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Acta Radiologica

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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

460


3/10

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

461


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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).

462


5/10

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-

463


6/10

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 )

6


7/10

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.

465


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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

466


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DEFECOGRAPHY

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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