Introduction
Methods
Guideline group selection
Guideline development
Results
1. Clinical indications for imaging | |
• It is recommended that anal imaging (usually MRI) may be used to investigate potential anal sepsis. Imaging can both diagnose and classify fistula-in-ano. Imaging may also be used to investigate acute ischioanal abscess (II) | |
• It is recommended that anal imaging (usually MRI) may be used to investigate potentially complex pilonidal sinus and hidradenitis suppurativa, where the differential diagnosis includes cryptoglandular infection (III) | |
• It is recommended that anal imaging (usually MRI) may be used to investigate anal pain in immunocompromised patients and anal necrotising fasciitis, since imaging reveals whether sepsis is present, and its extent (III) | |
• It is recommended that anal imaging (usually MRI) may be used to monitor the effect of therapy on anal sepsis in Crohn’s disease (e.g. biological/cellular/surgical). Imaging can also be used before medical treatment is commenced, to identify any abscess that may preclude biological therapy (II) | |
2. Imaging modalities | |
• MRI is recommended as the most clinically useful imaging modality to investigate potential anal sepsis (II) | |
• It is not recommended to use CT scanning as the primary investigation for fistula-in-ano where there is access to MRI and/or anal US. However, CT is sometimes still performed where MRI and/or anal US is unavailable, or in an emergency setting. In such circumstances, CT may provide useful information regarding the presence and extent of sepsis when interpreted by experienced observers. Where performed, it is recommended that CT employ intravenous contrast (V) | |
• It is not recommended to use contrast fistulography to investigate fistula-in-ano where there is access to MRI and/or anal US. However, fistulography is sometimes still performed where MRI and/or anal US is unavailable. In such circumstances, fistulography may provide useful information regarding the extent of sepsis when interpreted by experienced observers who are aware of its limitations (V) | |
3. Radiologist experience | |
• Competent interpretation of MRI to investigate fistula-in-ano requires prior experience. On average, interpretation of at least 50 mentored examinations is recommended to achieve reasonable competence for independent reporting (II) | |
4. Patient preparation for MRI | |
• It is not recommended that patients fast prior to MRI (V) | |
• It is not recommended that rectal emptying and/or distension is used. An anal lumen marker (e.g. a catheter) is also not recommended (V) | |
• It is not recommended that an intravenous smooth muscle relaxant (e.g. hyoscine n butylbromide) is used (V) | |
• It is recommended that patients are scanned supine | |
• It is recommended that 0.1 mmol/kg gadolinium is sufficient, where administered (V) | |
• It is recommended that no special modifications are necessary to image children (V) | |
5. MRI acquisition technique | |
• It is recommended that field strengths of 1.5 T or 3 T may be used, according to local availability and radiologist preference (V) | |
• It is recommended that a surface coil is used to enhance image quality (III) | |
• It is not recommended that endoanal receiver coils are used because they are unnecessary to achieve acceptable imaging quality (III) | |
• It is recommended that a minimal acceptable MRI examination for fistula-in-ano should include axial, coronal and sagittal planes, with the axial and coronal planes aligned to the anal canal axis (III) | |
• It is recommended that for at least one acquisition, the field of view is sufficient to capture extensions remote from the primary track, to include the supralevator and ischioanal compartments. This may be achieved by using at least one acquisition with “whole-pelvis” coverage (II) | |
6. MRI sequences | |
• MRI aims to identify sepsis and its precise relationship to the sphincter complex and adjacent structures. Multiple different sequences and orientations can be used to achieve this and will vary according to the personal preferences of the radiologist and the MRI platform(s) used (V) | |
• The planes and sequences considered mandatory by a majority of committee members were axial, coronal and sagittal T2-weighted (with or without fat suppression) (V) | |
• Many other sequences and orientations may be considered optional, and used to further facilitate interpretation. For example, these may include fat-suppressed T1-weighted sequences with gadolinium enhancement, short T-1 inversion recovery (STIR) sequences and diffusion-weighted sequences (V) | |
7. Examination timing | |
• It is recommended that MRI is acquired 4 weeks or more after therapeutic examination under anaesthetic (EUA). Interpretation of MR imaging following surgical intervention is challenging because of difficulties distinguishing between cavities created by surgical drainage and extensions that have not been treated (V) | |
8. Interpretation and reporting | |
• It is recommended that the radiological report include the clinical details (V) | |
• It is recommended that the radiological report include the Parks classification for any fistula identified (V) | |
• It is recommended that the radiological report include the St. James classification if used locally and believed useful, but not at the expense of the Parks classification (V) | |
• It is recommended that the total number of fistulas is stated where multiple fistulas are present. Each individual fistula should then be described in turn as per these guidelines (V) | |
• It is recommended that the exact radial location of any fistula is identified using the “clock face” nomenclature. Fistula location may also be described with reference to the appropriate anal quadrant, but not at the expense of an exact description (V) | |
• It is recommended that the exact radial location of the internal opening is identified using the “clock face” nomenclature. Location can also be described with reference to the appropriate anal quadrant, but not at the expense of an exact description (V) | |
