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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_1056_Библиотеки_им_академика_М_И_Перельмана.pdf
11 Magnetic Resonance and Traditional Radiology in the Diagnosis of... 179
Recent studies have judged the capability of DWI in the detection of perianal
fistula and their complications (Cavusoglu et al. 2017; Balcı et al. 2019). DWI may
help reveal the presence of the fistulous tract in the background of suppressed signals
from the surrounding tissues (Balcı et al. 2019). Low spatial resolution is a major
drawback of DWI, although its combination with other sequences, mainly
T2-weighted images, may help recognize small abscesses that would otherwise be
missed (Yoshizako and Kitagaki 2013; Dohan et al. 2014; Cavusoglu et al. 2017;
Balcı et al. 2019).
Yoshizako and Kitagaki (2013) reported that DWI was a practical method for
evaluating perianal fistula response to conservative treatment with antibiotics. This
study showed that the apparent diffusion coefficient was correlated to inflammation
activity and it was appreciably lower in the positive inflammation activity group
compared to the negative inflammation activity group.
The facts that DWI does not need for contrast agent or additional equipment and
has a short sequence period make it an easy and helpful diagnostic tool that can
easily be included in routine MRI evaluation of perianal fistula (Cavusoglu et al.
2017).
Up to this point, the combination of contrast-enhanced T1-weighted images
(CE-T1WI), assumed to be the best for anatomic and pathologic detection of fistulas
with axial T2-weighted images (T2WI), provided adequate information needed to
plan the surgical management (Baik et al. 2017). However, the administration of
contrast agents has some risks, such as the development of nephrogenic systemic
fibrosis in patients with severe renal impairment.
An additional role of MRI is the evaluation of the patients after surgery (Fig. 7).
When MRI was performed immediately after surgical intervention, it can spot the
presence of hemorrhage, which appears hyperintense on unenhanced T1-weighted
images differentiating it from the residual tract. Fat-containing “grafts” used for
filling cavities following restorative surgery may have similar hyperintensity. Seton
in situ will appear as a hypointense structure within the hyperintense fistulous tract.
Contrast-enhanced studies may be useful to study the postoperative tissue in search
of residual disease and abscesses (George et al. 2011).
Many studies compared the role of multiple MRI acquisition sequences for
identifying soft tissue pathology, comparing T1-weighted, T2-weighted, and DWI
images.
Hori et al. (2009) have evaluated the potent ial value of DWI and T2-weighted
imaging comparing them with gadolinium (Gd)-enhanced imaging in the assessment
of anal fistula. The diagnostic performance of diffusion-weighted and T2-weighted
images combined or those with Gd-enhanced and T2-weighted images combined
were importantly greater than T2-weighted images alone. They concluded that
diffusion-weighted MRI of anal fistulae is a useful resource and can be an adjunct
to T2-weighted imaging, in particular in patients in whom the administration of
contrast agents is not recommended.
Baik et al. (2017) compared the diagnostic value in evaluating perianal fistulas of
three imaging data sets: T2-weighted images, combined T2 images and DWI, and
contrast-enhanced-T1 images. They observed that combined DWI and contrast-
180 L. M. Minordi et al.
Fig. 7 (a, b) Sagittal CT images, (c) axial T2-weighted MRI image, (d) axial fat-suppressed
T2-weighted MRI image, and (e) coronal T2-weighted MRI image, show setons as hyperdense
(CT) or hypointense (MRI) tubular or dot-like structures (white arrows)
11 Magnetic Resonance and Traditional Radiology in the Diagnosis of... 181
enhanced T1 images might improve fistula conspicuity even if they showed a similar
diagnostic performance to T2 images.
Cavusoglu et al. (2017) also found that DWI and T2-weighted images combined
improved sensitivity and specificity compared to T2-weighted images alone.
Cattapan et al. (2019 ) showed that contrast-enhanced MR studies, even though
improving a radiologist’s confidence, had comparable diagnostic efficacy in recognizing perianal fistulas and their complication. Therefore, a non-contrast study may
be sufficient, especially in patients with severe renal dysfunction.
