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Magnetic resonance imaging (MRI) is commonly performed in the workup for anal fistula (AF), both for diagnosis and follow-up, since it allows a good visualization of AF and its extension in all three dimensions, the possible presence of secondary branches and abscesses, the morphological condition of anal sphincters and the anatomy of the perianal and perirectal region. Moreover intravenous contrast medium helps differentiate active fistulous tract from fibrotic scar.

St James Hospital University classification (J Morris, JA Spencer, NS Ambrose. MR imaging classification of perianal fistulas and its implications for patient management. Radiographics 20;2000;623-635) is based on MRI findings and identifies 5 grade: inter-sphincteric fistula with or without abscess or secondary track (I & II), trans-sphincteric fistula with or without abscess or secondary track (III & IV), supraelevator and traslevator disease (V). This classification has been readily adopted by radiologists, but the clinical utility is quite low for surgery planning since infralevator fistulas are anatomically divided in two broad categories (inter- and trans-sphincteric fistulas) and the classification assumes that all trans-sphincteric fistulas are complex: we know from a clinical point of view that not all trans-sphincteric fistulas are complex and they could be easily managed and vice versa with inter-sphincteric fistulas (P Garg. Comparing existing classification of fistula-in-ano in 440 operated patients: is it time for a nwe classification? A retrospecitve cohort study. Int J Surg. 2017;Jun;42:34-40)

I Sudoł-Szopińska, GA Santoro et al. in Magnetic resonance imaging template to standardize reporting of anal fistulas. Tech Coloproctol 2021 propose a template for MRI report of AF with the purpose of improving AF characterization, enhancing surgical decision planning, facilitating re-evaluations during the follow-up and allowing a better interobserver comparison.

The proposed template for a uniform description of AF includes:
– Parks classification of primary tract, location on a clock dial, height and maximum cross-sectional diameter (mm);
– Secondary extensions type, location and number;
– Internal outlets and location;
– Abscess presence, location, type and extension;
– Internal and external sphincter morphology, the presence of defects, tinning, scars or atrophy.

The template include also a graphic representation of the AF in the three dimensions.

The proposed template may be an effective way to improve standardization of MRI AF report and it can certainly be useful in the follow-up of patients with complex and multi-treated perianal disease (such as in Crohn’s Disease) and in case patients need to be evaluated by different specialists.

A study is in progress (NCT04541238) to evaluate the feasibility and acceptability of the MRI template and, certainly the most important point of the question, whether it is effective in enhancing surgical decision planning.

Anna Maffioli, Chirurgia 1, ASST Fatebenefratelli Sacco, Milano

Ultimo aggiornamento: 16 gennaio 2021
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Malattie e procedure coloproctologiche

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