The biggest Achilles heel in perianal fistulae surgery is the risk of recurrence. Since MR imaging identify the internal fistulous opening, classify the fistulae, and delineate the secondary tracts and extensions with a high degree of sensitivity and specificity, a preoperative MRI study can be extremely useful in charting the ball path of surgical management in complex and recurrent perianal fistulae. Forewarned of possible complicating factors, surgeon can plan the surgery well, and achieve a complete eradication of the disease.

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2. a p o l l o m e d i c i n e xxx ( 2 0 1 4 ) 1e5
Available online at www.sciencedirect.com
ScienceDirect
journal homepage: www.elsevier.com/locate/apme
Original Article
Significance of MR imaging in setting the ball path
of surgical management in perianal fistulae
Nishith Kumar a, Yatish Agarwal b,*, Avneet Singh Chawla c,
Brij Bhushan Thukral d
a Senior Resident, Department of Radiodiagnosis, Vardhman Mahavir Medical College and Safdarjung Hospital,
New Delhi 110029, India
b Professor and Consultant, Department of Radiodiagnosis, Vardhman Mahavir Medical College and Safdarjung
Hospital, New Delhi 110029, India
c Professor and Consultant, Department of Surgery, Vardhman Mahavir Medical College and Safdarjung Hospital,
New Delhi 110029, India
d Consultant and Head, Department of Radiodiagnosis, Vardhman Mahavir Medical College and Safdarjung
Hospital, New Delhi 110029, India
a r t i c l e i n f o
Article history:
Received 4 August 2014
Accepted 11 August 2014
Available online xxx
Keywords:
Gastrointestinal imaging
MRI
Perianal fistulae
Intersphincteric
Transsphincteric
a b s t r a c t
Objective: To study the role of magnetic resonance imaging (MRI) in surgical management of
perianal fistulae.
Materials and methods: This study comprises of 30 patients: 19 with complex and 11 with
recurrent perianal fistulae. Each had a DRE and pelvic MRI examination, and the imaging
features were correlated with intraoperative findings. Since the position of internal
opening, class of fistula and presence of secondary ramifications and/or abscess dictate the
surgical management and its success, special attention was paid to these characteristics
during MR imaging. Sensitivity, specificity, positive predictive value (PPV) and negative
predictive value (NPV) both for DRE and MR imaging were calculated with respect to these
characteristics with intraoperative data as gold standard.
Results: The sensitivity of DRE in detection of internal opening was 33.33%, and of MRI
96.67%. DRE could classify the disease accurately in 33.33%, whereas MRI was able to do so
in 86.67%. DRE could detect horseshoeing in 63.63% with a NPV of 82.60%, while MRI carried
a sensitivity and specificity of 100%.
Conclusion: The biggest Achilles heel in perianal fistulae surgery is the risk of recurrence.
Since MR imaging identify the internal fistulous opening, classify the fistulae, and delineate
the secondary tracts and extensions with a high degree of sensitivity and specificity, a pre-operative
MRI study can be extremely useful in charting the ball path of surgical manage-ment
in complex and recurrent perianal fistulae. Forewarned of possible complicating
factors, surgeon can plan the surgery well, and achieve a complete eradication of the disease.
Copyright © 2014, Indraprastha Medical Corporation Ltd. All rights reserved.
Abbreviations: MRI, magnetic resonance imaging; DRE, digital rectal examination.
* Corresponding author. Tel.: þ91 9811681790; fax: þ91 11 26198075.
E-mail addresses: dryatish@yahoo.com, dryatishagarwal@gmail.com (Y. Agarwal).
http://dx.doi.org/10.1016/j.apme.2014.08.005
0976-0016/Copyright © 2014, Indraprastha Medical Corporation Ltd. All rights reserved.
Please cite this article in press as: Kumar N, et al., Significance of MR imaging in setting the ball path of surgical management in
perianal fistulae, Apollo Medicine (2014), http://dx.doi.org/10.1016/j.apme.2014.08.005

3. 2 a p o l l o me d i c i n e x x x ( 2 0 1 4 ) 1e5
1. Introduction
Perianal fistula is an abnormal communication between the
anorectum and the perianal skin. Such a communication may
be associated with one or more secondary ramifications and/or
abscesses. A high internal opening and/or transsphincteric
location can exaggerate thecomplexity of a fistula. The surgical
challenge lies in finding success in eradication of fistula in toto,
including all its branches. The persistence of residual disease
complicates and upstages the complexity of remnant fistula.
