Perianal fistula protocol (MRI)

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MRI protocol for the assessment of perianal fistulas is a group of MRI sequences put together to asses the extension and anatomic relationships of inflammatory fistulas to the anal sphincters, helping to plan surgical management and monitor treatment response.

NB: This article is intended to outline some general principles of protocol design. The specifics will vary depending on MRI hardware and software, radiologist's and referrer's preferences, institutional protocols, patient factors (e.g. allergy) and time constraints.

Sequences

A good protocol for this purpose would include:

  • fine 3 mm slices
    • axial and coronal T2 FS or STIR
    • axial and coronal T2 are helpful in the delineation of sphincter anatomy
    • axial and coronal T1 FS with gadolinium-based intravenous contrast material
    • axial T1

Some authors recommend :

  • short-inversion-time inversion recovery (STIR)
  • gradient-echo T1-weighted with or without gadolinium-based intravenous contrast material
  • spin-echo T1-weighted
  • spin-echo T2-weighted with saline instillation (MR fistulography)

A novel method is the use of volume MRI sequences (more routinely used in neuro and musculoskeletal MRI). The benefits are reduced imaging times and isotropic data allowing multiplanar reformatting while maintaining comparable contrast resolution.