MAGNETIC-RESONANCE-IMAGING OF FISTULA-IN-ANO - TECHNIQUE, INTERPRETATION AND ACCURACY

The aim of this study was to document the appearances of fistula-in-an o on magnetic resonance imaging (MRI) and to prospectively evaluate th e accuracy of MRI in the pre-operative assessment of anal fistulae. Pa tients with a clinical diagnosis of fistula-in-ano and awaiting surger y (n=35) were examined with MRI. The fistulous tracks with their secon dary extensions and abscesses are readily seen as low signal on T1-wei ghted images and high signal areas on STIR images. In order to determi ne the accuracy of the MRI interpretations, an experienced coloproctol ogist operated on all 35 patients without the knowledge of the scan in terpretations and the findings at surgery were compared with the MRI s can interpretations. Concordance rates between MRI and operative findi ngs were 86% for presence and course of the primary track, 91% for the presence and site of secondary extensions or abscesses and 97% for th e presence of horse-shoeing. Although operative findings by an experie nced coloproctologist were taken as the gold standard, we have shown t hat in 9% of our study group, failure of healing was related to pathol ogy 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 choic e in the assessment of anal fistulae and its use may lead to a reducti on in the recurrence rate due to inaccurate surgical assessment.