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Transcript
EDUCATION EXHIBIT
817
RadioGraphics
Experience of 4 Years
with Open MR Defecography: Pictorial
Review of Anorectal
Anatomy and Disease1
ONLINE-ONLY
CME
See www.rsna
.org/education
/rg_cme.html.
LEARNING
OBJECTIVES
After reading this
article and taking
the test, the reader
will be able to:
䡲 Describe the normal anatomy and
landmarks of the pelvic floor and especially the anorectal
region.
䡲 Discuss the technique and advantages
of dynamic open MR
defecography.
䡲 Identify the different pathologic conditions of the anorectal
region according to
the findings at open
MR defecography.
Justus E. Roos, MD ● Dominik Weishaupt, MD ● Simon Wildermuth, MD
Jürgen K. Willmann, MD ● Borut Marincek, MD ● Paul R. Hilfiker, MD
Functional disorders of the pelvic floor are a common clinical problem.
Diagnosis and treatment of these disorders, which frequently manifest
with nonspecific symptoms such as constipation or incontinence, remain difficult. Fluoroscopic x-ray defecography has been shown to aid
in detection of functional and morphologic abnormalities of the anorectal region. With the advent of open-configuration magnetic resonance (MR) imaging systems, MR defecography with the patient in a
vertical position became possible. MR defecography permits analysis of
the anorectal angle, the opening of the anal canal, the function of the
puborectal muscle, and the descent of the pelvic floor during defecation. Good demonstration of the rectal wall permits visualization of
intussusceptions and rectoceles. Excellent demonstration of the perirectal soft tissues allows assessment of spastic pelvic floor syndrome
and descending perineum syndrome and visualization of enteroceles.
MR defecography with an open-configuration magnet allows accurate
assessment of anorectal morphology and function in relation to surrounding structures without exposing the patient to harmful ionizing
radiation.
©
RSNA, 2002
Abbreviations: ARA ⫽ anorectal angle, ARJ ⫽ anorectal junction, PCL ⫽ pubococcygeal line
Index terms: Defecography, 757.12143, 757.12144, 757.1288 ● Rectum, 757.92 ● Rectum, abnormalities, 757.159, 757.73 ● Rectum, MR,
757.12143, 757.12144, 757.1288
RadioGraphics 2002; 22:817– 832
1From
the Institute of Diagnostic Radiology, University Hospital Zurich, Switzerland. Recipient of a Certificate of Merit award for an education exhibit at the 2000 RSNA scientific assembly. Received November 9, 2001; revision requested December 13 and received February 27, 2002; accepted
March 5. Address correspondence to P.R.H., MR Institute, Private Hospital Bethanien, Toblerstrasse 51, CH-8044 Zurich, Switzerland (e-mail:
[email protected]).
©
RSNA, 2002
RadioGraphics
818
July-August 2002
Introduction
Disorders of anorectal function represent a common clinical problem and have a significant impact on quality of life. It is estimated that between
10% and 20% of patients seeking medical care in
gastrointestinal clinics have anorectal dysfunction
(1). Diagnosis remains difficult in many cases,
and findings at physical examination are frequently equivocal. Patients often present with
nonspecific symptoms such as constipation, incontinence, or pain. Incontinence, descensus, and
organ prolapse occur in varying combinations. To
arrive at a final diagnosis, an additional imaging
modality is imperative. During the past decades,
fluoroscopic x-ray defecography, which was described in 1952 (2), played a central role in diagnosis of functional and morphologic abnormalities of the anorectal region. Defecography provides insight into rectal function and structure. In
addition, it permits assessment of the anosphincteric, puborectal, and levator muscles (3). However, the technique is limited by its projectional
nature and its inability to depict the perirectal soft
tissues. To overcome these limitations, some authors have proposed, besides rectal administration of a contrast material enema, the simultaneous administration of contrast agent into the
urethra, bladder, vagina, small intestine, or peritoneum (4 – 6).
