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Perianal Crohn’s Disease: Assessment with Endoanal Ultrasonography 79
(Fig. 15), supralevator (Figs. 16, 17), pelvirectal and
horseshoe (Fig. 18) [16]. An anal fistula appears as a
hypoechoic tract, which is followed along its crossing
of the subepithelium, internal or external sphincters
and through the perianal spaces [16]. With regard to
the anal sphincters, according to the classification by
Parks et al. [4], the fistulous primary tract can be
classified into four types:
1. Intersphincteric tract, which is presented as a
band of poor reflectivity within the longitudinal
layer, causing widening and distortion of an oth-
erwise narrow intersphincteric plane (Fig. 19). The
tract goes through the intersphincteric space with-
out traversing the EAS fibres (Fig. 20).
2. Transsphincteric tract, in which the extension
through the EAS is clearly shown by a poorly
reflective tract running out through the EAS and
disrupting its normal architecture (Figs. 21, 22).
The point at which the main tract of the fistula
traverses the sphincters defines the fistula level
(high, medium or low). The low transsphincteric
tract traverses only the distal third of the EAS at
the lower portion of the medium anal canal. The
medium transsphincteric tract traverses both
sphincters, external and internal, in the middle
part of the medium anal canal (Fig. 23). The high
transsphincteric tract traverses both sphincters in
the higher part of the medium anal canal in the
space below the puborectalis (Fig. 24).
3. Suprasphincteric tract, which goes above or
through the puborectalis level (Fig. 25).
4. Extrasphincteric tract, which may be seen close to
but more laterally placed around the EAS (Fig. 26).
Rectovaginal fistula appears as a hypoechoic tract
connecting the rectal wall and the vagina. It can be
detected on endorectal ultrasonography with a stan-
Fig. 13. 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)
a
b
c
Anterior
Caudal
d
Anterior
Caudal
80 G.A. Santoro, M. Starck, L. Campana, B. Fortling
a
b
c
Fig. 14. Acute intersphincteric abscesses at 5 o’clock posi-
tion (a) and at 3 o’clock position (b, c)
Fig. 15. Acute abscess in the right ischiorectal space Fig. 16. Acute supralevator abscess presenting as an area of
low reflectivity deep to the puborectalis muscle
Perianal Crohn’s Disease: Assessment with Endoanal Ultrasonography 81
dard water balloon, performed immediately after
EAUS. Anovaginal fistulae are frequently small and
collapsed, and their assessment may be problematic
for both noncontrast and contrast-enhanced EAUS
(Fig. 27). On the other hand, EAUS is very useful in
the recognition of coexisting occult sphincter defects.
The major problems while investigating primary
tracts with EAUS occur because of the structure alter-
ations of the anal canal and perianal muscles and tis-
sues, which can overstage the fistula, or poor defini-
tion of the tract when filled with inflammatory tissue,
which can downstage the fistula. Differentiation
between granulated tracts and scars is sometimes dif-
ficult. Straight tracts are easily identified, but smaller
and oblique tracts are more difficult to image. Sec-
ondary tracts, when present, are related to the main
one and are classified as intersphincteric,
transsphincteric, suprasphincteric or extrasphinc-
teric. Similarly, horseshoe tracts, when identified, are
categorised as intersphincteric, suprasphincteric or
extrasphincteric (Fig. 28-30). The use of 3-D EAUS,
which enables reconstruction of transversal images
of the anal canal in the coronal and sagittal planes, is
very helpful in tracing the pathway of a tract.
The dentate line is not visible as an anatomical
structure but is assumed to be just below the mid-
point of the IAS. For this reason, the internal opening
of an anal fistula is seldom clearly defined.
Endosonographic criteria for the site of an internal
opening, according to Cho [17], are the following: (1)
an appearance of a root-like budding formed by the
intersphincteric tract, which contacts the IAS; (2) an
appearance of a root-like budding with an IAS defect;
(3) a subepithelial breach connecting to the inter-
sphincteric tract through an IAS defect. The site is
categorised as being above, at or below the dentate
Fig. 17. Acute supralevator abscess presenting as an area of
low reflectivity in the right side of the anal canal deep to the
puborectalis muscle (a). Three-dimensional reconstruction
in the coronal plane (b). Volume render mode (c)
a
c
b
82 G.A. Santoro, M. Starck, L. Campana, B. Fortling
line (in relation to the presumed location of the den-
tate line at the middle third of the anal canal) or in
the rectal ampulla. In addition, the site of the internal
opening can also be characterised by the clock posi-
tion, being classified from 1 o’clock to 12 o’clock. The
internal opening can be identified as hypoechoic
(when acute inflammation is present) or hyperechoic
(when chronically inflamed).
