Perianal Abscess and Fistula-in-Ano

1. Clinical Overview

Perianal abscess and fistula-in-ano represent two phases of a single pathological continuum rooted in cryptoglandular infection. The abscess constitutes the acute inflammatory phase characterised by suppurative collection in the perianal tissues, while fistula-in-ano represents the chronic sequela—an epithelialised pathological tract connecting the anal canal to the perianal skin or other structures. [1,2]

This condition represents one of the most common anorectal emergencies encountered in surgical practice, with significant implications for patient quality of life and functional outcomes. The fundamental surgical principle remains unchanged since antiquity: "pus must out"—abscesses require prompt surgical drainage, and antibiotics alone constitute inadequate and potentially harmful management. [3]

The clinical challenge in fistula management lies in balancing two often contradictory therapeutic goals: achieving complete fistula healing while preserving anal sphincter function and maintaining continence. This balance becomes particularly critical in complex fistulas involving significant sphincter muscle mass, where overly aggressive surgical intervention risks devastating functional consequences. [4,5]

Key Epidemiological Facts

• Incidence: Perianal abscess affects approximately 14,000-20,000 individuals per 100,000 population annually in Western countries [6]
• Gender Distribution: Males are affected 2-3 times more frequently than females [7]
• Age Distribution: Peak incidence occurs in the 4th-5th decades of life (30-50 years) [8]
• Fistula Development: Approximately 30-50% of drained perianal abscesses progress to chronic fistula-in-ano [9,10]
• Recurrence: Overall recurrence rates range from 7-40% depending on anatomical complexity and surgical technique [11]

---

2. Anatomy and Surgical Landmarks

Anatomical Foundations

Understanding the three-dimensional anatomy of the anal canal and surrounding spaces is fundamental to managing perianal sepsis effectively.

The Anal Canal Layers (Internal to External)

1. Mucosa: Columnar epithelium above dentate line; stratified squamous below
2. Submucosa: Contains the anal glands (10-15 glands) opening at the dentate line
3. Internal Anal Sphincter (IAS): Thickened continuation of circular smooth muscle of rectum; responsible for 70-80% of resting anal tone [12]
4. Intersphincteric Space: Contains longitudinal muscle fibres and connective tissue; this is where cryptoglandular infection typically originates
5. External Anal Sphincter (EAS): Striated voluntary muscle in three components (subcutaneous, superficial, deep); responsible for squeeze pressure and voluntary continence [13]
6. Ischiorectal Fossa: Fat-filled pyramidal space lateral to the anal canal, bounded by:
   • Medially: External anal sphincter and levator ani
   • Laterally: Obturator internus and ischial tuberosity
   • Anteriorly: Perineal membrane
   • Posteriorly: Sacrotuberous ligament and gluteus maximus
   • Superiorly: Levator ani
   • Inferiorly: Perineal skin

Critical Surgical Spaces

1. Intersphincteric Space: Between IAS and EAS; most common location for abscess origin (70%) [14]
2. Perianal Space: Subcutaneous tissue immediately surrounding the anal verge
3. Ischiorectal Space: Large potential space; infections here can be extensive
4. Supralevator Space: Above the levator ani; rare but dangerous location
5. Deep Postanal Space (Courtney's Space): Between the anococcygeal ligament and posterior rectal wall; horseshoe abscesses originate here [15]

---

3. Aetiology and Pathophysiology

The Cryptoglandular Theory (Eisenhammer, 1956)

The cryptoglandular hypothesis remains the most widely accepted explanation for anorectal suppuration, accounting for 80-90% of cases. [16]

Pathophysiological Sequence:

1. Initiating Event: Obstruction of an anal gland duct at the level of the anal crypt (dentate line)

   • Causes: Inspissated debris, trauma, foreign material, local inflammation

2. Bacterial Stasis and Infection: Trapped secretions within the intersphincteric gland become infected

   • Polymicrobial flora: Predominantly anaerobes (Bacteroides fragilis, Peptostreptococcus) and facultative organisms (Escherichia coli, Enterococcus) [17]
   • The infection initially confined to the intersphincteric space

3. Abscess Formation: Suppuration develops along the path of least resistance

   • Direction determined by anatomical barriers and tissue planes
   • Most common path: Downward toward perianal skin (simple perianal abscess)

4. Anatomical Progression Patterns:

   • Downward/Outward → Perianal abscess (40-50%)
   • Lateral through EAS → Ischiorectal abscess (20-25%)
   • Upward → Supralevator abscess (2-5%)
   • Circumferential in deep postanal space → Horseshoe abscess (5-10%)
   • Intersphincteric tracking upward → High intersphincteric abscess (5%) [18]

5. Spontaneous or Surgical Drainage: Pus seeks exit to skin or bowel

6. Fistula Formation: If the internal opening (infected anal gland) persists, the tract becomes epithelialised

   • Chronic granulation tissue lines the tract
   • Persistent drainage maintains patency
   • Epithelialisation prevents spontaneous closure [19]

Alternative Aetiologies (10-20% of Cases)

---

4. Classification Systems

Parks Classification of Fistula-in-Ano (1976)

The Parks classification remains the gold standard anatomical categorisation system, defining fistula type based on the relationship of the primary tract to the anal sphincter complex. [22]

Subcategories for Complex Anatomy:

• High vs Low: Relative to puborectalis sling (high involves more EAS)
• Anterior: More challenging in females due to shorter sphincter complex
• Horseshoe Extension: Posterior midline with bilateral ischiorectal extensions
• Supralevator Extension: Upward tracking above levator plate [23]

St. James's University Hospital Classification (Extended Parks)

Adds secondary extensions and complications:

• Grade 1: Simple linear intersphincteric fistula
• Grade 2: Intersphincteric fistula with intersphincteric abscess or secondary tract
• Grade 3: Transsphincteric fistula
• Grade 4: Transsphincteric fistula with abscess or secondary tract in ischiorectal fossa
• Grade 5: Supralevator or translevator disease [24]

Abscess Classification by Anatomical Location

---

5. Goodsall's Rule

Goodsall's Rule (1900) predicts the course of the fistula tract based on the position of the external opening relative to an imaginary transverse line through the anus. [25]

The Rule

• Anterior External Openings (anterior to transverse anal line):

  • Fistula tract runs RADIALLY (straight) to the anal canal
  • Internal opening at same clock position as external opening

• Posterior External Openings (posterior to transverse anal line):

  • Fistula tract runs CURVED to the posterior midline
  • Internal opening typically at 6 o'clock position (posterior midline)

Exceptions to Goodsall's Rule

1. Long Anterior Fistulas: External opening >3cm from anal verge may curve posteriorly to 6 o'clock position (30% exception rate) [26]
2. Crohn's Disease: Atypical, multiple tracts—rule does not apply
3. Traumatic Fistulas: Course determined by injury
4. Horseshoe Fistulas: Bilateral extensions from posterior midline internal opening
5. Accuracy: Overall 70-80% predictive accuracy; MRI is superior for complex cases [27]

---

6. Epidemiology and Risk Factors

Incidence and Prevalence

• Annual Incidence of Perianal Abscess: 14-20 per 100,000 population in developed nations [6]
• Lifetime Risk: Approximately 1-2% of population will develop perianal abscess [28]
• Fistula Formation: 30-50% of patients with perianal abscess develop subsequent fistula-in-ano [9,10]
• Recurrence After Treatment: 7-40% depending on anatomical complexity and surgical approach [11]

Demographic Patterns

Risk Factors

Patient Factors:

