DOI:10.2214/AJR.07.2920
AJR 2008; 190:671-682
© American Roentgen Ray Society
Cross-Sectional Imaging of the Anal Sphincter in Fecal Incontinence
Annette C. Dobben1,
Richelle J. F. Felt-Bersma2,
Fiebo J. W. ten Kate3 and
Jaap Stoker1
1 Department of Radiology, Academic Medical Center, G1-228, Meibergdreef 9, 1105
AZ, Amsterdam, The Netherlands.
2 Department of Gastroenterology, Free University Medical Centre, Amsterdam, The
Netherlands.
3 Department of Pathology, Academic Medical Center, Amsterdam, The
Netherlands.
Received January 12, 2007;
accepted after revision September 11, 2007.
Address correspondence to A. C. Dobben
(ac.bruijne{at}igz.nl).
CME
This article is available for CME credit. See
www.arrs.org
for more information.
Abstract
OBJECTIVE.Fecal incontinence is a disabling disorder.
Cross-sectional imaging techniques can be used to confirm the diagnosis and to
clarify the anatomy and function of the anorectal region.
CONCLUSION.Cross-sectional imaging has increased the understanding
of the sphincter complex, resulting in a more adequate evaluation of fecal
incontinence.
Keywords: 3D sonography • anal sphincter • endoanal MRI • endoanal sonography • external phased-array MRI • fecal incontinence
Introduction
Fecal incontinence is a complex problem of diverse causes
[1]. Childbirth and anorectal
surgery are the main causes because the external anal sphincter and the
pudendal nerve may be damaged.
A systematic evaluation of the patient should reveal the underlying
pathophysiology and lead to appropriate therapy
[2]. With digital rectal
examination the presence or absence of an external anal sphincter defect can
be assessed, and resting and squeeze pressure can be determined qualitatively.
Anorectal physiology tests give insight into the functional aspects of the
anorectal region. Imaging with an endocoil results in images with high
contrast resolution (sonography)
[3] or high spatial resolution
(MRI) [4]. Consequently, the
anatomy and pathology of the anal sphincter muscles can be visualized in
detail. We show the important findings (defects, scarring, and atrophy) at
endoanal sonography, 3D endoanal sonography, endo-anal MRI, and external
phased-array MRI.
Imaging Techniques
Endoanal Sonography
Several types of sonographic probes have been developed. Rigid radial
probes that are suitable for the anal sphincter with a 360° view are
preferable because they do not limit the field of view. The endoscopic radial
scanner (7.5–12 MHz) is flexible. Linear and curved array probes do have
a limited field of view. The imaging time is approximately 10 minutes (room
time).
Three-Dimensional Endoanal Sonography
For 3D endoanal sonography, we use a system with a 5–16-MHz rotating
endoscopic probe. The external diameter is 17 mm. After performance, the
images must be reconstructed to 3D images using computer software (Life
Imaging system 2000, L3Di, version 3.5.5, Bruel & Kjaer Medical),
resulting in the ability to view the images from every possible angle. In
addition, length and subsequent volume measurements can be obtained.
Endoanal MRI
Some differences exist in the design and diameter of endoluminal coils
[5]; we use a phased-array
endoluminal coil. A large-diameter coil (e.g., 17 mm) is recommended because
it will result in a more uniform signal intensity of the anal sphincters.
The optimal imaging protocol for endoluminal MRI is not established. We use
T2-weighted fast spin-echo sequences (at 1.5 T; TR range/TE range,
2,500–3,500/70–90; echo-train length, 10; field of view, 10
x 10 cm [axial] and 16 x 16 cm [coronal]; imaging matrix, 256
x 512; 3-mm slice thickness; 0.3 mm interslice gap; and 2 excitations).
Axial and coronal images are obtained perpendicular and parallel to the anal
sphincter to reduce partial volume effects. Although one can expect that image
quality on 3 T might be improved, at present no articles in the literature
support this. The imaging time is approximately 30 minutes (room time).