Magnetic resonance (MR) imaging is already
used in the evaluation of anorectal disease. It has
been shown to be capable of demonstrating congenital anomalies (7), helping stage neoplasms, as
well as enabling detection of inflammatory processes (8), pelvic floor descent, rectoceles, and
intussusceptions (9,10). To date, MR imaging of
defecation has been hampered by the closed ar-
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chitecture of conventional MR systems, limiting
the patient position to the horizontal plane. With
the advent of open-configuration MR systems,
which enable image acquisition in a vertical patient position, MR defecography with the patient
in the sitting position has become possible (Fig 1)
(11). Beyond the lack of ionizing radiation—fluoroscopic x-ray defecography produces a mean
effective dose of up to 4.9 mSv (12,13)—multiplanar imaging capability, unsurpassed soft-tissue
contrast, and reasonable temporal resolution add
to the attractiveness of MR defecography.
In the literature, a considerable variation regarding the optimal method of performing MR
defecography exists. Several studies have been
performed with the patient in the supine position
in closed-magnet MR systems (14 –17); owing to
the limited availability of vertically open-configuration systems, fewer studies have been performed with the patient in the sitting position
(11,18,19). The administration of contrast agent
also varies, from use of no contrast agent to filling
of the rectum, vagina, urethra, and bladder with
contrast agent; placement of markers in the vagina or rectum; or placement of urethral catheters
(14,15,20). For MR defecography, ultrasound gel
or mashed potatoes doped with gadopentetate
dimeglumine are frequently used for rectal filling
(15,18,19,21). A similar variety among the different groups of investigators has been reported regarding the imaging plane and the maneuvers
during MR imaging (11,14,21).
In this article, we describe our experience of
over 4 years performing open MR defecography
in a clinical setting, describe the technique of MR
imaging with the patient in a sitting position, review the anatomic structures that provide rectal
function, and discuss and illustrate imaging findings in patients with anorectal dysfunctions.
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Figure 1. Technical preparation and planning of dynamic MR defecography performed
with a superconducting open-magnet system. (a) Photograph shows a superconducting
open-configuration MR system (0.5 T), which is normally used for research and interventional purposes. (b) Photograph shows a removable wooden chair, which functions as a toilet and fits exactly into the gap between the two vertical magnets. The MR signal is transmitted and received with a flexible radio-frequency coil strapped around the pelvis. (c) Photograph obtained through the side hole of the magnet shows a volunteer in the sitting position
on the wooden chair with the radio-frequency coil strapped around the pelvis. This arrangement allows a vertical (physiologic) position of the patient during imaging with the anorectal
region right in the center of the image volume. (d) Axial MR image (spoiled gradient-echo
sequence; repetition time msec/echo time msec ⫽ 150/7.7; 60° flip angle; bandwidth ⫽ 12.5
kHz; field of view ⫽ 30 ⫻ 30 cm; section thickness ⫽ 10 mm). Such images are used as localizers for planning MR defecography, which is performed in the midsagittal plane (white
line). (e) Midsagittal 15-mm-thick multiphase T1-weighted spoiled gradient-echo MR section shows a cross section of the rectal canal.
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Patients and MR
Imaging Technique
Use of open MR defecography as a standardized
clinical examination started in August 1997 at our
institution. Over 250 patients (mean age, 56
years; range, 15–90 years) have been referred for
open MR defecography. Whereas most patients in
1997 were referred by staff at our hospital (surgeons, gastroenterologists), most patients currently referred for MR defecography (61%) are
outpatients from other hospitals or are referred by
clinicians in private practice. Eighty-six percent of
the patients have been female, and 65% had undergone pelvic surgery. The clinical indications
for MR defecography were constipation (33%), a
feeling of incomplete evacuation (29%), pain
(10%), incontinence (10%), organ prolapse
(8%), and other indications (10%). In January
1998, open MR defecography completely replaced conventional fluoroscopic x-ray defecography at our institution.
