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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_1110_Библиотеки_им_академика_М_И_Перельмана
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External
anal
sphincter
Section III • State of the Art in Pelvic Floor Imaging 41
Rectovaginal
septum
Bulbocavernosus
muscle
Transverse
perineal muscle
Central tendon
2. Mid: the anococcygeal ligament, superficial
part of the external sphincter, internal sphincter, perineal body, and vagina in females;
3. Low: the subcutaneous part of the external
sphincter.
The muscles of the lower and the upper part of
the anal canal are different. The first US image
recorded is normally at the puborectalis level and
labeled high (Fig. III.22). The puborectalis muscle
slings the anal canal instead of completely surrounding it. At its upper end, the puborectalis is
attached to the funnel-shaped levator ani muscle,
and the levator ani anchors the sphincter complex
to the inner side of the pelvis [10]. The deep part
of the external sphincter is similar in echogenicity to the puborectalis and so is indistinguishable
Fig. III.10. The perineal body lies within
the rectovaginal septum in the female
from it. Anteriorly, the circular fibers of the deep
part of the external sphincter are not recognizable
in females whereas in males, thin arcs of muscle
from the deeper part of the sphincter may be seen
extending anteriorly (Fig. III.22). This is particularly frequent in middle-aged to older women,
especially if multiparous. Anatomic studies
detailed the lower length of the ventral EAS in
females, showing that the differences with males
are already present in the fetus [20]. Threedimensional longitudinal imaging can offer sug-
gestive features of these anatomic characteristics
of EAS [15, 21, 22] (Fig. III.23). In examining a
female subject, the ultrasonographic differences
between the natural gaps (hypoechoic areas with
smooth, regular edges) and sphincter ruptures
(mixed echogenicity,due to scarring, with irregu-
Supralevator space
Intersphinteric space
Ischioanal space
Perianal space
Fig. III.11. Schematic representation of
the different perianal spaces
42 Benign Anorectal Diseases
anal sphincter
Subepithelial
a
b
External
tissue
c
Internal
muscle
ter
inal
Fig. III.12. Normal ultrasonographic
four-layer structure of the mid-anal
canal in a male. Axial image (a), threedimensional reconstruction (b),
schematic representation (c)
Fig. III.13. The muscularis submucosae ani can be sono-
graphically identified as a low reflective band within the moderately reflective subepithelium (arrows)
lar edges) occurring at the upper anterior part of
the anal canal must be kept in mind [8].Bollard et
al. [23] found manometric confirmation of the
EAS gaps identified by EAUS.
Moving the probe a few millimeters in the distal direction will appear an intact anterior EAS
(Fig. III.24), forming just below the superficial
transverse perineal muscles, imaged at 11 and
1 o’clock (Fig. III.25). This image is a mid-canal
projection in which the IAS, conjoining longitudinal muscle, and superficial EAS all are identified.
Section III • State of the Art in Pelvic Floor Imaging 43
This image will be labeled mid.As reported by
Bartram [3], in females, fibers between the transverse perineii fuse with the external sphincter so
that there is no plane of dissection between these
two structures. In males, a plane of fat persists
between the transverse perineii and the external
sphincter (Fig. III.25).The perineal body is seen as
a complex structure of concentric rings with a
hypoechoic or hyperechoic center. It is the central
portion of the perineum where the EAS, the bulbospongiosus, and the transverse perineal muscles
meet (Fig. III.25). EAUS is able to precisely identify differences of the perineal body between males
and females. However, it remains difficult to reliably measure this structure because of the lack of
clear limits. Also, the proposed use of a finger
introduced into the vagina as a landmark seems to
be of poor benefit, altering its normal configuration due to the digital compression on the central
perineum [24, 25].
Three-dimensional endosonography may provide accurate imaging of the perineal body in
females and more accurate measurement
(Fig. III.26).
The anococcygeal raphe is seen as a posterior
hypoechoic triangle (Fig. III.27).
When the probe is pulled further out, the
image of the IAS will disappear, and only the
subepithelium and the subcutaneous segment of
the longitudinal muscle plus the EAS will be seen.
This last image will be labeled low (Fig. III.28).
Fig. III.14. The internal sphincter in the
coronal (a),transverse (b), and sagittal (c)
planes
44 Benign Anorectal Diseases
a
b
Fig. III.16. The sphincter is intact but more echogenic and
inhomogeneous in texture in this 67-year-old man with a
minor degree of incontinence
Fig. III.15. The internal sphincter ends at
the level of the junction between the
superficial and subcutaneous external
sphincter. Its termination can be is symmetric (a) or not completely symmetric
(b) (arrows)
Fig. III.17. The longitudinal layer can be sonographically
identified as a moderately echogenic structure (arrows)
Section III • State of the Art in Pelvic Floor Imaging 45
a
External anal
sphincter
Longitudinal
Puborectalis
b
muscle
Normal Values
The anal canal length is the distance measured
between the proximal canal,where the puborectalis muscle is identified, and the lower border of the
subcutaneous external sphincter. It is significantly
longer in males than in females as a result of a
longer EAS whereas there is no difference in puborectalis length. In males, the anterior part of the
external sphincter is present along the entire
length of the canal (Fig. III.29). In females, the
anterior ring of the external sphincter is shorter.
