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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_1056_Библиотеки_им_академика_М_И_Перельмана.pdf
12 Utility and Limitations of Endoanal Ultrasound in the Diagnosis of Crohn’s... 199
Table 1 Ultrasound classification (de la Portilla Int J Colorectal Dis)
Type of
fistula Description
Type I Superficial fistula (subcutaneous)
Type II Only affects the smooth muscle (inter-sphincteric)
Type III Affects the striated and smooth muscle (transsphincteric, suprasphincteric)
Type IV The pathway does not reach the complex sphincter because it ascends parallel to
Nomenclature Anal fistula (AF), number of pathways (nT),type of pathways (I, II, III, IV)
the anal canal to enter the rectum (blind, extrasphincteric)
accompanied by an (a) if it has an abscess, (s) if it has a probe, and (h) if it is a
horse-shoe path
Each description of a pathway should be separated by a semicolon (;)
Example:
AF3T:IIIas;IIh;I (anal fistula with three pathways)
1. Pathway with a probe that affects both sphincters and has an abscess
(IIIas)
2. Pathway in the form of a horse-shoe with no associated collection
(IIh)
3. Superficial pathway with no associations (I)
Fig. 7 Large ischiorectal abscess in a patient presenting with pain and purulent discharge
4 Conclusion
Endoanal ultrasound is a simple, valuable, and inexpensive imaging modality for the
evaluation of fistulas related to Crohn’s disease, providing excellent imaging of the
anorectal region, including the anal sphincters and the intersphincteric planes. In
addition, with the 3D high-resolution transducers and oxygen peroxide enhanced
200 L. C. C. Oliveira
technique, it can demonstrate adequate position of the internal opening, essential for
planning surgical approach, minimizing the risks of sphincter damage and anal
incontinence.
5 Cross-References
▶ Anorectal Anatomy Related to Anal Fistula and Abscess
▶ Anorectal Physio logy Related to Anal Fistula and Abscess
▶ Endoanal Ultrasound in the Diagnosis of Cryptoglandular Anal Fistulas and
Abscesses
▶ Future Perspect ives in the Diagnosis of Anal Fistula and Abscess
▶ Magnetic Resonance and Traditional Radiology in the Diagnosis of
Cryptoglandular Anal Fistula and Abscess
▶ Magnetic Resonance Imaging in the Diagnosis, Characterization, and Manage-
ment of Crohn’s Fistula
References
Alabiso ME, Iasiello F, Pellino G et al (2016) #D-EAUS and MRI in the activity of anal fistulas in
Crohn’s disease. Gastroenterol Res Pract 2016:1895694
Botti F, Losco A, Vigano C, Oreggia B, Prati M, Cointessini AE (2013) Imaging techniques and
combined medical and surgical treatment of perianal Crohn’s disease. J Ultrasound 18(1):19–35
de la Portilla F, Durán V, Maestre MV et al (2015) Effectiveness of a three-dimensional anorectal
ultrasound in perianal Crohn’s disease: incompatibility with clinical and surgical examinations.
Int J Colorectal Dis 30(4):529–534
Fleshman J, Tay R (2014) Crohn’s disease. In: Abcarian H (ed) Anal fistula. Springer, New York,
pp 139–157
Losco A, Viganò C, Conte D, Cesana BM, Basilisco G (2009) Assessing the activity of perianal
Crohn’s disease: comparison of clinical indices and computer-assisted anal ultrasound. In flamm
Bowel Dis 15:742–749
Orsoni P, Barthet M, Portier F et al (1999) Prospective comparison of endosonographic, magnetic
resonance imaging and surgical findings in anorectal fistula and abscess complicating Crohn’s
disease. Br J Surg 86:360–364
Parks AG, Gordon PH, Hardcastle JD (1976) A classification of fistula-in-ano. Br J Surg 63:1–12
Santoro GA, Fortling B (2007) The advantages of volume rendering in three-dimensional endo-
sonographic of the anorectum. Dis Colon Rectum 50(3):359–368
Santoro GA, Murad-Regadas SM (2017) Endoanal ultrasonographic imaging of the anorectal
region. In: Practical pelvic floor ultrasonography. Springer, pp 253–276
Siddiqui MRS, Ashrafian H, Tozer P et al (2012) A diagnostic accuracy meta-analysis of endoanal
ultrasound and MRI for perianal fistula assessment. Dis Colon Rectum 55:576–585
Toyonaga T, Tanaka Y, Song JF et al (2008) Comparison of accuracy of physical examination and
endoanal ultrasonography for preoperative assessment in patients with acute and chronic anal
fistula. Tech Coloproctol 12(3):217–223
Viganò C, Losco A, Caprioli F, Basilisco G (2011) Incidence and clinical outcomes of
intersphincteric abscesses diagnosed by anal ultrasonography in patients with Crohn’s disease.
