Mri imaging of fistula : its inputs implications for surgical management

1. 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

2. 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.

3. OBJECTIVES
Illustrate the contribution of magnetic resonnance
imaging in the diagnosis and assessement of anal fistulas
for providing valuable assisstance in conducting surgical.

4. 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.

5. 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.

6. Results : EXAMPLE 1
a b
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 ( ).
c

7. RESULTS: EXAMPLE 2:
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.
a b c

8. 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

9. RESULTS: EXAMPLE 3 :
a
c
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. ( )

10. 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 ( ).

11. RESULTS : EXAMPLE 4:
d e
f
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.

12. RESULTS : EXAMPLE 5:
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.
a b c

13. RESULTS : EXAMPLE 5:
(d) Coronal sequence shows the
course of the fistula ( )
from the canal anal to the left
levator ani muscle .
d

14. 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.

15. 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.

16. 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 post-gadolinuim
images.

17. 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.

18. 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

19. 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.