After standard EAUS examination, in patients in
whom the external fistula opening is patent,
1.0–2.0 ml of 3% hydrogen peroxide (HP) can be
injected very slowly using an 18-gauge plastic cannu-
la via this opening while ultrasonic scanning of the
anal canal is performed [16]. When no obvious exter-
nal opening is present, a focal, elevated erythematous
region immediately adjacent to the anal orifice is fre-
quently identified. The soft catheter tip should be
firmly pressed onto or probed into the center of this
region, where the skin is easily broken, and the exter-
nal opening located. Gas is a strong ultrasound
Fig. 18. Horseshoe collection in the intersphincteric space
Fig. 19. Intersphincteric fistula at 3 o’clock position
Fig. 20. Intersphincteric fistula with internal opening at 6
o’clock position and horseshoe extension in the left lateral
intersphincteric space
Fig. 21. Posterior transsphincteric tract extending through
the external sphincter
Perianal Crohn’s Disease: Assessment with Endoanal Ultrasonography 83
reflector, and after injection, fistula tracks become
hyperechoic, and the internal opening is identified as
an echogenic breach at the submucosa (Figs. 31, 32).
This method can be particularly useful when an
active fistulous tract needs to be distinguished from
postsurgical or posttraumatic scar tissue that can
cause tissue alterations that are difficult to analyse.
During this technique, however, the operator must
be careful because the injected HP often results in
bubbling into the anal canal, which then acts as a bar-
rier to the ultrasound wave. Another disadvantage
inherent to HP injection is the very strong reflection
that occurs at a gas/tissue interface, which blanks out
any detail deep into this interface. The bubbles pro-
duced by HP induce acoustic shadowing deep into
the tract, so all information deep into the inner sur-
face of the tract is lost. To reduce this potential pitfall
of imaging, a volume-rendered 3-D data set can facil-
itate the following of a tortuous fistula tract due to the
transparency and depth information (Fig. 33) [16].
Fig. 23. Three-dimensional reconstruction in the sagittal
plane showing a transsphincteric fistula that traverses the
middle part of the external sphincter
Fig. 22. Anterior transsphincteric tract at the level of trans-
verse perineii
Fig. 24. Three-dimensional reconstruction in the sagittal
plane showing a high transsphincteric tract traversing both
sphincters in the higher part of the anal canal
Fig. 25. Suprasphincteric tract extending through the pub-
orectalis muscle
84 G.A. Santoro, M. Starck, L. Campana, B. Fortling
Accuracy
Imaging with EAUS has been shown to be a useful
method (accuracy ranging from 63% to 100%) for
evaluation of perianal abscesses and fistulae in CD
[7–11, 13, 18]. Van Outryve et al. [8] reported that the
routine proctological examination showed Crohn’s
lesions in 30% of patients and EAUS performed with
a linear probe detected anorectal anomalies in 75% of
patients. Moreover, EAUS was superior to CT scan in
the study of pararectal and para-anal abscesses and
fistulae. Schratter-Sehn et al. [19] demonstrated 46
fistulae, verified by surgery, in 36 patients with CD
using EAUS performed with a 5-MHz sector (270°)
scanner. Tio et al. [9] evaluated 36 patients with CD
and suspected perianorectal disease. In the 17
Fig. 26. Extrasphincteric fistula with direct communication
between the perineum and rectum and no anal canal
involvement
Fig. 27. Anovaginal fistula (arrow)
Fig. 28. Transsphincteric fistula (small arrows) with horse-
shoe secondary extension through the intersphincteric
space (large arrows)
Fig. 29. Posterior transsphincteric fistula with horseshoe
secondary extension in the ischioanal space (arrows)
Perianal Crohn’s Disease: Assessment with Endoanal Ultrasonography 85
patients that had surgically confirmed fistulae, EAUS
identified fistula in 14 (82.4%). Solomon [3] reported
that patients with CD often have high and complex
perianal fistulae. Using EAUS performed with a 7- to
10-MHz radial probe, they found that 40% of fistulae
involved the upper half of the anal sphincter, 30% of
patients had supralevator chronic abscess cavities
and 29% of women had rectovaginal fistulae.
