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JSSN 2016; 19 (1) JSSN 2016; 19 (1)

3T MR imaging evaluation of perianal fistulas: an initial 
experience in Nepal
Ghanshyam Gurung

Department of Radiology and Imaging, Tribhuvan University Teaching Hospital, Maharajgunj, Kathmandu, Nepal

Correspondence: Dr. Ghanshyam Gurung  

Email: ghanshyam_gurung@yahoo.com

Abstract

Introduction: Fistula–in–ano is an abnormal perianal tract that connects anal canal to the 
perianal skin. Improper visualization of primary fistulous tract and the associated abscesses or 
secondary tracts a r e  the causes of recurrence. Earlier imaging modalities like conventional 
fistulography, endosonography and CT scan have had limited role. Even without endorectal coils, 
3T MRI has multi-planar imaging capability and excellent soft tissue differentiation to show perianal 
anatomy, primary and secondary tracts with associated abscesses in relation to sphincter complex. 
It provides excellent road map to surgeons for preoperative evaluation. The objective of the study 
was to evaluate the role of 3T MR in imaging of perianal fistulas.

Methods: A retrospective study was done among 32 patients who were referred for MR 
fistulogram for suspected perianal fistula at Jeebanta Advanced Kathmandu Imaging, Durbar 
Marg, Kathmandu, Nepal. All images and findings were obtained and recorded with the help of 
Philips Ingenia 3T digital broadband MR scanner. Imaging was performed in oblique coronal and 
oblique axial plane. MR images were studied and grading system was applied according to the St 
James’s University Hospital Classification. The data were entered in a performa and was analyzed 
using IBM SPSS V21.

Results: Male to female ratio was 7:1. According to St. Jame’s University Hospital MR Imaging 
classification of perianal fistulas, most of the patients (25%) had Grade 4 followed by (12.5% 
each) Grade 0, Grade 1 and Grade 2 and (6.3% each) Grade 3 and Grade 5 fistulas. Mean age was 
37.28 y e a r s  (Std. deviation 11.9). Common internal opening in axial image was found at 5 0’ 
clock positions (31.3%). Mean length of the fistulous tract was 3.9 cm (Std. deviation 2.3).

Conclusion: Perianal fistulas are more common in males and Grade 4 fistulas are the commonest. 
MRI is well-tolerated, painless and noninvasive technique and has multiplanar capabilities with 
excellent tissue differentiation of pelvic muscle along with sphincter complex.

Keywords: Abscess; fistula; MRI; secondary tract. 

Introduction

Fistula–in- ano is an abnormal perianal tract lined with 
epithelialized surface that connects anal canal to the 
perianal skin.1 Fistula-in-ano is not a very common 
disease of the gastrointestinal tract. The prevalence rate is 
approximately 0.01% and more common in men than in 
women. Male female ratio is 2:1.2

On and off perianal discharge, itching, discomfort, fever and 
local pain are the common symptoms.3,4 Even though being 
an uncommon disease, Fistula-in-ano was first described 
in Hippocrates. In 1835, Frederick Salmon treated 131 
patients for fistula St Mark’s hospital in London.5 In 1900, 
David Henry Goodsall described the course of fistulous tract 

Original Article



26 27JSSN JSSNJournal of Society of Surgeons of Nepal Journal of Society of Surgeons of Nepal

JSSN 2016; 19 (1) JSSN 2016; 19 (1)

and developed Goodsall’s rule for fistulous tract. 6 “Parks’ 
initial classification of perianal fistula was presented in 
1976. It was based on surgical anatomy.7 Morris modified 
the Parks classification system in 2000. This on the basis of 
radiologic anatomy on pelvic MRI, which is known as the 
St. James university Hospital Classification.5

Obstruction by trauma or fecal material to the outlet duct 
of the mucous anal gland leads to stasis, infection and 
first stage of perianal abscess. Pus then follows the least 
resistance path between the internal and external anal 
sphincter and through the external anal sphincter into the 
skin or ischioanal fossa or both. Multiple secondary tracts 
is also developed.8

Postoperative recurrence rate of perianal fistula is very 
high. This is not due to surgical hands. The main cause is 
due to poor or lack of demonstration of anatomical details, 
primary fistulous tract and it’s multiple branches with 
abscess.5, 9 Three Tesla Magnetic Resonance imaging has 
excellent multiplanner imaging capability and provides 
excellent anatomical details (especially sphincter anatomy) 
in relation with primary, secondary tracts with abscess and 
can be performed without endorectal coils.10, 11 

The objective of the study was to evaluate 3T MR imaging 
of perianal fistula. High tesla MRI is very important in 
the evaluation of perianal fistulas including simple vs. 
complex fistulas along with secondary tracts and abscess 
in relation with anal sphincter complex. It will provide 
excellent road map for surgeon for preoperative evaluation 
for management.12

Methods

A retrospective study was done among 32 patients who 
were referred for MR fistulogram for clinically suspected 
perianal fistula with perianal discharge at Jeebanta Advanced 
Kathmandu Imaging Pvt. Ltd., Durbar Marg, Kathmandu, 
Nepal from 11th January, 2015 to 9th March, 2016.

