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IV.1.
Introduction
G.A. Santoro, G. Di Falco
Continence depends on a number of factor that
include stool consistency, the capacity of the sigmoid colon to retard progress of stool, the compliance and sensation of the urgency of the rec-
tum, the phasic contractions of the puborectalis
muscle to form a normal anorectal angle, a normal internal (IAS) and external (EAS) sphincter
function, and normal sensation in the anal canal
[1] (Fig. IV.1). The etiology of fecal incontinence
can be subdivided into three main groups
SIGMOID COLON:
contractions retard
progress of stool
RECTUM:
compliance
and sensation
of urgency
PUBORECTALIS MUSCLE:
phasis contractions and
ano-rectal angle
(Table IV.1): (1) functional, (2) sphincter weakness, and (3) sensory loss. The majority of
patients with incontinence are women with an
obstetric injury, and symptoms can occur even in
an elderly population who had experienced vaginal deliveries earlier in life [2].
Accurate evaluation of patients with fecal
incontinence is crucial for the treatment plan.
Physiology of defecation and continence has
been traditionally studied with anorectal
INT. ANAL SPHINCTER M.:
passive barrier
to leakage
POSTERIOR
EXT. ANAL SPHINCTER M.:
phasic contractions
ANTERIOR
Fig. IV.1. Schematic representation of the
different mechanisms of continence to
stool
84 Benign Anorectal Diseases
Table IV.1. Etiology of fecal incontinence
Category Mechanism Common causes
Functional Rapid transit Irritable bowel syndrome, inflammatory bowel disease, tumors
Pelvic floor dyssynergia Idiopathic, spinal cord injury
Psychological Dementia, psychosis, behavioral
Sphincter weakness Sphincter muscle injury Obstetrical trauma, accidental trauma, surgical trauma
Pudendal nerve injury Obstetrical trauma, idiopathic,peripheral neuropathy
Central nervous system injury Spina bifida, spinal cord injury, cerebrovascolar accident
Sensory loss Afferent nerve injury Diabetic neuropathy, spinal cord injury
manometry. This procedure, however, is able to
give a number of useful clinical data but can offer
only indirect and not very reliable information
on the integrity of anal sphincters based on registration of the resting pressure, squeeze pressure, and rectoanal inhibitory reflex. The importance of endoanal ultrasound (EAUS) in delineating the different structures of the anal canal and
the pelvic floor has been confirmed in numerous
studies [3–10]. The ultrasonographic images of
the IAS and EAS are realistic,and their modifications are well correlated to anorectal function
[11–16]. EAUS has better diagnostic specificity
and sensitivity when compared with digital
examination and computerized tomography
(CT). Magnetic resonance imaging (MRI) has
been suggested as a better diagnostic procedure.
However, differences in definition of anal canal
anatomy have been described in relation to the
technique used. Endoanal coil has been used for a
long time; however, it could distort the anatomy
and, recently, a phased-array technique has been
preferred [17–20]. With this procedure, all the
main features of the anal canal morphology
showed with EAUS are similarly confirmed: good
resolution of the IAS; shorter EAS at the anterior
anal canal in females; no precise subdivision of
the EAS into two or three parts; difficulty measuring the perineal body. The only significant
advantage of phase-array MRI over endoanal MR
and EAUS is the imaging of a wider field of view
[21–22]. Considering technical characteristics,
time consumption, costs, and availability of
instruments in hospitals, in our opinion MR
should be used in cases of clinical complexity
when EAUS is unable to give reliable information.
In the following sections, accuracy and reliability of EAUS in the evaluation of anal sphincter
injury will be discussed. Special attention will be
focused on the obstetric events leading to anal
sphincter damage and their assessment by EAUS.
EAUS and endoanal MRI will then be compared
to determine which technique is more accurate
for demonstration of sphincter lesions.
References
1. Jorge JM,Wexner SD (1993) Etiology and management
of fecal incontinence. Dis Colon Rectum 36:77–97
2. Oberwalder M, Dinnewitzer A, Baig K et al (2004)
The association between late-onset fecal incontinence and obstetric anal sphincter defects. Arch Surg
139:429–432
3. Stoker J, Halligan S, Bartram CI (2001) Pelvic floor
imaging. Radiology 218:621–641
4. Bartram CI (2003) Ultrasound. In: Bartram CI,
DeLancy.JOL Imaging pelvic floor disorders. Springer,
Berlin Heidelberg New York
5. Burnett SJD, Bartram CI (1991) Endosonographic variations in the normal internal anal sphincter. Int J
Colorectal Dis 6:2
6. Williams AB, Bartram CI, Halligan S, Marshall MM et
al (2001) Multiplanar anal endosonography – normal
anal canal anatomy. Colorectal Dis 3:169–174
7. Frudinger A, Halligan S, Bartram CI (2002) Female
Section IV • Endoanal Ultrasonography in the Assessment of Patients with Fecal Incontinence 85
anal sphincter: age-related differences in asymptomatic volunteers with high-frequency endoanal US.
