1. MRI of fistula in ano
C HOEFFEL
JM TUBIANA

2. Objectives
• Describe the impact of MRI in the
management of fistulas
• Propose protocols and report forms
used for fistula in ano evaluation

3. Fistula in ano
• Track communicating
with the rectum or the
anal canal via an
internal opening and
generally with an
external opening
• Infection of an
intersphincteric glandfollowed by drainage of
the abscess in every
directions

4. WHY MRI ?
• MRI versus clinical examination versus
endoanal ultrasound
– 104 patients evaluated with the three
modalities and follow-up (MRI or surgery) as
the gold standard.
• MRI versus Clinical examination
– Correct classification 90 vs 61 %
– Best for detection of abscesses, of
horseshoe fistulas
Buchanan Radiology 2004

5. WHY MRI ?
• MRI versus endoanal
ultrasonography
– Internal opening 97 vs 91 %
– Best detection of complex tracts and
abscesses with MRI
Buchanan Radiology 2004

6. WHY and WHEN MRI ?
• First suspicion of fistula
– 30 patients with pre-operative MRI,
surgery and rectal exam under GA +
follow-up with surgery and 12 months
MRI. Disagreement n=15
• Minor disagreement , n=12
• Change in management, n=3
• MRI ‘s impact on treatment decisions = 10 %
Buchanan Br J Surg 2003

7. WHY and WHEN MRI ?
• Recurrent Fistula 71 patients
– Agreement surgery/MRI, n=40
• 5 with recurrent fistulas
– Discrepancies surgery/ MRI, n=31
• 16 with recurrent fistula (52 %),
p=0.0005, at the location predicted by
MRI
• MRI guided surgery decreases recurrence
rate down to 75 %.
Buchanan Lancet 2002

8. WHY and WHEN MRI ?
• Endoscopic Ultrasonography
– Particularly for intersphincteric fistulas
– Less accurate in case of sepsis or complex
fistulas
• MRI
– First-step examination in case of recurrent
fistula
– If presence of a complex fistula at US or
clinical examination
– Before anti-TNF treatment
Williams Dis Colon Rectum 2007

9. MRI : HOW ?
• Technique
• Anatomy
• Classification

10. MRI Technique
• Sequence Selection
• Planes
• Slices orientation

11. MRI Technique
• 1.5 Tesla ou 3 T
• Phased-array coil, without any
preparation nor endorectal probe.

12. Sequences
– Anatomical views Sag T2 - Ax T2 Pelvis
– Fistula imaging
• STIR
• Fat Suppressed T2
• Gado Fat suppressed T1
3 DT2 w-TSE with post processing reformation ?

13. How to choose sequences ?
• T2 FS / STIR
– Simple
– No injection
– High signal intensity of the
inflammatory tract
– Fibrous areas low signal
intensity
– Less sensitive for very thin
tracts
– Difficult to differentiate
inflammation from fluid
HALLIGAN Radiology 2006
Before tt STIR
After tt STIR

14. Sequences: How to choose?
• T1 Gado FS
– Injection
– Inflammatory tract white
– Fibrosis/Fluid black
– May overinterpret a healing
fistula
T1 Gado FS

15. STIR vs T1 Gado FS
• STIR versus T1 Gado FS
Gado FS
– Overinterpretation of enhancement
with gado, while no fluid on STIR,
when a fistula is on its way to heal
B0
STIR

16. STIR vs T1 Gado FS
Differentiate granulation tissue from fluid
Before anti TNF treatment
Gado FS
STIR
Abscess?
Granulation tissue?
No abscess

17. STIR vs T1 Gado FS
STIR
Gado FS
Abscess

18. Sequences: How to choose?
• Combined T1 Gado FS + STIR
• Role of DW MRI?
T1 gado FS
Axial STIR
Axial diff b500

19. T2
Ax T1 Gado FS
Fusion diff-T2
Fusion diff-T2

20. MRI Technique
• Slice thickness
– 3-4 mm
• Section Planes
– Axial - relationship to sphincters
– Coronal - level of internal opening and
relationship to levator ani muscles.
– Sagittal may be useful (anovaginal
fistula)

21. MRI Technique- Slice positioning
Important to assess the level of internal opening with regard to
puborectal muscle and better evaluation of relationship/ levator ani

22. MRI Technique
• FOV – not just anal canal
– In some cases must cover perineum,
presacral space, supralevatorian space

23. Anatomy
External Sphincter-T2
• Prolongs puborectal muscle
• Striated muscle
• Circular
• Hyposignal
2 cm

24. Anatomy
Internal
Sphincter- T2/
STIR
• Prolongs rectal muscular
layer
• Smooth muscle
• Circular
• Intermediate to high signal

25. GADO FS

26. Classification
•
Why is it important?
ü Aims of surgery
o Continence
preservation
o Infectious foci and
secondary tracts
elimination
ü Surgical Options
o Seton tight or not
o FistulotomyFistulectomy
o Intersphincteric
amputation, Flap

27. o Fistulotomy-Fistulectomy
Pr Halligan

28. Intersphincteric
amputation

30. Superficial Fistula
Horsthuis AJR 2004
T2

31. Intersphincteric Fistula
Involvement of internal sphincter
No risk for continence
Horsthuis AJR 2004

33. Transphincteric Fistula
Involvement of both internal and external sphincters
External sphicter section threatens continence
Ax gado FS

34. Transphincteric Fistula
•
Sometimes internal opening less obvious but predictable,
located at the penetrating point of the external sphincter
or at the epicenter of the intersphincteric sepsis.

35. Suprasphincteric Fistula 20 %
Rare, upwards and crosses the levator ani muscle.
Its section may threaten continence. Often inaccurately classified

37. Extrasphincteric Fistula= primitive rectal
disease (CD, cancer, diverticulitis)

38. Ax Gado FS

39. Complications
• Abscess

40. Complications
Dr Damian Tolan, Leeds

41. Report
1.Fistula type - simple, complex,
anovaginal, horseshoe

42. Ax T2
fusion
Coro gado FS
Ax gado FS

43. Report
1.Fistula Type
2. Internal opening
Level and position (clockwise)

44. Report
1.Fistula type
2. Internal opening
Level and position (clockwise)
3. Primary fistula pathway to the
external opening
Location and hour

45. Report
1.Fistula type
2. Internal opening
Level and position (clockwise)
3. Primary fistula pathway to the
external opening
Location and hour

46. Report
1.Fistula type
2. Internal opening
Level and position (clockwise)
3. Primary fistula pathway to the
external opening
Location and hour
4. Number and position of
supralevatorian extensions?

47. Report
1.Fistula type
2. Internal opening
Level and position (clockwise)
3. Primary fistula pathway to the
external opening
Location and hour
4. Number and position of supralevatorian
extensions?
5. Number and positions of collections

48. Report
• Activity Criteria
– Hypersignal T2
– Enhancement

49. Ax gado FS
T2 Stir
B0
B1000

50. Report
• Sphincter
• Rectum
T1 FS Gado

51. • Main anatomic criteria
– Fistula type
•
•
•
•
Simple
Complex
Horseshoe
Ano-vaginal
– Relationship with levator
ani muscle
• Inflammation criteria
– Fistula
• Hypersignal T2
• Enhancemnet
– Abscess
– Rectal wall
– Parks’classification
•
•
•
•
Intersphincteric
Transsphincteric
Suprasphincteric
Extrasphincteric
– Openings
• Others
– Presence of a seton
– Distant extension
– Sphincteric ring
abnormalities (rupture…)