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9 Anorectal Physiology Assessment in Patients with Anal Fistula: When... 137
Nevertheless, performing such preoperative investigations should be avoided in
cases of abscesses or acute inflammation because there would be an impossibility to
perform or the final data won’t be completely reliable. In fact, it is suggested to
perform them in those patients with chronic fistula, drained or not with seton, thus
planning a sphincter-saving procedure.
Moreover, anorectal physiology assessmen t is useful in those affected by a simple
fistula suit able to be laid open in which there is an evident or occult preoperative
impaired anal continence which inevitably converts an anatomic simple fistula into a
complex fistula considering the whole clinical-functional condition. This would help
to better classify fistulas and their complexity into an anatomo-functional entity
which may have impact on the final outcome.
In this scenario, it was recently proposed the 3D HR-ARM as a single investigation able to correlate the anatomy and its defects such as anal fistula to the anorectal
function. A recent study, indeed, has shown a moderate to good visual agreement
between conventional fistula visualization using 3D-EUS and a 3D HR-ARM
reports where it was found a pressure drop in the correspondent area of the internal
orifice (Felt-Bersma et al. 2018).
Although these are interesting results, some questions remained still unanswered
as:
– Considering that 3D HR-ARM has not uniformly defined normal range values,
how much should be the pressure drop to be considered significant to get a
diagnosis of internal orifice and not related to anal irregular shape or even
postsurgical scar?
– How the width of the pressure reduction area may correlate to anal incontinence
or become as a predictive risk factor of postoperative impaired continence?
– Is it easily reproducible?
Anyhow, this was one of the first attempts to evaluate the impact of technological
advancement upon the anatomo-functional outcome in patients with anal fistula.
In conclusion, anorectal physiology assessment remains a specialistic approach
that should not be recommended as a routinely preoperative examination but proposed as complementary investigations in selected patients in which the preoperative
information (anamnestic and clinical) needs to be integrated with further examinations helping to get the final decision and better explain to the patients the likelihood
of postoperative complications.
Ethical Approval All procedures performed in studies involving human participants were in
accordance with the ethical standards of the institutional and/or national research committee and
with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Originality The chapter is an original work, has not been published before, and is not being
considered for publication elsewhere in its final form, in either printed or electronic media. The
authors declare that any republication of the data (e.g., in secondary analysis or translation) will not
constitute redundant publication, will not breach copyright, and will reference the original
publication.
138 A. Sturiale et al.
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Endoanal Ultrasound in the Diagnosis
of Cryptoglandular Anal Fistulas
10
and Abscesses
Richelle J. F. Felt-Bersma
Contents
1 Introduction . ............... .................................................................. 142
2 Anal Anatomy ........................... ............................................. ....... 143
3 Classification of Fistulas ................. ............................... .................... 145
4 EAUS Imaging ..... .................................... ..................................... 146
4.1 Probes EAUS . . . . ...................................................................... 146
4.2 Performing EAUS ..................................................................... 147
4.3 EUS in Perianal Fistulas ... . . . . ....................................................... 147
4.4 Adding Hydrogen Peroxide (H
4.5 Cryptoglandular Fistulas ................................... ........................... 148
4.6 Crohn’s Fistulas ................. .................................. .................... 152
5 Comparison with Other Diagnostic Modalities .................................... ......... 155
5.1 Comparison with Surgery . . ...... . . . . ...... . . . . ....... . . . . ...... . . . . ...... . . . . ....... . 155
5.2 Comparison with MRI ................................................................ 156
5.3 Perineal Ultrasound ................................................................... 158
5.4 Comparison with 3D High-Resolution Anorectal Manometry (3D-HRAM) ........ 159
6 Conclusion and Recommendation .......................................................... 161
References ............................ ............................................... ............ 161
) .................................................. 147
2O2
Abstract
Endoanal ultrasound (EAUS) is a technique that provides imaging of the anal
sphincters, its surrounding structures, and the pelvic floor. It has proven to be an
accurate diagnostic modality delineating anatomy of both cryptoglandular and
Crohn’s perianal fistula and abscesses.