External Phased-Array MRI
External phased-array MRI provides detailed imaging of the anal sphincter
and lower pelvic region without the use of an endoluminal coil. Standard
external phased-array coils can be used, with a scanning protocol comparable
to the endoanal protocol, except for adjustments to increase the local
signal-to-noise ratio (e.g., increasing the field of view). The imaging time
is approximately 20 minutes (room time).
Anatomy of the Anal Sphincter
The anal sphincter is composed of several cylindric layers
[6]. The innermost layer is the
subepithelium. The next layer is the cylindric internal anal sphincter (Figs.
1 and
2), which is relatively
hyperintense on MRI. The hypointense fibroelastic longitudinal muscle courses
through the fat-containing inter-sphincteric space
(Fig. 1). The outermost layer
is composed of relative hypointense striated muscle with the external anal
sphincter inferiorly (Figs. 1
and 3) and the puborectal
muscle superiorly (Fig. 4). The
puborectal muscle is part of the levator ani muscle, which also includes the
levator plate (Figs. 5 and
6).
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Fig. 1 —Transverse endoanal T2-weighted fast spin-echo (TR/TE,
2,500/70) MR image at midanal canal shows normal anatomy in 52-year-old man.
Longitudinal muscle (LM) is clearly shown as relatively hypointense layer in
intersphincteric space (ISS) between internal (IS) and external (ES) anal
sphincters. IAS = ischioanal space, CC = corpus cavernosum, CS = corpus
spongiosum, ICM = ischiocavernosum muscle, TPM = transverse perineal muscle,
BS = bulbospongiosus.
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Fig. 2 —Transverse T2-weighted fast spin-echo (TR/TE, 2,500/70)
external phased-array MR image in 56-year-old woman shows internal anal
sphincter (IS) as homogeneously isointense to hypointense circular band
surrounding anal canal. Difference of internal anal sphincter signal intensity
with external phased-array coil is most likely related to higher spatial
resolution of endoanal examination. ES = external anal sphincter, TPM =
transverse perineal muscle, IAS = ischioanal space.
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Fig. 3 —Transverse T2-weighted fast spin-echo (TR/TE, 2,500/70)
external phased-array MR image shows lower part of normal external anal
sphincter (ES) at distal anal canal in same 56-year-old woman as in
Figure 2. External anal
sphincter is less detailed on external phased-array MRI than on endoanal MRI
but can be readily identified. TPM = transverse perineal muscle, IAS =
ischioanal space, GM = gluteus muscle.
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Fig. 4 —Transverse endoanal T2-weighted fast spin-echo (TR/TE,
2,500/70) MR image at proximal anal canal in 68-year-old woman shows normal
puborectal muscle (PM). Puborectal muscle is relatively hypointense, slinglike
muscle. IAS = ischioanal space, V = vagina, U = urethra.
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Fig. 5 —Coronal endoanal T2-weighted fast spin-echo (TR/TE, 2,500/70)
MR image through anal canal shows normal anatomy of sphincter complex in
52-year-old man with relatively hypointense external anal sphincter (ES),
puborectal muscle (PM), and levator ani muscle (LAM) and relatively
hyperintense internal anal sphincter (IS). IAS = ischioanal space, LM =
longitudinal muscle, ISS = intersphincteric space.
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Fig. 6 —Coronal T2-weighted fast spin-echo (TR/TE, 2,500/70) external
phased-array MR image through anal canal obtained from same 56-year-old woman
as Figures 2 and
3 shows normal anatomy of
sphincter complex. It is difficult to make a reliable differentiation between
longitudinal muscle (LM) and external anal sphincter (ES) muscle because both
are hypointense. Internal anal sphincter (IS) is isointense to hypointense.
IAS = ischioanal space, PM = puborectal muscle, LAM = levator ani muscle.
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On endoanal sonography, the internal anal sphincter appears as a
well-defined, hypoechoic ring, usually symmetric in thickness
[3] (Figs.
7 and
8). The longitudinal muscle is
superiorly hypoechoic but more echoic in the lower canal (Figs.
7 and
8). The external anal sphincter
muscle is a ringlike structure of mixed echogenicity (Figs.
