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Section III • State of the Art in Pelvic Floor Imaging 51
Fig. III.27. The anococcygeal raphe (AR) is seen as a posteri-
or hypoechoic triangle
whereas both MRI methods enabled reliable measurement of all sphincter components.
Measurement errors of the longitudinal muscle
and external sphincter are related to the US features of these muscles, which show low contrast
with the surrounding hyperechoic fatty tissue.
Both the inner and outer borders of the external
sphincter are more difficult to define, leading to
less reliable measurement. In contrast, the internal sphincter is easy to define because it is a
hypoechoic structure that is highlighted against
hyperechoic fatty tissues. Williams et al. [21]
reported different results. They found an excellent
correlation for the interobserver measurement of
the external and internal sphincters and submucosal width on endosonography and poor correlation only for the longitudinal muscle.Frudinger et
al. [17] also reported that the EAS thickness was
difficult to define in only 2% of patients at all
three levels examined and in 3% at the subcutaneous level only.A significant negative correlation
with patient age was also demonstrated in this
study at all anal canal levels. In particular, the
anterior EAS part was found significantly thinner
in older subjects.
The high inherent soft-tissue contrast makes
MRI a more reliable imaging method to measure
anal sphincter components [29–35]. It is important to realize, however, that this limitation of
EAUS does not apply in the detection of localized
Fig. III.28. Image at the superficial level demonstrating the
subcutaneous external anal sphincter. The internal sphincter
is absent at this level
sphincter defects, where its benefit has been
proved [36–39]. It has been suggested that measuring sphincter thickness is important when
EAUS cannot depict any sphincter damage in
order to exclude diffuse structural sphincter
changes associated with idiopathic fecal incontinence, passive fecal incontinence, or obstructive
defecation disorders [40–43].
A postulated association between manometric
function of the sphincters and their sonographic
appearance, however, remained controversial in
the literature. Some authors found no correlation
between muscle thickness and muscle performance, neither resting nor squeeze pressure.
Scanning anal sphincter muscles may allow for
determination of their integrity but not for their
morphometric properties.
Multiplanar EAS has enabled detailed longitudinal measurement of the components of the anal
canal [44, 45] (Fig. III.29). Williams et al. [44]
reported that the anterior EAS was significantly
longer in males than in females (30.1 mm versus
16.9 mm; p <0.001).There was no difference in the
length of the puborectalis between males and
females, indicating that the gender difference in
anal canal length is solely due to the longer male
EAS. The IAS did not differ in length between
males and females. West et al. [45] reported similar results, with IAS and EAS volumes found larger in males than in females.
52 Benign Anorectal Diseases
a
b
References
1. Uz A, Elhan A, Ersoy M, Tekdemir I (2004) Internal
anal sphincter: an anatomic study. Clin Anat 17:17–20
2. Lunniss PJ, Phillips RKS (1992) Anatomy and function
of the anal longitudinal muscle. Br J Surg 79:882–884
3. Bartram CI (2003) Ultrasound. In: Bartram CI,
DeLancy JOL. Imaging Pelvic Floor Disorders.
Springer,Berlin Heidelberg New York
4. Williams AB, Bartram CI, Halligan S et al (2002)
Endosonographic anatomy of the normal anal canal
compared with endocoil magnetic resonance imaging.
