1. Imaging of Anal Fistula
Dr Sue Roach

2. Introduction
Pre-operative confirmation of fistula complexity has been shown to facilitate surgical planning of sphincter saving techniques[1] and to reduce the incidence of unidentified sepsis, which is the leading cause of fistula recurrence [2].

3. Imaging Objectives
Determine relationship of fistula to sphincter complex
Identify any secondary fistulous tracks

4. Imaging Modalities Fistulography Endoanal ultrasound
Magnetic resonance

5. Fistulography Acute tracks may not have a patent lumen
Difficult to relate the track to the sphincter and levator ani
Shown to be accurate in only 16% [3]
Helpful for chronic fistulae with an external opening distant from the anus

6. Endoanal ultrasound Operator dependent
Highly accurate at identifying the internal opening [4]
Depicts fewer secondary extensions than MR
Difficulty differentiating active track from fibrosis

7. Magnetic Resonance
Most accurate technique for evaluation of the primary track and any extensions [4].
More accurate predictor of patient outcome than surgical findings at EUA[5].

8. Prospective study 56 patients
Beets-Tan RGH, Beets GL, Gerritsen van der Hoop A. et al. Preoperative MR Imaging of Anal Fistulas: Does it Really Help the Surgeon? Radiology 2001; 218:75-84
Prospective study 56 patients
MR prior to surgery but result witheld from surgeon until end of surgery while patient still anaesthetised
Important additional information in 21%. Benefit greatest in crohns (40%), recurrent fistulas (24%), primary fistulas (8%)

9. Prospective study 48 patients
Spencer JA, Chapple K, Wilson D et al. Outcome After Surgery for Perianal Fistula: Predictive Value of MR Imaging. AJR 1998; 171:
Prospective study 48 patients
MR and then surgical exploration blinded to MR
MR categorised 41% complex. Surgery 38%. Only agreed in 8 cases
19 patients required further surgery. 13 of these considered complex on MR, 9 by surgery
MR better at predicting outcome than surgery

10. Gadolinium? Post operative problems
Complex cases such as crohns disease[6]

11. Endoanal coil?
Endocoils give superior anatomical resolution of fistula disease within the sphincter
Resolution falls off rapidly outside the sphincter
Complex tracks outside the sphincter are not well seen

15. MR Technique Phased array pelvic coil
Axial and coronal imaging of the perineum
T1 and short T1 inversion recovery (STIR) images obtained
Additional saggital high resolution T2 images occasionally helpful
IV gadolinium rarely administered

19. Morris J, Spencer JA, Ambrose S
Morris J, Spencer JA, Ambrose S. MR Imaging Classification of Perianal Fistulas and Its implications for Patient Management. Radiographics 2000; 20:

20. Grade 1 Simple Intersphincteric Fistula

21. Grade 2 Intersphincteric track with secondary track or abscess

22. Grade 3 Trans-sphincteric Fistula

23. Grade 4 Trans-sphincteric Fistula With Abscess or Secondary Track

24. Grade 5 Supralevator and Translevator Disease

25. Aims
To establish the common MR patterns of idiopathic peri-anal fistulation in Hope Hospital patients.

26. Methods Retrospective review
24 consecutive MR scans performed for idiopathic anal fistulation
Scans performed on a 1 Tesla MR scanner with phased array pelvic coil technique

27. Results
% of patients

28. Discussion
Majority (50%) of patients with idiopathic peri-anal fistulation have uncomplicated disease
25% have trans-sphincteric fistulae complicated by secondary tracks or ischiorectal abscess
Supra-levator or trans-levator disease is relatively rare in this patient group (8%).

29. Grade 1- Intersphincteric fistula

38. Grade 2- Intersphincteric fistula with collection

40. Grade 3- Trans-sphincteric fistula

76. Grade 4- Trans-sphincteric fistula with secondary track

81. Grade 5- Translevator disease

86. Summary
MR is a valuable modality in the assessment of peri-anal fistula
Accurately identifies disease complexity

87. References
1: Beets-Tan RGH, Beets GL, Gerritsen van der Hoop A. et al. Preoperative MR Imaging of Anal Fistulas: Does it Really Help the Surgeon? Radiology 2001; 218:75-84
2: Bartram C, Buchanan G. Imaging anal fistula. Radiol Clin N Am 41 (2003)
3: Kuijpers HC, Schulpern T. Fistulography for fistula-in-ano: is it useful? Dis Colon Rectum 1985;28:103-4
4: Buchanan GN, Halligan S, Bartram CI et al. Clinical Examination, Endosonography, and MR Imaging in Preoperative Assessment of Fistula in Ano: Comparison with Outcome-based Reference Standard. Radiology 2004; 233:
5: Spencer JA, Chapple K, Wilson D et al. Outcome After Surgery for Perianal Fistula: Predictive Value of MR Imaging. AJR 1998; 171:
6: Horsthius K, Stoker J. MRI of perianal crohn’s disease. AJR 2004; 183:
7: Morris J, Spencer JA, Ambrose S. MR Imaging Classification of Perianal Fistulas and Its implications for Patient Management. Radiographics 2000; 20: