an anterior rectocele and an
anterior mucosal prolapse depends on the angle
between the anterior rectal wall and the superior
margin of the pouch of the rectocele or mucosal
prolapse: an obtuse angle is associated with the an-
terior rectocele and an acute angle with anterior
mucosal prolapse.
When anterior and posterior mucosal prolapse
occur together and cause anorectal obstruction, a
rectal intussusception is confirmed (53). Some
authors also named the rectal intussusception
“internal circular prolapse’? (53) or “internal proci-
Fig.
4
A large anterior mucosal prolapse
(+)
seen during
straining. R=rectum .
Fig. 5. An intraanal rectal intu ssusce ption : the distal rectum
invaginates into the anal canal (+). Two posterior mu cosal pro-
lapses b ) are also seen.
dentia”
(10).
When the leading point of the intus-
susceptum passes out through the anus, the con-
dition is designated rectal prolapse (10, 16) (Fig.
1). Some authors differentiate the rectal prolapse
from an anal prolapse: the anal prolapse involves
only the anal mucosa, but the rectal prolapse in-
volves all layers of the rectum (10). The difference
is noticed on defecography as differing thickness
of the intussusception. In anal prolapse the a.p.
diameter of the intussusception does not exceed 1
cm, but in rectal prolapses the diameter is 2 to 4
cm (10).
Rectal prolapse is usually easy to recognize at
clinical examination, whereas rectal intussuscep-
tion can be better detected during defecography. It
is extremely difficult to demonstrate rectal intus-
susception during a physical examination or by ob-
servation with an endoscope or a barium enema
(1
8,
45). The diagnosis of rectal intussusception in
defecography should be based on a considerable
circular infolding of the rectal wall toward the lu-
men during straining. When the rectal infolding in-
vaginates into the anal canal, it is termed “intraan-
a1 rectal intussusception” (17) (Fig. 5). A minimal
infolding that disappears after the bolus has
passed is probably caused by a transient prolapse
of the mucosa and should not be considered
pathologic (1
6).
Milder intussusceptions are now
considered normal (41). The causes of rectal intus-
susception and rectal prolapse are not fully under-
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X.-M. YANG ET AL.
stood. An abn ormally deep pouch of D ouglas, de-
fective levator ani, insufficient attachment of the
rectum, and red undanc y of the sigmoid colon have
been suggested as predisposing factors (2, 39, 46,
49).
Solitary rectal ulcer syndrome (SRUS) is an en-
tity consisting of a benign rectal lesion in the distal
anterior wall of the rectum with common clinical
com plaints of rectal bleeding and
a
long history of
defecation disorders (17, 18). Sigmoidoscopic
manifestations in SRUS include ulcerative, ery-
thematou s, a nd erosive changes, which a re usually
located o n the anterio r wall within 10 cm from the
anal verge (16, 18). The mechanism of ulceration
in SRUS is thought to be a mechanical injury to
the mucosa, resulting in pressure necrosis (17, 18).
Two defecation disorders are considered possible
causes of SRUS: rectal intussusception and the
spastic pelvic syndrome (18). Invagination of the
rectal wall in rectal intussusception causes rupture
of submucosal vessels, ischemia, and ulceration
(48). A persistent contraction of the muscle in the
spastic pelvic syndrome results in inability to
empty the rectum, leading the patient to repeat
straining. The result of the repeat straining is the
development of anterior mucosal prolapse, finally
causihg ischemia and ulceration
(18).
Thus, de-
fecographic examination can demo nstrate some in-
direct findings of SRUS, including rectal intussus-
ception and anterior mucosal prolapse as well as
spastic pelvic floor syndrome.
Based on the literature, we have summarized the
frequency of different defecographic ab norm alities
in patients with defecation disorders in Table 1.
The most common findings are anterior rectocele
(28 ) and intussusception (19”/0),followed by en-
terocele or sigmoidocele (7 ), anterio r mucosal
prolapse (7 ), and rectal prolapse (3 ). However,
17
of
patients with defecation disorder have a
normal defecography.
Fig. 6. Measurements of different morphologic parameters: the
anorectal angle posterior (ARAp), the anorectal angle axis
(ARAa), the maximum width of the anal canal (WAC), the
maximum width of the rectal lumen (WRL), the size
of
rectoce-
le (SR), the rectovaginal separation (RVS), and the level of ano-
rectal junction (ARJ) from pubococcygeal line (PC line).
Quantitative evaluation measurements of anorectum
In the analysis of defecography, various morpho-
logic param eters of norm al and patho logic anorec-
tum are measured at rest and at different def-
ecation stages of squeezing and straining (Fig. 6).
FELT-BERSMAt al. (12) measured the anorectal
angle (ARA) in 2 different ways: 1) an angle
formed by the axis of the anal canal and a line
along the posterior edge of the distal rectal wall,
named the anorectal angle posterior (ARAp);
and 2) an angle between the axis of the an al canal
and a line alone the longitudinal axis of the rec-
tum, nam ed the anorectal angle axis (ARA a).
ARAp is the most frequently measured angle in
defecography (12, 13).
There is a wide range of normal values for the
AR A at rest, squeezing and straining
4,
0). For
example, GOEI(15) stated that the ARAp values
Table 1
Frequency of different defecographic Jindings in pati ents with defecation disorder s
Defecographic findings,
Y
Anterior
Authors Patients, Normal Anterior Enterocele/ mucosal Intussus- Rectal
(ref.) n rectocele Sigmoidocele prolapse ception prolapse
EKBERGt al.
(10) 90 28 . 13 16
11
23 12
TING t al.
(53) 170 23 32 18 20
KELVINet al.
(26) 74 73 17
GOEI
BAETEN
(16) 155 32
20
1 6 40 4
Total
489 83
(1
7 ) 138 (28 ) 34 (7 ) 35 (7 )
92
(1
9%)
16 (3 )
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DEFECOGRAPHY
in asymptomatic subjects are 107+24 at rest and
125219 during straining. EKBERGt al. (10) re-
ported that normal values for ARAa could vary
between 70 to 140 with a mean angle of 114 at
rest and 110 to 180 with a mean of 134 during
straining. FELT-BERSMAt al. (12) found that
ARAp was smaller than the ARAa both at rest
and during straining. ARA is not influenced by age
or sex (12, 19).
By
comparing the result of defeco-
graphy to that of anorectal manometry, KRUYT t
al. (28) concluded that there is a correlation be-
tween ARA and fecal continence. However, some
authors state that defecographic measurements of
ARA cannot be regarded as a reliable indicator of
the complicated physiologic condition of the pelvic
floor muscles 3, 15, 35, 36, 40). YOSHIOKAt al.
(60) suggested using a computer-drawn centroid of
the rectum instead of the posterior rectal wall.
Even though the results using the centroid appear
to be more consistent, there are theoretical prob-
lems with this concept not yet addressed.
The pelvic floor motion or the perineal level po-
sition is determined by measuring the distance be-
tween the anorectal junction (ARJ) and the pubo-
coccygeal line parallel to the longitudinal axis of
the anal canal (20, 53). The anorectal junction is
the apex of ARAp (19,41), and the pubococcygeal
line is a line extending from the most inferior por-
tion of the symphysis pubis to the last coccygeal
joint or the coccyx tip (53, 58). Some authors used
the ischial tuberosity as a reference point rather
than the coccyx tip for measuring the position of
the perineal level (26, 41). KRUYT t al. (27) pre-
ferred to relate the position of the anorectal junc-
tion to the symphysiosacral baseline instead of the
symphysiococcygeal baseline. Some studies have
demonstrated that the perineal descent during
straining was not influenced by gender, age or pa-
tient group, and was not different between patients
with obstipation and controls (3, 12). However,
contrary reports have shown an increased perineal
descent with age, incontinence, and constipation
(29, 33).
The size of the anterior rectocele is determined
by measuring the distance between a line through
the anterior demarcation of the anal canal and the
most anterior point of the anterior rectocele (25),
classified as small (4 cm in depth) (26,
53). The size of anterior rectocele less than 2 cm is
regarded as a normal variant (42).
During defecation, the anal canal forms a fun-
nel-shape with the wide portion at the proximal
end, and the maximal diameter of the anal canal
is usually referenced (19, 41, 45). The width of the
anal canal is not significantly different either be-
tween patients with defecation disturbance and
control subjects, or between male and female sub-
jects (15) . SHORVONt al. (52) found an open anal
canal at rest with loss of contrast medium in 7%
of healthy individuals.