MR imaging is performed with a 0.5-T superconducting, open-configuration MR system
(Signa SP; GE Medical Systems, Milwaukee,
Wis). A wooden chair, which fits into the open
space between the two magnet rings, allows imaging in the sitting position (Fig 1). Before the subject is placed on the seat, the rectum is filled with
300 mL of a contrast agent solution, which consists of a suspending agent (mashed potatoes)
doped with 1.5 mL of gadopentetate dimeglumine (377 mg/mL) (Magnevist; Schering, Berlin,
Germany). With a gadolinium concentration of
2.5 mmol/L, this regimen provides sufficient T1
shortening to permit visualization of the rectal
lumen on T1-weighted gradient-echo images. No
other particular preparation of the patients (eg,
voiding) is necessary. After contrast agent administration, the subject is placed on the seat in the
upright position. A flexible transmit/receive radiofrequency coil is strapped around the pelvis
(Fig 1).
On the basis of axial localizing images, a multiphase, 15-mm-thick, T1-weighted spoiled gradient-echo acquisition is planned, which traverses
the rectal canal in the midsagittal plane (Fig 1).
The imaging parameters are as follows: 23.9/11.3;
90° flip angle; bandwidth ⫽ 12.5 kHz; and one
signal acquired. A field of view of 32 cm and a
matrix of 256 ⫻ 128 produce an in-plane resolution of 1.25 ⫻ 2.5 mm. An image update is provided every 2 seconds. Images are obtained with
the patient at rest, at maximal sphincter contrac-
Figure 2. Drawing of defecographic landmarks and
measurements (female patient). The inferior pubococcygeal line (PCL) is defined as the line joining the inferior border of the symphysis pubis to the last coccygeal
joint. The anorectal angle (ARA) is defined as the angle
between the posterior border of the distal part of the
rectum and the central axis of the anal canal. The anorectal junction (ARJ) (black point at the intersection of
the two lines defining the ARA) is defined as the point
of taper of the distal part of the rectum as it meets the
anal canal. The wall protrusion of anterior rectoceles
(R) is determined by measurement of the depth beyond
the margin of the expected normal anterior rectal wall
(dotted line). U ⫽ uterus, UB ⫽ urinary bladder.
tion, during straining, and during defecation in
the midsagittal plane. When necessary, additional
axial or coronal gradient-echo images are obtained (eg, for imaging of intussusceptions or lateral rectoceles, respectively). Images are analyzed
on an attached workstation in the cine loop mode
and videotaped.
Normal Anatomy
The normal pelvic floor “suspension” is provided
by an interaction of bony structures, muscles, and
ligaments. Many structures such as the pelvic diaphragm, urogenital diaphragm, and endopelvic
fascia support the pelvic floor and its organs. The
anatomic complexity is furthermore underlined
by the fact that the pelvic floor—which is vertically traversed by the urethra, vagina, and rectum—must allow an opening to accommodate
excretion and parturition (22,23). Therefore, an
understanding of the relationships of the pelvic
floor organs is without a doubt crucial for accurate radiologic demonstration of pelvic floor dysfunction.
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Figure 3. Dynamic MR defecograms of a 60-year-old woman
(a, b) and a 73-year-old man
(c, d) with normal pelvic floor motion obtained at rest (a, c) and during maximal contraction of the anal
sphincter (b, d). The contrast
agent–filled rectum is clearly distinguished from the levator ani muscle
(black arrowhead), bladder (single
white arrowhead), uterus (arrow in
a), and enlarged prostate (arrow in
c). In general, no additional administration of contrast agent into the
vagina, bladder, small intestine, or
peritoneum is needed for assessment
of structures adjacent to the anorectum. The relative positions of the
pelvic floor compartments—the
bladder, vaginal vault, and rectum
(ARJ [double white arrowhead])—
are measurable (vertical lines) with
respect to the inferior PCL (horizontal line). The degree of pelvic floor
lift during maximal contraction of
the anal sphincter is well demonstrated.
The pelvic floor is divided into three compartments, which correspond to typical clinical symptoms or presentations of pathologic conditions:
the anterior compartment (lower urinary tract
symptoms, cystocele, urinary incontinence); the
middle compartment (vaginal vault or uterine
prolapse); and the posterior compartment (constipation, fecal incontinence, rectal prolapse)
(24). With MR defecography, assessment of adjacent structures and spaces is possible without the
additional application of contrast agent into the
vagina, small intestine, or peritoneum. The high
contrast resolution of soft tissue that is inherent to
MR imaging permits differentiation of surrounding structures like the prostate, vagina, bladder,
small intestine, or puborectal muscle from the
contrast agent–filled rectum (Figs 2, 3).