7 and
8). The puborectal muscle
appears as a sling.
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Fig. 7 —Transverse endoanal sonogram at midanal canal in 65-year-old
man shows normal anatomy at midanal canal of internal anal sphincter (IS),
longitudinal muscle (LM), and external anal sphincter (ES). Top of figure is
anterior.
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Fig. 8 —Three-dimensional endoanal sonogram, lateral view, from just
below midanal canal to above puborectal muscle in 60-year-old man shows normal
anatomy of four-layer structure of sphincter complex. Top of figure is
anterior. SE = subepithelial tissues, IS = internal anal sphincter, LM =
longitudinal muscle, ES = external anal sphincter.
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Anal Sphincter Complex Pathology
Anal Sphincter Defects and Scar Tissue
An anal sphincter defect commonly is defined as a discontinuity of the
muscle ring (anatomic defect) or is recognized by a hypo-intense deformation
(on MRI) or hypoechogenicity (on endoanal sonography) of the normal pattern of
the muscle layer due to replacement of muscle cells by fibrous tissue
(functional defect, scar tissue)
[3,
7]. With MRI, it is possible to
distinguish an anal sphincter defect from scarring
(Fig. 9). Although there are
differences in diagnosing a defect from scar tissue, the clinical consequences
do not differ.
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Fig. 9 —Transverse endoanal T2-weighted fast spin-echo (TR/TE,
2,500/70) MR image before surgery at midanal canal in 31-year-old woman after
complicated vaginal delivery (breech delivery and rupture) shows defect
(thin white arrows) from 10- to 2-o'clock positions and scar tissue
(arrowheads) anterior to external anal sphincter (ES). Note
discontinuity of sphincter ring, low signal intensity, and disordered
architecture. Also, anterior internal anal sphincter (IS) defect is depicted
(black arrows) from 9- to 4-o'clock positions, identifiable by
discontinuity of anterior part of internal anal sphincter.
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Preoperative evaluation—A recent study in 36 patients
[8] showed that both endoanal
sonography and endoanal MRI can be considered comparable for depicting
external anal sphincter defects, and therefore either technique is useful in
the selection of patients as candidates for surgery (Fig.
10A,
10B). The advantages of
endoanal sonography are its availability and limited costs. Furthermore,
endoanal sonography has been used for a longer time than MRI, resulting in
more radiologists who are experienced with the endoanal sonography technique
[9]. The advantage of 3D
endoanal sonography is the ease of viewing at different angles. The depiction
of sphincter defects is equal to that on conventional endo anal sonography
(Fig. 11), but longitudinal
sphincter measurements can be obtained with 3D endoanal sonography. In
contrast to (3D) endoanal sonography, endoanal MRI may allow clear
visualization of the external anal sphincter because of the large contrast
difference between the external anal sphincter and surrounding fat. External
phased-array MRI provides imaging of the anal sphincters without the use of an
endocoil. External phased-array MRI is more readily available than endoanal
MRI, which is primarily used at specialized centers when a dedicated device is
necessary. External phased-array MRI has been shown to be comparable to
endoanal MRI in the depiction of clinically relevant anal sphincter defects
[4] (Fig.
12A,
12B), provided sufficient
experience is available.
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Fig. 10A —53-year-old woman after complicated vaginal delivery
(rupture). ES = external anal sphincter, IS = internal anal sphincter.
Transverse endoanal sonogram at midanal canal shows external (area of
amorphous texture; thin arrows) and internal (discontinuity of
sphincter ring; arrowheads) anal sphincter defects from 10- to
2-o'clock positions. Compare anterior part with
Figure 7. Top of figure is
anterior.
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Fig. 10B —53-year-old woman after complicated vaginal delivery
(rupture). ES = external anal sphincter, IS = internal anal sphincter.