In the literature, several studies have reported on
ultrasonographic findings after treatment. West et al.
[20] evaluated the effect of combined ciprofloxacin
and infliximab in perianal CD using HP-enhanced 3-
D ultrasound (3-D HPUS). Only three of the 13
patients with a clinical response at week 18 also
showed improvement on 3-D HPUS. This result is in
agreement with van Bodegraven et al. [21], who
reported that although clinical improvement was seen
after short-term infliximab treatment, most fistulae
still persisted on EAUS. These persistent lesions may
lead to relapse of symptoms or abscess formation. In
a long-term study, Rasul et al. [22] evaluated whether
the clinical improvement after infliximab in 35
patients with Crohn’s disease perianal fistulae was
associated with endosonographic closure of fistula
Fig. 30. Transsphincteric fistula at 3 o’clock position (arrow)
with horseshoe secondary extension (HS) and forming an
abscess into the right ischioanal space (A)
Fig. 31. Posterior transsphincteric fistula, after hydrogen
peroxide injection, appearing as a hyperechoic tract
extending through the external sphincter, with a secondary
hyperechoic tract in the right ischioanal space
Fig. 32. Posterior transsphincteric fistula (small arrows) with horseshoe secondary intersphincteric extension (large
arrows) before (a) and after (b) hydrogen peroxide injection
a b
86 G.A. Santoro, M. Starck, L. Campana, B. Fortling
tracts. TPUS identified more fistulae than appreciated
clinically, as well as the presence of unsuspected fluid
collections. Short-term clinical response was higher
than radiographic response, and fistulous tracts on
TPUS were still present in many clinical responders at
week 8 (49% vs 14%, respectively). At week 56, com-
plete clinical closure of fistulae remained in approxi-
mately one half of patients; however, ultrasonograph-
ic healing occurred in 46% of patients, and this corre-
lated well with clinical healing. The main conclusion
of this study is that even though fistulae clinically may
have healed in the short term after initial treatment,
further long-term therapy may be required if defects
persist radiographically, even to a point that radiolog-
ical improvement is seen so that symptom relapse and
abscess formation can be prohibited.
A number of comparative studies have been per-
formed to assess the efficacy of EAUS and MRI in
evaluating perianal CD [8–11]. Some studies have
shown superiority for MRI [23] whereas others have
shown little difference [10, 11]. MRI scans can
involve use of an endoanal coil or phased-array coil.
Endoanal coil provides excellent spatial resolution
but is unable to detect deeper fistula tracts and dis-
tant abscess collections, which are better assessed
using phased-array coil [24]. MRI is useful for assess-
ing the integrity of the IAS and EAS as well as identi-
fying complex fistula tracts and abscesses [25]; how-
ever, pelvic MRI was shown to have a tendency to
miss short or superficial fistula tracts. Orsoni et al.
[11] conducted a prospective study comparing EAUS
performed with a linear probe, pelvic MRI performed
with body coil and examination under anaesthesia
(EUA) in 22 patients and found EAUS to be the most
sensitive modality. Agreement for fistulae with EAUS
and MRI when compared with surgical findings was
82% and 50%, respectively. Schwartz et al. [10] com-
pared the accuracy of MRI performed with phased-
array coil, EAUS performed with both radial and lin-
ear probe and EUA in 34 patients with Crohn’s peri-
anal fistulae. All three methods demonstrated good
agreement with the “consensus gold standard” (MRI,
87%; EAUS, 91%; EUA, 91%). In addition, when any
two of the three methods were combined, accuracy
was 100%. Maier et al. [23] showed that MRI was
superior to EAUS performed with a radial probe in
the assessment of fistulae in CD. Overall sensitivity of
EAUS and MRI was 73% and 91% for primary fistu-
lae and 69% and 88% for recurrent fistulae, respec-
tively. Wedemeyer et al. [13] showed an excellent
agreement (k >0.83) between MRI performed with a
phased-array surface coil and TPUS in 25 patients
with CD and clinical signs of perianal inflammatory
disease. They recommended TPUS as a screening
tool in acute perianal disorders in CD and to evaluate
treatment outcomes.