Gu et al. (2019) evaluated the capability of detection morphological information
of the internal orifice and the fistulas on the transverse images of fat suppression
T2-weighted imaging (FS T2WI), DWI, fat suppression T2-weighted imaging
combined with DWI, and fat suppression T1-weighted imaging combined with
gadolinium contrast enhancement (FS T1WI Gd-CE), in comparison with surgical
pathology results. The conspicuity and the diagnostic performance rate were compared between the four imaging data sets. Different observers evaluated all the
images, and there were consistent conspicuity scores and diagnostic performance
rates. The conspicuity of the internal orifice was higher for the set of FS T2WI, FS
T2WI + DWI, and FS T1WI + CE than DWI. The diagnostic performance rate of the
internal orifice was higher for the set of FS T2WI, FS T2WI + DWI, and FS
T1WI + CE than DWI. The conspicuity of the fistula was higher for the set of FS
T2WI + DWI and FS T1WI + CE than FS T2WI or DWI. There were no important
differences between the four sets of FS T2WI, DWI, FS T2WI + DWI, and FS
T1WI + CE in the diagnostic performance rate of the fistula. The set of FS T2WI
combined with DWI was similar to FS T1WI CE in assessing anal fistula morphology changes.
2.3.3 MRI Reconstruction Techniques and Fistulography MRI
Instead of creating new MRI scan sequences, the combination of two or more
scanning sequences into a single image is a valuable diagnostic tool. It enhances
image quality, abbreviates image analysis time, and increases the efficacy of
diagnosis.
In 2005 Shaefer et al. (2005) evaluated the utility of digital subtraction MR
fistulography (indirect MR fistulography) for tissue differentiation based on signal
intensity measurements in patients with inflammatory bowel disease. Thin-slice,
high-resolution, fast low-angle shot three-dimensional sequence in the axial plane
were analyzed before and after intravenous injection of gadobenate dimeglumine,
followed by image subtraction. The common femoral artery, the internal and external
sphincter muscles, and the gluteus muscle were the regions of interest established by
the operators to measure signal intensities of the inflamed fibrous walls of fistulas.
This technique allowed the differentiation between the fistulous tracts and the
adjacent anatom ic structures depending on the variation of the signal intensity
measurements.
In 2013 Day et al. ( 2013) proposed an intuitive, interactive, three-dimensional
(3D) MRI modeling technique to create a 3D image of fistula-in-ano. Standard
two-dimensional (2D) MRI sequences were used to generate the 3D model. Each
182 L. M. Minordi et al.
muscle and soft tissue layer was extracted from T1-weighted sequences and fistula
pathology from short TI inversion recovery (STIR) sequences, to create two different
volumes. Post-processing reconstructions allowed the fusion of these two volumes to
produce a 3D model. The final 3D model was incorporated into a PDF file that has an
integrated computer-aided design (CAD) viewer, giving to the surgeon the possibility to rotate it in any direction during preoperative planning or while in theatre. In
conclusion, this technique permitted clearer comprehension of fistula anatomy,
especially in complex cases.
In 2018 Sahnan et al. (2018) made a similar analysis, investigating alternative
platforms to understand complex perianal fistulas through three-dimensional
(3D) imaging. In this study three examples of 3D printed models were created in
order to display complex perianal fistula. The anatomical components were
represented in different colors (red, fistula tract; green, external anal sphincter and
levator plate; blue, internal anal sphincter and rectum). One of the models was split
in half, in order to display the internal opening and allow a finer assessment of the
inter-sphincteric space. An animation of MRI fistulography of a trans-sphincteric
fistula tract with a cephalic extension in the inter-sphincteric space was also created.
The authors concluded that 3D reconstructions of complex perianal fistula improved
surgical planning and communication with patients and augmented training.
In 2019 Feng et al. (2019) analyzed 32 patients with anal fistulas to determine
whether MRI fusion technology (combined T2-weighted imaging and fat-suppressed
T2 weighted imaging) notably improved the differentiation between anal fistulas and
surrounding structures. All available T2-weighted and fat-suppressed T2-weighted
images for each patient were used to produce a fusion image (T2WI-fusion) based on
theadditionofgreyvaluesacquiredfromeachpixelviaanMRpost-processing
workstation. The distinguishability of fistula, perianal sphincter, and perianal fat was
quantified in each patient in T2-weighted, fat-suppressed T2-weighted, and T2WIfusion images. They found that T2-weighted imaging and T2WI-fusion technology
enhanced the signal differences between anal fistulas and surrounding structures and
enabled a better evaluation of anal fistulas and sphincters.