Radiology 224:417–423
8. Williams AB, Cheetham MJ, Bartram CI et al (2000)
Gender differences in the longitudinal pressure profile
of the anal canal related to anatomical structure as
demonstrated on three-dimensional anal endosonography. Br J Surg 87:1674–1679
9. Nielsen MB, Hauge C, Rasmussen OO (1992) Anal
sphincter size measured by endosonography in
healthy volunteers. Effect of age, sex, and parity. Acta
Radiol 33:453–456
10. Kumar A, Scholefield JH (2000) Endosonography of
the anal canal and rectum. World J Surg 24:208–215
11. Gold DM, Halligan S, Kmiot WA, Bartram CI (1999)
Intraobserver and interobserver agreement in anal
endosonography. Br J Surg 86: 371–375
12. Enck P, Heyer T, Gantke B, Schmidt WU (1997) How
reproducible are measures of the anal sphincter muscle
diameter by endoanal ultrasound? Am J Gastroenterol
92: 293–296
13. Thakar R, Sultan A (2004) Anal endosonography and
its role in assessing the incontinent patient. Best Pract
Res Clinic Obstet Gynaec 18:157–173
14. Sultan AH, Kamm MA, Talbot IC et al (1994) Anal
endosonography for identifying external sphincter
defects confirmed histologically. Br J Surg 81:
463–465
15. Gold DM, Bartram CI, Halligan S (1999) Three-dimensional endoanal sonography in assessing anal canal
injury. Br J Surg 86:365–370
16. Bollard RC, GardinerA, Lindow S et al (2002) Normale
female anal sphincter: difficulties in interpretation
explained. Dis Colon Rectum 45:171–175
17. Stoker J, Rociu E, Zwamborn AW et al (1999) Endoluminal MR imaging of the rectum and anus: technique,
applications and pitfalls. Radiographics 19:383–398
18. Hussain SM, Stoker J, Lameris JS (1995) Anal sphincter
complex: endoanal MR imaging of normal anatomy.
Radiology 197:671–677
19. Williams AB, Malouf AJ, Bartram CI et al (2001)
Assessment of external anal sphincter morphology in
idiopathic fecal incontinence with endocoil magnetic
resonance imaging. Dig Dis Sci 46:1466–1471
20. Morren GL, Beets-Tan GH, van Engelshoven MA
(2001) Anatomy of the anal canal and perianal structures as defined by phase-array magnetic resonance
imaging. Br J Surg 88:1506–1512
21. Rociu E, Stoker J, Eijkemans MJC et al (1999) Fecal
incontinence: endoanal US versus endoanal MR imaging. Radiology 212:453–458
22. Beets-Tan RGH, Morren GL, Betts GL et al (2001).
Measurement of anal sphincter muscles: endoanal
US, endoanal MR imaging, or phased-array MR imaging? A study with healthy volunteers. Radiology 220:
81–89
IV.2.
Accuracy and Reliability of Endoanal
Ultrasonography in the Evaluation of Anal
Sphincter Injury
G.A. Santoro, G.Gizzi
Endoanal ultrasonography (EAUS) remains the
gold standard in delineating the anatomy of the
sphincter complex [1–8]. Features shown by
EAUS can help to differentiate between incontinent patients with intact anal sphincters and
those with sphincter lesions [9–14]. The operator
should identify if there is a combined lesion of
both internal (IAS) and external (EAS) sphincter
or if the lesion involves just one muscle.
Number, site, axial (in hours of the clock) and
longitudinal extension, radial angle of the
defect, presence of scarring, differences in
echogenicity and thickness of the sphincters,
and other local alteration should be carefully
assessed and should always be reported. If a
clear break is detected, it should be graded on
the basis of the degree of circumferential
involvement (<25% or >25%). Tears are defined
by an interruption of the fibrillar echotexture.
Scarring is characterized by loss of normal
architecture, with an area of amorphous texture
that usually has low reflectiveness [15].
