Management of Complex Fistula-in-Ano

Initial Assessment and Diagnosis

The World Journal of Emergency Surgery recommends emergent drainage for patients with sepsis, immunosuppression, diabetes, or diffuse cellulitis, and drainage should occur within 24 hours for stable patients without these risk factors 1

The World Journal of Emergency Surgery suggests performing incision and drainage of the abscess, and never probing for fistulas during acute abscess drainage to avoid iatrogenic complications 1
A loose draining seton should be placed at the time of drainage for any obvious fistula involving sphincter muscle, and fistulotomy can only be performed at initial drainage if the fistula is low and subcutaneous, not involving sphincter muscle 1

Setons can be left in place indefinitely if needed, though patients may prefer suppressive medical therapy over long-term seton placement, according to Gastroenterology 2
Endorectal advancement flap procedures can be performed for high perianal fistulas in patients without rectal inflammation, but recurrence rates are relatively high, so reserve this for patients with disabling symptoms, as recommended by Gastroenterology 2

Infliximab can completely close all fistula tracts in many patients with complex fistulas and is considered the initial treatment of choice by most gastroenterologists, according to Gastroenterology 2
Coadminister azathioprine, 6-mercaptopurine, or methotrexate routinely with infliximab to counteract immunogenic reactions and maintain remission, as recommended by Gastroenterology 2
Antibiotic administration is suggested only in the presence of sepsis, surrounding soft tissue infection, or immune response disturbances, according to the World Journal of Emergency Surgery 1

Patients who fail initial infliximab treatment should undergo anorectal endoscopic ultrasound or pelvic MRI plus EUA with seton placement as indicated, and continue treatment with infliximab, azathioprine or 6-mercaptopurine, and antibiotics, according to Gastroenterology 2
Tacrolimus or cyclosporine can be considered in patients who fail multimodality approach, though nephrotoxicity and side effects occur frequently and should be used with caution, as recommended by Gastroenterology 2 and 3
Fecal diversion may be considered for refractory cases, and proctectomy should only be undertaken as a last resort, according to Gastroenterology 2

Avoid routine EUA and seton placement before initiating infliximab therapy, as it is not mandatory, according to Gastroenterology 2
Do not delay imaging in stable patients, but ensure imaging does not delay surgical intervention in unstable patients, as recommended by the World Journal of Emergency Surgery 1

The American College of Radiology recommends MRI of the pelvis as the initial imaging procedure to define fistula anatomy and identify occult abscesses, with a higher diagnostic accuracy compared to CT scans 4, 5
Examination under anesthesia (EUA) by an experienced surgeon is the gold standard for assessment, and should be combined with MRI for the highest diagnostic accuracy 5, 6
Proctosigmoidoscopy should be performed to evaluate for concomitant rectal inflammation, particularly to exclude Crohn's disease 5
Endoanal ultrasound can be used as an alternative to MRI if rectal stenosis is excluded, but has lower diagnostic accuracy 5, 6

The American College of Surgeons recommends initial management with loose seton placement after drainage of any associated abscess, followed by sphincter-sparing procedures once inflammation is controlled 7, 8
More than two-thirds of complex fistulas have an associated abscess that must be drained before definitive intervention, with emergent drainage required in cases of sepsis, immunosuppression, diabetes, or diffuse cellulitis 5, 6, 7
A loose draining seton should be placed for all complex fistulas, with the seton establishing drainage, preventing abscess recurrence, and allowing time for medical optimization 7, 8

The European Crohn's and Colitis Organisation recommends initiating antibiotics (metronidazole and/or ciprofloxacin) in combination with seton drainage, with thiopurines or anti-TNF therapy (infliximab or adalimumab) added as second-line treatment for refractory disease 5
Medical therapy to control inflammation is imperative before attempting definitive surgical closure, with maintenance therapy with thiopurines, infliximab, or adalimumab combined with seton drainage required after surgery for Crohn's patients 5, 8

The American Gastroenterological Association recommends excluding underlying Crohn's disease in every patient, especially with recurrent abscesses, with complex and multifocal fistulas occurring in 13-27% of Crohn's patients 4, 6
Concomitant perianal skin tags in Crohn's patients should not be surgically treated, as this leads to chronic non-healing ulcers, and diverting ostomy or proctectomy may be required for refractory cases 5, 8

Clinical assessment (decreased drainage) is usually sufficient for routine monitoring, but MRI or endoanal ultrasound combined with clinical assessment is recommended to evaluate fistula tract inflammation improvement 5
Recurrence risk after drainage alone can be as high as 44%, emphasizing the need for complete drainage and appropriate definitive management, with minor incontinence rates ranging from 2.4% to 6% with appropriate surgical technique 7