Transcript Imaging of Anal Fistula

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; 171:403406
• 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
Results
8
13
25
29
Grade 0
Grade 1
Grade 2
Grade 3
Grade 4
Grade 5
% of patients
21
4
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
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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