Inflamm Bowel Dis 17(10):2102–2108
Zawadzki A, Starck M, Bohe M, Thorlacius H (2012) A unique 3D endoanal ultrasound feature of
perianal Crohn’s fistula: the ‘Crohn ultrasound fistula sign’. Colorectal Dis 14:e608– e611
Magnetic Resonance Imaging
in the Diagnosis, Characterization,
13
and Management of Crohn’s Fistula
Matthew Vincent, Phillip F. C. Lung, and Kapil Sahnan
Contents
1 Introduction . ............... .................................................................. 202
2 Imaging ...... . ................. ........................................................ ...... 203
3 Diagnosis ....................... ......................................... .................... 203
4 MRI Technique .......................................... .................................... 204
5 Disease Monitoring .......................................................................... 205
6 Future Directions ... . . . ...... . . . . ...... . . . . ...... . . . ..... . . . . . ...... . . . ....... . . . ...... . . . . .. 208
7 Conclusion ................................................................................... 209
8 Cross-References .......................... ............................................. ..... 209
References ............................ ............................................... ............ 209
Abstract
Complex fistulizing perianal Crohn’s disease (pCD) is a challenging affliction to
manage. Imaging alongside clinical examination helps the clinician elucidate the
morphology of the fistula which is one of the first steps of forming a management
strategy. MRI is and remains the gold standard investigation and can be used to
plan interventions and even further along the management pathway to assess the
effect of the healing intervention.
M. Vincent
Department of Metabolism, Digestion, and Reproduction, Imperial College London, Hammersmith
Hospital, London, UK
e-mail: matthew.vincent@nhs.net
P. F. C. Lung
Fistula Research Unit, St Mark’s Hospital and Academic Institute, Harrow, UK
e-mail: philliplung@nhs.net
K. Sahnan (
Fistula Research Unit, St Mark’s Hospital and Academic Institute, Harrow, UK
Department of Surgery and Cancer, Imperial College London, St Mary’s Hospital, London, UK
e-mail: ks303@doctors.org.uk
© 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_15
*)
201
202 M. Vincent et al.
Keywords
MRI · Fistula · Crohn’s disease
1 Introduction
Crohn’s disease (CD) is a type of inflammatory bowel disease (IBD) that globally
affects between 4 and 250 people per 100,000 population with a varied presentation
(Tarrant et al. 2008 ). Between a third and a half of all patients have perianal
manifestations (Keighley and Allan 1986). These are broadly classed as fistulizing
(encompassing abscesses and Crohn’s perianal fistulas) and non-fistulizing (fissures/
ulcers, strictures/stenosis, skin tags) (Adegbola et al. 2018). A recent epidemiological study found the prevalence of Crohn’s disease in the United Kingdom to be
400 in 100,000, with the incidence at 14.3 per 100,000 person-years, peaking at 18–
30 years and 60–70 years (King et al. 2020).
CD is characterized by full-thickness microscopic inflammation with
cobblestoning and abscess formation seen as hallmarks on endoscopic examination.
