Download - Imaging Anal Fistulae
Imaging of Anal Fistula
Dr Sue Roach
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
• Determine relationship of fistula to sphincter complex
• Identify any secondary fistulous tracks
Imaging Modalities
• Fistulography
• Endoanal ultrasound
• Magnetic resonance
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
• Operator dependent• Highly accurate at identifying the internal
opening [4]
• Depicts fewer secondary extensions than MR
• Difficulty differentiating active track from fibrosis
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].
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%)
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?
• Post operative problems
• Complex cases such as crohns disease[6]
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
• 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
Morris J, Spencer JA, Ambrose S. MR Imaging Classification of Perianal Fistulas and Its implications for Patient Management. Radiographics 2000; 20:623-635
Grade 1 Simple Intersphincteric Fistula
Grade 2 Intersphincteric track with secondary track or abscess
Grade 3 Trans-sphincteric Fistula
Grade 4 Trans-sphincteric Fistula With Abscess or Secondary
Track
Grade 5 Supralevator and Translevator Disease
Aims
• To establish the common MR patterns of idiopathic peri-anal fistulation in Hope Hospital patients.
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
Results13
29
421
25
8
Grade 0Grade 1Grade 2Grade 3Grade 4Grade 5
% of patients
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%).
Grade 1- Intersphincteric fistula
Grade 2- Intersphincteric fistula with collection
Grade 3- Trans-sphincteric fistula
Grade 4- Trans-sphincteric fistula with secondary track
Grade 5- Translevator disease
Summary
• MR is a valuable modality in the assessment of peri-anal fistula
• Accurately identifies disease complexity
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