Significance of MR imaging in setting the ball path of surgical management in perianal fistulae

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Original Article

Significance of MR imaging in setting the ball pathof 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, Indiab Professor and Consultant, Department of Radiodiagnosis, Vardhman Mahavir Medical College and Safdarjung

Hospital, New Delhi 110029, Indiac Professor and Consultant, Department of Surgery, Vardhman Mahavir Medical College and Safdarjung Hospital,

New Delhi 110029, Indiad 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

Abbreviations: MRI, magnetic resonance i* Corresponding author. Tel.: þ91 9811681E-mail addresses: [email protected], d

Please cite this article in press as: Kumarperianal fistulae, Apollo Medicine (2014),

http://dx.doi.org/10.1016/j.apme.2014.08.0050976-0016/Copyright © 2014, Indraprastha M

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 canplan the surgerywell, and achieve a complete eradication of the disease.

Copyright © 2014, Indraprastha Medical Corporation Ltd. All rights reserved.

maging; DRE, digital rectal examination.790; fax: þ91 11 [email protected] (Y. Agarwal).

N, et al., Significance of MR imaging in setting the ball path of surgical management inhttp://dx.doi.org/10.1016/j.apme.2014.08.005

edical Corporation Ltd. All rights reserved.

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http://dx.doi.org/10.1016/j.apme.2014.08.005



Table 1 e Classification of perianal fistulaea in the studycohort (n ¼ 30).

Fistula classification Number Percentage

Grade 1 (Intersphincteric with

no extensions)

4 13.33

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


1. Introduction

Perianal fistula is an abnormal communication between the

anorectum and the perianal skin. Such a communication may

be associatedwith one ormore secondary ramifications and/or

abscesses. A high internal opening and/or transsphincteric

location canexaggerate the complexity 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. Amild

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.Theseobservationswerecorrelatedwith

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.

Table 2 e Comparative accuracy of clinical vs. MRIfindings in classification of perianal fistulae.

Diseasecharacteristic

Clinicalclassification

MR imagingclassification

Surgicalvalidation

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

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.

OnMR examination, the internal openingwas 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%)

Please cite this article in press as: Kumar N, et al., Significance of Mperianal fistulae, Apollo Medicine (2014), http://dx.doi.org/10.101

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

R imaging in setting the ball path of surgical management in6/j.apme.2014.08.005



Table 3 e Correlation of preoperative clinical evaluation,MRI and intraoperative findings.

Diseasecharacteristics

Clinicalevaluation

MRimaging

Surgicaldata

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).

a p o l l o m e d i c i n e x x x ( 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 imagingwas 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% onMRI.

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 assessmentwas restricted

to 75%.9




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.


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




a p o l l o m e d i c i n e x x x ( 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.


r e f e r e n c e s

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2. Van Koperen PJ, Wind J, Bemelman WP, et al. Dis Colon Rectum.2008;51(10):1475e1481.

3. Garcia-Aguilar J, Belmonde C, Wong WD, Goldberg SM,Madoff RD. Anal fistula surgery. Dis Colon Rectum.1996;39(7):723e729.

4. Finlay IG, Lunniss PJ, Philips RKS. Objectives in Management ofAnal Fistula. Chapman and Hall; 1996:78e80.

5. Spencer JA, Ward J, Ambrose NS. Dynamic contrast enhancedMR imaging of perianal fistulae. Clin Radiol. 1998;53:96e104.

6. Abdul Kawy R. Classification of anal fistulas based onclinicopathological evidence. Bull Alexandria Fac Med.2007;43(2):1e8.

7. Parks AG, Gordon PH, Hardcastle JD. A classification of fistulain ano. Br J Surg. 1976;63:1e12.

8. Buchanan GN, Halligan S, Bartram CI, Williams AB, Tarroni D,Cohen RG. Clinical examination, endosonography and MRimaging in preoperative assessment of fistula in ano.Comparison with outcome-based reference standard.Radiology. 2004;233(3):674e681.

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Significance of MR imaging in setting the ball path of surgical management in perianal fistulae