Imaging Anal Fistulas

Dr Sue Roach FRCR

Powerpoint File

Introduction

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

The role of magnetic resonance (MR) imaging in the assessment of idiopathic anal fistulae, particularly in the setting of recurrence, is well established [3]. It has been shown to be the most accurate technique for evaluation of the primary track and any extensions [4]. It has also been shown to be a more accurate predictor of patient outcome than surgical outcome [5].

An MR categorisation system commonly utilised in the assessment of peri-anal fistulae is the St James's University Hospital classification [6], which consists of 5 grades and relates the Parks surgical classification to anatomy seen at MR in both axial and coronal planes (Fig. 1). This employs simple anatomical discriminators identifiable on coronal and axial images and has been validated by surgical exploration and long term clinical outcome.

Aims

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

Methods

A retrospective review of 24 consecutive MR scans performed for idiopathic peri-anal fistulation was undertaken between January 2004 and February 2005.

All scans were performed on a 1 tesla Siemens MR scanner utilising a phased array pelvic surface coil. A standard protocol with coronal and axial T1 weighted and STIR images through the perineum was utilised. Some patients underwent additional saggital high resolution T2 weighted images.

Results

Number of patients Percentage of patients St James University

Hospital Classification

3 13 0

7 29 1

1 4 2

5 21 3

6 25 4

2 8 5

Discussion

The majority of patients with idiopathic peri-anal fistulation have uncomplicated disease with a simple inter-sphincteric or trans-sphincteric fistula (50%). A further group of patients have trans-sphincteric fistulae complicated by secondary tracks or ischiorectal abscess (25%). Supra-levator or trans-levator disease is relatively rare in this patient group (8%).

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: Seow-Choen F, Phillips RKS. Insights Gained from the Management of Problematic Anal Fistulae at St. Mark's Hospital 1984-88. Br. J. Surg. 1991; 78:539-41

3: Buchanan GN, Halligan S, Williams A. et al. Effect of MRI on Clinical Outcome of Recurrent Fistula-in ano. Lancet 2002; 360: 1661-62

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