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P575. A new tool for the surveillance of Crohn's perianal fistulae

N.A. Yassin1, P.F. Lung1, A. Askari1, P.E. Edwards2, R.K.S. Phillips1, A. Gupta1, A.L. Hart1, 1St Mark's Hospital, and Academic Institute, London, United Kingdom, 2Imperial College London, Computer Science, London, United Kingdom


Magnetic Resonance Imaging (MRI) is the tool used to assess response to medical therapy for the treatment of perianal Crohn's fistulae. Quantifying fistula volumes would be more beneficial than relying on subjective MRI reports.

We aim to use computer software and MRI segmentation to design 3D models of fistula tracks and measure baseline and post-biologics treatment fistula volumes.


Ten baseline and post-biologics MRI images of Crohn's perianal fistulae were randomly selected. Three-Dimensional fistula models were independently created by a surgeon and radiologist

  • Manual fistula volumes were calculated for each patient and the results compared
  • Data were obtained on Perianal Disease Activity Index (PDAI) scores, clinical and radiological healing for these patients.

Data were analysed using Spearman's correlation to determine whether a change in fistula volume over a one-year period correlated with a change in PDAI score over the same time period. Fistula volumes and PDAI score were also correlated with degrees of clinical healing.


Baseline volumes for the surgeon showed a median of 9766 mm3 (IQR 4636, 30980). Post-biologics volumes had a median of 4200 mm3 (IQR 2720, 20070).

A change in baseline and post-treatment volumes was also observed by the radiologist; the median volume was 9207 mm3 (IQR 5132, 21710) for the baseline MRIs and 2872 mm3 (IQR 1827, 18830) for the post-treatment ones.

There was a positive correlation between change in fistula volume and change in PDAI scores over a one-year period (r = 0.654, p = 0.040). Similarly, there was a significant positive correlation between clinical healing and change in PDAI scores (rs=0.625, p = 0.050) but not between degree of clinical healing and the change in fistula volumes (r = 0.331, p = 0.351).

Figure 1. Three-dimensional model of a complex perianal fistula with surrounding anatomy.

Figure 2. Image of computer software showing a 3D model of an anal fistula (excluding the surrounding anatomy) and the volume measurement function in mm3.


MRI volume measurements of 3D Crohn's fistula models provide an accurate assessment tool as an adjunct to clinical follow up. Serial volume measurements are feasible and may guide the use of medical therapies such as anti-TNFs.