Dis Colon Rectum 45:176–183
5. Shafik A (1976) A new concept of the anatomy of the
Fig. III.29. Three-dimensional view
demonstrating that the anal canal is
longer in male (a) than in female (b) as a
result of a longer external anal sphincter
anal sphincter mechanism and the physiology of defecation III. The longitudinal anal muscle: anatomy and
role in sphincter mechanism. Invest Urol 13:271–277
6. Konerding MA, Dzemali O, Gaumann A et al (1999)
Correlation of endoanal sonography with cross-sec-
tional anatomy of the anal sphincter. Gastrointest
Endosc 50:804–810
7. Shafik A (1975) A new concept of the anatomy of the
anal sphincter mechanism and the physiology of defecation. The external anal sphincter: a triple-loop system. Invest Urol 12:412–419
8. Thakar R, Sultan A (2004) Anal endosonography and
its role in assessing the incontinent patient. Best Pract
Res Clinic Obstet Gynaec 18:157–173
Section III • State of the Art in Pelvic Floor Imaging 53
9. Santoro GA, Di Falco G (2004) Basic anatomy. In:
Santoro GA, Di Falco G. Atlas of endoanal and
endorectal ultrasonography. Springer Italy, Milan
10. Stoker J (2003) The anatomy of the pelvic floor and
sphincters. In: Bartram CI, DeLancy JOL. Imaging
Pelvic Floor Disorders. Springer, Berlin Heidelberg
New York
11. Woodman PJ, Graney DO (2002) Anatomy and physiology of the female perineal body with relevance to
obstetrical injury and repair. Clin Anat 15:321–334
12. Bartram CI, Frudinger A (1997) Handbook of anal
endosonography. Wrightson Biomedical, Petersfield
13. Burnett SJD, Bartram CI (1991) Endosonographic variations in the normal internal anal sphincter. Int J
Colorectal Dis 6:2
14. Vaizey CJ, Kamm MA, Bartram CI (1997) Primary
degeneration of the internal anal sphincter as a cause
of passive faecal incontinence. Lancet 349:612–615
15. Williams AB, Bartram CI, Halligan S et al (2001)
Multiplanar anal endosonography – normal anal canal
anatomy. Colorectal Disease 3:169–174
16. Sultan AH, Kamm MA, Talbot IC et al (1994) Anal
endosonography for identifying external sphincter
defects confirmed histologically.Br J Surg 81:463–465
17. Frudinger A, Halligan S, Bartram CI et al (2002)
Female anal sphincter: age-related differences in
asymptomatic volunteers with high-frequency
endoanal US. Radiology 224:417–423
18. Beets-Tan RGH, Morren GL, Beets 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
19. Stoker J, Halligan S, Bartram CI (2001) Pelvic floor
imaging. Radiology 218:621–641
20. Fritsch H, Brenner E, Lienemann A, Ludwikowski B
(2002) Anal sphincter complex: reinterpreted morphology and its clinical relevance. Dis Colon Rectum
45:188–194
21. 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
22. Gold DM, Bartram CI, Halligan S et al (1999) Three-
dimensional endoanal sonography in assessing anal
canal injury. Br J Surg 86:365–370
23. Bollard RC, Gardiner A, Lindow S et al (2002) Normal
female anal sphincter: difficulties in interpretation
explained. Dis Colon Rectum 45:171–175
24. Zetterstrom JP, Mellgren A, Madoff RD et al (1998)
Perineal body measurement improves evaluation of
anterior sphincter lesions during endoanal ultrasonography. Dis Colon Rectum 41:705–713
25. Oberwalder M, Thaler K, Baig MK et al (2004) Anal
ultrasound and endosonographic measurement of
perineal body thickness. A new evaluation for fecal
incontinence in females. Surg Endosc 18:650–654
26. Nielsen MB, Hauge C, Rasmussen OO et al (1992) Anal
sphincter size measured by endosonography in
healthy volunteers. Effect of age, sex and parity. Acta
Radiol 33:453–456
27. Enck P, Heyer T, Gantke B et al (1997) How reproducible are measures of the anal sphincter muscle
diameter by endoanal ultrasound? Am J Gastroenterol
92:293–296
28. Gold DM, Halligan S, Kmiot WA, Bartram CI (1999)
Intraobserver and interobserver agreement in anal
endosonography. Br J Surg 86:371–375
29. Williams AB, Bartram CI, Modhwadia D et al (2001)
Endocoil magnetic resonance imaging quantification
of external sphincter atrophy. Br J Surg 88:853–859
30. 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
31. Hussain SM, Stoker J, Zwamborn AW et al (1996)
Endoanal MR imaging of the anal sphincter complex:
correlation with cross-sectional anatomy and histology. J Anat 189:677–682