Three-dimensional imaging and the introduction of hydrogen peroxide
(HPUS) in the external fistula opening further improved accuracy. EAUS is
R. J. F. Felt-Bersma (*)
Department of Gastroenterology and Hepatology, Amsterdam University Medical Centre,
Amsterdam, The Netherlands
Proctos Clinic, Bilthoven, The Netherlands
e-mail: rjf.felt@amsterdamumc.nl
© Springer Nature Switzerland AG 2022
C. Ratto et al. (eds.), Anal Fistula and Abscess, Coloproctology,
https://doi.org/10.1007/978-3-030-76670-2_12
141
142 R. J. F. Felt-Bersma
comparable to examination under anesthesia and equally sensitive as (endoanal)
MRI in fistula detection. Except when more proximal fistulas or abscesses are
suspected, an additional MRI should be performed as it is more accurate. Since
fistula complexity can be expected in recurrent cryptoglandular fistula preoperative imaging is mandatory. Preoperative EAUS can help avoid missing tracks
during surgery lowering the chance for the fistula to persist or recur. It can easily
be perfor med in an outpatient setting at low costs and skills can easily be
acquired.
In conclusion, EAUS is a highly accurate tool for the assessment of perianal
fistulas, and EAUS or MRI is mandatory in recurrent cryptoglandular or Crohn’s
fistulas. Skills are quickly incremented, costs are low, and it has the potential to
improve outcome of patients with both cryptoglandular and fistulizing Crohn’s
disease.
Keywords
Peri anal fistula · Peri anal sepsis · Anal ultrasound · Endoanal endosography ·
Hydrogen peroxide
1 Introduction
A perianal abscess, a simple anorectal abscess, is the acute phase manifestation of
cryptoglandular disease. It results from infection of one of the 6–10 rudimental anal
glands that extend from the anal crypts. In comparison, a perianal fistula represents
the chronic phase of suppuration in this perirectal process. A perianal fistula is a
common benign anorectal condition with a prevalence of 1 per 10:000, mostly
affecting males in their 40s (Abcarian 2011).
Numerous other disorders can cause perianal sepsis including Crohn’s disease,
chronic fissures, pilonidal sinus, hidradenitis suppurativa, Bartholin’s gland abscess,
tuberculosis, HIV, actinomycosis, anal carcinoma, or hematologic malignancy.
However, cryptoglandular disease accounts for 90% of patients. Cryptoglandular
abscesses and fistulae are treated by surgery and efficiently eradicating perianal
sepsis whilst preserving anal sphincter integrity is the main goal. Preoperatively
missed tracts are considered the main reason for recurrence. Therefore, the exact
fistula pattern in relation to patient specific anatomy should be assessed before
performing definitive surgery. Preoperative imaging can help delineate fistula pattern, guiding surgical strategy without compromising the anal sphincters. An excellent imaging modality often used for this purpose is endoanal ultrasound (EAUS). A
rotating probe with a 3D 360
introduced into the anal canal up to the distal part of the rectum. Current clinical
indications for EAUS are fecal incontinence for the detection of anal sphincter
defects and atrophy, perianal disease to assess fistula pattern, and anorectal carcinoma for staging and follow up. This review will focus on the clin ical relevance of
EAUS concerning cryptoglandular and Crohn’s perianal abscesses and fistulae.
radius and a frequency between 5 and 16 MHz is
10 Endoanal Ultrasound in the Diagnosis of Cryptoglandular Anal Fistulas and... 143
2 Anal Anatomy
The anal canal is 2–4 cm long, starting at the most distal part of the anorectal ring, at
the puborectalis muscle (PR), and extending down to the anal orifice. The dentate
line is a wavy line which divides the upper two-thirds and lower one-third of the anal
canal. Proximal to the dentate line pain sensation is negligible as innervation is
sympatic and parasympatic. Below the dentate line however, nerve supply is
somatic, making the tissue highly sensitive which is important to know when
examining the anal canal. Immediately proximal to the dentate line the mucosa has
8–14 folds called the columns of Morgagni. It represents the funneling of the rectum
as it narrows into the anal canal. The anal glands empty into the anal crypts just at the
base of these columns of Morgagni. Glands sometimes extend through the internal
anal sphincter (IAS) and when its ducts are blocked, an anal abscess or fistula can
arise.
Normally there is no air present in the anal canal, therefore the anus lies tightly
around the endoprobe and outstanding images can be obtained with EAUS. The
reproducibility of endosonographic findings have been thoroughly investigated in
healthy volunteers (Law and Bartram 1989; Nielsen et al. 1992 ). Further studies
established basic endosonographic anatomy by making comparisons to anatomical
preparations (Sultan et al. 1993).
The muscles surrounding the anal canal are important for maintaining continence.
The subsequent layers which can be identified with EAUS are the mucosa/submucosa, the internal anal sphincter, the intersphincteric groove, the external anal
sphincter (EAS), and the PR. (Burnett and Bartram 1991; Papachrysostomou et al.
