The morphologic and dynamic examination of anorectal region
and the pelvic floor was made possible by means of defecography
more than 50 years ago, dramatically improving our knowledge of
evacuation dysfunctions. This technique was first described by Wallden
in 1953[
1]. During recent decades, interest in the study of evacuation
has grown; today it can also be performed with magnetic resonance imaging
(MRI). Nonetheless, this technique still represents a widely available
and cost-effective diagnostic tool[
2–
7].
Evacuation disorders, frequently found in elderly patients, are often
caused by morphologic and functional abnormalities that are unlikely
to be identified with static imaging techniques. Defecography evaluates
in real time the morphology of rectum and anal canal in correlation
with pelvic bony components both statically and dynamically by injection
of a thick barium paste into the rectum and its subsequent evacuation[2–5]. The most common indications are constipation, incomplete
evacuation or incontinence (often associated with rectal bleeding), mucous
discharge, and perineal pain or discomfort. The technique is also
important for follow-up of patients who have undergone surgery of the
pelvic region.
Other imaging techniques, such as double contrast barium enema, endocavitary
ultrasonography, and computed tomography (CT), are useful
for their detailed anatomic resolution, but they are not able to identify
the dynamic modifications of the anatomic structures[5,6]. Anal manometry
and electromyography provide complementary functional information[5,6]. Recently, MR defecography has been of increasing interest
because of its accuracy in morphologic and functional assessment, as
well as avoiding radiation exposure for the patient. Open configuration
MR systems are required to perform the study with the patient sitting
(providing natural conditions)[5,6]. Unfortunately, open configuration
MR systems are expensive and scarce. However, defecography can be
performed in any hospital with a fluoroscopic room; a relatively short
training time is required for the radiologist.
The purposes of this pictorial essay are to explain how to perform defecography
and to describe the main physiological and pathological findings
of anorectal region and pelvic floor. The most frequent indications
and disorders are presented from a database of more than 2,500 examinations
conducted in two radiology departments over a 15-year period.
Technique
Preparation
The patient fasts, beginning the evening before the procedure, and
performs a rectal cleaning enema at home a few hours before going to
the hospital. In the hospital, the patient receives an oral solution of
400 mL of barium solution to obtain opacification of the pelvic loops of the small bowel at the time of examination.
It is important to obtain a complete
clinical history of the patient with particular
attention to abdominal and pelvic
surgery; clinical conditions such as
diabetes, hypothyroidism, and systemic
disorders; and drug consumption.
Psychological and behavioral aspects
(e.g., hygienic education, diet, sexual
habits) are also important to consider as regards the deep relationship between
intestinal functions and the unconscious
representation of the body.
Defecography can be an embarrassing
experience for the patient, and the radiologist
must provide a clear explanation
of the procedure in order to obtain
complete collaboration. A relaxed and
cooperative patient is the sine qua non
condition to perform a correct defecography
examination.
Procedure
At the beginning of examination the
patient is positioned on the left side,
and about 300 mL of thick barium
paste is injected into the rectum by
means of a plastic syringe connected
to a catheter (Fig. 1). When the subject
reaches the stimulus to evacuate, the
anal bulb is completely filled and injection
can be interrupted.
Click to Enlarge |
Figure 1: Rectal probe attached to a 50 mL syringe filled with barium paste. The cup contains
barium solution for the preliminary opacification of ileal loops. |
Barium paste is obtained by mixing
equal proportions of potato starch and
barium solution with water. Barium
paste must have the consistency of
normal stool or a little more fluid to
permit ease of injection into the rectum.
According to our experience, we
use a galenic preparation with a viscosity
of about 800,000 centipoise (cP),
compared to physiological fecal viscosity
of >1 million cP. These characteristics
ease the injection of the barium
paste through a rectal probe without
alteration of the diagnostic results[8].
Finally, in female patients, the vagina
is opacified with a commercially available
barium sulfate paste for oral use.
The fluoroscopic table is tilted vertically,
and a special commode is attached
to the footboard with two or
three water-filled annular pillows. The
patient is then asked to sit on the commode
in right lateral projection (Fig. 2).
When the radiogenic tube is correctly
centered on the pelvis, the first radiograph
is acquired. The examination
is performed filming the dynamics of
defecation step by step with short radioscopic
sequences and radiographs.
The salient phases of defecography are:
(i) during rest with filled anal bulb, (ii)
during maximum contraction of anal
sphincters and pelvic floor muscles,
(iii) during straining without evacuation,
(iv) during evacuation, and (v)
during rest when evacuation is completed.
Click to Enlarge |
Figure 2: Fluoroscopic
table is tilted vertically
and a special commode is
attached to the footboard
with two fluid-filled ring
pillows. |
The patient must be instructed to
empty the rectum completely and without
interruption: this process takes less
than 30 seconds in physiologic conditions[9].