32. Rociu E, Stoker J, Eijkemans MJC, Lameris JS (2000)
Normal anal sphincter anatomy and age- and sexrelated variations at high-spatial-resolution endoanal
MR imaging. Radiology 217:395–401
33. 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
34. DeSouza NM, Puni R, Zbar A et al (1996) MR imaging
of the anal sphincter in multiparous women using an
enoanal coil: correlation with in vitro anatomy and
appearances in fecal incontinence. Am J Roentgenol
167:1465–1471
35. 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
36. Sentovich SM, Wong WD, Blatchford GJ (1998)
Accuracy and reliability of transanal ultrasound for
anterior anal sphincter injury. Dis Colon Rectum
41:1000–1014
37. Kumar A, Scholefield JH (2000) Endosonography of
the anal canal and rectum. World J Surg 24:208–215
38. Hussain SM, Stoker J, Schutte HE, Lameris JS (1996)
Imaging of the anorectal region. Europ J Radiol
22:116–122
39. Sultan AH, Kamm MA, Hudson CN et al (1993) Anal-
54 Benign Anorectal Diseases
sphincter disruption during vaginal delivery. N Engl J
Med 329:1905–1911
40. Zetterstrom JP, Mellgren A, Jensen LL et al (1999)
Effect of delivery on anal sphincter morphology and
function. Dis Colon Rectum 42:1253–1260
41. Burnett SJ, Spence-Jones C, Speakman CT et al (1991)
Unsuspected sphincter damage following childbirth
revealed by anal endosonography. Br J Radiol
64:225–227
42. Tjandra JJ, Milsom JW, Stolfi VM et al (1992)
Endoluminal ultrasound defines anatomy of the anal
canal and pelvic floor. Dis Colon Rectum 35:465–470
43. Nielsen MB, Rasmussen OO, Pedersen JF, Christiansen
J (1993) Anal endosonographic findings in patients
with obstructed defecation. Acta Radiol 34:35–38
44. Williams AB, Bartram CI, Halligan S et al (2001)
Multiplanar anal endosonography-normal anal canal
anatomy. Colorectal Dis 3:169–174
45. West RL, Felt-Bersma RJF, Hansen BE et al (2005)
Volume measurement of the anal sphincter complex
in healthy controls and fecal-incontinent patients
with a three-dimensional reconstruction of endoanal
ultrasonography images. Dis Colon Rectum
48:540–548
III.3.
Endosonographic Anatomy
of the Normal Rectum
G.A. Santoro, G. Di Falco
The normal rectum is 11- to 15–cm long and has a
maximum diameter of 4 cm. It is continuous with
the sigmoid colon superiorly at the level of the
third sacral segment and courses inferiorly along
the curve of the sacrum to pass through the pelvic
diaphragm and become the anal canal
(Fig. III.30). It is surrounded by fibrofatty tissue
that contains blood vessels, nerves, lymphatics,
and small lymph nodes. The superior one third is
covered anteriorly and laterally by the pelvic peritoneum. The middle one third is only covered
with peritoneum anteriorly, where it curves anteriorly onto the bladder in males and onto the
uterus in females. The lower one third of the rec-
Recto-sigmoid
junction
tum is below the peritoneal reflection and is related anteriorly to the bladder base, ureters, seminal
vesicles, and prostate in males (Fig. III.31a) and to
the lower uterus, cervix, and vagina in females
(Fig. III.31b).The rectal wall consists of five layers
surrounded by perirectal fat or serosa (Fig.III.32).
On ultrasound, the normal rectal wall is 2- to
3–mm thick and is composed of a five-layer structure [1, 2]. There is some debate as to what the
actual layers represent anatomically. Hildebrandt
and Feifel [3] believe that three layers are anatomical while the other layers represent interfaces
between the anatomical layers. Beynon et al. [4],
however, have produced both experimental and
Longitudinal muscle
Circular muscle
Mucosa
External
anal
sphincter
Deep
Superficial
{
Subcutaneous
Columns of Morgagni
Anal margin
Levator ani muscle
Level of the
anorectal ring
Internal anal
sphincter
Fig. III.30. Coronal anatomy of the
anorectum
56 Benign Anorectal Diseases
Bladder
Prostate
a
Seminal
vesicles
Rectum
External
sphincter
Bladder
Fig. III.31. Sagittal anatomy of the
anorectum in males (a) and females (b)
clinical evidence that the five anatomic layers are
recognizable. These five layers cannot be seen in
all patients and at all levels. Good visualization
depends on maintaining the probe in the center
lumen of the rectum and having adequate distension of the water-filled balloon with good acoustic contact with rectal wall.
