What is the management and treatment of a fistula in ano in an adult patient with a history of anal abscesses or inflammatory bowel disease?

Management and Treatment of Fistula in Ano

Initial Assessment and Diagnosis

For any patient with suspected fistula in ano, immediate surgical drainage of any associated abscess is mandatory before definitive fistula treatment, as more than two-thirds of patients have an abscess associated with their fistula. 1

Clinical Evaluation

• Perform examination under anesthesia (EUA) by an experienced colorectal surgeon to identify fistula tract anatomy, internal and external openings, and assess for complications—this correctly classifies 91% of perianal fistulae 1
• Assess rectal mucosa during EUA, as rectal inflammation significantly worsens outcomes (29% proctectomy rate with rectal involvement vs 4% without) 1
• Evaluate for inflammatory bowel disease (IBD), particularly Crohn's disease, through history and endoscopy if atypical features present 1

Imaging Strategy

• Obtain pelvic MRI or endoanal ultrasound in combination with EUA for optimal assessment—using two of these three modalities provides the best diagnostic accuracy 1
• MRI demonstrates 85-89% sensitivity for defining fistula anatomy and identifies non-fistulizing perianal disease that may be missed clinically 1
• CT scan has poor spatial resolution in the pelvis and is less accurate than endoanal ultrasound for detecting fistulae 1

Acute Phase Management: Abscess Drainage

Surgical drainage with incision and drainage is the definitive treatment for anorectal abscesses and must be performed before any fistula intervention. 1, 2

Surgical Approach

• Make the incision as close as possible to the anal verge to minimize potential fistula length while ensuring adequate drainage and avoiding sphincter damage 1, 2
• Base timing on sepsis severity—emergent drainage required for patients with sepsis, immunosuppression, diabetes, or diffuse cellulitis 1, 2
• Ensure complete drainage including all loculations, as inadequate drainage increases recurrence risk up to 44% 1, 2
• Consider outpatient management only for fit, immunocompetent patients with small perianal abscesses without systemic sepsis signs 1

Antibiotic Therapy

• Initiate broad-spectrum antibiotics covering gram-negative bacteria and anaerobes (piperacillin/tazobactam 4g/0.5g q6h for 4 days) for immunocompetent patients with adequate source control 3
• Continue antibiotics up to 7 days for immunocompromised or critically ill patients based on clinical response 3
• Never start anti-TNF therapy until abscesses have been completely drained and treated with antibiotics 1

Definitive Fistula Management

For Non-Crohn's Disease Patients

Simple, superficial fistulas involving minimal sphincter muscle should undergo fistulotomy, while complex fistulas require loose seton placement to prevent incontinence. 1, 2

Fistulotomy Indications

• Subcutaneous or superficial fistulas 1
• Submucosal, intersphincteric, or trans-sphincteric fistulas in the lower third of anal sphincter 1
• Provides excellent results but carries some incontinence risk 4

Seton Placement

• Place loose draining setons for fistulas involving significant sphincter muscle rather than performing immediate fistulotomy 2
• Setons establish drainage, minimize abscess recurrence risk, and facilitate hygiene 1
• Primary fistulotomy and cutting setons have equivalent incontinence rates depending on fistula complexity 5

Sphincter-Sparing Techniques

• Consider mucosal advancement flap, ligation of intersphincteric fistula tract (LIFT), fibrin glue, fistula plug, or video-assisted anal fistula treatment (VAAFT) for complex fistulas 1
• These techniques have higher recurrence rates but preserve continence 5, 6

For Crohn's Disease Patients

Medical therapy to control disease-related inflammation is imperative before and after surgery, using the most conservative surgical approach to avoid soft tissue damage and prevent extensive scarring. 1

Surgical Indications

• Symptomatic patient with no concomitant abscess, medically controlled proctitis, and preferably anatomically defined fistula tract 1
• Drain sepsis using loose setons before any definitive treatment to allow inflammation to subside and prevent abscess recurrence 1
• Asymptomatic low anal-introital fistulae do not need surgical treatment 1

Medical Therapy Integration

• Use thiopurines, infliximab, or adalimumab as maintenance therapy, either alone or combined with seton drainage 1
• Infliximab has Level 1 evidence for perianal fistulizing Crohn's disease 1
• Active Crohn's disease with rectal inflammation must be treated medically before and after surgery to prevent recurrence 1

Refractory Disease Management

• Consider diverting ostomy for patients refractory to medical treatment 1
• Proctectomy is the last resort 1

Follow-Up and Monitoring

Clinical Assessment

• Clinical assessment (decreased drainage) is usually sufficient for evaluating treatment response in routine practice 1
• Use MRI or anal endosonography combined with clinical assessment to evaluate fistula tract inflammation improvement 1
• Routine imaging after incision and drainage is not required unless there is recurrence, suspected IBD, evidence of persistent fistula, or non-healing wound 1

Critical Pitfalls to Avoid

• Never rely on antibiotics alone for abscesses >3cm or in immunocompromised patients without drainage—this increases recurrence risk 3
• Avoid inadequate drainage or failure to identify loculations, which significantly increases recurrence rates 1, 2
• Do not perform fistulotomy on complex fistulas involving significant sphincter muscle without considering seton placement first 2
• Never surgically treat concomitant perianal skin tags in Crohn's patients, as this leads to chronic non-healing ulcers 1
• Avoid starting anti-TNF therapy before complete abscess drainage 1
• Do not discontinue antibiotics prematurely—patients requiring >7 days warrant diagnostic re-evaluation 3

Risk Factors for Recurrence

• Inadequate drainage 1, 2
• Presence of loculations 1, 2
• Horseshoe-type abscess 1, 2
• Delayed time from disease onset to incision 1, 2
• Fistula complexity (multiple tracts) 1
• Associated stenosis 1