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.
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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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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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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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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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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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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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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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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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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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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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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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