Transverse endoanal T2-weighted fast spin-echo (TR/TE, 2,500/70) MR image
shows defect of anterior external anal sphincter (arrowheads) and
internal anal sphincter (thin arrows) from 11- to 1-o'clock positions
by discontinuity of outer and inner sphincter rings. High intrinsic contrast
resolution makes delineation of external anal sphincter boundaries clearly
visible. Because of severe fecal incontinence, patient underwent surgery. IAS
= ischioanal space, VI = vaginal introitus.
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Fig. 11 —Three-dimensional endoanal sonogram at midanal canal of
37-year-old woman shows large obstetric tear involving both internal anal
sphincter (open arrows, IS) from 10- to 5-o'clock positions and
external anal sphincter (arrowheads, ES) from 10- to 3-o'clock
positions after complicated vaginal delivery. Tears are visualized by
discontinuity of inner and outer sphincter rings. Scar tissue (solid thin
arrows) of external anal sphincter is depicted anteriorly by segments of
hypoechogenicity. Top of figure is anterior.
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Fig. 12A —42-year-old woman with fecal incontinence after complicated
vaginal delivery (long labor, assisted delivery, rupture). IS = lower part of
internal anal sphincter, TPM = transverse perineal muscle, IAS = ischioanal
space. In transverse T2-weighted fast spin-echo (TR/TE, 2,500/70) external
phased-array MR image, compare structure of scar tissue (black
arrows) with that in B. Note that scar tissue of external anal
sphincter (ES) is more hypointense, with distorted and asymmetric architecture
on endoanal MRI. GM = gluteus muscle.
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Fig. 12B —42-year-old woman with fecal incontinence after complicated
vaginal delivery (long labor, assisted delivery, rupture). IS = lower part of
internal anal sphincter, TPM = transverse perineal muscle, IAS = ischioanal
space. Transverse endoanal T2-weighted fast spin-echo (2,500/70) MR image on
same level as A shows scar tissue of external anal sphincter (ES) from
1- to 2-o'clock positions (black arrows).
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Postoperative evaluation—For postoperative assessment, the
role of imaging has not been thoroughly investigated. A recent pilot study
concerning the role of endoluminal imaging in the clinical outcome of anal
sphincter repair [10] showed
that endoanal sonography can reveal relevant residual sphincter defects
despite the difficult visualization of sphincter overlap
(Fig. 13A). Although endoanal
MRI can clearly depict sphincter overlapping
(Fig. 13B), the authors found
that the depiction of residual external anal sphincter defects on MRI was
insufficient. MRI showed that baseline measurement of preserved external anal
sphincter thickness correlated with a better outcome.
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Fig. 13A —53-year-old woman after complicated vaginal delivery
(rupture) (same patient as in Fig.
10A,
10B). ES = external anal
sphincter, IS = internal anal sphincter. Transverse endoanal sonogram obtained
after anterior anal sphincter repair shows sphincter overlap (thin
arrows) at midanal canal. Overlap of anal sphincter ends is difficult to
visualize because of low soft-tissue contrast resolution. Area with scar
tissue (arrowheads) is depicted. Surgery failed for this patient, who
still has fecal incontinence. Top of figure is anterior.
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Fig. 13B —53-year-old woman after complicated vaginal delivery
(rupture) (same patient as in Fig.
10A,
10B). ES = external anal
sphincter, IS = internal anal sphincter. Transverse endoanal T2-weighted fast
spin-echo (TR/TE, 2,500/70) MR image after anterior anal sphincter repair
shows clear overlap of both external anal sphincter ends, left over right
(small arrows). Although appearances on endoluminal imaging after
anterior anal sphincter repair show overlap of both sphincter ends, surgery
failed for this patient. IAS = ischioanal space, VI = vaginal introitus.
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Even though internal anal sphincter disorders are adequately depicted on
either endo-anal sonography or endoanal MRI, still no consensus exists about
the preferred technique [9,
11].
Puborectal muscle lesions (Fig.
14) are relatively uncommon and are generally seen in patients
with substantial pelvic floor trauma in combination with internal or external
anal sphincter lesions.