The layers represent (Fig. III.33):
Uterus
Rectum
Urethra
Vagina
b
1. The hyperechoic interface between the waterfilled balloon and the mucosa;
2. The hypoechoic deep mucosa (lamina propria
plus muscularis mucosae);
3. The hyperechoic submucosa;
4. The hypoechoic muscularis propria (in rare
cases seen as two layers: inner circular and
outer longitudinal layer);
Section III • State of the Art in Pelvic Floor Imaging 57
5
a b
Fig. III.32. Diagrammatic representation of five-layer structure of the normal rectal wall (a, b): 1 mucosa,2 submucosa, 3 mus-
cularis propria-circular layer, 4 muscularis propria-longitudinal layer; 5 serosa/perirectal fat
4
3
2
1
a b
Fig. III.33. Schematic ultrasound representation of rectal wall (a). Layers: 1 acoustic interface with mucosal surfaces, 2 mucosa,
3 submucosa, 4 muscularis propria, 5 perirectal fat interface. Normal pattern of rectal wall (b). T = Transducer
5. The hyperechoic interface between the rectal
wall and the perirectal fat tissue or serosa.
fully assessed [6]. Attention must be focused on
the third hyperechoic layer. Once it has been
ascertained that the middle hyperechoic line is
The ultrasonographer must have a clear
understanding of what each of these five lines represent anatomically [5]. When staging a rectal
cancer, various levels of the tumor must be optimally imaged and the integrity of the lines care-
broken, then an invasive lesion is recognized, and
attention is then turned to the thickness of the
muscularis propria and the integrity of the outer
hyperechoic line to see if the perirectal fat is
invaded.
58 Benign Anorectal Diseases
a b
c
Fig. III.34. Sonographic view of blood vessels (a). Three-dimensional reconstruction (b) and multiview image presentation (c)
showing the elongated pattern of vasculare structure
Section III • State of the Art in Pelvic Floor Imaging 59
Fig. III.35. Sonographic view of the bladder (B) and seminal
vesicles (SV)
Fig. III.37. Sonographic view of the vagina (V) Fig. III.38. Sonographic view of the intestinal loops (IL)
Fig. III.36. Sonographic view of the prostate (P)
The fibrofatty tissue surrounding the rectum
contains blood vessels, nerves, and lymphatics and
has an inhomogeneous echo pattern. Very small
2–3 mm, round to oval, hypoechoic lymph nodes
may be seen and must be distinguished from
blood vessels, which are also circular hypoechoic
areas but when followed longitudinally, they seem
to extend further than the corresponding diameter
and can often be seen to branch and to elongate in
a longitudinal fashion, confirming that this is a
blood vessel and not a node (Fig. III.34) [7].
Anteriorly, the bladder, seminal vesicles,
(Fig. III.35) and prostate (Fig. III.36) can be identified in males and the uterus, cervix, and vagina in
females (Fig. III.37). Intestinal loops can also easily identified as elongate structures (Fig. III.38).
Technology progress has allowed an increased
resolution of the five distinct layers of the rectal
wall. Three-dimensional (3-D) rectal ultrasound
offers images of the rectal wall in the coronal
plane as well as in the transaxial and the longitudinal planes (Fig. III.39) [1, 8]. Moreover, with the
new, high-frequency probes the five layers are
more clearly distinguished.
60 Benign Anorectal Diseases
a
b
References
1. Santoro GA, Di Falco G (2004) Basic anatomy In:
Santoro GA, Di Falco G. Atlas of endoanal and
endorectal ultrasonography. Springer Italy, Milan
2. Bartram CI, Frudinger A (1997) Handbook of anal
endosonography. Wrightson Biomedical, Petersfield
3. Hildebrandt U, Feifel G, Schwarz HP, Scherr O (1986)
Endorectal ultrasound: instrumentation and clinical
aspects. Int J Colorectal Dis 1:203–207
4. Benyon J, Foy DM, Temple LN, et al (1986) The endo-
Fig. III.39. Normal ultrasound anatomy
of the rectal wall in three-dimensional
images (a, b)
scopic appearance of normal colon and rectum. Dis
Colon Rectum 29:810–813
5. Kumar A, Scholefield JH (2000) Endosonography of
the anal canal and rectum. World J Surg 24:208–215
6. Hildebrandt U, Feifel G (1985) Preoperative staging of
rectal cancer by intrarectal ultrasound. Dis Colon
Rectum 28:42–46
7. Hussain SM, Stoker J, Schutte HE, Lameris JS (1996)
Imaging of the anorectal region. Europ J Radiol 22:116–122
8. Hunerbein M, Schlag PM (1997) 3D-endosonography
for staging of rectal cancer.Ann Surg 225:432–438
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