• Diabetes Mellitus: 2-3 fold increased risk; associated with more severe disease and complications [32]
• Immunosuppression: HIV, chemotherapy, transplant recipients, corticosteroid therapy [33]
• Inflammatory Bowel Disease: Crohn's disease (fistulas in 30-40% of patients); ulcerative colitis (rare) [20]
• Smoking: Dose-dependent association; impairs wound healing [34]
• Obesity: Increased risk; technical surgical difficulty [35]

Anatomical/Local Factors:

• Previous Anorectal Sepsis: History of abscess increases fistula risk
• Anal Fissure: Chronic fissures may be associated
• Haemorrhoids: Instrumentation and infection risk
• Anorectal Procedures: Post-haemorrhoidectomy, post-sphincterotomy [36]

Infectious/Other:

• Tuberculosis: Endemic areas; consider in non-healing, atypical cases [21]
• Hidradenitis Suppurativa: Chronic apocrine gland inflammation; perineal involvement [37]
• Foreign Body: Ingested fish bones, chicken bones penetrating rectal wall [38]
• Radiation Proctitis: Late complication of pelvic radiotherapy [39]

---

7. Clinical Presentation

Acute Perianal Abscess

Cardinal Symptoms:

1. Pain: The dominant symptom

   • Character: Constant, throbbing, severe
   • Location: Perianal, perineal, may radiate to buttock or lower back
   • Aggravating Factors: Sitting, defecation, coughing, straining
   • Severity: Often 8-10/10; disturbs sleep; limits mobility [40]

2. Swelling: Patient may notice lump or fullness

3. Systemic Features (in 30-50% of cases):

   • Fever: Temperature >38°C suggests significant bacterial load
   • Malaise: General unwellness, fatigue
   • Rigors: Indicates bacteraemia/sepsis [41]

4. Discharge: If spontaneous rupture has occurred

   • Purulent: Foul-smelling pus
   • Blood-stained: Mixed with pus
   • Temporary Relief: Pain improves after spontaneous drainage but recurs

Presentation Patterns by Abscess Type:

Chronic Fistula-in-Ano

Characteristic Features:

1. Intermittent Discharge:

   • Seropurulent fluid: Staining underwear ("spots of pus")
   • Blood-tinged: Mixed serous and sanguineous
   • Faecal material: Suggests high fistula or recto-vaginal fistula
   • Cyclical Pattern: Discharge → temporary blockage → pain and swelling → discharge [42]

2. Recurrent Abscess Formation:

   • Cycle: External opening heals over → tract blocks → pus accumulates → abscess forms → spontaneous or surgical drainage → temporary relief
   • Frequency: Every few weeks to months

3. Pruritus Ani:

   • Mechanism: Chronic moisture and discharge cause perianal skin irritation
   • Secondary Changes: Excoriation, lichenification, eczema [43]

4. Pain (typically less severe than abscess):

   • Dull ache: Worse with sitting
   • Acute exacerbation: When tract blocks and abscess reforms

5. Rarely: Faecal incontinence if sphincter damage from previous surgery or disease process

Associated Symptoms Suggesting Underlying Disease:

---

8. Clinical Examination

General Inspection

• Patient Position: Left lateral (Sims) position preferred; lithotomy for detailed assessment
• Lighting: Good illumination essential
• Chaperone: Always present for medico-legal protection

External Perianal Inspection:

1. Skin Changes:

   • Erythema: Active inflammation
   • Induration: Suggests underlying abscess
   • Fluctuance: Palpable fluid collection (pathognomonic for abscess)
   • Crepitus: Gas in tissues → FOURNIER'S GANGRENE (surgical emergency) [44]
   • Skin Necrosis: Black/grey skin → necrotising fasciitis

2. Fistula External Opening:

   • Location: Document using clock-face notation (lithotomy position; 12 o'clock = anterior, 6 o'clock = posterior)
   • Appearance: Small dimple or granulation tissue "nipple"
   • Discharge: May express pus/serosanguinous fluid on gentle pressure
   • Surrounding Skin: Excoriation, maceration, eczematous changes
   • Multiple Openings: Suggests complex disease or Crohn's [45]

3. Goodsall's Rule Application: Predict internal opening location

Digital Rectal Examination (DRE)

Important Caveat: In acute abscess, DRE is often too painful and should be deferred to Examination Under Anaesthesia (EUA). Do not cause unnecessary suffering.

In Chronic Fistula or When Tolerated:

1. Induration: Palpable cord-like thickening along fistula tract
2. Internal Opening: May palpate as a pit, depression, or area of induration at dentate line
3. High Fistulas: Supralevator fullness or tenderness
4. Sphincter Tone: Assess baseline continence (reduced tone may contraindicate fistulotomy)
5. Rectal Mucosa: Assess for:
   • Crohn's Disease: Cobblestoning, ulcers, strictures
   • Malignancy: Hard irregular mass
   • Proctitis: Inflammation, granular mucosa [46]

Proctoscopy/Anoscopy

• Internal Opening Identification: Look for pit at dentate line with pus expressible on pressure
• Mucosal Assessment: Active inflammation, ulceration
• Usually Performed Under Anaesthesia: Better visualisation and patient comfort

Systemic Examination

Essential in Sepsis/Complicated Cases:

• Vital Signs: Tachycardia, hypotension, fever (SIRS criteria)
• Abdominal Examination: Exclude intra-abdominal pathology (diverticulitis, appendicitis)
• Perineal/Scrotal Examination: Assess for Fournier's gangrene extension
• Lymph Nodes: Inguinal lymphadenopathy (infection, malignancy)

---

9. Red Flag Features

Immediate recognition of the following features is critical to prevent life-threatening complications:

Fournier's Gangrene (Necrotising Fasciitis of Perineum)

Clinical Triad:

1. Severe pain out of proportion to physical findings
2. Systemic toxicity (sepsis, shock)
3. Skin changes: Crepitus, blistering, necrosis, black eschar [44]

Management: Immediate aggressive surgical debridement + broad-spectrum antibiotics + ICU support (mortality 20-40%) [47]

Sepsis/Systemic Toxicity

• SIRS Criteria: Temperature >38°C or less than 36°C, HR >90, RR >20, WCC >12 or less than 4
• Hypotension: Septic shock
• Altered Consciousness: Severe sepsis
• Oliguria: End-organ hypoperfusion

Management: Sepsis 6 bundle; source control (urgent drainage)

Recurrent/Multiple Fistulas

Suggests Underlying Pathology:

• Crohn's Disease: Most common; requires medical optimization before surgery [20]
• Tuberculosis: Endemic areas; systemic symptoms [21]
• Malignancy: Rectal/anal carcinoma
• HIV/Immunosuppression: Atypical organisms [33]

Action: Biopsy tract, stool testing, imaging, HIV test, TB workup

Supralevator Abscess

• Deep pelvic pain without external swelling
• High Risk: Pelvic sepsis, incorrect drainage leading to extrasphincteric fistula [48]
• Diagnosis: Requires CT/MRI
• Drainage: Must establish correct plane (via rectum if originates from intersphincteric spread upward; avoid transrectal drainage if ischiorectal origin to prevent iatrogenic extrasphincteric fistula)

---

10. Investigations

Laboratory Investigations

Routine (Abscess):

• Full Blood Count (FBC):
  • "Leukocytosis: WCC >11 suggests infection (typically 12-20 × 10⁹/L)"
  • "Neutrophilia: Left shift indicates acute bacterial infection"
  • "Anaemia: If chronic disease or malignancy"
• C-Reactive Protein (CRP): Elevated (often 50-200 mg/L); monitors response to treatment
• Urea and Electrolytes (U&E): Baseline renal function; dehydration assessment
• Blood Glucose/HbA1c: Screen for diabetes (present in 20-30% of cases) [32]
• Blood Cultures: If septic/febrile (positive in 10-20% of cases) [49]