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Fig. 14 —Transverse endoanal T2-weighted fast spin-echo (TR/TE,
2,500/70) MR image obtained in 66-year-old woman with fecal incontinence after
complicated vaginal delivery (high birth weight, long labor, episiotomy) 43
years earlier shows defect of puborectal muscle (PM) from 8- to 11-o'clock
positions (arrowhead; compare with normal left side). IAS =
ischioanal space, IS = internal anal sphincter, LM = longitudinal muscle, V =
vagina, U = urethra.
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Anal Sphincter Atrophy
Atrophy of the external anal sphincter is characterized by severe thinning
of the muscle fibers or replacement of muscle fibers by fat
[7]. Microscopic investigation
confirms findings of external anal sphincter atrophy. Histologically, the
external anal sphincter is considered to be atrophied when striated muscle
tissue' exhibits diminished volume in association with replacement by fatty
tissue [12] (Figs.
15 and
16A,
16B,
16C,
16D).
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Fig. 16A —61-year-old woman with fecal incontinence who had complicated
vaginal delivery (breech delivery, heavy child, rupture) 35 years earlier.
Photomicrograph of specimen from anus wall biopsy of moderate atrophic
external anal sphincter muscle composed of striated muscle (arrow)
with replacement by fat tissue (arrowhead). (H and E, x16)
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Fig. 16B —61-year-old woman with fecal incontinence who had complicated
vaginal delivery (breech delivery, heavy child, rupture) 35 years earlier.
Transverse endoanal T2-weighted fast spin-echo (TR/TE, 2,500/70) MR image
shows moderate generalized atrophy of external anal sphincter (thin white
arrow). In addition, note internal anal sphincter (IS) defect (black
arrows) from 9- to 2-o'clock positions and scar tissue of external anal
sphincter (ES) from 10- to 1-o'clock positions (arrowheads). IAS =
ischioanal space.
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Fig. 16C —61-year-old woman with fecal incontinence who had complicated
vaginal delivery (breech delivery, heavy child, rupture) 35 years earlier.
Photomicrograph of specimen from anus wall biopsy of anal sphincter muscle
shows closer, more detailed view of atrophy of external anal sphincter, shown
by striated muscle (arrow) that is characterized by fingerprint
structure. Replacement of muscle by fat tissue (arrowhead) is seen. C
= connective tissue. (Immunostain with antibodies against desmin,
x80)
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Fig. 16D —61-year-old woman with fecal incontinence who had complicated
vaginal delivery (breech delivery, heavy child, rupture) 35 years earlier.
Photomicrograph of specimen from anus wall biopsy of internal anal sphincter
shows mild atrophy. Smooth muscle (arrow) is surrounded by connective
tissue (C); replacement of muscle by fat tissue (arrowhead) is also
seen. (Immunostain with antibodies against smooth muscle antigen,
x16)
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Endoanal MRI can accurately depict atrophy of the external anal sphincter
(Figs. 17A,
17B and
18) and can differentiate
between moderate (< 50% thinning or fat replacement) and severe (
50%
thinning or fat replacement) atrophy
[13].
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Fig. 17A —Atrophy of external anal sphincter. IAS = ischioanal space.
Transverse endoanal T2-weighted fast spin-echo (TR/TE, 2,500/70) MR image
shows severe thinning of external anal sphincter (ES) and diffuse replacement
by fat (compare with B) in 46-year-old man with fecal incontinence
resulting from neurologic spinal disorder. At this level, anterior inferior
edge of internal anal sphincter (IS) is just visible.
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Fig. 17B —Atrophy of external anal sphincter. IAS = ischioanal space.
Transverse endoanal T2-weighted fast spin-echo (2,500/70) MR image at midanal
canal shows normal anatomy of 35-year-old-woman. External anal sphincter (ES)
is outer part of sphincter ring at this level and is relatively hypointense;
inner part of sphincter ring constitutes internal anal sphincter (IS) and is
shown as relatively hyperintense. V = vaginal introitus with bulbospongiosus
muscle.
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Fig. 18 —Coronal endoanal T2-weighted fast spin-echo (TR/TE, 2,500/70)
MR image obtained in same 46-year-old man with fecal incontinence as in
Figure 17A shows severe
thinning of external anal sphincter (ES), puborectal muscle (PM), and levator
ani muscle (LAM) (compare with Fig.