1994; Sultan et al. 1994; Poen et al. 1999). The submucosa shows as a mixed
echogenic structure and is partly collapsed by pressure of the endoprobe. Its thickness increases slightly with age, which is caused by physiological distal displacement plus enlargement of the anal cushions, and has been found to a larger extent in
internal hemorrhoids. The mucosa/submucosa cannot be identified separately with
the frequencies used.
The internal anal sphincter (IAS) is the thickened continuation of the circular
smooth muscle layer of the rectum. This muscle ends above the external sphincter
and is important for passive continence. It is a 1–3 mm thick involuntary muscle
which appears as a black hypoechoic band on endoanal ultrasound. It is possible to
partially divide the internal sphincter by fistulotomy without causing significant
incontinence. However, anterior or posterior division can lead to leakage of stool
due to the creation of an oval-shaped defect, known as a keyhole deformity. The
internal anal sphincter increases in thickness and echogenicity with age, both in
patients and in healthy volunteers. Histological evidence suggests that aginginduced sclerosis of the internal anal sphincter is responsible for this finding. The
muscle thickness is not related to sex, body weight, or length.
The external anal sphincter (EAS) is a 4–10 mm thick voluntary skeletal muscle.
In women the external sphincter is thinner and shorter anteriorly, making it more
vulnerable to obstetric anal sphincter injury. Besides being related to gender, thickness is also correlated to body weight and age. Due to the structure of striated muscle
144 R. J. F. Felt-Bersma
the external sphincter appears as a band of mixed echogenicity on EAUS. Proximally the EAS weaves itself into the puborectalis and levator ani muscles. Distally it
ends slightly past the IAS. As a resul t, an intersphincteric groove can be palpated on
digital examination. This intersphincteric groove can be made visible during EAUS;
however, its importance is controversial.
EAUS of the anal canal identifies these layers and structures (Fig. 1). The PR
muscle is almost always easily visualized and can serve as a point of orientation: it
appears as a V-shaped echogenic band, which slings dorsally around the rectum
(Fig. 1a). When withdrawing the probe, the echogenic band is closing anteriorly,
thus forming the external anal sphincter (Fig. 1b). Figure 1c and d represent the
lateral and coronal view respectively.
Other anatomical structures which can be seen using EAUS are the anococcygeal
ligament (posterior), the levator ani, the transverse perineal muscles, the
ischiocavernous muscles, the urethra, and the pubic bones. The anococcygeal
Fig. 1 Normal EAUS image of the anal sphincter. (a) Transversal image, level of the puborectal
muscle, (b) transversal image, mid-sphincteric level, (c) sagittal image, (d) frontal image. P ¼ probe,
PR ¼ puborectal muscle, EAS ¼ external anal sphincter, IAS ¼ internal anal sphincter
10 Endoanal Ultrasound in the Diagnosis of Cryptoglandular Anal Fistulas and... 145
Fig. 2 Transversal vaginal image; the probe (P) is positioned in the vagina. (a) Level of the
puborectal muscle and (b) mid-sphincteric. P ¼ probe, Pb ¼ puborectal bone, R ¼ rectum,
EAS ¼ external anal sphincter, IAS ¼ internal anal sphincter
ligament appears as a hypo echoic triangle and causes narrowing of the external
sphincter. The levator ani comprises of three parts, the mentioned puborectal muscle,
the ileococcygeal muscle, and the pubococcygeal muscle.
The normal rectum measures 11–16 cm in length with a maximum diameter of
4–5 cm. On EAUS the normal rectal wall is 2–3 cm thick and composed of the same
five-layer structure as the entire digestive tract. It is generally filled with some remainders of fecal material or air. These circumstances can make it challenging to obtain an
optimal acoustical surrounding. Infusion of water into the rectum using a flexible plastic
cannula is a manner in which imaging quality can be improved. When EAUS is not
possible due to extreme anal stenosis, pain or an asymmetrical anal canal vaginal
endosonography can be performed as an alternative (Fig. 2) (Poen et al. 1998a).
3 Classification of Fistulas
In cryptoglandular disease nearly all abscesses originate in the intersphincteric
space. From here they can migrate up, down, or circumferentially around the anal
canal. Abscesses are classified according toward where they have extended as
perianal, intersphincteric, ischiorectal, or supralevatoric. In around half undergoing
surgical incision and drainage of an abscess, a fistula will develop. In
cryptoglandular disease perianal fistulae are classified in relation to the striated
muscle structures they surpass as submucosal (15%), inter- (24%), trans- (58%),
supra- (3%), or extrasphincteric (<1% (Rosa et al. 2006). It is a slightly adapted
version of the surgical classification first described by Parks et al. (1976)
which lacked submucosal fistulae. These are located superficially and not involve
the anal sphincter complex. Intersphincteric fistulae are characterized by a course
through the intersphincteric space without penetrating the external anal sphincter.