Fistulizing perianal Crohn’s disease (pCD) repres ents an especially aggressive
phenotype that is notoriously difficult to treat, is associated with significant morbidity, and carries a greater chance of the patient suffering a severe and disabling disease
course, fistulas being known to cause pain and discharge, resulting in reduced quality
of life (Mahadev et al. 2011). Schwartz and colleagues demonstrated that the
cumulative risk of at least 1 perianal fistula 1 year after CD diagnosis was 12%,
after 10 years was 21%, and after 20 years was 26% in a population study (Schwartz
et al. 2002).
Optimal management of pCD relies on multidisciplinary discussion with input
from a gastroenterologist, IBD nurse, radiologist, and colorectal surgeon. Initial
assessment includes a history, examination including proctosigmoidoscopy followed
by imaging, and ideally with magnetic resonance imaging (MRI). The aim is to
assess the patient in terms of their general health (comorbidities), their CD (concomitant luminal disease, previous/current therapies, etc.), and then specifically their
perianal manifestations (previous surgeries, current symptoms, etc.). Morphological
assessment of the tract can be performed through imaging and examination under
anesthesia (EUA), whereby one aim s to delineate the anatomy of the tracts themselves and their relation to the sphincter and levator plate (Tozer et al. 2011).
Established treatment principles involve drain ing the sepsis and aggressively managing proctitis while treating the fistula medically, usually with a combination of
antibiotics, thiopurines, and anti-TNF therapies (Adegbola et al. 2020).
This book chapter will provide an overview of the role of MRI in the diagnosis
and characterization of pCD, its role in the management and tracking of disease
course in patients, and finally its capacity to be used for operative planning of
complex fistulizing disease.
13 Magnetic Resonance Imaging in the Diagnosis, Characterization, and.. . 203
2 Imaging
The European Crohn’s and Colitis Organisation’s (ECCO) guidelines (Gionchetti
et al. 2017) state that contrast-enhanced pelvic MRI is considered the ideal initial
procedure for the assessment of perianal fistulizing CD. MRI has been shown to be
more effective in the assessment of treatment response in pCD, while also being
crucial for preoperative planning, and more recently, to enable conversion into 3D
models that facilitate surgical understanding of this condition.
While MRI has been shown to be the gold standard imaging method of diagnosing and characterizing pCD, other imaging modalities have been trialed and have
their place in the evaluation of the condition. Endoanal ultrasound (EUS) and
transperineal ultrasound (TPUS) represent low-cost, quick imaging methods that,
in the hands of skilled operators, have high sensitivity and specificity for identifying
fistulizing disease (Schwartz et al. 2001). The main drawbacks of ultrasonography
include a relatively low sensitivity to detect secondary or deep tracts (Buchanan et al.
2004) and their inability to differentiate fibrosing fistula tracts from acutely inflamed
disease.
3 Diagnosis
The perianal fistulizing disease is typically categorized according to the Parks
classification as intersphincteric, transsphincteric, suprasphincteric, and extrasphincteric relative to its anatomical relationship to the anal sphincter complex
(Parks et al. 1976). A fistula can then be further described as “simple” if it consists
of one tract connecting two epithelialized surfaces and complex if it contains any
extensions or branches off this primary tract (Parks et al. 1976). Another method of
classifying perianal fistulas is the St. James University Hospital categorization
system, which gives grades of 1 to 5 based on the anatomical features of the tract
as well as the presence of secondary extensions or abscesses (Morris et al. 2000).
Accurate understanding of the anatomical relations of the fistula tract is essential to
ensure effective clearance of any sepsis in the initial operation, thereby decreasing
the likelihood of recurrence (Choen and Phillips 1991). Studi es have shown that
inaccurate evaluation of fistula anatomy by surgeons, which can occur in scarred and
complex disease, leads to increased recurrence and therefore worse outcomes
(Beckingham et al. 1996; Spencer et al. 1998). Moreover, injudicious operations
will lead to scarring and derangement of pelvic anatomy, making further operations
more difficult. As such, precise and reliable assessment of fistula anatomy and its
anatomical relations is essential in the management of pCD.
MRI in pCD has a sensitivity of 97% and a specificity of 96% (Sahni et al. 2008).
MRI is especially useful in detecting abscesses (sensitivity 96%, specificity 97%)
and horseshoe fistulas (sensitivity 100%, specificity 100%) (Beets-Tan et al. 2001).