Parameters
The anorectal angle (ARA) is measured
between the anal canal longitudinal axis
and the posterior rectal line, parallel to
the longitudinal axis of the rectum. In
resting conditions, its average value is
95°–96° (physiological range, 65°–100°),
without noticeable differences between
men and women (Fig. 3)[9–11]. ARA is an indirect indicator of the puborectal
muscle activity. Fibers of the puborectal
muscle insert into the symphysis pubis
and form a V-shaped sling around the
posterior wall of the anorectal junction
(levator ani). At rest, the anal canal
is almost completely closed, and
the anorectal angle is about 90°; during
muscle contraction, the angle becomes
more acute, while during relaxing phase
it becomes obtuse.
Click to Enlarge |
Figure 3: a, b. Normal defecography at rest in lateral projection (a). Anorectal angle (ARA) is measured between the anal canal longitudinal axis
and the posterior rectum line parallel to the rectum longitudinal axis (a). Vaginal lumen is opacified by means of barium paste (arrow, a). Note
the ileal loops previously opacified with barium solution per os (arrowhead, a). Schematic representation (b) of the puborectal sling, rectal bulb
(RB), pubo-rectal muscle (PRM), and anal canal (AC). |
The second important parameter to
evaluate is movement of the anorectal
junction (ARJ) during straining. The
line drawn between the ischial tuberosities
is called the bis-ischiatic line and
can be used as a fixed bony landmark.
Another fixed reference point is represented
by the tip of the coccyx. The
craniocaudal migration of anorectal
junction indirectly represents the elevation
and descent of pelvic floor. The
reproducibility and reliability of these
two parameters as usually measured
have been confirmed, but their clinical
significance is still controversial[9].
Normal findings
In the resting phase, the anal canal
is almost completely closed and the
impression of puborectal sling is visible
on the posterior wall of caudal
rectum. In this condition, the angle
between the anal canal and rectum is
95°–96° (Fig. 4a).
Click to Enlarge |
Figure 4: a–d. Normal defecography phases. At rest (a). During forced contraction (b). Note the deeper impression exerted by the puborectal
sling and the cranial migration of the distal rectum, (arrow, b). During straining with closed sphincters (c), the first tract of the anal canal
widens but sphincters are contracted. Caudal migration of the anorectal junction is accompanied by initial rectilinearization of the ventral profile
of the rectum (open arrow, c). During evacuation, the anal canal opens and the angle increases (d). |
During voluntary contraction of
the pelvic floor, the anorectal angle decreases to about 75°, and the ARJ
migrates cranially. The puborectal
impression becomes more evident because
of the contraction of levator ani,
pulling the ARJ toward its insertion at
the symphysis pubis (Fig. 4b).
When the patient is asked to strain,
the converse is seen: the anorectal angle
increases with partial to complete
loss of puborectal impression, and the
pelvic floor descends (Fig. 4c). The degree
of caudal migration as measured
in relation to the bony landmarks
(bis-ischiatic line and tip of the coccyx)
is considered normal when less
than 3.5 cm relative to the resting position[12].
During evacuation, the anal canal
and the rectum migrate caudally.
The anal canal opens and the anorectal
angle increases in relation to the
relaxation of external and internal
sphincters and puborectal muscle,
respectively. Puborectalis sling impression
on the rectum posterior wall
disappears almost completely, and the
anal canal reaches the widest diameter
(Fig. 4d). During the late phases
of evacuation, the rectal bulb funnels
and its walls progressively collapse.
The entire process lasts less than 30 s
in physiologic conditions[13]. At the
end of evacuation, the resting condition
is reached when the anal sphincters
close and levator ani restores its
tone, pulling the anorectal junction
cranially. The rectum is completely empty, and only minimal barium dye
can be found.
Pathological findings
Intussusception and rectal prolapse
Rectal prolapse can be categorized
as intrarectal, rectoanal, or external,
depending on extension inside the viscus;
and as simple or complete, depending
on the involved wall layers. The
pathological condition called simple
prolapse or procidentia occurs when
the mucosal layer protrudes into the
lumen. Complete prolapse or intussusception
can be observed when all layers
of the wall are involved[13]. Clinical
manifestations frequently associated
with rectal prolapse are chronic stypsis,
rectal blockage, tenesmus, hematochezia,
and incontinence. Symptoms
are caused by the obstructive effect of
the prolapsed wall on the propulsion
of rectal contents. This condition is
frequently found in association with
solitary ulcer syndrome[14].
