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Magnetic resonance imaging of fistula-in-ano: technique, interpretation and accuracy
P G Barker1, P J Lunniss, P Armstrong
1Department of Radiology, St Bartholomew's Hospital, West Smithfield, London.
Abstract:
The aim of this study was to document the appearances of fistula-in-ano on magnetic resonance imaging (MRI) and to prospectively evaluate the accuracy of MRI in the pre-operative assessment of anal fistulae. Patients with a clinical diagnosis of fistula-in-ano and awaiting surgery (n = 35) were examined with MRI. The fistulous tracks with their secondary extensions and abscesses are readily seen as low signal on T1-weighted images and high signal areas on STIR images. In order to determine the accuracy of the MRI interpretations, an experienced coloproctologist operated on all 35 patients without the knowledge of the scan interpretations and the findings at surgery were compared with the MRI scan interpretations. Concordance rates between MRI and operative findings were 86% for presence and course of the primary track, 91% for the presence and site of secondary extensions or abscesses and 97% for the presence of horse-shoeing. Although operative findings by an experienced coloproctologist were taken as the gold standard, we have shown that in 9% of our study group, failure of healing was related to pathology missed at surgery which had been documented on pre-operative MRI. It is probable, therefore, that the accuracy of MRI is higher than the figures quoted above. MRI is advocated as the imaging method of choice in the assessment of anal fistulae and its use may lead to a reduction in the recurrence rate due to inaccurate surgical assessment.
Insights
Magnetic resonance imaging (MRI) accurately assesses anal fistulae, identifying tracks and abscesses. This imaging method aids surgeons, potentially reducing recurrence rates by improving pre-operative evaluation.
Area of Science:
- Radiology
- Gastroenterology
- Surgical Assessment
Background:
- Fistula-in-ano presents diagnostic challenges in pre-operative assessment.
- Accurate imaging is crucial for effective surgical planning and reducing recurrence.
Purpose of the Study:
- To document magnetic resonance imaging (MRI) appearances of fistula-in-ano.
- To prospectively evaluate MRI's accuracy in pre-operative anal fistula assessment.
Main Methods:
- 35 patients with fistula-in-ano underwent MRI.
- MRI findings were compared with intraoperative findings by an experienced coloproctologist.
- Image analysis focused on T1-weighted and STIR sequences.
Main Results:
- High concordance rates were observed: 86% for primary tracks, 91% for extensions/abscesses, and 97% for horseshoeing.
- MRI identified pathology missed during surgery in 9% of cases, suggesting higher accuracy.
- Low signal on T1 and high signal on STIR images characterized fistulous tracks and abscesses.
Conclusions:
- MRI is a highly accurate imaging modality for fistula-in-ano assessment.
- Pre-operative MRI can improve surgical planning and potentially decrease recurrence rates.
- MRI is recommended as the imaging method of choice for anal fistulae evaluation.