Conclusion
EAUS evaluation of perianal complications of CD has
been demonstrated to be superior to fistulography
and CT and equal or superior to MRI. This imaging
modality should be part of the diagnostic workup,
helping guide therapy and preventing unnecessary
surgery [26].
Fig. 33. Transsphincteric fistula (arrow) with an ischiorectal abscess (a). Three-dimensional reconstruction using “volume
render mode” after hydrogen peroxide injection
a
b
Perianal Crohn’s Disease: Assessment with Endoanal Ultrasonography 87
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Endoscopic Diagnosis of Crohn’s Disease
Endoscopy plays a major role in the diagnosis of
Crohn’s disease, especially with colonoscopy and
ileoscopy; however, upper gastrointestinal
endoscopy, enteroscopy, capsule endoscopy and
endoscopic ultrasound (EUS) may help confirm and
determine the extent of disease. Direct visualisation
of mucosal lesions and the possibility of obtaining
histologic specimens make endoscopic procedures
the first-line tests in the evaluation of gastrointestinal
diseases. However, radiology and magnetic reso-
nance imaging (MRI) contribute to the diagnosis
when visualising the small bowel [1].
Endoscopic Features of Crohn’s Disease
Morphologic pictures observed during an endoscop-
ic procedure are protean. The earliest endoscopic
finding is the aphthous ulcer with a diameter of a few
millimeters surrounded by a thin red halo of oede-
matous tissue [2], which is found in about 30–40% of
patients with Crohn’s colitis. Focal oedema and spo-
radic red spots are present in the “preaphthoid phase
[3]
. These lesions usually are multiple, becoming
stellate or linear in shape, with normal intervening
mucosa, and can be rounded or long and serpigi-
nous. Cobblestone-like areas are formed when ulcers
assume a longitudinal and transverse pattern form-
ing a grid. This is due to submucosal oedema, includ-
ing nonulcerated mucosa [4]. Sometimes, these
lesions differ little from inflammatory polyps or
pseudopolyps also often present in Crohn’s colitis
[5]. The presence of punched-out ulcers adjacent to
inflamed mucosa gives rise after healing to mucosal
bridges. Stenosis is often present in areas of severe
inflammation, especially in the pyloric sphincter,
ileocecal valve and rectosigmoid junction [6]. Length
may vary from less than 3 cm to more than 10 cm and
a width of less of 5 mm. Fistulae have been reported
in more than 8% of patients affected by Crohn’s coli-
tis, often near stenoses [7]. Less common manifesta-
tions are diffuse mucosal irregularities with erythe-
ma, oedema, granularity.
Carrying out multiple biopsies in areas both
involved and uninvolved by the disease increases
diagnostic accuracy of endoscopy and pathology.
The use of large biopsy forceps should be taken in
consideration for obtaining a better specimen of the
submucosa [8]. Finally, during colonoscopy, it is
mandatory that intubation of the terminal ileum is
performed in order to take biopsies that may
increase the procedure’s sensitivity and specificity
[9].
Colonoscopy
Colonoscopy is an important aid in diagnosis and
management of patients with inflammatory bowel
disease (IBD). This procedure, with multiple biop-
sies, is indicated when adequate data are not avail-
able from clinical, sigmoidoscopic or radiologic stud-
iesand there is strong clinical suspicion of IBD. How-
ever, colonoscopy carries an increased risk of perfo-
ration when the bowel wall is inflamed and presents
with ulcers and fistulae. Known or suspected severe
inflammation is a relative contraindication to
colonoscopy. Toxic megacolon is an absolute con-
traindication to endoscopy if performed only for
diagnostic purpose because of the weakness of the
colonic wall, which is paper thin [10]. Endoscopy
monitoring to assess response to therapy has been
evaluated by a randomised study in which patients
were treated with steroids. In one group, steroid
tapering was decided on following clinical remission;
in the other group, the decision was based on endo-
scopic findings. The conclusion was that
colonoscopy was not necessary to decide when to
taper steroids, as the two groups did equally well
[11].
Colonoscopy evaluation of the extent of disease is
also part of preoperative assessment in order to
decide the extent of resection and define the seg-
ments free from disease. The ileocecal area is the
Endoscopy in Crohn’s Disease
Andrea Ederle, Paolo Inturri, Piero Brosolo, Alberto Fantin, Monica Preto
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