The situation may be compounded if the anal sphincter com-plex
suffers any damage. This can lead to incontinence. A mild
to moderate incontinence may occur in up to 50% cases.1e3
If the level and site of internal opening, anatomy of pri-mary
tract and presence of secondary ramifications and/or
abscesses can be accurately identified before the surgeon
embarks upon the surgery, such complicating factors can be
nullified, and a complete eradication of the disease can be
achieved. A preoperative pelvic MRI can help achieve these
primary goals.4
2. Materials and methods
This prospective study comprises of 30 consecutive patients
with complex or recurrent perianal fistulae. Each was suitably
counseled, a written informed consent was obtained, and the
findings on digital rectal examination (DRE) were recorded.
This was followed by a pelvic MRI examination.
A high FOV (field of view) localiser sequence was used to
plan out the T1 and T2 weighted sequences followed by pre
and post contrast T1 weighted fat-saturation sequence in axial
and coronal oblique plane. The characteristics of perianal
fistulae were recorded with regard to the site of internal fis-tulous
opening, class of fistula,5 presence of secondary rami-fications
and/or abscess and horseshoeing.
During the course of surgical exploration, intraoperative
findingswere recorded.These observations were correlatedwith
pelvic MRI data. With intraoperative findings as gold standard,
sensitivity, specificity, positive predictive value and negative
predictive value both for DRE and MR imaging were calculated.
3. Results
This study includes 19 first-time patients with complex peri-anal
fistulae and 11 with recurrent disease. DRE could identify
the external opening in all 30 patients. The internal opening
was felt in 10 (33.33%); induration of the tract with a possibility
of supralevator disease in 13; while in 7 the disease was
thought to be extrasphincteric with a high internal opening in
the rectum. DRE could also detect secondary extensions and
abscesses in 8, and horseshoeing in 7 patients.
On MR examination, the internal opening was visualized in
29 (96.67%) patients; while 1 was classified as perianal sinus.
Abscess were found in 9, horseshoeing in 11 and secondary
tracts in 18 patients.
The study cohorts were classified in accordance with St.
James University Classification5 (Table 1). Nine (30.0%)
Table 1 e Classification of perianal fistulaea in the study
cohort (n ¼ 30).
Fistula classification Number Percentage
Grade 1 (Intersphincteric with
4 13.33
no extensions)
Grade 2 (Intersphincteric with
secondary extensions)
4 13.33
Grade 3 (Transsphincteric with
no extensions)
7 23.34
Grade 4 (Transsphincteric with
secondary extensions)
9 30.00
Grade 5 (Extrasphincteric/
Suprasphincteric)
6 20
Total 30 100
a St. James University MRI Classification.5
patients had grade 4 (transsphincteric fistula with secondary
extensions/abscesses) perianal fistulae; 7 (23.34%) had grade 3
(transsphincteric with no extensions) perianal fistulae; 6 (20%)
had grade 5 (extrasphincteric/suprasphincteric) perianal
fistulae; and 4 (13.33%) patients each had grade 1 (inter-sphincteric
with no extensions) and grade 2 (intersphincteric
with secondary extensions) perianal fistulae.
While DRE could correctly grade the disease in 10/30 pa-tients,
MRI succeeded in doing so in 26/30 patients. The
comparative sensitivity, therefore, was 33.33% for DRE, and
86.67% for MRI (Table 2).
DRE could identify 8/9 associated abscesses with a sensi-tivity
of 88.89%, while MRI could pick all, with a sensitivity of
100%. DRE identified horseshoeing in 7/11 patients, with a
sensitivity of 63.63% and NPV of 82.60%. MRI identified all 11,
with a sensitivity, specificity, PPV and NPV of 100%.The sec-ondary
tracts were felt in 8/19 patients on DRE with a detec-tion
rate of 42.11%, while MRI detected secondary tracts in 18
cases with a sensitivity of 94.74% (Table 3).
4. Discussion
This study probes into the clinical usefulness of MRI in oper-ative
management of complex and recurrent perianal fistulae.
This usefulness hinges on accurate localization of site and
level of internal opening, delineating the primary tract and
identifying its secondary ramifications. In this study, MRI
demonstrated a high degree of accuracy in identifying each of
the three characteristics.
The external opening was localized on DRE in all 30 sub-jects.
Of them, 17 (56.67%) were situated in posterior and
posterolateral position. The high precedence of this location is
Table 2 e Comparative accuracy of clinical vs. MRI
findings in classification of perianal fistulae.
Disease
Clinical
MR imaging
characteristic
classification
classification
Surgical
validation
Fistulae correctly
classified
10(33.33%) 26(86.67%) 30(100%)
Fistulae falsely
classified
20(66.67%) 4(13.33%) 0
Total 30 30 30
Please cite this article in press as: Kumar N, et al., Significance of MR imaging in setting the ball path of surgical management in
perianal fistulae, Apollo Medicine (2014), http://dx.doi.org/10.1016/j.apme.2014.08.005

4. a p o l l o m e d i c i n e xxx ( 2 0 1 4 ) 1e5 3
related to anatomy of anal glands, which open posteriorly into
the anal crypts most commonly. Similar results were found in
400 subjects, with the external opening in 44.7% subjects being
posterior and lateral in location.6 This evaluation of external
opening on DRE is critical from the perspective of triage
making use of the Goodsall's rule in pre-empting the
complexity of fistula.
MR imaging was far superior to DRE in defining the internal
opening of perianal fistulae. The sensitivity of DRE in detec-tion
of internal opening was 33.33% and on MRI 96.67% and
both had a PPV of 100%. This failure of DRE in its inability to
detect the internal opening may relate to several reasons: in
some patients, the internal opening was flush with the rectal
mucosa, and in others, the induration and inflammation from
preceding surgery made the differentiation between the
granulation tissue at the internal opening and the healed scar
of previous surgery difficult. Even on MR imaging, the detec-tion
of internal opening of perianal fistulae is not always easy.
The opening must be inferred by following the course of fis-tulous
tract in the intersphincteric space and the area of
maximum intersphincteric sepsis. In the solitary case, where
MRI failed us, the failure occurred due to confusion between
possible postoperative signal alteration and active inter-sphincteric
sepsis. Since this was a patient with recurrent
disease, we mistook the intersphincteric sepsis as a post-operative
tissue change.
On MR imaging, the largest number (16/30; 53.34%) were
transsphincteric fistulas, i.e., St. James University Hospital
Classification Grade 3 and 4. These results are divergent from
other studies,5,7 which report intersphincteric fistulas to be
the commonest. This difference in the type of fistulae possibly
relates to inclusion of far more complex recurrent perianal
fistulas in the present series.
The MR imaging is able to delineate the pelvic anatomy
well and with high resolution (Fig. 1a and b). Due to these
virtues, it is capable of demonstrating the relationship of the
perianal fistula with sphincter complex and helps in accurate
categorization of perianal fistula (Fig. 2). In this series, we
could classify the fistulae accurately with MR imaging in 26
(86.67%) patients. Of the 4 patients where we failed, 3 were
transsphincteric fistulae. We mistook them as intersphinc-teric.
Each of them had recurrent disease, with gross distor-tion
of perianal anatomy which interfered with the
visualization of outer interface of external sphincter muscle.
When we retrospectively analyzed the MR images in these
patients, we found the primary fistulous tract was criss-crossing
the external sphincter muscle randomly, and this
could have contributed to the blemish.
The results of this study show a linear increasing trend
between clinical and MR imaging for their accuracy in
classifying the disease as the sensitivity for correctly classi-fying
the disease was 33.33% on DRE as against 86.67% on MRI.
This trend is similar to that recorded by Steve Halligan et al.
who reported a significant linear trend (p ¼ 0.001) in the pro-portion
of fistula tracks (n ¼ 108) correctly classified with each
modality, as follows: clinical examination, 66 (61%) patients;
endosonography, 87 (81%) patients; MR imaging, 97 (90%)
patients.8
A study from the St Mark's Hospital Intestinal Imaging
Centre has also recently concluded that MR imaging is an
optimal technique for discriminating complex from simple
perianal fistula. While the sensitivity of MRI in this study
was found to be 95%, that of clinical assessment was restricted
to 75%.9
Table 3 e Correlation of preoperative clinical evaluation,
MRI and intraoperative findings.
Disease
Clinical
MR
characteristics
evaluation
imaging
Surgical
data
Internal opening 10 (33.33%) 29 (96.67%) 30 (100%)
Abscesses 8 (88.89%) 9 (100%) 9 (100%)
Horse shoeing 7 (63.64%) 11 (100%) 11 (100%)
Secondary extensions 8 (42.11%) 18 (94.74%) 19 (100%)
Fig. 1 e (a and b): Normal MR Anatomy of sphincter
complex. Axial T1 weighted image (a) of perianal region
shows the intermediate signal intensity internal (short
arrow) and external sphincter (long arrow) muscles. The
high signal intensity ischioanal fat bounds them on either
side. Coronal T1 weighted image (b) shows puborectalis
muscle (short arrow) which continues as external
sphincter (long arrow).