This procedure has a key role in choosing the
correct therapeutic option and has almost completely replaced the invasive and painful electromyography in mapping sphincter defects.
However, finding a sphincter defect does not
necessarily mean that it is the cause of fecal
incontinence [16] whereas an anal sphincter
that looks normal, without lesion, can have
degeneration or atrophy [17]. The size of defect
correlates with the severity of fecal incontinence [18]; however, a recent study failed to
demonstrate a relationship between muscle
injuries and the severity of clinical symptoms
[19]. EAUS should, therefore, be complementary
to anorectal manometry and neurophysiologic
studies [20, 21].
Internal Anal Sphincter
Abnormalities
The majority of lesions to the IAS are due to
obstetric or iatrogenic injuries. Minor degrees of
fecal incontinence (soiling) due to IAS injuries
have been reported in 29% of patients after hemorrhoidectomy or mucoprolapsectomy [22].
Manual anal dilatation [23] or lateral internal
sphincterotomy [24] for the treatment anal fissure
have been associated with anal incontinence in
27% and 50% of patients, respectively. Up to 60%
of patients can be rendered incontinent following
fistula surgery [25].
Defects of the IAS are easily recognized given the
prominent appearance of the IAS in the mid anal
canal, and they appear as hyperechoic breaks in
the normally hypoechoic ring. The pattern of
sphincter disruption is related to the type of
surgery [26]. Patients incontinent following manual dilatation exhibit a diffuse thinning of the IAS
or disruption of the IAS at more than one site
(Fig. IV.2). Patients incontinent after sphincterotomy have a single defect in the IAS associated
with a thickening of the remaining muscle for a
retraction phenomenon (Fig. IV.3). Patients who
become incontinent following hemorrhoidectomy
have defects in the site of the hemorrhoidal cush-
88 Benign Anorectal Diseases
Fig. IV.2. Fragmentation of the internal anal sphincter follow-
ing manual dilatation
fecal incontinence and intact anal sphincter. The
IAS appeared thinner than normal and hyperechoic, and these conditions were combined with
reduced resting pressure and normal squeeze
pressure, rectal sensitivity, and pudendal latency.
Incontinent patients with IAS degeneration were
found to be older than those with obstetric trauma incontinence [5].
An apparently opposite EAUS condition is an
abnormal thickness of the IAS (Fig. IV.10). It seems
typical of older ages without differences of anal
canal levels [5, 17, 27]. Interestingly, decreased thickness of the IAS can be frequently observed in
patients with chronic anal fissure, a sign of an
increased sphincter tone. Imaging of an IAS break
following internal sphincterotomy for a fissure can
help to follow-up clinical results of the operation or
the unexpected sequelae (persistence of anal fissure
and pain or,on the other hand, fecal incontinence).
ions (Figs. IV.4 and 5). Fistula surgery or obstetric
trauma is associated with combined internal and
external sphincter injuries (Figs. IV.6–8).
A thinning of IAS of less than 2 mm in a patient
more than 50 years old is abnormal, and the term
“primary degeneration of IAS” has been used to
describe this (Fig. IV.9). Vaizey et al. [17] reviewed
the EAUS examinations of 38 patients with passive
External Anal Sphincter
Abnormalities
One of the most important contribute of EAUS
has been in the correct imaging of the EAS [1–8],
which is of major importance for continence.
The most frequent cause of fecal incontinence is
an obstetric injury to the EAS. The appearance of
Fig. IV.3. Complete division of the internal anal sphincter
(arrows) at the level of the transverse perineii (TP) following
a left lateral internal sphincterotomy for fissure. The remaining muscle appears slightly thicker for a retraction phenomenon
Fig. IV.4. Two complete defects of the internal anal sphincter
between 2 and 6 o’clock (120°) and between 7 and 10 o’clock
(90°) (black arrows) following hemorrhoidectomy
Section IV • Endoanal Ultrasonography in the Assessment of Patients with Fecal Incontinence 89
Fig. IV.5. Two complete defects of the internal anal sphincter
between 5 and 7 o’clock (60°) and between 10 and 12 o’clock
(60°) (dots) following hemorrhoidectomy
a b
Fig. IV.6. Combined internal (between 1 and 6 o’clock, black
arrows, and between 10 and 11 o’clock, white arrows) and
external (between 10 and 2 o’clock, dots) anal sphincter
defects following multiple operations for a recurrent high fistula (a). Three-dimensional coronal images showing the
absence of the internal sphincter in the left side of the anal
c
canal (b, c)
90 Benign Anorectal Diseases
a b
Fig. IV.7. Obstetric trauma with an internal sphincter defect anteriorly (arrows) and scarring in the external sphincter between
11 and 1 o’clock (dots) (a, b)
an EAS defect is a break in the circumferential
integrity of the mixed hyperechoic band
(Figs. IV.11 and 12). A defect can have either a
hypoechoic or a hyperechoic density pattern.