The dynamic process of defecography is demonstrated by using multiphase sagittal gradientecho images. Analyses during straining or defecation show an increase in the ARA, widening and
opening of the anal canal, functioning of the puborectal muscle, as well as positioning of the pelvic floor and descent of the perineum (Figs 3, 4).
In addition, the anterior and posterior rectal walls
are well depicted. The spatial resolution appears
adequate to demonstrate the relevant surrounding
morphology. The temporal resolution, with one
image update every 2 seconds, is sufficient for the
depiction of defecational dynamics.
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Figure 4. Measurement of the ARA (white lines) with dynamic fluoroscopic defecography (a– c) and open MR
defecography (d–f) with the patient at rest (a, d), during maximal contraction of the anal sphincter (b, e), and during straining (c, f). There is good correlation between the ARA measurements obtained with fluoroscopic defecography and those obtained with MR defecography. The ARA decreases during maximal contraction of the anal sphincter
and increases during straining, followed by descent of the ARJ.
The ARA is defined—in accordance with conventional defecography (25)—as the angle between two lines that intersect at the ARJ; these
lines are formed along the posterior border of the
distal part of the rectum and along the central axis
of the anal canal (23). Measurements of the ARA
based on MR and x-ray fluoroscopic images obtained with the patient at rest, during maximal
contraction of the anal sphincter, and during
straining correlate well (Figs 2, 4) (11,23,26).
Pathologic Conditions
MR defecography permits detection and characterization of various anorectal abnormalities with
a diagnostic impact often superior to that of fluoroscopic defecography (11,27). We have developed a standardized classification system for
evaluation of anorectal and pelvic floor abnormalities with dynamic MR defecography. This
classification system is slightly different from that
Grading System for Findings at Open MR
Defecography
Abnormality
Rectal descent
Bladder descent
Vaginal vault descent
Enterocele
Anterior rectocele
Small
Moderate
Large
⬍3 cm*
⬍3 cm*
⬍3 cm*
⬍3 cm*
⬍2 cm
3–6 cm*
3–6 cm*
3–6 cm*
3–6 cm*
2–4 cm
⬎6 cm*
⬎6 cm*
⬎6 cm*
⬎6 cm*
⬎4 cm
Source.—Reference 28.
Note.—Intussusceptions are classified as intrarectal,
intraanal, or extraanal (prolapse). No grading system is used for spastic pelvic floor syndrome.
*Extent below the inferior PCL.
of Comiter et al (21), who suggest a global grading and classification system for pelvic floor prolapse and dysfunction. We measure rectal descent, bladder descent, and vaginal vault descent
with respect to the inferior PCL and grade the
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Figure 5. Enterocele and rectal prolapse in a 30-year-old mentally handicapped man with
incontinence. (a, b) MR defecograms obtained at the beginning of defecation show rectal
prolapse (arrowhead). (c, d) MR defecograms obtained during defecation show a huge enterocele that protrudes downward. The enterocele consists of sigmoid colon (arrow), omental and mesenteric fat, and small intestine (arrowheads).
abnormalities at our institution as small, moderate, and large on the basis of specific, defined
measurements (Table) (28). The PCL is defined
as the line joining the inferior border of the symphysis pubis to the last coccygeal joint (Figs 2, 3).
In the following paragraphs, we describe various pathologic conditions depicted with MR defecography performed with an open-configuration, superconducting magnet system.
Enterocele
An enterocele is a herniation of a peritoneal sac
downward and along the ventral rectal wall into
the cul-de-sac or pouch of Douglas. At fluoro-
scopic defecography, separation of the opacified
vagina and the upper rectum during straining or
defecation suggests an enterocele (4,25). This
enlarged rectogenital fossa may contain small intestine, omental fat, or sigmoid colon; it is difficult to distinguish these contents from each other
with conventional defecography without additional opacification of the intestine or intraperitoneal cavity. In contrast, MR defecography plays a
useful role in detection and characterization of
enteroceles (Fig 5). Most enteroceles lie posterior
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Figure 6. Enterocele in a 23-year-old man with chronic constipation
and rectal prolapse for 3 years. (a) MR defecogram obtained with the patient at rest shows normal muscular function of the pelvic floor. (b) MR
defecogram obtained during early defecation shows the clinically known
rectal prolapse (single arrowheads) and a small rectocele (double arrowhead). (c) MR defecogram obtained during the middle and end of defecation shows simultaneous voiding and formation of a moderate enterocele
extending to the pelvic floor (arrow). (d) MR defecogram obtained after
defecation shows spontaneous repositioning of the enterocele and rectal
prolapse.