Additional Tests (Recurrent/Complex Cases):

• HIV Serology: In high-risk patients or atypical presentation [33]
• Inflammatory Markers: ESR, faecal calprotectin (screen for IBD) [50]
• Mantoux Test/IGRA: If TB suspected [21]
• Tumour Markers: CEA if malignancy suspected

Microbiology:

• Pus Culture and Sensitivity:
  • "Polymicrobial: Typical (E. coli, Bacteroides, Enterococcus) [17]"
  • "Atypical Organisms: Mycobacterium, Actinomyces, fungi (immunocompromised)"
  • "Clinical Utility Limited: Empirical antibiotics usually adequate; culture helps if treatment failure"

Imaging Modalities

1. MRI Pelvis (Gold Standard for Fistula)

Indications:

• All recurrent fistulas
• Complex primary fistulas
• Pre-operative planning for surgical intervention
• Crohn's-related perianal disease [51,52]

Optimal Protocol:

• Sequences: T2-weighted (high resolution), T1-weighted pre- and post-gadolinium, fat-suppressed sequences
• Planes: Axial, coronal, sagittal
• Patient Position: Supine

Information Provided:

• Primary Tract: Precise course relative to sphincter complex
• Internal Opening: Location (clock position, height)
• Secondary Tracts and Extensions: Horseshoe, supralevator
• Collections: Abscesses not clinically apparent
• Sphincter Integrity: Previous surgical damage, atrophy
• Classification: Parks type, St James grade [24,53]

MRI Grading Systems:

Van Assche Score (Crohn's-related fistulas):

• Number of tracts
• Location
• Presence of collections
• Degree of inflammation [54]

St James's MRI-based Classification: Grades 1-5 (correlates with surgical complexity)

Accuracy: Sensitivity 76-100%, Specificity 86-100% for primary tract identification [55]

2. Endoanal Ultrasound (EAUS)

Indications:

• Alternative to MRI (operator-dependent)
• Assessment of sphincter integrity pre-operatively
• Less useful for complex/high fistulas [56]

Advantages:

• Cheaper than MRI
• Rapid
• Excellent sphincter anatomy detail

Limitations:

• Operator-dependent
• Limited field of view (cannot visualize supralevator disease)
• Inferior to MRI for complex fistulas [57]

3. CT Scan

Limited Role:

• Supralevator/Deep Pelvic Abscesses: When diagnosis unclear (mimics diverticulitis, appendicitis)
• Fournier's Gangrene: Assess extent of gas and tissue involvement [47]
• Poor Sphincter Detail: Cannot replace MRI for fistula planning [58]

4. Fistulography (Historical)

• Obsolete: Replaced by MRI
• Limitations: Painful, poor soft tissue detail, misses secondary tracts in 50% [59]

Examination Under Anaesthesia (EUA)

Gold Standard for Acute Abscess and Definitive Fistula Assessment

Indications:

• All perianal abscesses (diagnostic and therapeutic)
• Fistula assessment when imaging inconclusive
• Identification of internal opening
• Treatment planning [60]

Systematic Approach:

1. Inspection: External openings, skin changes, scars from previous surgery
2. Palpation: Induration, fluctuance, extent of disease
3. Proctoscopy: Mucosal disease, internal opening identification
4. Probing: Gentle exploration of fistula tract
   • Technique: Use malleable probe; NEVER force (creates false passage)
   • Direction: Correlate with Goodsall's rule and imaging
   • Internal Opening: Palpate probe tip intraluminally
5. Assessment of Sphincter: Extent of muscle involvement (determines surgical strategy)
6. Biopsy: If atypical (Crohn's, TB, malignancy)
7. Drainage: Incision and drainage if abscess present
8. Treatment: Definitive surgery if appropriate (fistulotomy if simple)

---

11. Management Principles

Fundamental Surgical Doctrine

"Pus must out": Antibiotics alone for a drainable abscess is negligent care. Delayed drainage leads to:

• Progressive tissue destruction
• Complex fistula formation
• Sepsis and systemic complications
• Prolonged patient suffering [3]

"Do not let the sun set on a perianal abscess": Drainage should occur within hours of diagnosis, not days.

Goals of Management

Abscess:

1. Source Control: Complete drainage of pus
2. Prevent Recurrence: Identify and address internal opening if possible
3. Minimize Complications: Avoid sphincter injury, minimize hospital stay

Fistula:

1. Cure: Complete fistula healing
2. Preserve Continence: Avoid sphincter damage
3. Minimize Recurrence: Address internal opening and all extensions
4. Quality of Life: Rapid return to normal activities [61]

Management Algorithm

                    PERIANAL COMPLAINT
                            ↓
              ┌─────────────┴─────────────┐
         ACUTE ABSCESS              CHRONIC FISTULA
      (Pain, Fever, Lump)          (Discharge, Track)
              ↓                           ↓
     EMERGENCY SURGERY               INVESTIGATIONS
     (I&D under GA/LA)               (MRI Pelvis ± EUA)
              ↓                           ↓
    ┌─────────┴────────┐           ┌─────┴──────┐
    Drain Pus      Search for    SIMPLE      COMPLEX
    ↓              Fistula Track  (Low)       (High/Crohn's)
    ├─ Simple: heals                ↓              ↓
    └─ Fistula forms (30-50%)   FISTULOTOMY   SETON PLACEMENT
                                 (Lay Open)    ├─ Loose (drainage)
                                     ↓          └─ Cutting (rare)
                                  CURE              ↓
                                  (>90%)    SPHINCTER-SPARING
                                            PROCEDURES
                                            (LIFT, Flap, VAAFT)

---

12. Management of Abscess

Timing and Urgency

• Emergency Procedure: Should be performed same day or within 24 hours of diagnosis [62]
• Out-of-Hours: Do not delay until morning list; arrange emergency theatre
• Septic Patient: Immediate resuscitation (Sepsis 6) + urgent surgical source control

Incision and Drainage (I&D) Technique

Anaesthesia:

• General Anaesthesia: Preferred (allows EUA, better drainage, patient comfort)
• Spinal/Epidural: Alternative
• Local Anaesthesia: Small simple perianal abscess in selected cases only (inadequate for ischiorectal/complex)

Surgical Steps:

1. Patient Positioning: Lithotomy or prone jack-knife (surgeon preference)

2. Systematic Examination: EUA as above (inspection, palpation, proctoscopy)

3. Incision:

   • Location: Closest point of fluctuance to anal verge (minimize tract length if fistula forms)
   • Shape:
     • Cruciate Incision: Traditional; creates flaps that prevent premature closure
     • Elliptical Excision of Skin: Modern preference; "deroofing" creates wide opening [63]
   • Extent: Adequate to allow drainage and prevent premature skin closure

4. Drainage:

   • Break Down Loculations: Use finger to explore cavity; break all septations (horseshoe requires bilateral counter-drainage incisions)
   • Send Pus for Culture: Routine (guides antibiotics if treatment failure)
   • Irrigation: Copious saline lavage

5. Search for Internal Opening:

   • Careful Probing: Gentle exploration with probe (do NOT create false passage)
   • If Found: Document location; consider primary fistulotomy if low and simple
   • If Not Found: Do NOT force; 50% have no fistula; re-assess in 6-8 weeks [9]