Direct MR fistulography is another modality that has been proved by a few
centers to show a better visualization of fistulous tracts and their relationship to
the surrounding perianal structures. This procedure involves an injection of diluted
gadolinium (George et al. 2011) or a mixture of hydrogen peroxide and gadolinium
into the tract through an infant feeding tube (Waniczek et al. 2015). This technique
may be convenient especially in evaluating complex fistulas and tracts with relatively sparse secretion (George et al. 2011). Another approach requires saline
instillation into the external opening or rectal contrast medium, but it is rarely
adopted due to its major level of complexity (Halligan 2020).
2.3.4 Internal and Cutaneous Opening
The MRI descrip tion of fistulas is based on the anal clock system, the same utilized
by surgeons to describe injuries around the anal region. The patient lies on his back
with the hips and knees flexed and the thighs apart (the lithotomy position); in this
position the anterior perineum is located at 12 o’clock, and the natal cleft is at
11 Magnetic Resonance and Traditional Radiology in the Diagnosis of... 183
6o’clock; the left lateral aspect of the anal canal is at 3 o’clock, and the right lateral
aspect is at 9 o’clock (Morris et al. 2000). The most common location of the internal
opening of fistulas is at the level of the dentate line (Halligan and Stoker 2006), even
though extra-sphincteric fistulas make an exception.
There is sometimes more than one external cutaneous opening, which may also
be outside the perianal region, for example, in the cases of gluteal, perineal, labial, or
retro-scrotal openings. It may be difficult to identify the external orifice in chronic
fistulas where the damaged tissue may develop scars. In the proximity of the external
orifice, the previous surgical interventions usually determine signal void artifacts,
and the fluid content of the tract may be reduced or entirely absent. If the primary
tract terminates blindly in subcutaneous fat tissue, we should refer to it as a sinus
track (Erden et al. 2017).
Even though any type of cryptogenic fistula may potentially present without an
external opening, the majority are inter-sphincteric fistulas (Abou-Zeid 2011).
2.3.5 Classifications of Perianal Fistulas and Abscesses
Anal fistulas are classified on the basis of their spatial relationship with the anal
sphincter and other pelvic floor structures.
Parks (1961) classified perianal fistulas as inter-sphincteric, trans-sphincteric,
supra-sphincteric, and extra-sphincteric fistula according to the perianal fistula
relationship to the anal sphincter complex (Table 1).
In line with crypto-glandular hypothesis, inter-sphincteric fistulas are the most
common subgroup. They usually develop close to the anal sphincter complex and are
often relatively small. Inter-sphincteric fistulas open at the anal canal (internal
opening) and need to pass through the internal sphincter and the inter-sphincteric
space to reach the perianal skin (external opening). The external sphincter is usually
not traversed by this type of fistula, therefore serving as a barrier and confining the
spread of the infection (Fig. 5).
Trans-sphincteric fistula, as the name suggests, passes through the internal
sphincter, the inter-sphincteric space, and the external sphincter, to finally reach
ischiorectal and ischioanal fossae (Fig. 6).
Supra-sphincteric fistulas progress upward into the inter-sphincteric space, pass
over the top of the puborectalis muscle, and then descend through the levator plate to
the ischiorectal fossa and finally to the skin.
Extra-sphincteric fistulas open at the rectum (internal opening) and pass through
the levator muscles and ischiorectal fossa to reach the perianal skin (external
opening). This type of fistula does not involve the anal canal, lying entirely outside
Table 1 Parks
classification
Classifications Parks
Grade I Inter-sphincteric
Grade II Trans-sphincteric
Grade III Supra-levator
Grade IV Extra-sphincteric
184 L. M. Minordi et al.
the anal sphincter. This fistula has a different pathogenesis and can’t be explained by
the crypto-glandular hypothesis.
This class ification system includes, from most to least common, inter-sphincteric
(45%), trans -sphincteric (30%), supra-sphincteric (20%), and extra-sphincteric fistulas (5%) (Parks 1961; Erden et al. 2017). The ilio-cocygeal and pubo-rectal
components of levator ani muscle help to distinguish supra-levator from infralevator fistulas (Erden et al. 2017).
Each type of fistula has several variations that can occur.
Infection of the surrounding tissues may determine the development of abscess
cavities along the course of fistulous tracks (Erden et al. 2017).
Any clear widening of the fistula tract is considered a fistulous abscess.