The MRI protocol for all of the sequences was standard. 
All images were obtained with a Philips Ingenia 3T digital 
broadband MR scanner.  Patient was placed in supine 
position with head first body coil was placed over the 
pelvis region placing center at the level of symphysis 
pubis. T1 3D GRE sequences in 3 planes were taken as 
localizer. For all sequences, distal rectum and subcutaneous 
tissue was included in imaging volume. Imaging plane was 
also included supralevator space to ensure no extension.

Imaging was performed in oblique coronal and oblique 
axial planes. The plane for oblique coronal plane was 

parallel to anal canal and plane for oblique axial plane was 
perpendicular to oblique coronal.

Following sequences were taken as standard sequences.

1. T1W oblique axial TR/TE 450/8ms, field of view
(FOV) 18-20 cm, slice 3mm with 0.9 mm gap and
matrix 348x298.

2. T2W oblique axial TR/TE 2400/90ms, field of view
(FOV) 18-20 cm, slice 3mm with 0.9 mm gap and
matrix 328x267

3. T2W SPAIR in oblique axial and oblique coronal TR/
TE 3400/65ms, field of view (FOV) 18-20 cm slice
3mm with 0.9 mm gap and matrix 276x254

4. 3DT2W SPAIR in sagital plane TR/TE /8ms 1500/145,
field of view (FOV) 20 cm, continuous slice of 1mm
with isometric voxel having matrix of 200x198.These
3D data were sent to Philips intellispace portal and
further analyzed in different planes (MPR/ MIP) to
see the extension of fistula to other area and to project
the lesion better.

Image Analysis

MR images were interpreted by a single radiologist with 
more than 13 years of experience in abdominal imaging 
with experience in perianal fistula imaging. MR imaging 
was described and grading was done according to the 
St James’s University Hospital classification. 
According to this grading system, normal findings is 
grade 0 (Figure 1), simple linear intersphicteric fistula 
is grade 1 (Figure 2), intersphicteric fistula with 
intersphicteric abscess or secondary tract is grade 2 
(Figure 3), transphicteric fistula is grade 3 (Figure 4), 
transsphicteric fistula with abscess or secondary tract 
within the ischioanal or ischiorectal fossa is grade 4 
(Figure 5) and tract extending to supralevator region of 
translevator region is grade 5 (Figure 6).

Figure 1. Normal Findings



26 27JSSN JSSNJournal of Society of Surgeons of Nepal Journal of Society of Surgeons of Nepal

JSSN 2016; 19 (1) JSSN 2016; 19 (1)

Figure 2. Grade 1

Figure 3. Grade 2

Figure 4. Grade 3

Figure 5. Grade 4

Figure 6. Grade 5

The fistulous internal opening was described as clockwise 
fashion. 12 o’clock position is anterior and 6 o’clock 
position is posterior. Length of the track was measured from 
internal opening to skin surface, and number of secondary 
tract and tract direction was also mentioned. Fistulous 
tract associated with presence or absence of abscess in 
the ischioanal, ischiorectal or supralevator spaces were 
carefully evaluated.

The data was entered in a predesigned performa. Data 
analysis was done by commercially available software 
package (using IBM SPSS V21). Numeric variables were 
presented as mean and standard deviation and categorical 
variables were presented as number and percentage.

Results

Out of 32 patients, 4 (12.5%) were normal while 28(87.5%) 
were abnormal MRI findings. Amongst the abnormal 
findings, 8 (25%) of the patients had intersphincteric 
fistulas followed by 10 (31.3%) transsphincteric fistulas, 6 
(18.8%) sinus tract, 2 (6.3%) supralevator/translevator and 
pilonidal sinus (Figure 7).

Figure 7. MRI Findings



28 29JSSN JSSNJournal of Society of Surgeons of Nepal Journal of Society of Surgeons of Nepal

JSSN 2016; 19 (1) JSSN 2016; 19 (1)

Associated Ischianal/ Ischiorectal abscess and secondary 
tracts were found in 5(15.6%) and 17(53.1%) patients 
respectively.

Abnormality was seen maximum in male patients 
28(87.5%) rather than female patients 4 (12.5%)  and 
male female ratio was 7:1. Minimal age was 18 years and 
maximum age was 63 years. Mean age was 37.28 (std 
deviation 11.9). External fistulous opening at anal region 
were found right side 13(40.6%), left side 14(43.8%) and 
inferiorly 3(9.4%) associated with multiple opening in 
5(15.6%), single opening in 25(78.1%) and no external 
opening seen in 2(6.3%) patients.

Common internal opening (sphincteric) in axial MR image 
was found in 5 0’clock position in 10(31.3%) patients 
while least common 1(3.1%) of the patients had 1, 4, 11 
0’clock position. 

Maximum length of the tract was found 9cm while 
minimum length was 1cm. Mean tract length was 3.9 (std. 
Deviation 2.3) and anterosuperior direction of the tract was 
found in maximum patients 9(28.1%). 