6. Haemostasis: Usually minimal bleeding; diathermy/pressure

7. Dressing:

   • Packing: Controversial
     • Traditional: Ribbon gauze or alginate (Sorbsan) to keep cavity open
     • Modern: No packing (equally effective, less painful) [64]
   • Absorbent Pad: Manage discharge

8. Post-Operative Instructions: (see below)

Special Considerations:

Primary Fistulotomy at Index Procedure

When to Consider:

• Low Intersphincteric Fistula with clear internal opening identified
• Minimal Sphincter at Risk: less than 30% of EAS would be divided
• Experienced Surgeon: Confident assessment [65]

Advantages: Single procedure; immediate cure Risks: Incontinence if assessment incorrect; over-treatment

Many Surgeons Prefer Staged Approach: Drain abscess → reassess at 6-8 weeks → definitive fistula surgery if needed

Role of Antibiotics

NOT Indicated Routinely: Abscess drainage is definitive treatment; antibiotics do NOT penetrate pus [3]

Indications for Antibiotics:

Empirical Coverage: Gram-negatives + Anaerobes (polymicrobial infection) [17]

Antibiotic Monotherapy WITHOUT Drainage is Harmful:

• Sterilizes pus but cavity remains ("antibioma")
• Mass effect persists
• Chronic induration
• Difficult delayed drainage
• Promotes complex fistula formation [66]

Post-Operative Care

Analgesia:

• Regular Paracetamol: 1g QDS
• NSAIDs: Ibuprofen 400mg TDS or Diclofenac 50mg TDS (if no contraindication)
• Opiates: Oxycodone/Morphine PRN for first 24-48 hours (constipation problematic)
• Local: Topical lidocaine gel PRN

Wound Care:

• Keep Clean: Shower or bath twice daily
• Irrigation: Sitz baths or bidet (warm water promotes healing, comfort)
• Dressing Changes: Daily initially; reduce as discharge decreases
• Avoid Constipation: Stool softeners (lactulose, macrogol) to prevent pain on defecation

Follow-Up:

• 2 Weeks: Wound check; ensure healing from base outward (not skin closure first)
• 6-8 Weeks: Assess for fistula formation (30-50% develop chronic fistula) [9,10]
• If Persistent Discharge: Arrange MRI and fistula surgery planning

---

13. Management of Fistula-in-Ano

Pre-Operative Assessment

Essential:

1. MRI Pelvis: Defines anatomy (Parks classification, extensions)
2. EUA: Correlates imaging with clinical findings; identifies internal opening
3. Assess Continence: Baseline Wexner Incontinence Score (guides surgical decision) [67]
4. Screen for Crohn's: Faecal calprotectin, colonoscopy if suspicious [20]

Surgical Decision Tree:

              FISTULA CONFIRMED (MRI + EUA)
                        ↓
          ┌─────────────┴─────────────┐
       LOW FISTULA              HIGH FISTULA
   (less than 30% EAS involved)      (>30% EAS involved)
          ↓                          ↓
     FISTULOTOMY              SPHINCTER-SPARING
     (Lay Open)                  APPROACH
          ↓                          ↓
    >90% Cure              ┌─────────┴────────┐
    Low Incontinence      SETON            LIFT/Flap/VAAFT
                          ↓                     ↓
                   Loose (drainage)      Variable Success
                   Cutting (rare)        (50-80%)

---

Surgical Techniques

1. Fistulotomy (Lay Open Technique)

Principle: Unroof the fistula tract, converting it into a groove that heals by secondary intention from base upward. [68]

Indications:

• Low Intersphincteric Fistula: No EAS involvement
• Low Transsphincteric Fistula: less than 30% of EAS would be divided
• Superficial Fistula: Subcutaneous tract

Technique:

1. Identify Internal and External Openings: Probe gently; inject dilute hydrogen peroxide/methylene blue if needed (bubbles/dye at internal opening)
2. Pass Probe: From external to internal opening along tract
3. Lay Open: Incise tissue over probe (skin, subcutaneous tissue, ± sphincter)
4. Curettage: Remove granulation tissue from tract (sends for histology)
5. Marsupialization (optional): Suture edges to keep wound open
6. Haemostasis: Diathermy

Outcomes:

• Cure Rate: 92-98% [69]
• Recurrence: 2-8%
• Incontinence: 0-15% (depends on amount of sphincter divided; higher if >1/3 EAS) [70]

Post-Operative Care: As per abscess drainage (analgesia, hygiene, stool softeners)

---

2. Seton Placement

Principle: Thread a suture/silicone loop through the fistula tract and tie it loosely or tightly depending on intent. [71]

Types:

Indications for Loose Seton:

• High Transsphincteric/Suprasphincteric Fistula: Temporize before definitive sphincter-sparing procedure
• Crohn's Disease: Long-term drainage; surgery often avoided [20]
• Active Sepsis: Control infection before complex repair
• Patient Not Fit: Palliation in elderly/comorbid patients
• Assess Sphincter Function: "Test sphincter division"
• if incontinence develops with seton, sphincter-sparing procedure mandatory [74]

Technique:

1. Pass Probe: Through fistula tract
2. Thread Seton: Silicone vessel loop or silk suture
3. Tie Loosely: Secure but not tight (drainage not cutting)
4. Document: Position, type

Long-Term Seton:

• Well-Tolerated: Most patients adapt
• Hygiene: Daily cleaning
• Replacement: May need changing if falls out or erodes

---

3. LIFT Procedure (Ligation of Intersphincteric Fistula Tract)

Principle: Access the intersphincteric plane, ligate and divide the fistula tract at the level between sphincters; removes infected tissue without sphincter division. [75]

Indications:

• Transsphincteric Fistula: Where fistulotomy would risk incontinence
• Failed Seton: After drainage seton matured tract

Technique:

1. Incision: Intersphincteric groove (between IAS and EAS)
2. Dissection: Enter intersphincteric space; identify fistula tract
3. Isolation: Dissect tract free from IAS and EAS
4. Ligation: Suture ligate tract on both sides (internal and external)
5. Division: Divide tract between ligatures
6. Excision: Remove external component of tract (to skin)
7. Closure: Primary closure of intersphincteric incision

Outcomes:

• Success Rate: 57-94% (variable; meta-analysis ~74%) [76,77]
• Incontinence: Minimal (less than 5%)
• Recurrence: 20-40% (higher if residual sepsis, Crohn's)

Advantages: Sphincter-preserving; single procedure Disadvantages: Moderate success rate; technically demanding

---

4. Advancement Flap Procedures

Principle: Excise internal opening and cover with healthy vascularized rectal mucosa/muscle flap; external tract curetted but left to heal secondarily. [78]

Types:

• Rectal Advancement Flap: Most common; full-thickness flap (mucosa + muscle)
• Dermal/Cutaneous Flap: Rarely used

Indications:

• High Transsphincteric Fistula
• Anovaginal/Rectovaginal Fistula
• Crohn's Disease (controversial; lower success)
• Failed Previous Procedures

Technique (Rectal Advancement Flap):

1. Curettage External Tract: Scrape out granulation; leave open to heal
2. Identify Internal Opening: Proctoscopy
3. Raise Flap: Incision 2-3cm proximal to internal opening; dissect flap incorporating mucosa, submucosa, and circular muscle (base wider than tip for vascularity)
4. Excise Internal Opening: Remove diseased tissue
5. Advance Flap: Bring flap down to cover defect without tension
6. Suture: Absorbable sutures; tension-free closure

Outcomes:

• Success Rate: 60-80% (first attempt); 40-60% (recurrent) [79,80]
• Incontinence: Low (0-10%)
• Complications: Flap necrosis (5-10%), recurrence (20-40%)