Transsphincteric fistulae breach through the external sphincter, pass into the
146 R. J. F. Felt-Bersma
ischiorectal fossa and find their way to the perianal skin. They are often subcategorized into low- and high-transsphincteric fistulae depending on the amount
of external sphincter involvement. There is some discussion about what should be
considered high or low; some consider higher than one-third of the sphincter high
and others half of the sphincter.
Suprasphincteric fistulae surpass the m. puborectalis, move into the ischiorectal
fossa, and reach the perianal skin. Extrasphincteric fistulae have no relation to the
sphincter complex and are found in patients after prior surgery or in non-cryptoglandular
disease.
4 EAUS Imaging
4.1 Probes EAUS
Endoanal ultrasound is performed with a transrectal ultrasound probe. The rigid
rotating endoprobes with a 360
view are preferable. Rigid mechanical probes are
provided by Bruel & Kjaer (BK) Medical (Herlev, Denmark) and Hitachi-Aloka
ASU-67 (7.5–10 MHz, Tokyo, Japan). The latter is no more available. We use a BK
Hawk type 2050, with a rotating endoprobe (6–16 MHz, focal range 2–4.5 cm) with
a water filled hard sonolucent cone (diameter 1.7 cm), producing a 3D 360
view
(Fig. 3). The frequency used in EAUS lies between 2.5 and 16 MHz, and images are
formed by reflection at the interfaces of two structures. Part of the signal is transmitted and part is reflected. Reflections from deeper structures are weaker, due to
greater signal attenuation. This can be corrected by changing the MHz frequency;
lower frequencies (2.5 MHz) penetrate better into deeper layers, and superficial
structures are better visualized with higher frequencies (16 MHz).
Fig. 3 EUS device. (a) Apparatus and (b) the probe
10 Endoanal Ultrasound in the Diagnosis of Cryptoglandular Anal Fistulas and... 147
4.2 Performing EAUS
In our department, the patient is positioned in the left lateral decubitus position with
the anus at the very edge of the bed, allowing movement of the probe by the operator.
Before introducing the probe, inspection of the perineal area is performed to look for
external fistula openings. Next, a digital rectal examination is performed to rule out
possible abnormalities (stenosis, painful lesion, or a tumor). To optimize conductance and for hygienic reasons the rigi d probe is covered with a condom filled with
ultrasound gel. The probe is then covered with lubrication gel and gently introduced
into the anus up to the distal part of the rectum. Important landmarks are the prostate,
the vagina, and the PR muscle. Then the probe is first (manually) slowly withdrawn
and enters the anal canal were the anorectal anatomy as described earlier can be
visualized. When there is loss of contact with the anal canal due to an asymmetrical
anus or the presence of air, reverberation can occur. Reverberation is an artifact due
to mismatch of acoustic impedance at an interface. The signal echoes back and forth
giving rise to a series of concentric black and white rings. Improving acoustic
qualities by gently maneuvering the probe solves this problem. Next the probe is
repositioned above the PR muscle and the automatic puller is started.
4.3 EUS in Perianal Fistulas
The need to better establish the fistula tracts, the use of conventional 2D EAUS in
anorectal imaging was announced in 1989 by Law and Bartram as “a quick and
minimally invasive technique for obtaining high-resolution images of the anal canal
and surrounding structures.” Using the technique for the evaluation of perianal
fistula was first reported later that same year (Law et al. 1989).
Additional studies reported diagnostic accuracy rates up to 94% regarding pre-
operative classification of the primary fistula tract (Deen et al. 1994; Choen et al.
1991) and accuracy rates up to 93% regarding prediction of the site of the internal
opening. Furthermore, these studies reported a favorable outcome of EAUS when
compared with digital examination in preoperative fistula evaluation. With digital
examination and probing fistula assessment is often possible; however, EAUS
improved anatomic fistula definition.
4.4 Adding Hydrogen Peroxide (H2O2)
Aperianalfistula presents itself as a hypoechogenic area with the shape of a “track.”
Abscesses are largerand wider hypoechogenic areas. Sometimes, when the fistula tract
is wide or when there is easy contact with air in the bowel or outside a spontaneous
air-artifact is visible. This mimics the effect of adding hydrogen peroxide to obtain
better visualization.
In case of the presence of an externa fistula opening, hydrogen peroxide as a
contrast agent can be introduced. With this technique hydrogen peroxide is gently