imaging of anal fistula
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Imaging of Anal Fistula. Dr Sue Roach. Introduction.

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Presentation Transcript
introduction
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].

imaging objectives
Imaging Objectives
  • Determine relationship of fistula to sphincter complex
  • Identify any secondary fistulous tracks
imaging modalities
Imaging Modalities
  • Fistulography
  • Endoanal ultrasound
  • Magnetic resonance
fistulography
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
endoanal ultrasound
Endoanal ultrasound
  • Operator dependent
  • Highly accurate at identifying the internal opening [4]
  • Depicts fewer secondary extensions than MR
  • Difficulty differentiating active track from fibrosis
magnetic resonance
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].
slide8

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%)
slide9
Spencer JA, Chapple K, Wilson D et al. Outcome After Surgery for Perianal Fistula: Predictive Value of MR Imaging. AJR 1998; 171:403-406
  • 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
gadolinium
Gadolinium?
  • Post operative problems
  • Complex cases such as crohns disease[6]
endoanal coil
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
mr technique
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
slide19

Morris J, Spencer JA, Ambrose S. MR Imaging Classification of Perianal Fistulas and Its implications for Patient Management. Radiographics 2000; 20:623-635

slide25
Aims
  • To establish the common MR patterns of idiopathic peri-anal fistulation in Hope Hospital patients.
methods
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
results
Results

% of patients

discussion
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%).
summary
Summary
  • MR is a valuable modality in the assessment of peri-anal fistula
  • Accurately identifies disease complexity
references
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) 443-457
  • 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; 233:674-681
  • 5: Spencer JA, Chapple K, Wilson D et al. Outcome After Surgery for Perianal Fistula: Predictive Value of MR Imaging. AJR 1998; 171:403-406
  • 6: Horsthius K, Stoker J. MRI of perianal crohn’s disease. AJR 2004; 183:1309-1315
  • 7: Morris J, Spencer JA, Ambrose S. MR Imaging Classification of Perianal Fistulas and Its implications for Patient Management. Radiographics 2000; 20:623-635
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