in the superior portion of the rectovaginal or rectovesical space (Fig 6).
After surgery in the pelvic region, an undetected enterocele may result in progressive symptoms and the need for repeat surgery (Fig 7) (29).
The range of symptoms is usually very broad; for
example, the enterocele may follow the sacral
curve and result in compression of the distal part
of the anorectum. These patients frequently experience incomplete evacuation due to the resulting
outlet obstruction.
Rectocele
A rectocele is a bulge of varying size of the anterior wall of the rectum or less frequently the posterior or lateral wall due to inadequate support
and laxity of the endopelvic fascia above the anal
canal. Rectoceles are more frequently found in
women, usually as a result of obstetric injury. Different approaches to quantifying the extent of rectoceles have been described. For an anterior rectocele, we measure the depth of wall protrusion
beyond the expected margin of the normal anterior rectal wall (Figs 2, 8). Other authors draw the
reference line upward through the anterior wall of
the anal canal (9,15). At our institution, the extent of the rectocele is reported to the clinicians
according to our grading system (Table). Rectoceles smaller than 2 cm are frequently found in
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Figure 7. Enterocele in a 60-year-old woman 2 years after perimenopausal hysterectomy and ampullopexy.
(a) MR defecogram obtained with the patient at rest shows an enterocele (arrow) that protrudes toward the anterior
compartment and bulges into the vagina. The ARA is pathologic (150°). (b) MR defecogram obtained during
squeezing shows that the ARA is almost normalized (106°) and the enterocele is repositioned. (c) MR defecogram
obtained during defecation shows the enterocele (arrow) protruding clearly distal to the PCL; the enterocele consists
mainly of fat. In addition, a small anterior rectocele is evident (arrowhead).
Figure 8. Anterior rectocele in a 50year-old woman. The rectocele was diagnosed at physical examination. (a) MR
defecogram obtained with the patient at
rest shows a moderate rectocele. (b) MR
defecogram obtained during straining and
defecation shows that the rectocele (arrow)
enlarges and becomes severe. Dotted
line ⫽ expected normal rectal wall. (c) MR
defecogram shows the patient evacuating
the rectocele by pressing on the posterior
vaginal wall with her fingers (arrowhead).
This case includes all of the clinically significant criteria for a rectocele: size larger
than 2 cm, retention of contrast medium,
reproducibility of the symptoms, and need
for evacuatory assistance.
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Figure 9. Intussusception in a 54-year-old man with painful defecation. (a) MR defecogram obtained during middefecation shows a mural intussusception (arrow) protruding into
the anal canal and a small rectocele (arrowhead). (b) Axial localizing MR image obtained
after defecation shows the invagination, which is reproducible with maximal pressure and
appears as a double lumen (arrow).
Figure 10. Intussusception and anterior rectocele in a 35-year-old woman
with pain and perineal discomfort after defecation. (a) MR defecogram obtained during straining and the start of defecation. (b) MR defecogram obtained during defecation shows a circumferential mural intussusception (arrowheads) that extends into the rectal ampulla. An anterior rectocele is also
evident (arrow).
asymptomatic individuals (30). The clinical significance of a rectocele depends on fulfillment of
the following criteria: size exceeding 2 cm, retention of contrast media, reproducibility of the
symptoms, and need for evacuatory assistance
(eg, digital pressure on the posterior vaginal wall
for complete defecation) (Figs 8 –10) (31). MR
defecography provides objective information
about the size of the rectocele, the dynamics of its
emptying, and coexistent enteroceles or sigmoidoceles, many of which are missed at physical
examination.
