MR IMAGING OF FISTULA : ITS
INPUTS AND IMPLICATIONS FOR
SURGICAL MANAGEMENT
H.Tayar*i, A.Daghfou*s, F.Jabnoun**, K.Bouzaid**i, L.Rezgui Marhou*l
Radiology services
Trauma center*, Tunisia
Taher Maamouri’s Hospita**l, Nabeul
GI27
INTRODUCTION

Anal fistula is a benign condition but may cause considerable distress to the
patient and difficulty for the surgeon.

Fistulae are intimately related to the anal sphincter complex, so that incision and
drainage may damage these muscles to avariable degree with the risk of anal
incontinence.

The correct balance between eradication of infection and maintenance of
continence depends upon accurate pre-operative assessment of fistula
geography, namely the site and level of any internal opening, the anatomy of the
primary track and the presence of any secondary ramifications.

These questions are best answered by MRI, which is more accurate than all
other pre-operative investigations.
OBJECTIVES
Illustrate the contribution of magnetic resonnance
imaging in the diagnosis and assessement of anal fistulas
for providing valuable assisstance in conducting surgical.
MATERIALS AND METHODS

Retrospective study.

The study population comprised teen adult patients
complaining of anal fistula and whose all received a
clinical examination by a surgeon and a pelvic MRI.

The protocol includes T1 and T2 weighted sequences in
three planes, a sequence of diffusion and T1 Fat Sat
gadolinuim injection in three planes.
RESULTS

Average age: 38 years.

Sex ratio: 6 men/4women.

All patients were followed for crohn’s disease.

Pelvic MRI has objectified 6 complex fistula and 4 cases
of simple fistula.

Collections were observed in 5 cases.
RESULTS : EXAMPLE 1
a
b
c
Simple linear intersphincteric fistula.
Axial T2-weighted (a) and STIR images (b) show fistulous tracks in the intersphincteric
plane ( ).
Coronal T1-weighted postcontrast image at the same level (c) demonstrates
hyperenhancement in the same region, representing inflammation ( ).
RESULTS: EXAMPLE 2:
a
b
c
Complex intersphincteric fistula with horseshoe track.
43-year-old man with complex fistulating Crohn’s disease.
The intersphincteric fistulous track (
in axial T2 Weighter”a”and STIR”b” images)
crosses the midline in the anterior interhemispheric space (
in coronal T2-Weighter
images“c”) forming a horse-shoe track.
RESULTS: EXAMPLE 2 :
d
e
f
Enhancement on contrast administration is noted in the three plans axial (d),
coronal (e) et sagittal (f) T1-weighted postcontrast images (
):
ACTIVE FISTULA
RESULTS: EXAMPLE 3 :
a
b
Simple transphincteric fistula
29-year-old woman with long-standing Crohn’s disease.
(a) STIR image showing a transsphincteric fistula.
(
)
(b) Axial and ( c) coronal Sagittal T1-weighted
postcontrast images in the same patient demonstrates
hyperenhancement along fistulous tract. (
)
c
RESULTS : EXAMPLE 4:
a
b
c
Trans-sphincteric complex fistula with abscess
There are axial T2-Weighted images:
The trans-sphincteric track is seen entering the anal canal at 6 o’ clock
(
).
In addition, an abscess in the left ischioanal fossa is seen ( ).
RESULTS : EXAMPLE 4:
d
e
Axial T1-weighted postcontrast image (d) in the same
patient demonstrates hyperenhancement along a
contiguous fistulous tract to the skin (
).
Axial and coronal T1-weighted postcontrast images (e-f)
shows partial enhancement of rim (
), indicating
presence of fluid in center with rim of inflammatory
tissue: abcesses.
f
RESULTS : EXAMPLE 5:
a
b
c
Complex fistula and voluminous abcesses
(a) Axial T2-weighted image shows large abscess extending into right gluteus and
levator ani muscles.(
)
(b) Axial fat-saturated T2-weighted image shows abscess (a) more clearly because
bright signal of fat, in which abscess is located, is suppressed. (
)
(c ) T1-weighted image after administration of IV contrast medium clearly shows rim
enhancement of lesions on right (
), indicating presence of large amount of pus.
RESULTS : EXAMPLE 5:
(d) Coronal sequence shows the
course of the fistula (
)
from the canal anal to the left
levator ani muscle .
d
DISCUSSION





Anal fistula is a common disease that has long
challenged surgeons’ skills.
Perianal fistula, if not treated properly will result in one
of two terrible complications, recurrence or
incontinence.
The key to successful management of fistula-in-ano lies
in correctly identifying the full extent of disease and its
relationship to the sphincter complex.
It’s the role of Magnetic Resonnance Imaging.
This exam is more sensitive than even surgical
exploration of the tract.
DISCUSSION



MRI imaging of perianal fistulae relies on the inherent
high soft tissue contrast resolution and the multiplanar
display of anatomy by this modality.
It’s especially useful in patients with fistulae associated
with Crohn’s disease and those with reccurent fistulae, as
these entities are associated with branching fistulous
tracts.
Missed extensions are the commonest cause of
recurrence.
DISCUSSION




T2W images (TSE and fat-suppressed) provide good
contrast between the hyperintense fluid in the tract and
the hypointense fibrous wall of the fistula, while
providing good delineation of the layers of the anal
sphincter.
Gadolinuim-enhanced T1W images are useful to
differentiate a fluid-filled tract from an area of
inflammation.
The tract wall enhances, whereas the central portion is
hypointense.
Abscesses are also very well depicted on postgadolinuim images.
DISCUSSION





The exact location of the primary tract (ischioanal or
intersphincteric) is most easily visualized on axial
images.
The presence of disruption of the external anal sphincter
differenciates a transsphincteric fistula from an
intersphincteric one.
The internal opening of the fistula is also best seen in
this plane.
Coronal images depict the levator plane, thereby
allowing differentiation of supralevator from infralevator
infection.
A combination of an axial and a longitudinal series
(coronal, sagittal or radial) will provide all the necessary
details.
DISCUSSION
MRI also allows to classify anal fistulas in five grades
according to:
JAMES’S UNIVERSITY HOSPITAL MR IMAGING
CLASSIFICATION OF PERIANAL FISTULAS
Grade
Description
 0
Normal appearance
 1
Simple linear intersphincteric fistula
 2
Intersphincteric fistula with intersphincteric
abscess or secondary fistulous track
 3
Trans-sphincteric fistula
 4
Trans-sphincteric fistula with abscess or
secondary track within the ischioanal or
ischiorectal fossa
 5
Supralevator and translevator disease
CONCLUSION

Magnetic resonance imaging has become a powerful tool
in the evaluation of anal anatomy.

In patients with complex disease, MRI is an important
adjunct in delineating disease location and extent, its
relationship to sphincter muscles, and in planning
management.

MRI also plays an important role in evaluating the
response to medical and surgical therapies.