Williams et al. [21] reported that the anterior EAS
occupied 58% of the male anal canal compared
with 38% of the female canal (p <0.01). In females,
Puboanalis
Internal
anal
sphincter
Fig. III.18. The puboanalis is seen as a
low-reflective, triangular-shaped band of
muscle just medial to the puborectalis
(a). Schematic representation (b)
the puborectalis occupied a significantly larger
proportion of the canal than in males (61% versus
45%; p=0.02). There was no difference in the length
of the IAS between males and females (34.4 mm
versus 33.2 mm) or the proportion of the anal canal
that it occupied (67% versus 73%; p=0.12).
Normal values for sphincter dimensions differ
between techniques. The importance of defining
the true values of sphincter muscle thickness is
not relevant because the purpose of measuring
anal sphincters is to distinguish a normal versus
abnormal measurement, regardless of the absolute values. Measurement should be taken at the 3
and 9 o’clock positions in the midlevel of the anal
canal. The thickness of IAS varies from 1.8±0.5
46 Benign Anorectal Diseases
a
b
mm and increases with age owing to the presence
of more fibrous tissue as the absolute amount of
muscle decreases [3], measuring 2.4–2.7 mm <55
years and 2.8–3.5 mm >55 years. Any IAS >4 mm
thick should be considered abnormal whatever
the patient’s age; conversely, a sphincter of 2 mm
is normal in a young patient but abnormal in an
elderly one. The longitudinal muscle is 2.5±0.6
mm in males and 2.9±0.6 mm in females. The
average thickness of the EAS is 8.6±1.1 mm in
males and 7.7±1.1 mm in females.
Many studies have specifically addressed the
problems of the reproducibility of EAUS sphincter measurements [17, 18, 26–28]. Enck et al. [27]
Fig. III.19. Three-dimensional recon-
struction in the transverse plane showing
the longitudinal muscle (LM) joining the
puboanalis (PA ) to form the conjoined
longitudinal layer (CLL) (a).Volume render mode (b)
Fig. III.20. The external sphincter can be sonographically
identified as a structure with mixed echogenicity (arrows)
Longitudinal
muscle
Section III • State of the Art in Pelvic Floor Imaging 47
Rectum
Puborectalis
} HIGH
Deep
EAS
Fig. III.21. Schematic representation of the three levels (high, mid and low) of the anal canal with the probe in situ. EAS exter-
nal anal sphincter,IAS internal anal sphincter
examined a small group of healthy volunteers and
concluded that EAUS did not provide reliable
measurements of internal and external sphincter
thicknesses. Gold et al. [28] examined 51 patients
and found that measurements of the internal
sphincter were more reproducible than those of
Superficial
Subcutaneus
the external sphincter. These findings are consistent with results from Beets-Tan et al. [18], which
compared EAUS, endoanal MRI, and phasedarray MRI for anal sphincter measurement in
healthy volunteers. EAUS enabled reliable measurement of only internal sphincter thickness
MID
}
} LOW
a b
Fig. III.22. Normal ultrasound anatomy of the deep level of the anal canal demonstrating the puborectalis (PR). Anteriorly, a
thin arc of muscle from the deeper part of the sphincter may be seen in males (a) whereas the deep part of the external sphincter is not recognizable in females (b)
48 Benign Anorectal Diseases
a
c
b
d
e f
Fig. III.23. Three-dimensional endosonographic reconstruction demonstrating that the anterior anal sphincter is shorter in the
female: male (a), female (b). Sagittal images: male (c), female (d). Schematic representation: (e, f). LM longitudinal muscle, EAS
external anal sphincter,(d = deep; s = superficial; sc = subcutaneous)
Section III • State of the Art in Pelvic Floor Imaging 49
a
b
Fig. III.24.Formation of the anterior ring
of the external sphincter in females:
upper anal canal (a), junction between
upper and mid-anal canal (b), mid-anal
c
canal (c)
50 Benign Anorectal Diseases
b
B
a b
rineii
Perineal
c
External
anal sphi
l
ter
Fig. III.25. Bulbospongiosus muscle,
transverse perineal muscles, and external
anal sphincter meet in the perineal body.
In males (a), a plane of fat persists
between the transverse perineii and the
external sphincter whereas in female (b),
the transverse perineii fuse with the
external sphincter. Schematic representation (c)
Fig. III.26. Sagittal image demonstrating
the length of the perineal body (PB) that
extends from the rectovaginal septum
(RV S) to the external sphincter (EAS)
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