Radiologically, evacuation of less than 50 of
the thick barium within 30
s
is considered poor
emptying or incomplete evacuation (41, 42). In a
previous study, we measured the maximum width
of the rectal lumen (WRL) because we expected
that WRL could be a parameter for quantitative
assessment of rectal emptying (59). Our study
demonstrated a mean WRL of 4.7 cm at rest which
decreased to 2.1 cm during straining. The diagnos-
tic relevance of WRL at different stages of def-
ecation needs to be investigated further.
By
plani-
metrically estimating the amount of retained bar-
ium, some authors correlated the retained volume
to the patient's sense of incomplete emptying. They
found that defecographic findings did not explain
incomplete emptying, although the reproducibility
of the planimetric method was good (53).
The rectovaginal separation, a space between the
vaginal posterior apex and the anterior rectal wall,
is an indicator for detecting enterocele or sig-
moidocele. If the separation is 2 cm or more after
evacuation, an enterocele may be suspected. The
depth of the enterocele is measured along an axis
parallel to the opacified vagina, starting at the line
of the rectovaginal separation (26).
Unfortunately, there is a large variation in the
patterns of anorectal function among healthy indi-
viduals, and there is a large interobserver variation
in the measurements of the anorectal configuration
during the defecographic examination. The inter-
observer variation of the ARA measurements is
mainly due to variations in drawing the tangent to
the curved caudal inner rectal wall (27). The study
by GOEI
(15)
showed large intraindividual vari-
ations of measuring the anal canal width. Using
kappa statistic analysis, we evaluated the reprodu-
cibility of measuring 5 anorectal morphologic par-
ameters, including anorectal angle posterior,
anorectal angle axis, maximum width of anal ca-
nal, maximum width of rectal lumen, and the size
of a rectocele. Our results showed that the 5 par-
ameters were not reproducible, because of the high
inter- and intraobserver inconsistency (59). De-
fecographic measurements and observations
should, therefore, be interpreted with caution and
should not be used as the only criteria for treat-
ment (13, 19, 34).
Clinical relevance
Table 2 presents the main symptoms associated
with different defecographic findings.
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X.-M.
YANG
ET AL.
Table 2
Clinical relevance of defecographic J ndings
Defecographic findings
Morp holog ic changes Measurements Main symptoms
Anterio r rectocele RS > 2 cm Incomplete evacuation
Enterocele or sigmoidocele RVS
> 2
cm Backache and dragging sensation when
upright, and relief by lying down
Fecal incontinence, constipation
Constipation and obstipation
Intussusception or rectal prolapse Incomplete evacuation, constipation
Descending perineum syndrome
Spastic perineal floor syndrome
A R A >
130
at rest and
>155
during
straining, AR J
>4
cm at rest
N o ARA and ARJ changes from rest to
straining
RS=rectocele size; RVS=rectovaginal separation; ARA =an orecta l angle; and ARJ= ano rectal junction.
The main symptom associated with
a
rectocele
is a feeling of incomplete emptying (38). Anterior
rectocele is a frequent dysfunction of pluriparas
and often one of the main reasons for dyschezia in
female subjects (57). In male patients, the pressure
of the anterior rectocele pouch on the prostate
gland, like a digital pressure, can produce disturb-
ance of the prostate during defecation straining
(9). Typical symptoms with enterocele or sig-
moidocele are backache and a dragging sensation
or a pressure sensation on the rectum when up-
right, diminishing on lying down (26). The most
common symptoms of intussusception are incom-
plete emptying of the rectal ampulla and consti-
pation (16, 24), because, during downward strain-
ing, the intussusceptum occludes the anal canal,
preventing further evacuation of rectal contents. If
intussusception and/or rectal prolapse result in
SRUS, rectal blood loss and mucosal discharge oc-
cur (17). The treatment for the intussusception is
the same as that for classic rectal prolapse:
rectopexy and sigmoid resection with rectal fix-
ation (34).