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Figure 11. Intussusception and mucosal prolapse in an 18-year-old patient with clinical findings of rectal hemorrhoids. (a) MR defecogram obtained with the patient at rest shows that the perineum bulges downward. However, its
position normalized during maximal contraction of the anal sphincter. (b) MR defecogram obtained during midevacuation shows that the anorectal mucosa protrudes downward (arrow) to the anal canal and comes to rest right in
the anal canal. (c) MR defecogram shows that the muscular part of the rectum does not shift. Therefore, this case
represents an exquisite mucosal intraanal intussusception or so-called mucosal anal prolapse.
Figure 12. Rectal prolapse and sigmoidocele in a 50-year-old man. (a) MR defecogram obtained with the patient
at rest shows no abnormalities. (b, c) Dynamic MR defecograms obtained during straining show rectal prolapse (arrows) as well as a sigmoidocele (arrowhead).
Intussusception
and Rectal Prolapse
Invaginations of the rectal wall that descend toward the anal canal are called rectal intussusceptions. The involved rectal wall differs in thickness,
and the invagination includes mucosal or mural
components. The location can be anterior or posterior or even affect the rectum circumferentially.
The intussusception may remain internal (intrarectal) (Fig 10), extend into the anal canal (in-
traanal) (Fig 9), or even pass the anal sphincter,
resulting in an external rectal prolapse (extrarectal or extraanal) (Fig 11). Therefore, the widely
used clinical term rectal prolapse corresponds anatomically to an extrarectal intussusception (Figs
5, 6). With descent of the rectal wall, an opening
pouch anterior to the rectum is formed, which
can contain an additional enterocele (Figs 5, 12).
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Figure 13. Descending pelvic floor syndrome with an enterocele and anterior rectocele in
a 56-year-old multiparous woman with diffuse perineal pressure and pain after hysterectomy.
There was no incontinence, but the patient had a sensation of incomplete defecation. (a) MR
defecogram obtained with the patient at rest shows obvious bulging of the whole peritoneum
under the PCL (white line). (b) MR defecogram obtained during maximal contraction of the
anal sphincter shows reduced raising of the pelvic floor, thus confirming the presence of pelvic floor weakness. (c) MR defecogram obtained during defecation shows protrusion of a
large enterocele into the extended, convex perineum (arrow) as well as an anterior rectocele
(arrowhead). (d) MR defecogram obtained after defecation shows that the rectocele and the
main part of the enterocele are unchanged.
Similarly to rectoceles, invagination of parts of
the rectal wall into the ARJ (intrarectal) is a relatively common finding in asymptomatic patients
(30). If the intussusception reaches the anal canal
(intraanal), patients may experience incomplete
defecation due to severe outlet obstruction. Most
patients with external rectal prolapse (extraanal)
have associated incontinence (Fig 5).
Descending Perineal Syndrome
In the descending perineal syndrome, the muscle
tone of the pelvic floor is pathologically decreased
mainly due to pudendal nerve damage. However,
the relation of this syndrome to age, gender, incontinence, or constipation is not absolutely convincing. The diagnosis is based on the results of
clinical examination, electrophysiologic tests, and
imaging. Although pelvic floor descent can occur
at rest, it typically occurs during straining or defecation. Typically, bulging of the whole perineum
is seen (Fig 13). It may involve only one compartment or all three compartments (Figs 14, 15).
There are many grading systems in the literature.
Along with others, we prefer to measure descent
of the rectum, bladder, and vaginal vault as the
main structures of the three compartments with
respect to the inferior PCL (28). Open MR defecography is a straightforward and reproducible
method of grading cases as small, moderate, and
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Figure 14. Descending pelvic floor syndrome in a 45-year-old multiparous woman with incomplete defecation after hysterectomy and rectopexy. (a) MR defecogram obtained with the patient at rest shows a bulging perineum. A
cystocele is also evident (arrow). (b) MR defecogram obtained during maximal contraction of the anal sphincter
shows insufficient pelvic lift. Because of the combination of these three findings, this case meets the criteria for general pelvic floor insufficiency (all three compartments). (c) MR defecogram obtained after several defecation maneuvers shows incomplete stool evacuation along with a small rectocele (arrowhead).