This corresponds to replacement of the normal
striated muscle with granulation tissue and
fibrosis (Fig. IV.13). The majority of obstetric
injuries are associated with a single, large, defect
in the EAS anterior to the anal canal that can be
combined to an additional division of the IAS
(Fig. IV.14). In examining a female subject, it is
important to remember the ultrasonographic
Fig. IV.8. Obstetric trauma with a well-defined defect of the
external sphincter at 12 o’clock (yellow arrows) due to an epi-
siotomy and an internal sphincter division between 10 and 2
o’clock (white arrows)
Fig. IV.9. A 68-year-old woman with passive fecal inconti-
nence. The internal sphincter is intact but thinner than nor-
mal for this age (1.3 mm), indicative of primary degeneration
Section IV • Endoanal Ultrasonography in the Assessment of Patients with Fecal Incontinence 91
Fig. IV.10. Abnormal thickness of the internal anal sphincter
(4.1 mm) in a 42-year-old woman with intra-anal prolapse
(arrows)
differences between the natural gaps (hypoechoic areas with smooth, regular edges, occurring in the upper part of the anal canal) and the
sphincter ruptures (mixed echogenicity due to
scarring, with irregular edges) occurring at the
upper anterior part of the anal canal [6, 14]
(Fig. IV.15). Surgery for a fistula can also be
responsible for damage to the EAS. This can
more likely occur during treatment of complex,
high fistulas or in patients who have undergone
multiple operations for a recurrent or persistent
fistula (Fig. IV.6).
A limitation of EAUS is the definition of EAS
atrophy in patients with idiopathic fecal incontinence because of the vague contours of the mus-
a b
Fig. IV.11. The appearance of an external
anal sphincter defect is a break in the circumferential integrity of the mixed
hyperechoic band (a). The extent of the
defect is measured in the axial plane as an
angle (b). Three-dimensional image
demonstrating the defect (arrow) in the
c
coronal plane (c)
92 Benign Anorectal Diseases
Fig. IV.12. Obstetric trauma with a well-
defined defect of the external sphincter at
1 o’clock (circumferential involvement
<25%)
a b
Fig. IV.13. Hypoechoic area of scarring in the external sphincter (dots) following obstetric trauma. The internal sphincter is
thinned anteriorly but is intact (a, b)
a b
Fig. IV.14. Obstetric external sphincter tear between 10 and 2 o’clock (black arrows) with a small defect of the internal sphinc-
ter from 11 to 12 o’clock (white arrows) (a, b)
Section IV • Endoanal Ultrasonography in the Assessment of Patients with Fecal Incontinence 93
a b
c d
Fig. IV.15. Differences between a natural gap (hypoechoic areas with smooth, regular edges, occurring in the upper part of the
anal canal) (a) and a ruptured external sphincter (mixed echogenicity,due to scarring, with irregular edges) (b–d)
cle ring [15, 28]. Endoanal magnetic resonance
Accuracy and Reliability
imaging (MRI) is more accurate in detecting atrophy as a thinner EAS,with replacement of muscle
by fat [15, 29, 30]. EAUS also serves as a surveil-
lance tool to monitor results following sphincteroplasty [17, 31] (Fig. IV.16). Savoye-Collet et al.
[32] reported that in the 21 patients in whom
EAUS documented closure of the EAS defect, 18
(86%) noted improvement in fecal incontinence.
In contrast, eight of the ten patients who had a
persistent defect in the EAS still had significant
fecal incontinence.
The accuracy of EAUS in the evaluation of incontinence has been supported by surgical findings.
Gold et al. [9] and Enck et al. [10] reported that
sensitivity and specificity in locating the defect
was 100% and accuracy in the topographic
detection of the defect was 90%. Deen et al. [33]
investigated 44 incontinent patients with EAUS.
All sonographically detected EAS defects were
confirmed at operation, and 21 of 22 IAS defects
were also confirmed at surgery. The sensitivity
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