204 M. Vincent et al.
This is especially valuable when these are not associated with any induration or
clinical signs of their presence (Garros et al. 2014).
Beets-Tan et al. (2001) assessed the clinical value of preoperative MRI in the
early 2000s by having patients due for EUA undergo MRI prior to their operation.
The MRI findings were shared with the surgeons during the operation, with the
option of then continuing to operate based on their novel findings. The study showed
that in 21% of patients, MRI revealed more anatomical information than EUA alone.
This effect was more significant in patients with Crohn’s disease, as 40% had
additional anatomical information on MRI compared to EUA.
Buchanan et al. (2002) further looked into the effect of preoperative MRI on EUA
and long-term clinical outcome in 40 patients. At the end of the operation, MRI
findings were revealed, and the surgeons could decide whether to perform a further
exploration under anesthesia or leave the operation as is. In operations where the
MRI and EUA findings disagreed and surgeons did not perform further exploration,
the authors found that 50% of these patients developed disease recurrence, all of
which were at the site predicted by MRI. The authors found that the use of MRI to
inform surgery led to a 75% decrease in disease recurrence.
4 MRI Technique
To enable accurate assessment of the anal canal and perianal fistulas, sagittal views
are performed, which allow correct orientation along the plane of the anal canal
(Fig. 1), resulting in true axial and coronal sequences through the anal canal. The
field of view should include all of the anal canal and fistulating disease and extend
above the levator plate to allow assessment of the rectum and supralevator disea se.
Fig. 1 Orientating the MRI in the correct plane
13 Magnetic Resonance Imaging in the Diagnosis, Characterization, and.. . 205
Fat-suppressed T2 weighted sequences are used to make the T2 high signa l fistula
more visible, while nonfat-suppressed sequences provide more detail on anal canal
and pelvic floor anatomy.
Coronal and sagittal images can guide the clinician to the level of the internal
opening and its relation to the anorectal anatomy, such as the levators. Axial
sequences show the fistula in relation to the internal and external sphincters. Preand post- gadolinium T1 sequences have also been used to problem solve and
identify enhancing fistulas, although it remains unclear how this relates to fistula
activity.
There are a few limitations to the use of MRI in evaluating pCD. One is the
relative expense of the imaging modality, making it prohibitive in certain environments. Another drawback is that, while MRI is effective in identifying abscesses and
fistula tracts, it is not as good at identifying ulcerations or strictures (Garros et al.
2014; Scholefield et al. 1997). Schwartz and colleagues found that, in their study of
32 patients with perianal Crohn’s fistula, diagnostic accuracy could be improved if
any two modalities (MRI, endoanal ultrasound, EUA) were used in combination
(Schwartz et al. 2001).
5 Disease Monitoring
One of the drawbacks of clinical trials on interventions in pCD has been the inability
to produce a rigorous, objective outcome measure of disease improvement. The
ACCENT-II trial evaluating the role of Infliximab in treatment for pCD used clinical
remission (defined as a decrease of >50% in the drainage of fistulizing disease) as
their primary outcome measure (Sands et al. 2004). However, it has been wellreported that the decrease in fistula drainage is only a marker of external fistula
closure, and does not reflect the internal fistula environment (Ng et al. 2009;Van
Assche et al. 2003; Jones and Tremaine 2005).
The perianal disease activity index (PDAI) represents a validated score to assess
disease burden in patients with perianal Crohn’s disease (Pikarsky et al. 2002). The
scale consists of point scores relating to a number of disease aspects including the
presence of abscesses, fistula, incontinence, and ulcers. While the PDAI has been
shown to associate with disease severity, a number of the scoring parameters
represent binary factors (i.e., presence of fistula, presence of multiple abscesses)
that do not measure how the individual factor changes over time in response to
treatment (i.e., shrinkage of fistula, decrease in size of the abscess, etc.). The fistula
disease assessment (FDA) defined clinical remission as the cessation of drainage
from all external openings and clinical improvement as a decrease in >50% in the
drainage of fistulizing disease (Present et al. 1999). This index has the limitation of
only looking at fistula drainage, which purely focuses on the patency of the external
opening and may not reflect the internal fistula environment (Ng et al. 2009; Jones
and Tremaine 2005).