Figure 15. Pelvic floor insufficiency in a 19-year-old woman with rectal
prolapse during defecation 2 years after a traumatic vaginal delivery. No
incontinence or feeling of incomplete defecation was present. (a) MR defecogram obtained with the patient at rest shows normal positioning of the
anterior and middle pelvic compartments. The posterior compartment
was clearly lowered under the PCL. A small anterior rectocele is also evident (arrow). (b) MR defecogram obtained during maximal contraction
of the anal sphincter shows normal muscular function of the puborectal
sling. (c) MR defecogram obtained during defecation shows a rectocele
(arrow) and lowering of the anterior and middle compartments with simultaneous voiding. Anorectal prolapse (arrowheads) has become evident
under maximal intraabdominal pressure. (d) MR defecogram obtained
after defecation shows spontaneous repositioning of the rectal prolapse,
but the rectocele remains partially filled with contrast agent.
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Figure 16. Spastic pelvic floor syndrome in a 51-year-old woman with
absence of voluntary rectal emptying and a need for daily digital disimpaction after hysterectomy. (a) MR defecogram obtained with the patient at
rest shows normal findings. (b, c) MR defecograms obtained during
straining and attempted defecation show paradoxical contraction of the
puborectal sling (arrowhead). (d) MR defecogram obtained after several
attempts at defecation shows an anterior rectocele below the contracted
part of the puborectal muscle (arrowhead). No stool evacuation is observed. The diagnosis was confirmed with electromyography.
large (Table). In cases of descending perineal syndrome, decreased raising of the pelvic floor at
maximal contraction is usually observed (Figs 13,
14). The syndrome is often associated with perineal discomfort and pain and a feeling of incomplete evacuation, leading to increased straining
during defecation. The latter represents an additional neuropathic injury of the external anal
sphincter, resulting in incontinence.
Spastic Pelvic Floor Syndrome
Usually, when an individual is at rest, the puborectal muscle constantly pulls the rectum anteriorly to maintain the ARA and as a result to maintain the continence. With spastic pelvic floor
syndrome, no physiologic relaxation of the puborectal muscle during defecation is observed; in
contrast, the muscle becomes hypertonic during
different phases of defecation (Fig 16). Patients
experience constipation and incomplete defecation. Anorectal manometry reveals increased
pressure at rest and during defecation, and electromyography shows pathologic signals. With dynamic MR defecography, the lack of lowering of
the pelvic floor and the paradoxical contraction of
the frequently hypertrophic puborectal muscle
during straining and defecation are easily documented (Fig 17).
Conclusions
Functional disorders of the pelvic floor represent
a common clinical problem. Diagnosis and treatment of these disorders, which frequently manifest with nonspecific symptoms such as constipation or incontinence, remain difficult. Incontinence, descensus, and organ prolapse occur in
varying combinations. MR defecography with an
open-configuration magnet allows accurate assessment of anorectal morphology and function in
relation to surrounding structures without exposing the patient to harmful ionizing radiation.
Multiphase sagittal gradient-echo imaging allows
complete assessment of the anal canal; the posi-
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Figure 17. Spastic pelvic floor syndrome in a 31-year-old patient with a feeling of incomplete defecation. (a, b) MR
defecograms obtained with the patient at rest (a) and during maximal contraction of the anal sphincter (b) show a
hypertrophic puborectal muscle (arrow). (c) MR defecogram obtained during straining shows paradoxical contraction of the puborectal muscle. Instead of the pelvic floor being lowered and the ARA increasing, the pelvic floor is
lifted slightly and the ARA is unchanged. The diagnosis was confirmed with electromyography and manometry.
tions of the ARJ, vaginal vault, and bladder base;
and the function of the puborectal muscle. Open
MR defecography with the patient in the sitting
position has completely replaced conventional
defecography at our institution; the number of
MR defecography examinations performed has
increased substantially since 1997, and this imaging modality is widely accepted by clinicians and
patients.
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This article meets the criteria for 1.0 credit hour in category 1 of the AMA Physician’s Recognition Award. To obtain
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