What are the symptoms and treatment options for an adult patient with a suspected fistula in ano, possibly related to a history of Crohn's disease or previous anal surgery?

Fistula in Ano: Clinical Presentation and Management

Clinical Symptoms

Patients with fistula-in-ano typically present with drainage of blood, pus, or fecal material from an external opening in the perianal region, accompanied by intermittent pain and perianal itching. 1

Cardinal Presenting Features:

• Perianal drainage (blood, purulent material, or fecal content) from an external opening 1
• Intermittent pain in the perianal region 1
• Perianal pruritus (itching) 1
• Visible redness and swelling of the anus in acute presentations 1
• Throbbing pain when associated with active abscess 1

Key Demographic and Clinical Context:

• Male predominance (2:1 male-to-female ratio) with mean age at presentation of 40 years 1, 2
• The majority of anal fistulae arise from preexisting abscesses, representing a spectrum of cryptoglandular disease 1, 2, 3
• Recurrence rate after simple abscess drainage can reach 44% 2, 3

Critical Differential Considerations

Crohn's Disease Association:

It is mandatory to exclude underlying Crohn's disease in every patient presenting with anorectal fistula, especially if recurrent. 1, 3

• Perianal fistulae occur in 13-27% of Crohn's disease patients 1, 2
• May be the initial manifestation of Crohn's disease in up to 81% of patients who develop perianal disease 1
• Complex and multifocal fistulae are more common in Crohn's disease 1
• A focused medical history should assess for inflammatory bowel disease symptoms including diarrhea, weight loss, and abdominal pain 3

Other Etiologies to Consider:

• Radiation proctitis 2
• Prior anal surgery 1, 2
• Infections (HIV, tuberculosis, actinomycosis) 1, 2
• Malignancy (approximately 11% of colovesical/colovaginal fistulae; carcinomas may rarely arise in chronic fistulae) 1, 2

Physical Examination Findings

Essential Examination Components:

• Careful inspection of the perineum for surgical scars, anorectal deformities, signs of perianal Crohn's disease, secondary cellulitis, or external fistula openings 1
• Digital rectal examination revealing tenderness, indurated areas, or palpable tracts 1
• Internal opening at the dentate line is pathognomonic for cryptoglandular fistulas 3
• Cord-like structure may be palpable in intersphincteric fistulas 3

Important Clinical Pitfall:

Symptoms are frequently absent or diminished in older patients, diabetics, immunosuppressed individuals, and those with necrotizing soft-tissue infections, requiring high clinical suspicion and aggressive evaluation. 1

Diagnostic Imaging

When to Image:

Imaging is not routinely required for diagnosis but should be obtained in cases of atypical presentation, suspected occult supralevator abscess, complex anal fistula, or suspected perianal Crohn's disease. 1

Imaging Modality Selection:

MRI is the preferred imaging modality for complex fistulae and surgical planning, with high detection rates for anorectal abscesses and superior accuracy for secondary extensions. 1, 3

• MRI advantages: High detection rates, excellent for complex fistulae and Crohn's disease evaluation 1, 3

• MRI limitations: Limited emergency access, long acquisition time 1

• Endoanal ultrasound (EUS): Some studies suggest superior accuracy to MRI for detecting abscesses and evaluating complex fistulas in Crohn's disease, though this is debated 1

• EUS limitations: Requires special skills, often precluded by intense anal pain in emergency settings 1

• CT scan: Offers short acquisition time and widespread availability, useful in acute settings 1

• CT limitations: Poor spatial resolution in pelvis, difficulty differentiating fistula tract from inflammation, 77% overall sensitivity 1

• CT protocol: IV contrast preferred to visualize fluid collections and fistulous tracts; water-soluble rectal contrast may help delineate perforation but generally not necessary 1

Treatment Approach

Initial Management Principles:

Before any definitive treatment, sepsis must be drained using loose setons to allow inflammation to subside and prevent abscess recurrence. 1

Non-Crohn's Disease Fistulae:

For simple, superficial fistulas (subcutaneous or low intersphincteric), fistulotomy with tract debridement is the treatment of choice. 1

• Fistulotomy appropriate for fistulas in lower third of anal sphincter 1
• Complete healing achieved in 71.4% of cases with average healing time of 3.5 months 4
• Good postoperative function in 71.5% of patients 4

For complex or high fistulae, loose seton drainage is preferred to maintain drainage while minimizing sphincter damage. 1

• Setons can be removed in up to 98% of patients at median of 33 weeks 1
• Endorectal advancement flap is a successful option for high fistulae where sphincter division would compromise continence 1

Crohn's Disease-Associated Fistulae:

Indications for surgery in Crohn's disease include symptomatic patients with no concomitant abscess, medically controlled proctitis, and preferably anatomically defined fistula tract. 1

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

Maintenance Therapy Options:

• Thiopurines 1
• Infliximab (highest level evidence) 1
• Adalimumab 1
• Seton drainage alone or in combination with medical therapy 1

Refractory Cases:

Patients refractory to medical treatment should be considered for diverting ostomy, with proctectomy as the last resort. 1

Special Considerations:

• Asymptomatic low anal-introital fistulae do not require surgical treatment 1
• Active Crohn's disease with rectal inflammation should be treated medically before and after surgery to prevent recurrence 1
• Concomitant perianal skin tags should not be treated surgically as this can lead to chronic, non-healing ulcers 1

Critical Pitfalls to Avoid

• Never assume benign disease: Raise concern for malignancy when imaging shows soft mass, mass-like thickening of anorectal wall, or malignant-appearing lymphadenopathy 1, 2
• Always exclude Crohn's disease in recurrent presentations through focused history 1, 3
• Avoid aggressive sphincter division in Crohn's disease patients, as functional outcomes are worse than cryptoglandular fistulas 5
• Do not proceed with definitive surgery without imaging for complex or high fistulae 3
• Recognize that surgical outcome for high or complex Crohn's fistula remains disappointing with unpredictable recurrence 5