Advantages: Preserves sphincter Disadvantages: Technically challenging; moderate success; requires bowel prep

---

5. VAAFT (Video-Assisted Anal Fistula Treatment)

Principle: Minimally invasive endoscopic visualization of fistula tract; destruction of tract using diathermy/laser; closure of internal opening. [81]

Indications:

• High Fistulas: Transsphincteric, suprasphincteric
• Recurrent Fistulas: After failed conventional surgery
• Complex Anatomy: Horseshoe, multiple tracts

Technique:

1. Diagnostic Phase:

   • Fistuloscope (angled endoscope) inserted via external opening
   • Visualize Tract: Identify internal opening, secondary tracts, abscesses

2. Operative Phase:

   • Destruction of Tract: Diathermy brush or laser ablates granulation tissue
   • Closure of Internal Opening: Suture or staple closure

Outcomes:

• Success Rate: 71-85% [82,83]
• Incontinence: Minimal
• Recurrence: 15-30%

Advantages: Sphincter-preserving; visualizes anatomy; outpatient procedure Disadvantages: Requires equipment; learning curve; cost

---

6. Fibrin Glue and Fistula Plugs

Principle: Obliterate fistula tract with biocompatible material.

Fibrin Glue:

• Technique: Curettage tract; inject fibrin glue to fill tract from internal opening
• Success: 10-50% (disappointing; rarely used now) [84]

Fistula Plug (Bioprosthetic):

• Technique: Insert conical plug into tract from internal to external; suture to secure
• Success: 35-87% (variable; early enthusiasm not sustained) [85]

Limitations: High recurrence; expensive; no advantage over traditional methods

---

7. Stem Cell Therapy (Emerging)

Adipose-Derived Stem Cells: Injected into fistula tract; promotes healing

• Evidence: Promising in Crohn's fistulas (ADMIRE-CD trial: 50% closure at 24 weeks) [86]
• Availability: Limited; expensive; not routine practice yet

---

Special Situations

Crohn's Disease Perianal Fistulas

Prevalence: 30-40% of Crohn's patients develop perianal disease [20]

Characteristics:

• Complex: Multiple tracts, anterior in females, recurrent
• Poor Healing: Active inflammation impairs wound healing
• High Recurrence: 50-70% after surgery

Management Principles:

1. Medical Optimization FIRST: Anti-TNF therapy (infliximab, adalimumab) induces remission in 50-60% [87]
2. Surgical Goals: Drainage of sepsis; symptom control (NOT definitive cure)
3. Avoid Aggressive Cutting: Fistulotomy contraindicated (high incontinence, poor healing)
4. Loose Setons: Long-term drainage preferred [88]
5. Advancement Flaps: Reserved for selected cases; lower success than non-Crohn's
6. Diverting Stoma: Severe refractory disease; allows healing but recurs after reversal
7. Proctectomy: Last resort for intractable disease

---

Anovaginal and Rectovaginal Fistulas

Aetiology:

• Obstetric Injury: Most common (prolonged labor, forceps, 3rd/4th degree tears)
• Crohn's Disease
• Radiation
• Post-Surgical: After haemorrhoidectomy, fistula surgery

Symptoms: Passage of flatus/stool per vagina; recurrent vaginitis

Management:

• Conservative: Initial period (3-6 months) for inflammation to settle
• Surgical: Advancement flap, interposition graft, sphincteroplasty
• Success: Variable (50-80% depending on aetiology and size) [89]

---

Tuberculous Anal Fistula

Epidemiology: Endemic areas (Asia, Africa); immunocompromised patients [21]

Characteristics:

• Indolent Course: Painless, chronic discharge
• Multiple Sinuses: Undermined bluish edges
• Poor Healing: Non-responsive to standard surgery

Diagnosis: Biopsy (caseating granulomas); PCR for TB; culture (takes weeks)

Management:

• Anti-TB Therapy: 6-9 months (rifampicin, isoniazid, pyrazinamide, ethambutol)
• Surgery: Minimal; drainage if abscess; avoid fistulotomy (poor healing)
• MDT Approach: Infectious diseases + surgery

---

14. Complications

Post-Operative Complications (Immediate)

Long-Term Complications

1. Recurrence

Incidence: 7-40% (depends on complexity and technique) [11]

Causes of Recurrence:

• Missed Internal Opening: Most common (persistent source) [90]
• Undiagnosed Secondary Tracts: Horseshoe, supralevator extension
• Underlying Crohn's Disease: Unrecognized at initial surgery
• Premature Wound Closure: Skin heals before cavity obliterates (re-abscess formation)
• Inadequate Drainage: Incomplete breaking of loculations
• Technical Error: Incorrect surgical plane

Management of Recurrence:

• Re-Investigation: MRI pelvis (anatomy may have changed)
• EUA: Identify problem (missed opening, new tract)
• Revision Surgery: Tailored to findings
• Consider Crohn's: Faecal calprotectin, colonoscopy, histology

---

2. Faecal Incontinence

Incidence: Variable (0-60% depending on procedure and definition) [70]

Risk Factors for Incontinence:

• Amount of Sphincter Divided: >30% EAS high risk
• Anterior Fistulas in Females: Shorter sphincter complex [91]
• Repeat Surgery: Cumulative sphincter damage
• Pre-Existing Weak Sphincter: Obstetric injury, age, diarrhea
• Crohn's Disease: Inflammation + surgery = high risk

Types of Incontinence:

• Flatus Incontinence: Most common (10-20%)
• Liquid Stool Incontinence: Moderate impact (5-10%)
• Solid Stool Incontinence: Devastating (less than 5% but severe QOL impact)

Assessment: Wexner Incontinence Score (0 = continent, 20 = complete incontinence) [67]

Management:

• Conservative:
  • "Dietary Modification: Avoid triggers; bulk stool (loperamide, fiber)"
  • "Pelvic Floor Physiotherapy: Biofeedback, Kegel exercises"
  • "Skin Care: Barrier creams, hygiene"
• Surgical:
  • "Sphincter Repair: If anatomical defect identified (sphincteroplasty)"
  • "Sacral Nerve Stimulation: Functional incontinence [92]"
  • "Injectable Bulking Agents: Limited success"
  • "Colostomy: Last resort for intractable incontinence"

---

3. Anal Stenosis

Incidence: 1-5% (after extensive tissue excision)

Causes:

• Excessive Tissue Removal: Large fistulotomy, multiple procedures
• Circumferential Scarring: Fibrosis
• Healing by Secondary Intention: Contracture

Symptoms: Difficulty defecation, ribbon stools, pain

Management:

• Mild: Stool softeners, digital dilation
• Moderate-Severe: Anal dilation under anaesthesia, anoplasty (advancement flap to widen canal)

---

4. Chronic Pain

Incidence: 5-10%

Causes: Neuroma formation, chronic inflammation, psychological

Management: Pain clinic referral; neuropathic agents (gabapentin); psychological support

---

5. Hidradenitis Suppurativa (Secondary)

Association: Chronic perianal sinuses may coexist with or trigger HS [37]

Management: Dermatology referral; antibiotics; biologics; wide excision if localized

---

15. Prognosis and Outcomes

Abscess

Immediate Outcomes:

• Complete Drainage: Pain relief within 24-48 hours
• Healing Time: 3-6 weeks (depends on cavity size)
• Return to Work: 1-2 weeks (office work); 4-6 weeks (manual labor)

Long-Term:

• 50% Heal Completely: No fistula formation
• 30-50% Develop Fistula: Manifest 6-12 weeks post-drainage [9,10]
• Recurrence Without Fistula: 5-10% (inadequate drainage, missed sepsis)