At the end of defecation, small infoldings
thinner than 3 mm can be frequently
observed without any clinical
significance. Larger protrusions have
been also observed in asymptomatic patients[10,12]. Intussusception usually
originates 6–8 cm above the anal canal
at the level of the main rectal fold[12].
Simple intrarectal prolapse is identified
with defecography as a wall protrusion
inside the rectal lumen more
evident during straining and evacuation (Fig. 5a). Mucosal protrusions are
almost exclusively found on the anterior
rectal wall with a thickness less than
1 cm because of their simple mucosal
composition.
Click to Enlarge |
Figure 5: a–d. Rectal prolapse. The anterior rectal wall (left arrow) protrudes into the bulb during evacuation (a). An annular groove
(arrowheads) deepens into the rectal lumen causing intussusception (b). Complete rectal intussusception with the prolapsed rectal wall passing
through the anal canal (arrowheads) and anus (open arrows) during evacuation (c, d). |
In complete prolapse, all layers of
the wall are involved. At defecography,
dilation of the anal canal is evident
during evacuation, and a circular
infolding of the rectal wall invaginates
into the lumen (Fig. 5b, c). Descent
can be so dramatic as to pass through
the anus and prolapse externally (Fig.
5d). Evacuation can be blocked by the
intrarectal prolapsed wall which creates
a plug obstructing the stool transit,
causing barium paste to stagnate
inside the viscus. During intussusception, the rectum pulls the anterior peritoneum
caudally, covering the rectum
and resulting in a deep pouch that can
contain small bowel (i.e., enterocele).
Defecographic evidence of intussusception
in a clinical setting of blocked
defecation is an indication for surgical
treatment[7].
Descending perineum syndrome
This syndrome represents a condition
of pelvic floor muscle hypotonia
and presents with difficult evacuation,
incomplete emptying of the
rectum, and/or incontinence. This
condition is usually found in elderly
women; risk factors are chronic stypsis,
neurologic dysfunction, perineal trauma, multiparity, and surgical procedures[13].
The main radiographic feature is the
caudal migration of the anorectal junction
more than 3.5 cm during straining
(Fig. 6)[9]. The degree of descent is calculated
from the resting position to the
most caudal position during straining
or evacuation in relation to the bony
landmark (bis-ischiatic line or coccygeal
tip). Similarly, the anorectal angle
is more than 130° at rest and increases
to more than 155° during straining[14–16].
Click to Enlarge |
Figure 6: a, b.
Descending
perineum
syndrome. Note
the descent of
the anorectal
junction
(asterisk)
between resting
position (a)
and during
evacuation (b).
Bis-ischiatic
line (BIL) is
considered as
the reference
level. A large
rectocele is
also evident
(arrowheads). |
Caudal migration of the anorectal
junction indirectly represents the perineal
descent caused by increased intra-
abdominal pressure during straining associated with relaxation of the
puborectalis and pelvic muscles. In
this pathological condition, muscles of
the perineum are hypotonic and overwhelmed
by the caudal migration of
abdominal organs, so that the descent
of ARJ is abnormally pronounced[12].
This repeated stretching of pelvic
floor chronically causes damage to
the nervous structures, most notably
the pudendal nerve, and determines
dysfunction of continence and pain.
Incontinence is frequently associated
with this syndrome[12]. If this process
is chronic, a vicious cycle is established
in which intense and prolonged strain
is necessary to evacuate, leading to further
stretching and weakening of the
pelvic muscles. Descending perineum
syndrome can be conservatively treated
by means of suppositories to reduce
straining during evacuation[7].
Rectocele
Rectocele is the most common cause
of obstructed evacuation treated by
surgery. It consists of an anterior bulge
of the rectal wall wider than 2 cm in
the anteroposterior diameter (7). This
condition is most commonly found
in females because of laxity of the rectovaginal
septum (congenital or caused
by obstetrical traumas or surgical procedures).
Outpouchings smaller than
2 cm are frequently found in asymptomatic
females; these outpouchings
are without clinical significance and are not considered pathological[10].
Outpouchings larger than 2 cm are significantly
associated with evacuation
disorders[17].
On defecography, an anterior outpouching
of the anterior rectal wall
bulges and dislocates the opacified
vaginal lumen during straining and
evacuation (Fig. 7). A certain degree of
radiopaque paste can be retained inside
the pouch and persists at the end
of defecation.
Click to Enlarge |
Figure 7: Rectocele bulging on the opacified vaginal lumen during
evacuation. The anterior rectal wall protrudes over the expected
position (open arrow) and the vaginal lumen is dislocated anteriorly
(arrowheads). |
There are three degrees of rectocele:
first degree is <2 cm in anteroposterior
diameter (not clinically significant);
second degree is between 2 and 4 cm;
and third degree is >4 cm. Excessive
straining may also cause posterior
bulges of the rectum because of hernias
of the levator ani on posterolateral pelvic
floor[16]. Clinical manifestations
are caused by incomplete emptying of
the rectum; some patients apply digital
rectal or vaginal maneuvers to complete
evacuation.
