Introduction
Methods
Systematic review and clinician survey
Expert consensus panel
Results
Voting option | Consensus threshold |
---|---|
Always report (even if absent*) | 70% of all votes |
Report if remarkable or relevant | 70% of all votes or Votes for always report + remarkable/ relevant = 70% |
Report in surgical subset | 70% of all votes or Votes for always report + remarkable/ relevant + surgical subset = 70% |
Report in pCD subset | 70% of all votes or Votes for always report + remarkable/ relevant + surgical subset + pCD subset = 70% |
Never report | 70% of all votes |
Feature | Always report | Report if remarkable or relevant to clinical scenario** |
---|---|---|
Classification | • Parks classification subtype | |
General characteristics | • Number of tracts • If tract is single, single-branched or multiple | |
Internal opening | • Anal clock location • Height in upper/middle/lower thirds of anal canal* • If internal opening is anal or rectal • Number of internal openings | • Diameter |
Path of the fistula tract through the sphincters | • Location where tract crosses EAS or puborectalis • Height that tract crosses EAS or puborectalis in upper/middle/lower thirds of anal canal* | • General characteristics of IAS/EAS • Course of IS fistula through IS space |
External opening | • Anal clock location • Anatomical location (e.g. gluteal, labial) | |
Extensions | • Presence of extensions, even if absent • If extensions are single or multiple • Anatomical location • Location relative to levator ani (supra/infralevator) • Location of point of communication to primary tract • Shape (e.g. horseshoe, blind tract) | • Description of course of extensions |
Collections | • Presence of collections, even if absent • Connection to the primary tract • Anal clock location • Anatomical location (e.g. perianal, ischioanal) • All collections should be reported, with size defined as [34]: • Small (3–10 mm, not including tracts > 3 mm diameter) • Medium (11–20 mm) • Large (> 20 mm) • Large collections should be notified to the referring team | • Height of collections |
Measurements | • Tract length • Tract diameter | |
Other features | If present, comment on: • Fistula activity: fibrotic, healed or scarred tract • Rectum and large bowel: presence of proctitis, presence of small- and large-bowel inflammation • Features of previous surgery: setons, drainage catheters, air foci, gas in fistula • Other pathologies: rectal wall thickening, involvement of pelvic organs, pelvic abscess with fistulous tracts, inflammation of adjacent tissues, retrorectal cysts, bone marrow oedema, osteomyelitis, anogenital fistulation, lymphadenopathy, malignant transformation of fistula, peritoneal psuedocysts, unilateral thickening of levator ani, tuberculosis, diverticulitis • Other perianal pathology: pilonidal sinus, hydradenitis suppurativa, haemorrhoids, fissure | |
Surgical subset** (report when planned surgical intervention is indicated on request) | ||
• Angulation through EAS/IS space • Direction through EAS (cephalad/caudad) • Angulation of branches • Distance between external opening and anal verge • Distance between extensions and primary tract • Height of extensions • Features of previous surgery: if present, comment on fat containing grafts, scarring | ||
Perianal Crohn’s disease subset** (report when Crohn’s disease is present or suspected on request) | ||
• Tract activity: active vs inactive tract |
Features to be reported if remarkable or relevant | |
Internal opening diameter | • Remarkable if very large or easily visualised on MRI • Relevant in procedures where the internal opening requires closure, e.g. video-assisted anal fistula treatment (VAAFT), fistula laser closure (FiLaC). • Advancement flap: determines flap size and tension required for closure |
General characteristics of IAS/EAS | • Remarkable if incomplete, thinning or poor quality, e.g. previous surgery or obstetric injury • Relevant in patients reporting incontinence, or in procedures requiring further muscle division, e.g. fistulotomy or advancement flap involving muscular layers |
Course of an IS fistula through the IS space | • Remarkable if the primary tract is angulated or curving/horseshoeing • Relevant in fistulotomy, indicating the size of the wound, or if FiLaC or VAAFT is being considered, where tight angulations may preclude the procedure (Figure 5) |
Description of the course of extensions | • Remarkable if the course of an extension is angulated or curving, or extends over a long distance from its origin • Relevant if the extension is to be laid open, indicating the size of the operative wound, or if VAAFT is planned, which can be precluded by tight or successive angulation of tracts |
Height of collections | • Remarkable if very high—this may indicate difficulty in drainage, or may be best drained via trans-luminal route in supralevator collections • Relevant in fistulae of all aetiologies and in most surgical procedures—collections need adequate drainage to ensure the highest chances of success, and appreciating height guides the surgical procedure |
Tract length | • Remarkable in very long fistula tracts • Relevant in specific surgical procedures where evidence suggests tract length is correlated with success (e.g. anal fistula plug more successful in tracts > 4 cm) |
Tract diameter | • Remarkable in very wide tracts or very narrow tracts • Relevant when considering: ○ VAAFT: diameter must allow cannulation by 3.7 × 4.4 mm scope ○ FiLaC: laser penetration may be less effective in wide tracts ○ LIFT: diameter of the intersphincteric portion to be dissected and ligated ○ Plug: determines plug size |
Surgical subset | |
Angulation through EAS/IS space | • Fistulotomy: cephalad angulation through EAS or IS space would result in division of more muscle than expected based on assessment of internal opening alone (Figure 3) • LIFT may be precluded by angulation through the IS space as this would make dissection and ligation of the tract challenging • VAAFT and FiLaC are precluded by tight or successive angulations • Tight angulations would make plug placement more challenging |
Direction through EAS (Cephalad/caudad) | • Tight or successive angulation would make procedures such as VAAFT and FiLaC more challenging • When considering fistulotomy, cephalad angulation of the tract through EAS would result in greater division of EAS than suggested by the height of the internal opening alone |
Angulation of branches | • When probing the tract during examination under anaesthesia, tight or wide angulations make passage of the probe, or subsequent seton insertion more challenging, and if undetected, can raise the risk of creating a false passage • Tight or successive angulations are more difficult to negotiate with VAAFT or FiLaC (Figure 4) |
Distance between external opening and anal verge | • A large distance between external opening and anal verge would result in a large wound if fistulotomy is considered |
Distance between extensions and tract | • Indicating the length of extensions can identify the parts of the tract that require treatment with VAAFT, or the extent of the wound if the extension needs to be laid open |
Height of extensions | • Relevant in cephalad or high extensions when a fistulotomy is being considered, as this would influence how much sphincter is to be divided |
Features of previous surgery | • The presence of fat containing grafts within the fistula tract • The presence of scarring, as healing on MRI can lag behind clinical healing |
Perianal Crohn’s disease subset | |
• Distinction between an active or inactive tract, which can be determined by hyperintensity on T2-weighted images best seen with fat saturation for active tracts, or lack of hyperintensity on T2-weighted images for inactive tracts • Can help determine disease activity/response to treatment particularly when compared with previous scans |
Location and height of a specific feature of fistula morphology (e.g. internal opening, branches or extensions)
General characteristics
Internal opening
Path of the fistula tract through the sphincters
Extensions
Features of fistula activity
Fistula tract measurements
Other pathologies and other perianal pathologies
Collections
Minimum dataset for MRI request
Features that should be included in the MRI request | |
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• History of inflammatory bowel disease • Colorectal configuration (e.g. intact, ileorectal anastomosis, ileal pouch anal anastomosis) • Previous fistula surgery • Known fistula anatomy • Clinical findings and symptoms • Presence of seton • Specific clinical question Surgical subset: • State if a specific surgical procedure is planned/being proposed |