Further studies (Tozer et al. 2012) reveal that, despite clinical remission, fistula
tracts in asymptomatic patients remained T2 hyperintense for a median of 13 months.
206 M. Vincent et al.
This “deep healing,” i.e., the resolution of T2 hyperintensity of fistula tracts, has
been seen as a more effective and prognostically relevant method of evaluating
disease progression than clinical remission (Chambaz et al. 2019) and currently can
only be demonstrated through MR imaging.
Recently, in response to the lack of a standardized measurement of disease
activity in perianal Crohn’s disease, a core outcome set was developed in order to
better standardize clinical trials and allow for meta-analyses of trial data (Sahnan
et al. 2019a). This consisted of patient-reported outcomes (including incontinence,
general quality-of-life assessment) and clinically derived outcomes including a
validated disease activity score. MR imaging was incl uded as an optional outcome,
with fistula response on MRI and an activity-based MRI score responsive to change
being the aspects recommended. A numbe r of groups have attempted to develop
such a score, with varying degrees of success.
Van Assche et al. (2003) developed a fistula scoring system to assess perianal
fistula activity through imaging. The components of the Van Assche score reflect
characteristics that may increase fistula complexity or activity such as the complexity
of the fistulizing disease, number of fistulas, and presence of proctitis. While it has
been used to determine disease response to treatments including infliximab, it has
been shown to lack sensitivity to change over time (Ng et al. 2009; Samaan et al.
2017) and has a weak correlation with PDAI (r ¼ 0.371, p ¼ 0.036) (Horsthuis et al.
2011), limiting its utility in assessing treatment progression (Fig. 2).
Samaan et al. (2017) reviewed the characteristics of the Van Assche index and
through expert consensus agreement modified the score by removing areas of
disagreement and adding some further elements. On attempted validation, the
modified Van Assche score was found to have similar problems with the original,
namely, its insensitivity to clinical response over time, and had no benefit over the
original score (van Rijn et al. 2020).
Recently, the MAGNIFI-CD score was developed f ollowing further modification to the van Assche and modified van Assche scores through further expert
consensus and internal validation using a cohort of patients gleaned from a trial
for stem cell treatment for pCD (Hindryckx et al. 2019). The authors found that the
MAGNIFI-CD score provided better inter- and intra-rater variability with increased
sensitivity to changes in disease status compared with the original and modified Van
Assche indices. The major limitation with this score is its novelty, as it has only
undergone internal validation and is still awaiting external assessment through a
clinical trial. Notably, the MAGNIFI-CD score was found to correlate poorly with
clinical determinants of perianal Crohn’s disease severity including the PDAI and
FDA, further showing the heterogeneity of assessment measures for disease
activity.
Along with the variations on the Van Assche score, a number of other groups have
looked into radiological methods of quantifying disease. Ng et al. (2009) developed
a more holistic scoring system, preferring to refl
ect an overall gestalt of the MRI
image over time (improving, worsening, no improvement, remission) to reflect
disease progression following treatment. Villa and colleagues (2012) have looked
into a method of quantifying the degree of inflammation in fistula tracts by taking the
13 Magnetic Resonance Imaging in the Diagnosis, Characterization, and.. . 207
Fig. 2 Van Assche score.
(Adapted form Van Assche
et al. (2003))
Number of fistula tracks
None 0
Single, unbranched 1
Single, branched 2
Multiple 3
Locaon
Extra- or intersphincteric 1
Transsphincteric 2
Suprasphincteric 3
Extension
Infralevator 1
Supralevator 2
Hyperintensity on T2-weighed images
Absent 0
Mild 4
Pronounced 8
Collecons (cavies > 3mm diameter)
Absent 0
Present 4
Rectal wall involvement
Normal 0
Thickened 2
degree of T1 hyperintensity following gadolinium injection compared with surrounding fat. This technique was shown to correlate well with objective clinical
indices including PDAI and FDA. Fistula diameter (Barnhoorn et al. 2020) has also
been used as a measure for radiological disease burden. These measures have been
used occasionally but have not gained widespread traction overall in monitoring
pCD radiologically.