This appearance is often seen in high fistulas blindly ending at the roof of the
ischioanal fossae. When the diameter of the lumen is wider than 1 cm, some authors
prefer to call it “abscess-like widening of fistula” (Erden et al. 2017).
Initially, superficial fistulas were not comprised in the original publication of
fistula classifications by Parks and colleagues (1961); they have been subsequently
added to describe fistulas that do not involve the anal sphincter complex.
Complex fistulas were also not included in the original classification by Parks and
colleagues, and they refer to a primary fistula associated with secondary tracts (also
known as extensions) and/or abscesses. The secondary tracts are branches that may
arise along the course of the primary tract, and they most frequently arise in the
ischioanal fossa or inter-sphincteric space (Jayarajah et al. 2017).
In 2000 a new MR imaging-based classification system for peria nal fistulas was
proposed by Morris et al. (2000). The major difference with the Parks classification
is that this classification considers relevant findings at MR imaging and describes not
only the primary fistulous tract, but it also takes acc ount of secondary extensions and
associated abscesses. This classification system, called St. James classification,
utilizes reproducible and reliable anatomic landmarks and therefore can be easily
used by radiologists to supply precise information to surgeons. St. James classification is based on the anatomy appreciated on MR imaging using the axial and the
coronal planes and includes five grades of fistulas (Table 2).
Grade 1: simple linear inter-sphincteric fistula. The fistulous tract extends from the
anal canal through the inter-sphincteric space to reach the perianal skin. There are
no secondary tracts or abscesses in the inter-sphincteric space or ischiorectal and
ischioanal fossae. The external sphincter confines the fistula and it is not
involved.
Grade 2: inter-sphincteric fistula with an abscess or secondary tract. A primary tract
and any numbers of secondary tracts (which may present as “horseshoeing”)or
abscesses occur in the inter-sphincteric space. The external sphincter confines the
fistula and it is not involved.
Grade 3: trans-sphincteric fistula. The trans-sphincteric fistula crosses both layers of
the sphincter complex and then reaches the perineal skin through the ischiorectal
and ischioanal fossae. The site of the internal opening varies, even though is often
located at the dentate line. Since trans-sphincteric fistulas involve both the
11 Magnetic Resonance and Traditional Radiology in the Diagnosis of... 185
Table 2 St. James’
classification
Classification St James University Hospital
Grade I Inter-sphincteric single tract
Grade II Inter-sphincteric with abscess or secondary tract
Grade III Trans-sphincteric single tract
Grade IV Trans-sphincteric with abscess or secondary tract
Grade V Supra-levator trans-levator
internal and external sphincter, the surgical treatment is complicated and had a
high risk of causing fecal incontinence.
Grade 4: trans-sphincteric fistula associated with an abscess or secondary tract within
the ischiorectal fossa. This type of fistula also passes through the external
sphincter, and then it is complicated by abscesses, which usually distort or fill
the ischiorectal or ischioanal fossa, or it is seen as an expansion along the primary
tract.
Grade 5: supra-levator and trans-levator disease. This is a rare type of fistula, where
the fistulous tract extends above the insertion of the levator ani muscle. Supra-
levator fistulas reach the inter-sphincteric space and pass over the top of the
levator ani to penetrate through the ischiorectal fossa. This type of fistula often
suggests the existence of a primary pelvic disease and represents the same type as
Parks classification’s supra-sphincteric and extra-sphincteric fistulas.
The aim of this classification is to reveal the presence of complex diseases that
may need expert surgical treatment and to guide the surgical management.
Essentially:
1. When at MRI the disease is limited to the sphincter complex and the ischioanal
and ischiorectal fossae are not affected (inter-sphincteric fistulization, grade 1 or
2), a simple surgical management is satisfactory and will most likely have a
favorable outcome.
2. When the MRI examination identifies the presence of a complex fistula with a
fistulous track or abscess within the ischiorectal fossa (usually trans-sphi ncteric
fistulization, grade 3 or 4), more complex surgery may be needed to allow
healing.
3. If the fistulous track crosses the levator plate (trans-levator fistula, grade 5), a
source of pelvic sepsis should be investigated.
Low fistula, less than 1/3 of external sphincter involvement; high fistulas, 1/3
sphincter involvement.