In a normal subject, the ARJ at rest is located
near or on the pubococcygeal line. In the de-
scending perineum syndrome, the ARJ position is
lower than 4 cm below the pubococcygeal line at
rest and/or it descends more than 4 cm from rest
to straining, while ARA is more than 130 at rest
and more than 155 during straining (17,
19, 20,
26). These pathologic changes cause incontinence,
manifested as daily uncontrollable loss of feces (17,
24, 34). The main treatment for this condition is
to eliminate all straining during defecation. Sup-
positories may aid in defecation without straining
(34). In patients with spastic pelvic floor syndrome
or puborectalis paradox , constipation is the
main symptom (56). In this condition, the ARA
does not increase and contrast medium is not
evacuated during straining
(1
5,
26). Biofeedback
has recently become the therapy
of
choice for spas-
tic pelvic floor syndrome (34). However, some
authors have concluded that measurements of the
anorectal angle and perineal descent during strain-
ing give insight into the pathophysiology of def-
ecation but lack clinical relevance (12, 22, 41) be-
cause even in normal subjects, abnormalities of de-
fecography can also be found (4, 33,
51).
Role
of
defecography
Different investigative procedures are available in
detecting defecation disorder of the anorectum
(Table 3). Among those, clinical history and physi-
cal examination cannot supply details of either
anorectal morphology or anorectal function, ex-
cept when rectal prolapse is directly observed.
Proctoscopy or rectoscopy only presents the ano-
rectal morphologic status without supplying the
anorectal functional information. In contrast,
physiologic examinations, such as anal man-
ometry, the saline infusion test, rectal capacity
measurement, and anal electromyography, supply
Table 3
Different modalities for evaluation
o
defecation
Morphologic Functional
Exam inations evaluation evaluation
Clinical history and physical
examination
roctoscopy or rectoscopy
Imaging modalities
barium enema
CT
M R
defecography
Physiological examination
anal manometry
+
saline infusion test
+
rectal capacity
anal electromyography
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only the anorectal functional information without
revealing the anorectal morphologic status (12, 20,
28).
A barium enema study, like proctoscopy or rec-
toscopy, is a static examination that does not allow
detection of functional abnormalities of the ano-
rectum (1 7). It is important that patients are sitting
down during the examination procedure, since
much of the physiologic nature of defecation is lost
when the patient is lying down as for a standard
barium enema (10). This can be overcome with de-
fecography, in which the patient is studied while
sitting. This
is
a more physiologic means of as-
sessing rectal dysfunction (10). The main appli-
cations of defecography are 1) the functional de-
tection of anorectal anatomic abnormalities as
possible causes of defecation disturbances; and 2)
as an anatomic guide to any necessary surgical
procedure (15).
Defecography is especially suitable for revealing
rectal intussusception which can easily be treated
with rectopexy (10, 12). Another main contri-
bution of defecography
is
its use in detecting en-
teroceles and sigmoidoceles that are easily missed
at physical examination and overlooked at surgery
(26). In addition, some authors have shown that
ARA can play a valuable role in deciding which
surgical procedure is appropriate to restore fecal
continence (28). The disadvantages of defecogra-
phy are: 1) a wide range of the anorectal angle and
ARJ position among healthy individuals; and 2) a
large interobserver variation in measuring anorec-
tal morphologic parameters (19, 27).
Recently, reports have dealt with assessment of
rectal function with MR imaging (27, 58). The ad-
vantages of MR imaging over defecography are as
follows: 1) the patient avoids ionizing radiation;
2) opacification of the vagina and rectum is not
necessary because gas is an excellent contrast me-
dium; 3) the interobserver variation with MR im-
aging for the measurements of ARA and ARJ is
far less than that for defecography;
4
movements
of the posterior rectal wall at the level of the plica
of Kohlrausch can be analyzed with MR imaging
(27). However, MR imaging does not provide the
detailed, physiologic information about the pos-
terior compartment of pelvic prolapse, which is
easily seen with defecography (26). Moreover, pa-
tients have to take a prone position during MR
imaging, which cannot truly. reflect the natural
anorectal function.
In
summary defecography is a useful imaging
modality for detecting anorectal functional and
anatomic abnormalities as possible causes of def-
ecation disturbances and for anatomically guiding
anorectal surgery. The main contribution of
defecography is its specific ability to reveal rectal
intussusception and enterocele as well as sig-
moidocele. However, the wide range of morpho-
logic variations among healthy individuals and a
large interobserver variation in the measurements
prevent defecography from being an ideal examin-
ation of anorectal defecation disturbances.
1 .
2.
3.
4.
5.
6.
7.
8.
9.
10.
11 .
12.
13.
14.
15.
16.
17.
18.
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