4). IS = internal anal sphincter.
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External phased-array MRI has been shown to be comparable to endoanal MRI
in the depiction of sphincter atrophy
[13] (Fig.
19A,
19B), provided that sufficient
experience in assessing the phased-array images is available. This is because
the anal sphincters are easier to show on endoanal MRI due to the high spatial
resolution.
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Fig. 19A —69-year-old woman with fecal incontinence and no risk factors
in her past for pudendal nerve damage. Transverse (A) and coronal
(B) T2-weighted fast spin-echo (TR/TE, 2,500/70) external phased-array
MR images show severe thinning of external anal sphincter (ES) and diffuse
replacement by fat. IS = internal anal sphincter, IAS = ischioanal space, PM =
puborectal muscle, LAM = levator ani muscle, GM = gluteus muscle.
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Fig. 19B —69-year-old woman with fecal incontinence and no risk factors
in her past for pudendal nerve damage. Transverse (A) and coronal
(B) T2-weighted fast spin-echo (TR/TE, 2,500/70) external phased-array
MR images show severe thinning of external anal sphincter (ES) and diffuse
replacement by fat. IS = internal anal sphincter, IAS = ischioanal space, PM =
puborectal muscle, LAM = levator ani muscle, GM = gluteus muscle.
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Generalized thinning of the internal sphincter (thinner than 2 mm)
represents internal sphincter atrophy on both endoanal sonography and endoanal
MRI.
The depiction of sphincter atrophy with 3D endoanal sonography has not been
thoroughly evaluated (Fig.
20). Measurements with 3D endoanal sonography studies in young
control subjects concerning thicknesses of various layers have been compared
with endoanal MRI to determine equivalent-depth axial images. Good
intraobserver and interobserver correlation has been shown
[3]. In a recent study of 18
patients, 3D endoanal sonography and endoanal MRI showed no difference in the
assessment of external anal sphincter atrophy, but there was a substantial
difference in grading [14].
Another study of 18 patients with fecal incontinence showed that volume
measurements have been disappointing and that the reproducibility of volume
measurements is moderate
[15].
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Fig. 20 —Three-dimensional endoanal sonography at midanal canal in
65-year-old woman shows moderate atrophy of external anal sphincter (ES) after
history of constipation and fecal incontinence. Compare anterior and posterior
double arrows. Some atrophy at internal anal sphincter (arrowhead,
IS) is also depicted. Top of figure is anterior.
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Pitfalls
A normal external anal sphincter can be misinterpreted on endoanal MRI as a
defect when viewing the edges of the sphincter axially. The sphincter ring
seems not to be continuous (Figs.
21 and
22), but normal anatomy can be
recognized from structured muscle layers without hypointense deformation and
no disordered architecture.
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Fig. 21 —Transverse endoanal T2-weighted fast spin-echo (TR/TE,
2,500/70) MR image at distal anal canal in 57-year-old woman shows normal
anatomy of external anal sphincter (ES). Posterior part of ES seems to
discontinue at this level (arrowheads), which is normal variant and
not a defect. ES has posterior extension to anococcygeal ligament. IS = lower
edge internal anal sphincter, VI = vaginal introitus, BS = bulbospongiosus
muscle, ACL = anococcygeal ligament.
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Fig. 22 —Transverse endoanal T2-weighted fast spin-echo (TR/TE,
2,500/70) MR image at distal anal canal in 77-year-old man shows normal
anatomy of external anal sphincter (ES). ES anteriorly is shown as a cap,
which might be interpreted as defect because muscle layer seems not continuous
(arrows). IAS = ischioanal space.
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Conclusion
For the depiction of external anal sphincter defects, endoanal MRI,
external phased-array MRI, and 3D endoanal sonography are all useful.