Garg et al. (2017) proposed a new classification in 2017. He compared preoperative MRI scans and operative findings of 440 consecutive patients who underwent
surgery for treatment of perianal fistula. It was assessed whether the amenability to
fistulotomy (measurement of fistula simplicity) correlated with the fistula-in-ano
grades in different classifications. He proposed a new classification, dividing perianal fistulas into five grades in order of increasing complexity (Table 3).
186 L. M. Minordi et al.
Table 3 Garg’s classification
Classification
Grade 1 Low linear inter-sphincteric
Low linear trans-sphincteric
Grade 2 Low complex inter-sphincteric or trans-sphincteric fistula with abscess, multiple,
Grade 3 High linear trans-sphincteric fistula
Grade 4 High trans-sphincteric fistula with either abscess, multiple or horseshoe tract
Grade 5 High trans-sphincteric fistula with inter-sphincteric supra-levator extension
horseshoe tract
Fistula with associated Crohn’s disease, sphincter injury, post-radiation
exposure, or anterior fistula in a female
Supra-sphincteric fistula
Extra-sphincteric fistula
For the author the previous classifications had some limits. In his opinion Parks
classification(Parks 1961) is clinicallynot relevantdue to the fact that this classification
was proposedin the era when MRI was not available and the author classified400 anal
fistulas only relatingto clinical information and operative findings. Another limit of the
Parks classification is that the majority (91.5%) of patients was categorized in the first
two grades (grades 1 and 2), and only a very few patients (8.5%) had a more advanced
grade (grade 3 and 4) fistula. This determined confusion in the management of 1 and
2gradefistulas which includeda vast heterogeneity of fistulas.For the author St James
Hospital University (SJHU) classification was an improvement over previous Parks
classification,as it was basedon MRI findings (Morris et al. 2000). Though radiologists
readily accepted this classification, it had little approval amongst surgeons. The main
reason for this was that SJHU classification did not have a much greater clinical
relevance compared to Parksclassification. EssentiallyParksgrades1 (inter-sphincteric
fistulas) and 2 (trans-sphincteric fistulas) had been split into two additional grades
(grade 1 into SJHU 1 and 2 and grade 2 into SJHU 3 and 4). On the other hand Parks
grade 3 and 4 had been fused into one grade (SJHU grade 5). According to this
classification, all trans-sphincteric fistula were assumed to be complex and needed
surgical treatmentwith a high risk for fecal incontinence. For Garg the major drawback
of both these classifications was that they were too simplistic in dealing with infralevator fistulas, which were divided into just two large categories(inter-sphinctericand
trans-sphincteric fistulas). The Garg classificationdividedfistulasinto five gradesin the
order of increasing complexity. Grades 1 and 2 are simple fistulas, which could be
conveniently treated with fistulotomy. Grades 3–5 are high complex fistulas and
consequently need more elaborated surgical procedures to be performed.
Currently, Parks and St. James classifications are the classifications applied all
over the world, including our hospital.
2.3.6 Deep Posterior Anal Fistulas and Abscess
The infection of the posterior anal crypt is the pathological cause, which determines
the development of deep posterior anal fistulas. Successively, caused by the
11 Magnetic Resonance and Traditional Radiology in the Diagnosis of... 187
infection, the primary abscess develops in the posterior inter-sphincteric space, then
penetrates the external anal sphincter, reaches the ischiorectal fossa, and extends
unilaterally or bilaterally to the perianal skin through an external opening (secondary
orifice) (Araki et al. 2018). When deep posterior anal fistulas reach the ischiorectal
fossa bilaterally, they are named horseshoe fistulas (Araki et al. 2018).
It was long believed that the primary abscesses associated with deep posterior
anal fistulas existed in the deep post-anal space, located between the elevator ani
muscle and the superficial external anal sphincter muscle, posterior to the deep
external anal sphincter muscle. This space, first described by Courtney, is also called
Courtney’s space. It was thought that Courtney’s space might be a closed space
because the superficial external anal sphincter muscle could connect to the coccyx,
therefore making it difficult for an abscess in this location to drain (Courtney 1949).
Other authors (Araki et al. 2018), on the other hand, analyzing several MRI
findings of deep posterior anal fistulas found that the primary abscesses of deep
posterior anal fistulas were located in a different position: the posterior intersphincteric space or in the external anal sphincter muscle itself, not in Courtney’s
space as previously believed.