Dyskinetic puborectalis muscle syndrome
Also known as spastic pelvic floor
syndrome, this condition is due to an
inappropriate contraction of the puborectalis
muscle during evacuation instead
of physiologic relaxation. Most
cases are idiopathic, although focal
pathological alterations such as fistulas,
solitary ulcers, and thrombotic hemorrhoids
can be associated with this
syndrome[14].
At defecography this syndrome is
characterized by a lack of pelvic floor
descent during straining and evacuation
and paradoxical contraction of
the levator ani (Fig. 8). Another less
specific feature is an aberrantly deep
impression of the puborectalis sling on
the posterior rectal wall at rest; this is
even more evident during squeezing.
This sign is caused by the presence of
a hypertrophic levator ani muscle, but
its specificity is low; it can be also observed
in asymptomatic subjects[18].
Measurement of the anorectal angle
changes showed no significant difference
between symptomatic subjects
and asymptomatic controls and is not
a reliable parameter of this syndrome[19].
Click to Enlarge |
Figure 8: Dyskinetic puborectalis muscle syndrome. The arrow indicates
an abnormally deep puborectal impression at the beginning of the
evacuation phase. The anal canal is opening (arrowheads) and a little
rectocele is appearing (asterisk). |
Clinical manifestations are prolongation
of evacuation time and incomplete
emptying. Evacuation time
longer than 30 s is highly predictive
of dyskinetic puborectalis muscle syndrome[20].
Enteroceles and sigmoidoceles
Herniation of a peritoneal sac into
the pouch of Douglas containing
ileal loops or part of the sigmoid are
respectively called enterocele and sigmoidocele.
They are almost exclusively
found in female subjects; pelvic surgical
procedures are risk factors for this
condition, especially gynecological
procedures such as hysterectomy or
urethropexy[12]. Patients describe a sensation of pelvic oppression during
evacuation and incomplete emptying
of the rectum. These symptoms are
usually not associated with obstructed
defecation, and rectum emptying is
complete at defecography[7].
Good opacification of ileal loops is
essential for identification of intestinal
herniation into the rectovaginal space.
Descent of barium-filled ileal loops is
evident during evacuation in the space
between the rectum and vagina that
is widened (Fig. 9). Widening of this
space is also an indirect sign of enterocele
when opacification of ileal loops
is not achieved. The presence of air between
the rectum and opacified vaginal
lumen can confirm this suspicion[13].
These signs are evident during straining
or evacuation (increased abdominal
pressure). Occasionally enteroceles
become evident only when the rectum
has been completely emptied and sufficient
space is left for the small bowel
loops to herniate. Protrusion of herniated
viscera on the anterior rectal wall
frequently causes an associated rectal
prolapse[12].
Click to Enlarge |
Figure 9: a, b. Enteroceles in different patients. The recto-vaginal space is widened because of the descent of opacified intestines (a, b).
Herniated ileal loops (arrow) are opacified due to the previous oral administration of barium solution (about 2 hours before) (a). In another
case, a larger sigmoid loop (arrow) is being demonstrated after a longer period of time (b). In both cases, the anal canal and rectal bulb are
compressed (asterisks in a, b) by the herniated loops causing obstruction during defecation. |
The main limitations of defecography
are related to the conventional
technique: low-contrast resolution and
bidimensional imaging. Failed visualization
of soft tissues is partially overcome
with opacification of viscera near
the anal canal and rectum such as the
vagina and ileal loops. Another limitation is patient exposure to ionizing radiation,
although the age of subjects is
high in most cases.
During the last 15 years, MR defecography
has been described and proposed
as an alternative technique to
study the pelvic region dynamically
with high-contrast resolution and
multiplanarity and without radiation
exposure of the patient. However, MR
defecography is far less available and
more expensive than conventional
defecography. Normal MRI devices require
supine position of the patient,
and unfortunately open MRI systems
are far less available[7].
Conclusion
Defecography is a cost-effective procedure,
simple to perform and widely
available in every hospital equipped
with a fluoroscopy room. This method
has the highest accuracy in diagnosing
rectal intussusception, prolapse,
and enteroceles. The main limitation
of this technique is patient exposure to
ionizing radiation in comparison with
MR defecography, but MR defecography
has limited availability. Defecography
still represents a unique diagnostic
technique for the examination of defecation
dysfunctions.
Acknowledgement
We thank Yves Doessant for helping us in
preparing our manuscript.
Ahead of Print)
)
)
)
)
)
)
)
)