Generalized atrophy of the sphincter muscles can be assessed with either
endoanal MRI or external phased-array MRI, provided sufficient experience is
available. With endoanal sonography, an impression about atrophy can be
obtained. With 3D endoanal sonography, the advantage of multiplanar viewing
makes sphincter assessment easier and might result in improved diagnostic
confidence.
Preoperatively performed sphincter thickness measurement on endoanal MRI
might function as a potential predictor for surgical outcome. In the
postsurgical workup, endo-anal sonography is useful to depict residual
sphincter defects.
In summary, to select patients as candidates for surgery, MRI is
recommended; for the postsurgical evaluation, endoanal sonography is
preferred.
References
- Osterberg A, Edebol Eeg-Olofsson K, Graf W. Results of surgical
treatment for faecal incontinence. Br J Surg2000; 87:1546
–1552[CrossRef][Medline]
- Diamant NE, Kamm MA, Wald A, Whitehead WE. AGA technical review on
anorectal testing techniques. Gastroenterology1999; 116:735
–760[CrossRef][Medline]
- Bartram CI. Ultrasound. In: Bartram CI, DeLancy JOL, Halligan S,
Kelvin FM, Stoker J, eds. Imaging pelvic floor
disorders. Berlin, Germany: Springer-Verlag, 2003:69
–80
- Terra MP, Beets-Tan RG, van de Hulst V, et al. Anal sphincter
defects in patients with fecal incontinence: endoanal versus external
phased-array MRI. Radiology 2005;236
: 886–895[Abstract/Free Full Text]
- Stoker J, Rociu E, Zwamborn AW, Schouten WR, Lameris JS.
Endoluminal MRI of the rectum and anus: technique, applications, and pitfalls.
Radio-Graphics 1999;19
: 383–398[Abstract/Free Full Text]
- Stoker J. The anatomy of the pelvic floor and sphincters. In:
Bartram CI, DeLancy JOL, Halligan S, Kelvin FM, Stoker J, eds.
Imaging pelvic floor disorders. Berlin, Germany:
Springer-Verlag, 2003:1
–26
- Rociu E, Stoker J, Zwamborn AW, Lameris JS. Endoanal MRI of the
anal sphincter in fecal incontinence. RadioGraphics1999; 19:S171
–S177[Medline]
- Dobben AC, Terra MP, Slors JFM, et al. Comparison of endoanal MRI
and endoanal ultra-sonography in the depiction of external anal sphincter
defects in fecal incontinent patients. Radiology2007; 242:463
–471[Abstract/Free Full Text]
- Stoker J, Rociu E, Wiersma TG, Lameris JS. Imaging of anorectal
disease. Br J Surg 2000;87
: 10–27[CrossRef][Medline]
- Dobben AC, Terra MP, Deutekom M, et al. The role of endoluminal
imaging in clinical outcome of overlapping anterior anal sphincter repair in
patients with fecal incontinence. AJR2007; 189: 334;
[web] W70–W77
- Malouf AJ, Williams AB, Halligan S, Bartram CI, Dhillon S, Kamm MA.
Prospective assessment of accuracy of endoanal MRI and endosonography in
patients with fecal incontinence. AJR2000; 175:741
–745[Abstract/Free Full Text]
- Briel JW, Zimmerman DD, Schouten WR. Factors predictive of outcome
after surgery for faecal incontinence. Br J Surg2001; 88:729
–730[Medline]
- Terra MP, Beets-Tan RG, van der Hulst VPM, et al. MRI in evaluating
atrophy of the external anal sphincter in patients with fecal incontinence.
AJR 2006; 187:991
–999[Abstract/Free Full Text]
- Cazemier M, Terra MP, Stoker J, et al. Atrophy and defects
detection of the external anal sphincter: comparison between 3D anal
endosonography and endoanal MRI. Dis Colon Rectum2006; 49:20
–27[CrossRef][Medline]
- West RL, Dwarkasing S, Briel JW, et al. Can 3D endoanal
ultrasonography detect external anal sphincter atrophy? A comparison with
endoanal MRI. Int J Colorectal Dis 2005;20
: 328–333[CrossRef][Medline]
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Abstract
Introduction