Fistula

Cure Rates by Procedure (Meta-Analyses):

Prognostic Factors for Success:

Good Prognosis:

• Low intersphincteric or transsphincteric fistula
• Single tract, no secondary extensions
• No Crohn's disease
• No previous surgery
• Experienced surgeon

Poor Prognosis:

• Crohn's disease (recurrence 50-70%) [87]
• Recurrent fistula (success drops 20-30% with each reoperation)
• Horseshoe or supralevator extension
• Anterior fistula in females (shorter sphincter, higher failure)
• Anovaginal/rectovaginal fistula (50-80% success only) [89]

Quality of Life:

• Untreated Fistula: Significant impairment (chronic discharge, pain, social embarrassment)
• Post-Successful Surgery: Return to normal QOL
• Post-Surgery with Incontinence: Severely impaired QOL (worse than pre-op in some cases) [93]

---

16. Prevention and Screening

Primary Prevention

Limited Scope (cryptoglandular infection largely idiosyncratic), but modifiable factors:

• Diabetes Control: Optimize HbA1c (less than 7%); reduces infection risk [32]
• Smoking Cessation: Improves wound healing and reduces recurrence [34]
• IBD Management: Early aggressive medical therapy for Crohn's reduces perianal complications [94]
• Hygiene: Perianal cleanliness (speculative benefit)

Secondary Prevention (Prevent Fistula After Abscess)

• Adequate Drainage: Complete I&D reduces fistula formation (but 30-50% still develop fistula despite optimal drainage) [9,10]
• Early Surgery: Delayed drainage increases complex fistula risk [62]
• Identify Internal Opening: If found at index procedure, consider primary fistulotomy (selected cases)

Tertiary Prevention (Prevent Recurrence After Fistula Surgery)

• Complete Tract Excision/Closure: Address all secondary tracts
• Internal Opening Eradication: Essential for cure [90]
• Avoid Premature Wound Closure: Healing from base outward
• Smoking Cessation: Post-operative [34]
• Crohn's Disease: Maintain medical remission (anti-TNF therapy) [87]

---

17. Key Guidelines and Evidence

Major Society Guidelines

Landmark Studies

1. Parks AG, Gordon PH, Hardcastle JD. A classification of fistula-in-ano. Br J Surg. 1976;63(1):1-12.

   • Established: Anatomical classification system (still used) [22]

2. Buchanan GN, Halligan S, Bartram CI, et al. Clinical examination, endosonography, and MR imaging in preoperative assessment of fistula in ano. Lancet. 2003;361(9360):1653-1657.

   • Showed: MRI superior to clinical exam and EUS for complex fistulas [51]

3. Rojanasakul A, Pattanaarun J, Sahakitrungruang C, Tantiphlachiva K. Total anal sphincter saving technique for fistula-in-ano: the ligation of intersphincteric fistula tract. J Med Assoc Thai. 2007;90(3):581-586.

   • Introduced: LIFT procedure [75]

4. Panes J, Garcia-Olmo D, Van Assche G, et al. Expanded allogeneic adipose-derived mesenchymal stem cells (Cx601) for complex perianal fistulas in Crohn's disease: a phase 3 randomised, double-blind controlled trial. Lancet. 2016;388(10051):1281-1290.

   • ADMIRE-CD Trial: Stem cell therapy effective in Crohn's fistulas (50% closure) [86]

---

18. Examination Focus (MRCS, FRCS)

Common Viva Questions

Q1: "Classify fistula-in-ano."

Model Answer: "Fistula-in-ano is classified using the Parks classification (1976), which categorizes fistulas based on their relationship to the anal sphincter complex:

• Type I - Intersphincteric (70%): Tract confined between internal and external sphincters
• Type II - Transsphincteric (23%): Tract crosses the external sphincter into the ischiorectal fossa
• Type III - Suprasphincteric (5%): Tract passes over the puborectalis, then down through levator ani
• Type IV - Extrasphincteric (2%): Tract entirely outside sphincter complex, from rectum to skin

The classification guides surgical management—low intersphincteric fistulas can be laid open safely, whereas high transsphincteric and suprasphincteric require sphincter-sparing techniques to avoid incontinence." [22]

---

Q2: "What is Goodsall's Rule?"

Model Answer: "Goodsall's Rule predicts the course of a fistula tract based on the position of the external opening relative to an imaginary transverse line through the anus:

• Anterior openings: Tract runs radially (straight) to the anal canal
• Posterior openings: Tract runs curved to the posterior midline (6 o'clock)

Exceptions include:

• Anterior openings >3 cm from the anal verge may curve to the posterior midline
• Crohn's disease and traumatic fistulas do not follow the rule

The rule has 70-80% accuracy, and MRI is superior for surgical planning in complex cases." [25,26,27]

---

Q3: "How would you manage a patient presenting with a perianal abscess?"

Model Answer: "Perianal abscess is a surgical emergency requiring prompt drainage. My approach:

Initial Assessment:

• History: Pain, fever, duration, immunosuppression, IBD
• Examination: Identify abscess location, assess for Fournier's gangrene (crepitus, skin necrosis)
• Investigations: FBC, CRP, blood glucose; imaging (CT/MRI) if supralevator suspected

Management:

• Emergency I&D under GA: Same-day or within 24 hours
• Technique: Cruciate incision or elliptical excision closest to anal verge; break all loculations; search for internal opening
• Send pus for MC&S
• Antibiotics: ONLY if sepsis, extensive cellulitis, immunosuppression, or diabetes (co-amoxiclav or metronidazole + ciprofloxacin)

Post-Operative:

• Analgesia, hygiene, stool softeners
• Follow-up at 6-8 weeks: Assess for fistula formation (30-50% risk)

Principles: 'Pus must out'—antibiotics alone are inadequate and harmful." [3,62]

---

Q4: "What are the sphincter-sparing options for high anal fistula?"

Model Answer: "High anal fistulas involving significant external sphincter require sphincter-sparing techniques to avoid incontinence:

Options:

1. Loose Draining Seton: Silicone loop placed through tract; controls sepsis and symptoms; may be long-term or temporizing before definitive procedure. Success: symptom control (not cure). [72]

2. LIFT (Ligation of Intersphincteric Fistula Tract): Access intersphincteric space, ligate and divide tract without sphincter division. Success: 57-94%; minimal incontinence. [75,76,77]

3. Advancement Flap: Excise internal opening, cover with vascularized rectal flap; curettage external tract. Success: 60-80%; technically demanding. [79,80]

4. VAAFT (Video-Assisted Anal Fistula Treatment): Endoscopic fistuloscopy, ablate tract, close internal opening. Success: 71-85%; minimally invasive. [82,83]

5. Cutting Seton: Rarely used (high incontinence 10-60%). [73]

Choice depends on anatomy (MRI), surgeon experience, patient preference, and previous surgery. Crohn's disease typically managed with long-term loose seton." [4,5]

---

Q5: "What are the causes of recurrent perianal abscess and fistula?"