2.3.7 MRI Report
In MRI evaluation of perianal fistulas, radiologists should recognize the primary
track and describe its orientation with reference to the anal clock corresponding to
the surgeon’s view of the perianal region.
The course of the fistula and its relation with surrounding stru ctures, especially
the anal sphincter complex, should be described. On this b asis the fistula should be
graded according to the previously described classification systems.
Mention of its radial site of internal opening according to clock position should
also be made.
In the evaluation of multiple tract fistulas, the radio logist should search for
communication among the tracts. In case of associated secondary extensions or
abscesses, they should be defined by their anatomical location, ischioanal , intersphincteric, or supra-levator, and they are considered horseshoe if they cross the
midline to the contralateral side.
2.3.8 MRI in Cryptogenic Fistulas and Abscesses Vs Crohn’s Fistulas
and Abscesses
To date, even though several studies have analyzed the features of perianal fistulas
on MRI, the differences on MRI between Crohn’s and non-Crohn’s fistulas have not
been compared yet.
It is crucial to identify the MRI features when first studying patients presenting
with perianal fistulas, as this may be the first manifestation of inflammatory bowel
diseases.
In 2017 Oliveira et al. (2017) evaluated imaging features of perianal fistulas
comparing patients with and without Crohn’s disease. A total of 126 patients were
included, of which 96 (76.2%) had Crohn’s disease and 30 (23.8%) did not. The
most common type of fistula was trans-sphincteric (38.5% of Crohn’s and 50% of
188 L. M. Minordi et al.
non-Crohn’s) and inter-sphincteric (33.3% of Crohn’s and 35.4% of non-Crohn’s).
On the other hand, supra-sphincteric fistulas were infrequent (only one case for
patients with CD and 0 case for non-CD patients). Abscesses occurred more often in
the group of patients affected by CD, 41 cases in total, 32 (33.3%) in the Crohn’s
group, and 9 (30.0%) in the non-Crohn’s group. Many patients presented with
multiple-branched fistulas (25.0% of patients with CD and 16.7% of patients without
CD), which are complex fistulas with multiple branches arising from the same
mucosal origin. Although these complex fistulas appeared to be more frequent in
patients with CD, the difference between the two groups was not signi ficant. Rectal
inflammation was also more common in patients with CD, appearing in 29 of them
(29.2%) and in 2 without CD (6.7%). This was the most significant finding that had a
large difference between the two groups. The authors concluded that, even though
the presence of rectal inflammation is a finding that has a correlation with CD, other
imaging features such as Parks classification, mucosal opening, distance from the
anal verge, and activity signs could not be used to distinguish one group to the other.
For this reason physicians should not entirely rely on them to suspec t or exclude
Crohn’s diagnosis in a patient first presenting with a perianal fistula.
2.3.9 MR Role in the Evaluation of the Crypto-Glandular Fistulas
The MRI assessment of the entire crypto-glandular fistula, including the identification of external opening, the primary track, secondary tracks, associated abscesses,
and the internal opening, is crucial for a correct classification of the fistula and
therefore a right treatment planning. Inadequate interpretation of images can result in
developing a simple fistula into a complex fistula, leading to a more invas ive surgical
treatment. Failing at recognizing secondary extensions may result in recurrent sepsis
and unnecessarily extend the clinical course (de Miguel Criado et al. 2012; Balcı
et al. 2019).
In addition, to preserve continence, accurate presurgical assessment of the relationship between the fistulous track and the anal sphincters is essential before
performing any surgical treatment, especially sphincter-interrupting procedures.
The information acquired with MRI seems to be a more precise predictor of
postoperative outcome than the infor mation obtained from surgical exploration
(Chapple et al. 2000).
MRI appears also crucial to clarify the characteristics of supra-levator abscesses,
their origin, and displaying the easiest route for drainage (Garcia-Granero et al.
2014).
The first MRI studies in radiologic journals were published in 1989 (Koelbel et al.
1989); however, surgeons did not entirely comprehend the real capacities of MRI
until the seminal description by Lunniss et al. (1992). This study took place in 1992
and included 16 patients with crypto-glandular fi stulas who were studied by bodycoil MRI. This study compared the MRI capacity of identifying fistulas with surgical
findings under anesthesia.
The real potential of MRI appeared clear, and authors concluded that MRI is the
most precise method for recognizing the presence and course of anal fistulas and that
it may reduce recurrence due to inaccurate surgical assessment (Lunniss et al. 1992).