• It is recommended that the exact radial location of the external opening is identified using the “clock face” nomenclature. Location can also be described with reference to the appropriate anal quadrant, but not at the expense of an exact description (V) | |
• It is recommended that the height of the internal opening should be described relative to adjacent structures (e.g. presumed level of dentate line, puborectalis, anal verge). An exact measurement (in mm) may also be provided if possible, but not at the expense of a relative description (V) | |
• Occasionally a single primary fistula track may have multiple internal openings. Where this is the case, it is recommended that this fact is stated along with the number and location of internal openings. The same applies to multiple external openings (V) | |
• Occasionally multiple fistula tracks may share a single internal opening. Where this is the case, it is recommended that this fact is stated along with the location of the internal opening. The same applies to shared external openings (V) | |
• The length of the fistula may be reported if this can be measured with reasonable precision, but is optional and not mandatory (V) | |
• It is recommended that whether a fistula contains a seton is reported (noting that setons are occasionally difficult to identify with certainty) (V) | |
• It is recommended that the anatomical location of any extension(s) identified is reported, irrespective of whether it is inter-sphincteric, ischio-anal, supralevator, or in any other anatomical location (V) | |
• In addition to reporting the anatomical location of any extension(s) identified, it is recommended that an indication of the size should be given. Since the morphology of extensions is variable and true volume measurement is difficult, maximal cavity diameter is often used to reflect size (V) | |
• It is recommended that a “horseshoe” extension is defined radiologically as a semilunar region of sepsis that spreads in the horizontal plane either side of an internal opening, to involve two or more adjacent quadrants. Horseshoe extensions may be ischioanal, intersphincteric, or supralevator (V) | |
• It is not recommended to describe individually all of those anatomical compartments that are free of disease. However, a general summary covering regions free of disease can be included if wished (V) | |
• It is recommended to report less common findings when encountered. Such findings might include proctitis or sacral osteomyelitis, for example (V) | |
• It is recommended that comment is made regarding the anatomical integrity of the external and internal sphincters, especially where there is evidence of sphincter disruption (perhaps contingent on prior fistula surgery) (V) | |
• It is recommended that the report reference any prior MR imaging where this is available, and that it describes how the present examination relates to these (V) | |
9. Recent developments | |
• Fistula activity may be reflected by various imaging biomarkers, including MR T2 signal intensity and/or enhancement following gadolinium contrast. Assessment of activity is relatively novel and criteria for “active” vs. “inactive” disease need precise definition. Accordingly, while it is not mandatory to report fistula “activity”, it is recommended that this information is provided where deemed useful by the radiologist and/or referring clinicians (III) | |
10. Anal endosonography | |
• Competent interpretation of anal endosonography to investigate fistula-in-ano requires prior experience. On average, interpretation of at least 50 mentored examinations is recommended to achieve reasonable competence for independent performance and reporting (V) | |
• It is recommended that patients require no special preparation and are usually examined in the left-lateral position. The prone position is an alternative (III) | |
• Instillation of hydrogen peroxide into the fistula is not recommended | |
• Generally, most patients tolerate the examination well and sedation/analgesia is not recommended (V) | |
• It is recommended that a 360° axial endoprobe between 7 and 10 MHz is used. A convex endoanal axial probe (e.g. for prostatic imaging) can be used where a full 360° probe is unavailable (V) | |
• 3D image acquisition is not recommended as it is unnecessary to achieve maximal diagnostic accuracy. However, it can be helpful where it is necessary to review the examination subsequently (V) | |
• It is recommended that simple grey-scale imaging is sufficient for optimal diagnostic accuracy (V) | |
• Children are a special case and it is recommended that practitioners be especially sensitive regarding the intimate and potentially distressing nature of the examination. It is recommended that practitioners provide as reassuring an environment as possible. In young children, who may not be able to cooperate, general anaesthesia may be considered to facilitate the examination (V) | |
• In the context of fistula-in-ano, anal endosonography is usually deployed to answer specific clinical questions. It is recommended that MRI is the primary modality with which to image fistula-in-ano (II) | |
• Given this, it is recommended that anal US is used where MRI is contraindicated, to image the internal opening with greater spatial resolution than MRI, and to assess prior or anticipated sphincter division (V) |
Discussion
Item | |
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1. Clinical details | State the clinical question being asked of the radiologist. |
2. Fistula | State whether a fistula is present or not (or sinus, or isolated abscess, etc.); its radial location (clock-face); its Parks classification; radial location and level of internal opening; radial location of external opening. Repeat for multiple fistulas. Describe shared internal/external openings, etc. State if seton present. Describe activity if used locally. |
3. Extensions | State whether an extension(s) is present or not and its anatomical location. Indicate the maximal cavity diameter. |
4. Sphincter integrity | Comment on internal and external sphincter integrity. |
5. Associated findings | e.g., Proctitis, osteomyelitis |
6. Comparison with prior imaging | Describe how imaging relates to prior studies where available. |