Model Answer: "Recurrence affects 7-40% of patients. Common causes:

Surgical Factors:

• Missed internal opening: Persistent source of infection (commonest cause) [90]
• Undiagnosed secondary tracts: Horseshoe, supralevator extensions
• Inadequate drainage: Loculations not broken; premature skin closure

Patient Factors:

• Crohn's Disease: Undiagnosed at initial presentation; complex, recurrent fistulas [20]
• Tuberculosis: Endemic areas; poor healing [21]
• Immunosuppression: HIV, diabetes, chemotherapy [33]
• Smoking: Impairs healing [34]

Management:

• Re-investigate: MRI pelvis, EUA
• Screen for Crohn's: Faecal calprotectin, colonoscopy, biopsy (non-caseating granulomas)
• Revision Surgery: Address missed pathology
• Medical Optimization: Anti-TNF if Crohn's; optimize diabetes control"

---

Common Exam Mistakes

❌ Mistake 1: Treating abscess with antibiotics alone (without drainage)

• Why Wrong: Antibiotics do NOT penetrate pus; delay causes progression; creates "antibioma" [3,66]
• Correct: Emergency surgical drainage

❌ Mistake 2: Performing fistulotomy for high transsphincteric fistula

• Why Wrong: Divides >30% EAS → high incontinence risk (15-40%) [70]
• Correct: Seton or sphincter-sparing procedure (LIFT, flap)

❌ Mistake 3: Missing Crohn's disease in recurrent/complex fistulas

• Why Wrong: Surgery alone fails; high recurrence; aggressive cutting causes severe incontinence [20]
• Correct: Screen with faecal calprotectin, colonoscopy; medical therapy (anti-TNF) + loose seton

❌ Mistake 4: Draining supralevator abscess via incorrect route

• Why Wrong: Creates iatrogenic extrasphincteric fistula [48]
• Correct: Determine origin (upward intersphincteric → drain via rectum; ischiorectal extension → drain via ischiorectal fossa)

❌ Mistake 5: Not recognizing Fournier's gangrene

• Why Wrong: Delays life-saving debridement; mortality 20-40% [44,47]
• Correct: Emergency radical debridement + ICU + broad-spectrum antibiotics

---

Viva Pearls

Opening Statement for Perianal Abscess: "Perianal abscess is an acute suppurative infection of the perianal tissues, most commonly arising from cryptoglandular infection of the anal glands at the dentate line. It affects 14-20 per 100,000 annually, predominantly males aged 30-50 years. Management is surgical drainage—antibiotics alone are inadequate. Approximately 30-50% progress to chronic fistula-in-ano." [1,6,7,9,10]

Opening Statement for Fistula-in-Ano: "Fistula-in-ano is a chronic epithelialized tract connecting the anal canal to the perianal skin, representing the chronic phase of cryptoglandular infection. It is classified by the Parks system based on sphincter involvement. Management balances complete fistula healing with preservation of continence—low fistulas are laid open, while high fistulas require sphincter-sparing techniques such as seton, LIFT, or advancement flap. MRI is the gold standard for pre-operative assessment." [1,22,51,52]

Key Statistics to Quote:

• Abscess incidence: 14-20 per 100,000 [6]
• Male:Female ratio: 2-3:1 [7]
• Fistula after abscess: 30-50% [9,10]
• Parks classification: 70% intersphincteric, 23% transsphincteric, 5% suprasphincteric, 2% extrasphincteric [22]
• Fistulotomy cure: >92% [69]
• LIFT success: 57-94% [76,77]
• Crohn's perianal disease: 30-40% of Crohn's patients [20]

---

19. Patient and Layperson Explanation

What is a Perianal Abscess?

A perianal abscess is a collection of pus near your back passage (anus). It happens when a tiny gland inside the anal canal gets blocked and infected. Think of it like a boil, but deeper and more painful because it's in a very sensitive area with lots of nerve endings.

Symptoms:

• Severe pain near your bottom, worse when sitting or going to the toilet
• Swelling or a lump you can feel
• Fever and feeling generally unwell

Why Surgery is Needed: Antibiotic tablets cannot cure an abscess because they can't get into the pus pocket to kill the bacteria. The only way to fix it is to drain the pus surgically—this is called "incision and drainage." You'll have a general anaesthetic (put to sleep) so you won't feel anything during the operation.

What Happens After:

• You'll wake up with a dressing or packing in the wound
• The wound is left open to heal from the inside out (takes 3-6 weeks)
• You'll need painkillers and to keep the area clean (daily baths help)
• Most people (about half) heal completely; the other half may develop a fistula (see below)

---

What is a Fistula?

Sometimes after the abscess drains, the tunnel (tract) that formed between the inside of your bowel and your skin doesn't heal up properly. It stays open as a small tube called a fistula. This can leak fluid, pus, or even a tiny bit of stool onto your skin, causing damp patches in your underwear and irritation.

Symptoms:

• Discharge (pus or fluid) from a small hole near your bottom
• Recurrent pain and swelling if the hole blocks up and the abscess comes back
• Itching from moisture

How We Fix It: Treatment depends on where the fistula is and how much muscle is involved:

• Simple (Low) Fistula: We can "unroof" it by cutting it open so it heals from the bottom up. This cures >90% but you need to be careful not to damage the muscle that controls your bowel movements.

• Complex (High) Fistula: If the fistula goes through important muscle, we can't just cut it open because you might lose control of your bowels. Instead, we might:

  • "Put in a seton: A soft rubber thread that keeps the tunnel draining while we plan further treatment"
  • Use special techniques like LIFT or flap surgery to close the fistula without cutting muscle

Will I Lose Control of My Bowels? Your surgeon's main goal is to cure the fistula without affecting your ability to control bowel movements. That's why complex fistulas need more sophisticated surgery. With modern techniques, serious incontinence is rare (less than 5% with sphincter-sparing procedures).

---

How Long Until I'm Better?

• Abscess drainage: Back to light activities in 1-2 weeks; full healing 3-6 weeks
• Simple fistula surgery: 4-8 weeks to heal
• Complex fistula surgery: May need multiple operations over months

---

When Should I Worry?

Go to A&E immediately if:

• The pain is getting worse despite treatment
• You develop a high fever (>38°C) and feel very unwell
• You see black or grey skin around the wound (sign of serious infection)
• You pass air or stool from your vagina (women)—this is a different type of fistula needing urgent assessment

---

20. References

1. Vogel JD, Johnson EK, Morris AM, et al. Clinical Practice Guideline for the Management of Anorectal Abscess, Fistula-in-Ano, and Rectovaginal Fistula. Dis Colon Rectum. 2016;59(12):1117-1133. doi:10.1097/DCR.0000000000000733

2. Zanotti C, Martinez-Puente C, Pascual I, et al. An assessment of the incidence of fistula-in-ano in four countries of the European Union. Int J Colorectal Dis. 2007;22(12):1459-1462. doi:10.1007/s00384-007-0334-7

3. Whiteford MH. Perianal abscess/fistula disease. Clin Colon Rectal Surg. 2007;20(2):102-109. doi:10.1055/s-2007-977488

4. Steele SR, Kumar R, Feingold DL, et al. Practice parameters for the management of perianal abscess and fistula-in-ano. Dis Colon Rectum. 2011;54(12):1465-1474. doi:10.1097/DCR.0b013e31823122b3

5. Limura E, Giordano P. Modern management of anal fistula. World J Gastroenterol. 2015;21(1):12-20. doi:10.3748/wjg.v21.i1.12

6. Sainio P. Fistula-in-ano in a defined population. Incidence and epidemiological aspects. Ann Chir Gynaecol. 1984;73(4):219-224. PMID: 6508203

7. Vasilevsky CA, Gordon PH. The incidence of recurrent abscesses or fistula-in-ano following anorectal suppuration. Dis Colon Rectum. 1984;27(2):126-130. doi:10.1007/BF02555110

8. Mazier WP. The treatment and care of anal fistulas: a study of 1,000 patients. Dis Colon Rectum. 1971;14(2):134-144. doi:10.1007/BF02560987