Please cite this article in press as: Kumar N, et al., Significance of MR imaging in setting the ball path of surgical management in
perianal fistulae, Apollo Medicine (2014), http://dx.doi.org/10.1016/j.apme.2014.08.005

5. 4 a p o l l o me d i c i n e x x x ( 2 0 1 4 ) 1e5
The identification of the secondary tracts also poses great
difficulty in patients with complex recurrent fistulae. Such
patients tend to have secondary extensions several centime-ters
away from the anal canal and, to make things worse,
these tracts traverse virtually in any direction (Fig. 3). In the
present study, 19 patients were found to have secondary ex-tensions
at the time of surgery. Of them, 18 (95%) could be
picked on MR imaging. This failure could be due to spuriously
high signal in scarred (healed) tract or faulting secondary tract
for adjacent vessel.
The sensitivity of DRE was 42%, while that of MRI was a
robust 94.74%, with 100%specificity and 91.67% NPV. Similar
results have been reported by others. Spencer et al., in a study
of 42 patients with perianal fistulae, found DRE failed to pick
abscesses in 8 of the 22 patients, and was unable to detect
complex secondary tracts in 3/6 (50%) patients with complex
perianal fistula.5
Horseshoe extensions can be identified by their unique
configuration when the extension occurs in horizontal plane
on either side of midline (Fig. 4). In the present study, DRE
identified the associated abscesses and horseshoeing well,
with a detection rate of 89% (8/9) and 64% (7/11) respectively.
This finding however is in contrast to findings of Halligan
et al.; they could identify only 23/68 (36%) horseshoe exten-sions.
8 In the present study, MRI identified the abscess and
horseshoeing in all cases and enjoyed 100% sensitivity, spec-ificity,
PPV and NPV.
The information gleaned from MR imaging in the present
study had a palpable effect on the patient's surgical manage-ment.
Besides the 10 (33%) internal openings identified on
clinical assessment, MR imaging could pick the internal
Fig. 2 e Relationship of the fistula tract with sphincter
complex. Coronal T1 weighted MR image of perianal region
shows slightly hyperintense fistula tract (white long arrow)
in the right perianal region traversing the external (short
colored arrow) and internal anal sphincter muscle (long
colored arrow) with uninvolved levator ani muscles
bilaterally (vertical arrow) consistent with right sided
trans-sphincteric fistula (Grade 3).
Fig. 3 e Axial T1 weighted MRI of perianal region. Multiple
secondary tracts (arrows) are seen on either side of anal
canal in a complex trans-sphincteric fistula (Grade 4).
Fig. 4 e Axial post contrast T1 weighted MR image of
perianal region. There is evidence of a complex trans-sphincteric
fistula (Grade 4) with horseshoeing across the
midline posteriorly and widening of fistula tract (vertical
arrow) with low signal air foci within the abscess.
Please cite this article in press as: Kumar N, et al., Significance of MR imaging in setting the ball path of surgical management in
perianal fistulae, Apollo Medicine (2014), http://dx.doi.org/10.1016/j.apme.2014.08.005

6. a p o l l o m e d i c i n e xxx ( 2 0 1 4 ) 1e5 5
opening in another 19 (63%) patients. If clinical evaluation
could correctly classify the disease in 10 (33.33%) patients, MR
imaging could do so in 16 (53.33%) more. Likewise, besides the
8 secondary tracts detected on DRE, MRI could identify 10
(52.63%) more.
MR imaging is therefore an optimal modality for the eval-uation
of complex and recurrent perianal fistulae. It can
identify the internal opening, classify the disease, and delin-eate
the secondary tracts and extensions well. This provides
an excellent roadmap to the operating surgeon, who can
achieve a complete eradication of disease by excising the fis-tula
in toto.
5. Conclusion
A precise preoperative anatomic detailing of the fistula is
essential from the standpoint of its complete eradication. This
can be best achieved with MR imaging of the perianal region,
particularly in such cases, where a perianal fistula is thought
to be complex or the disease is recurrent.
Conflicts of interest
All authors have none to declare.
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Please cite this article in press as: Kumar N, et al., Significance of MR imaging in setting the ball path of surgical management in
perianal fistulae, Apollo Medicine (2014), http://dx.doi.org/10.1016/j.apme.2014.08.005

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