The use of MRI to assess the overall volume of fistulating disease as an objective
measure of disease activity has been recently evaluated as a possible index for
treatment response in Crohn’s disease (Lung et al. 2018). The authors measured
fistula volumes manually, taking on average roughly 4 min per case, which may be
prohibitively time-consuming depending on reporting burden. Fistula volume did
not correlate significantly with clinical activity, which is likely due to the study’s
small size as a proof-of-concept paper. Further research is needed to validate fistula
volume and other scoring systems, as an objective and reliable outcome measure, if
found to be related to clinical outcomes, would be attractive for use in clinical trials.
At present, there is no consensus on radiological outcome measures to accurately
characterize the response of fistulating pCD to treatment with studies using a variety
of measures, limiting valid comparisons between studies.
208 M. Vincent et al.
6 Future Directions
Previous MRI innovations include reducing scan times by utilizing higher field
strengths and greater signal-to-noise ratio (Dagia et al. 2010), breath-hold image
capture (Magnano et al. 2003), fat suppression (Essary et al. 2007), and the use of
oral/intravenous contrast agents, such as gadolinium (Darbari et al. 2004; Laghi et al.
2003).
While MRI is known to be effective in accurately characterizing fistula anatomy,
the images are still a two-dimensional representation of a complex three-dimensional
(3D) structure. The surgeons’ ability to understand the findings of the study relies on
their ability to read the MRI images or understand the radiologists’ report. Moreover,
the surgeon still has to mentally reconstruct the 2D image into a 3D picture in order
for the study to be useful in preoperative planning. One method to improve understanding of two-dimensional images is 3D reconstruction.
Wake and colleagues evaluated surgeons’ abilities to correctly reconstruct in a
three-dimensional model the location of a renal tumor using CT and MRI images
with and without 3D reconstructions (Wake et al. 2019). Surgeons reviewed CT and
MRI imaging of renal tumors and then were asked to reproduce the location of the
tumor on a 3D model of a kidney. The authors found that surgeons found difficulty in
reproducing imaging findings and in 25% there was no overlap between the imaging
and the surgeons’ guesses. The ability of surgeons to reproduce these findings was
significantly improved by 3D reconstructions of the images, with all of the reconstructions having some overlap with the true anatomical findings and an increase in a
subjective overlap score noted, showing that even experienced surgeons may benefit
from 3D representations of cross-sectional imaging.
3D reconstructions of MRI images have previously been shown to be effective in
aiding in modeling the complex anatomy involved in pelvic operations (Sands et al.
2004; Ng et al. 2009; Zeng et al. 2016; Li et al. 2018; Tang et al. 2009). Sahnan and
colleagues evaluated the effectiveness of segmentation of 2D MRI images in creating three-dimensional models of perianal Crohn’s fistula (Sahnan et al. 2018a). MRI
images were performed with manual segmentation of the levator ani, anal sphincters,
and fistula tract done. These structures were then reconstructed in three dimensions,
allowing for easy characterization of the anatomy of the fistula tract. This reconstruction is especially helpful for visualizing complex fistula with multiple extensions above the levator ani in order to help with operative planning. Along with 3D
modeling, MRI images have also been manipulated using an immersive reality
platform to allow trainee surgeons to simulate complex fistula operations (Sahnan
et al. 2019b).
Along with virtual 3D reconstructions of images, a physical three-dimensional
model of anatomical structures is an effective way to communicate operative
anatomy and easily facilitate the simulation of operations prior to the real thing.
3D printing has been used in a number of surgical situations in order to facilitate
effective rehearsal for the actual operation (Bianchi et al. 2019). MRI images of
perianal fistulas were manipulated in order to produce three-dimensional models
consisting of the fistula tract, external sphincter/levator ani, and internal sphincter