ABSTRACT ID NO:1030
Why this study?
Imaging techniques for perianal fistula
usually consist of two-dimensional
sequences like axial and sagittal T2 ,STIR
coronal and post-contrast T1 weighted fat
saturated images.
 Less number of studies have concentrated
on 3D sequences and its correlation with
surgery
 The following study uses threedimensional sequences i.e.,syngo SPACE




SPACE enables acquisition of high resolution 3D
datasets within a clinically acceptable timeframe and
without SAR(specific absorption rate) limitations.
This study answers whether there is concordance
between MRI and surgical findings.
It also investigates whether MRI can provide more
information that could be missed in surgery and can
replace or add to surgical findings as gold standard
SPACE - Sampling Perfection with Application
optimized Contrasts using different flip angle
Evolution, Siemens Medical Solutions, Erlangen,
Germany
Aims and objectives
To assess the three-dimensional
magnetic resonance imaging features in
patients with perianal fistulae.
 To correlate MR imaging features with
intra-operative surgical findings.

Research Question

What is the concordance between 3
dimensional MR imaging and surgical
findings for perianal fistulae?
Materials and Methods
Descriptive correlative study
 Duration of 2 years from June 2012 to
May 2014
 Sample size n=46


Inclusion Criteria
 Patients clinically diagnosed as having
perianal fistulae.
 Exclusion criteria
 Patients having contra-indication to MR
imaging like pacemakers, surgical clips,
metallic implants.
 Patients refusing consent or unwilling to
undergo MR imaging.
Study design
Patients referred for MRI with clinical diagnosis of perianal fistulae
(n=46)
MRI done using SPACE (T2-SPACE-3D for anatomy; T2-SPACE-STIR
for track delineation and extension )
No prior preparation
No contrast
Image evaluation by by radiologist experienced in reading pelvic MR
images
Parameters studied were primary track(Parks classification),Internal and
external opening,,Collections,,Supralevator extension,,Horseshoeing ,St
James Hospital University Grading.
Findings recorded on a form with formula simulating the standard
fistula paper of St. Mark’s Hospital fistula surgery form with some
modifications and given to the patient.
Surgeon was not blinded to MR findings
Surgery on same group of patients
Surgeon would record same
parameters confirmed with surgery
in a similar fistula surgery form
Correlation
Parameters studied
Primary track(Parks classification)
 Internal and external opening,
 Collections,
 Supralevator extension,
 Horseshoeing if any
 St James University Hospital Grading

Imaging technique
1.5 Tesla MRI unit (MAGNETOM Avanto)
Sequences –
2D T2 sagittal
T2 weighted SPACE(TR- 1500 milli sec,TE141 milli sec, acquisition time-5 to 6 min,
slice thickness-0.9mm)
 T2 -SPACE -STIR(short tau inversion
recovery)(TR-2500 milli sec,TE-127 milli
sec,TI-160 milli sec, acquisition time-6 to 7
min, slice thickness-1.2mm)
 No IV gadolinium




PROFORMA
Statistical Analysis





Surgical findings were taken as the reference
standard against which the MR imaging
findings were compared.
Outcomes were expressed in percentages.
Kappa statistics was used for the agreement
between MRI and surgery on classification of
fistulas with respect to primary track, external
and internal opening.
Extra yield was expressed in percentages.
The entire statistical analysis was conducted
using IBM SPSS 20.0 version and graphs
were drawn using Microsoft Excel.
IMAGES







NORMAL ANATOMY
1-Apposed anal
mucosa;
2-Internal sphincter;
3-External
sphincter(pubococcyg
eus part of levator
ani);
4-Iliococcygeus part of
levator ani;
5-Right Ischioanal
fossa;
6-Supralevator plane.

Simple Intersphincteric fistula(arrow) (Grade
1 St James University Hospital
Classification)

Oblique Axial reformats of T2-3D-SPACESTIR showing Simple Intersphincteric fistula
(arrow)(Grade 1 St James University Hospital
Classification)

Oblique Axial reformat of 3D-SPACE T2 weighted
image showing Intersphincteric fistula(thick
arrow) with a secondary track(thin arrow) (Grade
2 St James University Hospital Classification)
(a)
(b)

Oblique Coronal reformats of (a)3D SPACE T2 weighted image (b) T23D SPACE STIR showing simple trans-sphincteric fistula(arrow) (Grade
3 St James University Hospital Classification)

Oblique Coronal reformat of 3D-T2-SPACE-STIR
image showing Trans-sphincteric fistula (thick
arrow)with a secondary track(thin arrow)(Grade 4
St James University Hospital Classification)

Oblique Coronal reformat of 3D-T2-SPACE image showing extrasphincteric fistula(thick arrow) with supralevator extension(curved arrow)
and horse-shoe component(thin arrow)(Grade 5 St James University
Hospital Classification)

Oblique Coronal reformat of 3D-T2-SPACE-STIR image showing
extrasphincteric fistula(arrow) with supralevator extension.
( Grade 5 St James University Hospital Classification )

Oblique Coronal(a) and Axial (b) reformats of 3D-T2-SPACE-STIR showing extrasphincteric
fistula(thick arrow) with supralevator extension(thin arrow) with anterior supralevator horseshoeing(notched arrow).

