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Imaging of Anal Fistula. Dr Sue Roach. Introduction.

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Imaging of Anal Fistula

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Imaging of anal fistula l.jpg

Imaging of Anal Fistula

Dr Sue Roach


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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].


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Imaging Objectives

  • Determine relationship of fistula to sphincter complex

  • Identify any secondary fistulous tracks


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Imaging Modalities

  • Fistulography

  • Endoanal ultrasound

  • Magnetic resonance


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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


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Endoanal ultrasound

  • Operator dependent

  • Highly accurate at identifying the internal opening [4]

  • Depicts fewer secondary extensions than MR

  • Difficulty differentiating active track from fibrosis


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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].


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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%)


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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


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Gadolinium?

  • Post operative problems

  • Complex cases such as crohns disease[6]


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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


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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


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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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Grade 1 Simple Intersphincteric Fistula


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Grade 2 Intersphincteric track with secondary track or abscess


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Grade 3 Trans-sphincteric Fistula


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Grade 4 Trans-sphincteric Fistula With Abscess or Secondary Track


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Grade 5 Supralevator and Translevator Disease


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Aims

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


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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


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Results

% of patients


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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%).


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Grade 1- Intersphincteric fistula


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Grade 2- Intersphincteric fistula with collection


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Grade 3- Trans-sphincteric fistula


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Grade 4- Trans-sphincteric fistula with secondary track


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Grade 5- Translevator disease


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Summary

  • MR is a valuable modality in the assessment of peri-anal fistula

  • Accurately identifies disease complexity


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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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