Perianal Crohn classification: Park anatomic classification - intersphincteric, transsphincteric, suprasphincteric, extrasphincteric. AGA grading - simple (low transsphincteric, single tract, no abscess, no rectovaginal/anorectal stricture, no proctitis) vs complex (high transsphincteric, multiple tracts, abscess, rectovaginal fistula, anorectal stricture, proctitis). Imaging - MRI pelvis (gold standard) defines anatomy, internal openings, secondary tracts, abscesses; transrectal ultrasound complementary. Examination under anesthesia (EUA) with surgeon is essential for accurate mapping. Disease activity assessment - PDAI (Perianal Disease Activity Index), fistula closure (clinical and MRI healing).
Treatment algorithm: Phase 1 (sepsis control) - drainage of abscesses, placement of loose (draining) setons through fistula tracts to control sepsis; Phase 2 (medical induction) - anti-TNF therapy (infliximab 5 mg/kg loading and maintenance, adalimumab 160-80 mg loading) preferred first-line; combination with antibiotic (ciprofloxacin + metronidazole 12 weeks); immunomodulator addition (azathioprine, 6-MP, methotrexate) in select cases; ustekinumab, vedolizumab, risankizumab as alternatives; Phase 3 (maintenance and closure) - continued biologic, seton removal once inflammation controlled (typically 3-12 months) and definitive closure technique. Perioperative biologic optimization (no need to discontinue anti-TNF; consider trough levels) is key.
Definitive closure techniques: 1) Fistulotomy - simple low fistulas only (incontinence risk in complex/Crohn); 2) LIFT (ligation of intersphincteric fistula tract) - 50-70% success in selected complex cases; 3) Endorectal advancement flap (ERAF) - mucosal/submucosal flap to cover internal opening, 60-70% success; 4) Fistula plug (Surgisis, Gore Bio-A) - 30-50% success, easy revision; 5) Fibrin glue - 15-30% success, often combined with plug; 6) Darvadstrocel (Cx601) - allogeneic adipose-derived mesenchymal stem cells injected around fistula tract; ADMIRE-CD trial 50% combined remission at 24 weeks; 7) VAAFT (video-assisted anal fistula treatment); 8) FiLaC (laser closure); 9) Diversion (loop ileostomy/colostomy) for severe refractory disease; 10) Proctectomy with permanent stoma in end-stage. Long-term success 50-70% combined with biologic; recurrence 30-40%.