In our study, St. Jame’s University Hospital MR Imaging 
classification of perianal fistulas identified Grade 4 
(Transsphincteric fistula with secondary tract/abscess) in 
most of the patients 8 (25%), Grade 0 (normal), Grade 
1 (simple linear intersphicteric fistulas) and Grade 2 
(intersphicteric fistula with secondary tract/abscess) in 
4(12.5%) patients and Grade 3 (transsphincteric fistula) 
and Grade 5 (supralevator and translevator) in 2(6.3%) 
patients (Table 1).

Table 1. St. Jame’s University Hospital MR Imaging 
Classification of Perianal Fistulas

Grade Frequency Percent
Grade 0 (normal findings)

4 12.5

Grade 1 (simple linear 
intersphicteric fistula) 4 12.5

Grade 2 
(intersphicteric fistula 
with intersphicteric 
abscess or secondary 
fistulous tract

4
12.5

Grade 3 (Trans-
sphicteric fistula) 

2 6.3

Grade 4 (Trans-sphicteric 
fistula with abscess or 
secondary tract within the 
ischioanal or ischiorectal 
fossa)

8 25

Grade 5 
(supralevator and 
translevator disease)

2 6.3

Sinus tract + 

Pilonidal sinus
8 25

Total 32 100

Data was evaluated regarding clinical complaints 
which showed 14(43.8%) perianal discharge followed 
by 11(34.4%) recurrent fistula past H/O operation and 
1(3.1%) perianal bleed, past H/O fissure operation and H/O 
discharge and 2(6.3%) pilonidal sinus with discharge.

Discussion

Because of its excellent capability of demonstration of 
soft tissue contrast and multiplanner capabilities, MRI is 
the best choice of the pre operative evaluation of perianal 
fistulas.12, 13

Lunniss et al first utilize the MRI for preoperative evaluation 
of fistula. They correlated MR and surgical findings and 
found 86-88% concordance rate.14 Subsequent studies 
with high tesla MRI suggested that MRI is more sensitive. 
Dynamic contrast enhanced magnetic resonance imaging 
(DCEMRI) was more accurate to identify complex fistula 
than surgical exploration and had a sensitivity of 97%.15

T2W SPAIR images (fat-suppressed) shows high signal 
intensity fluid in the tract and low signal intensity fibrous 
wall of the fistula which provides the good contrast and 
delineate the layers of the anal sphincter.16, 17

In our experience, axial T2W SPAIR and 3DT2W SPAIR 
(fat - suppressed images) was the most useful for locating 
the fistulous tract, its internal opening, secondary tracts and 
collection.

Gadolinium enhanced T1W images and substraction 
contrast MR fistulography are useful to detect abscess 
and active inflammation. STIR (short inversion recovery) 
and DWI (Diffusion weighted Imaging) are additional 
sequences to whom contrast is contraindicated.12, 18

STIR sequence sometimes gives fallacious high signal 
intensity in healed fibrous tract. T2W and dynamic contrast 



28 29JSSN JSSNJournal of Society of Surgeons of Nepal Journal of Society of Surgeons of Nepal

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enhanced MR sequence should be carefully evaluated 
which will help to avoid this fallacy.15 Axial images provide 
the exact location of the primary tract, internal opening 
and differentiate intersphincteric from a transsphicteric 
fistula; the presence of involvement external anal sphincter. 
Coronal images differentiate extension of supralevator 
from infralevator tract. In our study we found all positive 
cases of perianal fistula using combination of different MR 
sequences and imaging planes, which provided necessary 
details.

In our study we found St. James University Hospital 
classification grading of fistulas applicable in 24 of 32 
cases. This MR based classification system provides simple 
anatomic details, which can be seen in axial and coronal 
images. Classification or grading is important because 
it provides the treatment option, simple fistulotomy to 
complex surgical procedures.6

Preoperative MRI evaluation provides detail about primary, 
secondary tracts, abscess and high and low fistula and 
associated Crohn’s disease which will benefit the patient. 
Recurrent fistula is headache to surgeons and is a cause 
of anxiety to patients, and is associated with branching 
fistulous tract.13 Incomplete diagnosis and missed 
extensions are the commonest cause of recurrence. In our 
study recurrence fistulae rate was 11(34.4%). All cases had 
not undergone preoperative MR examination.

In last few years, MRI has emerged as the best modality of 
choice in the detection and classification of perianal fistula. It 
has ability to detect complex fistula in simple way which helps 
the surgeon decide therapy with positive patient outcome.

Conclusion

Perianal fistulas are more common in males and according 
to the St. Jame’s University Hospital MR Imaging 
classification; Grade 4 fistulas are the commonest. MRI 
is a well-tolerated, painless and noninvasive technique 
and has multiplanner capabilities with excellent tissue 
differentiation of pelvic muscle along with sphincter 
complex. MR imaging provides the excellent information 
about the fistulas, secondary tracts and abscess in relation 
to pelvis structures.

Acknowledgement

I would like to express my sincere gratitude to Dr. Dan 
Bahadur Karki for the great suggestion and support during 
the study. Further, I would like to thank Dr. Anup Pradhan 
and Ms. Amrita Chaulagain for their help in preparing 
manuscript.

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