Oblique Axial reformat of 3D-T2-SPACE-STIR image
showing Posterior supralevator horseshoeing(arrow)

Oblique Axial(a) and coronal(b) reformats of 3D-T2-SPACE image
showing extrasphincteric supralevator fistula with posterior
supralevator horseshoeing(arrow)

Oblique coronal reformat of 3D-T2-SPACE
image showing superficial type of fistula (arrow)
Results
Age and gender distribution
FREQUENCY
PERCENT (%)
MALES
44
4.3
FEMALES
2
95.7
TOTAL
46
100.0
Intersphincteric
4.40%
10.90%
Superficial
PRIMARY TRACKS
FREQUENCY
PERCENT (%)
INTERSPHINCTERIC
21
45.6
SUPERFICIAL
12
26.1
TRANS-SPHINCTERIC
6
13
EXTRA-SPHINCTERIC
5
10.9
OTHERS
2
4.4
TOTAL
46
100.0
13%
26.10%
45.60%
Trans-sphincteric
Extrasphincteric
Others
Primary tracks
PRIMARY TRACKS
FREQUENCY
PERCENT (%)
INTERSPHINCTERIC
21
45.6
SUPERFICIAL
12
26.1
TRANS-SPHINCTERIC
6
13
EXTRA-SPHINCTERIC
5
10.9
OTHERS
2
4.4
TOTAL
46
100.0
Primary tracks
Agreement with Surgery
Total
Frequency
Percent (%)
Yes
41
89.1
No
5
10.9
46
100.0
Kappa value for agreement between surgery and MRI with
respect to primary track was 0.81(almost perfect agreement)
Internal opening and External
opening
Internal opening
Frequency
Percent (%)
External opening
Agreement with
Yes
44
Frequency
Percent (%)
Yes
45
97.8
No
1
2.2
46
100.0
95.6
Agreement with Surgery
Surgery
No
2
4.4
Total cases
Total cases
46
100.0
Kappa value for agreement between surgery and MRI with respect to
internal and external opening was 0.47 and 0.49 respectively (moderate
agreement)
Agreement with respect to each
type
Track
No of cases
No of cases
No of cases
detected in
detected in MRI
misclassified or
surgery
Agreement
missed on MRI
Intersphincteric
21
21
0
100% of cases
Trans-sphincteric
6
6
0
100% of cases
Extrasphincteric
5
5
0
100% of cases
Superficial
12
7
5
58% of cases
Total
46
41
5
Frequencies of secondary
tracks,collections,horseshoeing
Secondary tracks
Frequency
Percent (%)
Present
13
28.3
Absent
33
71.7
Total
46
100.0
Collection
Frequency
Percent (%)
Present
6
13
Absent
40
87
Total
46
100
Horseshoeing
Frequency
Percent (%)
Present
4
8.7
Absent
42
91.3
Total
46
100
St James hospital grading
St James Hospital Grading
17.40%
grade 1
39.10%
grade 2
grade 3
19.60%
grade 4
grade 5
Others
6.50%
10.90%
6.50%
Discussion



Of 46 cases most common primary fistulous track
was intersphincteric(45.6%) followed by
superficial(26.1%),trans-sphincteric(13%) and
extrasphincteric(10.9%).
MRI correctly classified 41(89.1%) out of 46 cases
with respect to the primary track.5 of superficial
tracks were misclassified i.e., 2 as intersphincteric,2
trans-sphincteric,1 extrasphincteric.
Probable causes can be due to time delay between
MRI and surgery causing healing of intersphincteric,
trans or extra-sphincteric component or findings
could have been missed by surgeon

It was less accurate with respect to
superficial track where it misclassified 5
among 12 cases(58%).
Internal opening
In our study, MRI helped the surgeon in
knowing the direction of internal opening
which was not easily appreciable by perrectal examination,
 Thus facilitated probing of the tracts and
avoided creation of false tracts or internal
openings
 Two cases had internal opening on MRI,
which were not revealed at surgery
possibly could have partially healed
because of conservative treatment

External opening
Even though clinical examination in
lithotomy position could reveal external
opening,
 MRI helped in confirming the presence
of external opening and differentiated it
from healed scars without any primary
fistulous track.
 It correctly detected external openings
in 45(97.8%) out of 46 cases

Secondary tracks
MRI accurately identified the secondary
tracks in 13(28.3%) out of 46 cases.
 Any hyper intense tubular branch running
away from primary track opening into anal
canal or ending blindly were considered to
be secondary tracks.
 This provided surgeon to look more keenly
for extensions from primary track and
excise/drain as much as possible without
causing incontinence.

Collections
Collections were detected in 6(13%)
cases.
 3 of which were supralevator collections
which were additional information given
by MRI.
 Surgeons did not completely drain these
collections because of the risk of
incontinence.

Horse shoeing
Horse-shoeing was noted in 4(8.7%)
cases.
 Track crossing to opposite side anterior
or posterior to anal canal was detected
accurately with MRI.
 Three of them were supralevator one of
them infralevator.
 Two of them were anterior and other two
posterior.

Limitations of the study
Sample size achieved was less because
all patients who underwent MRI could
not be followed up in surgery
 There was significant time delay
between MRI and surgery in few of the
patients.
 Contrast was not used in the study.
Differentiation of abscesses from
collections was difficult




Chronic and fibrotic fistulous tracks could not
be differentiated from active tracks as former
do not show any enhancement with contrast
T1 weighted images were not taken therefore,
differentiation between hemorrhagic material
and active granulation tissue was not possible
as former will be hyper intense and latter
would be hypo intense.
As surgeon was not blinded to MR findings
there was always problem of information and
misclassification bias
Conclusion
3-dimensional MRI is a reliable
investigational tool in the evaluation of
anorectal fistula and has high
agreement with intra-operative findings.
 3-dimensional MRI can be a useful
investigation in the preoperative
assessment of complex anorectal
fistulae