9. Ramanujam PS, Prasad ML, Abcarian H, Tan AB. Perianal abscesses and fistulas. A study of 1023 patients. Dis Colon Rectum. 1984;27(9):593-597. doi:10.1007/BF02553945

10. Hamadani A, Haigh PI, Liu IL, Abbas MA. Who is at risk for developing chronic anal fistula or recurrent anal sepsis after initial perianal abscess? Dis Colon Rectum. 2009;52(2):217-221. doi:10.1007/DCR.0b013e31819a5c52

11. van Koperen PJ, Wind J, Bemelman WA, et al. Long-term functional outcome and risk factors for recurrence after surgical treatment for low and high perianal fistulas of cryptoglandular origin. Dis Colon Rectum. 2008;51(10):1475-1481. doi:10.1007/s10350-008-9354-9

12. Lestar B, Penninckx F, Kerremans R. The composition of anal basal pressure. An in vivo and in vitro study in man. Int J Colorectal Dis. 1989;4(2):118-122. doi:10.1007/BF01649764

13. Fritsch H, Brenner E, Lienemann A, Ludwikowski B. Anal sphincter complex: reinterpreted morphology and its clinical relevance. Dis Colon Rectum. 2002;45(2):188-194. doi:10.1007/s10350-004-6145-x

14. Parks AG. Pathogenesis and treatment of fistuala-in-ano. Br Med J. 1961;1(5224):463-469. doi:10.1136/bmj.1.5224.463

15. Hanley PH. Horseshoe fistula-in-ano. Surg Gynecol Obstet. 1965;120:1093-1095. PMID: 14281176

16. Eisenhammer S. The internal anal sphincter and the anorectal abscess. Surg Gynecol Obstet. 1956;103(4):501-506. PMID: 13360649

17. Brook I, Frazier EH. Aerobic and anaerobic microbiology of perirectal abscess in children. J Pediatr Surg. 1997;32(8):1175-1177. doi:10.1016/s0022-3468(97)90680-6

18. Shouler PJ, Grimley RP, Keighley MR, Alexander-Williams J. Fistula-in-ano is usually simple to manage surgically. Int J Colorectal Dis. 1986;1(2):113-115. doi:10.1007/BF01648443

19. Parks AG, Stitz RW. The treatment of high fistula-in-ano. Dis Colon Rectum. 1976;19(6):487-499. doi:10.1007/BF02590969

20. Schwartz DA, Loftus EV Jr, Tremaine WJ, et al. The natural history of fistulizing Crohn's disease in Olmsted County, Minnesota. Gastroenterology. 2002;122(4):875-880. doi:10.1053/gast.2002.32362

21. Shukla HS, Gupta SC, Singh G, Singh PA. Tubercular fistula in ano. Br J Surg. 1988;75(1):38-39. doi:10.1002/bjs.1800750113

22. Parks AG, Gordon PH, Hardcastle JD. A classification of fistula-in-ano. Br J Surg. 1976;63(1):1-12. doi:10.1002/bjs.1800630102

23. Morris J, Spencer JA, Ambrose NS. MR imaging classification of perianal fistulas and its implications for patient management. Radiographics. 2000;20(3):623-635. doi:10.1148/radiographics.20.3.g00ma15623

24. Morris J, Spencer JA, Ambrose NS. MR imaging classification of perianal fistulas and its implications for patient management. Radiographics. 2000;20(3):623-635. doi:10.1148/radiographics.20.3.g00ma15623

25. Goodsall DH, Miles WE. Diseases of the Anus and Rectum. London: Longmans Green; 1900.

26. Cirocco WC, Reilly JC. Challenging the predictive accuracy of Goodsall's rule for anal fistulas. Dis Colon Rectum. 1992;35(6):537-542. doi:10.1007/BF02050531

27. Buchanan GN, Halligan S, Bartram CI, et al. Clinical examination, endosonography, and MR imaging in preoperative assessment of fistula in ano: comparison with outcome-based reference standard. Radiology. 2004;233(3):674-681. doi:10.1148/radiol.2333031724

28. Ommer A, Herold A, Berg E, et al. German S3 Guideline: anal abscess and fistula (AWMF Register Nr. 088/003). Langenbecks Arch Surg. 2017;402(2):191-201. doi:10.1007/s00423-017-1563-z

29. Abcarian H. Anorectal infection: abscess-fistula. Clin Colon Rectal Surg. 2011;24(1):14-21. doi:10.1055/s-0031-1272819

30. Visscher AP, Schuur D, Roos R, et al. Long-term follow-up after surgery for simple and complex cryptoglandular fistulas: fecal incontinence and impact on quality of life. Dis Colon Rectum. 2015;58(5):533-539. doi:10.1097/DCR.0000000000000362

31. Nelson RL, Cintron J, Abcarian H. Dermatologic analysis of the perianal skin in patients with anal fistula. Dis Colon Rectum. 1994;37(12):1215-1218. doi:10.1007/BF02257783

32. Henriksen M, Jahnsen J, Lygren I, et al. Clinical course in Crohn's disease: results of a five-year population-based follow-up study (the IBSEN study). Scand J Gastroenterol. 2007;42(5):602-610. doi:10.1080/00365520601076124

33. Sentovich SM. Fibrin glue for anal fistulas: long-term results. Dis Colon Rectum. 2003;46(4):498-502. doi:10.1007/s10350-004-6587-z

34. Lindsey I, Smilgin-Humphreys MM, Cunningham C, et al. A randomized, controlled trial of fibrin glue vs. conventional treatment for anal fistula. Dis Colon Rectum. 2002;45(12):1608-1615. doi:10.1007/s10350-004-7247-0

35. Emile SH, Elgendy H, Sakr A, et al. Gender-based analysis of the characteristics and outcomes of surgery for anal fistula: analysis of more than 560 cases. J Coloproctol. 2018;38(3):199-206. doi:10.1016/j.jcol.2018.03.005

36. van Tets WF, Kuijpers JH. Continence disorders after anal fistulotomy. Dis Colon Rectum. 1994;37(12):1194-1197. doi:10.1007/BF02257779

37. Alharbi Z, Kauczok J, Pallua N. A review of wide surgical excision of hidradenitis suppurativa. BMC Dermatol. 2012;12:9. doi:10.1186/1471-5945-12-9

38. Garg P. To lay open or keep high anal fistulas closed: a randomized trial of treatments--10 years on. Colorectal Dis. 2015;17(12):1054-1057. doi:10.1111/codi.13158

39. Andreyev HJ, Vlavianos P, Blake P, et al. Gastrointestinal symptoms after pelvic radiotherapy: role for the gastroenterologist? Int J Radiat Oncol Biol Phys. 2005;62(5):1464-1471. doi:10.1016/j.ijrobp.2004.12.087

40. Scoma JA, Salvati EP, Rubin RJ. Incidence of fistulas subsequent to anal abscesses. Dis Colon Rectum. 1974;17(3):357-359. doi:10.1007/BF02586992

41. Cox SW, Senagore AJ, Luchtefeld MA, Mazier WP. Outcome after incision and drainage with fistulotomy for ischiorectal abscess. Am Surg. 1997;63(8):686-689. PMID: 9247434

42. Garcia-Aguilar J, Belmonte C, Wong WD, et al. Anal fistula surgery. Factors associated with recurrence and incontinence. Dis Colon Rectum. 1996;39(7):723-729. doi:10.1007/BF02054434

43. Felt-Bersma RJ, Bartelsman JF. Haemorrhoids, rectal prolapse, anal fissure, peri-anal fistulae and sexually transmitted diseases. Best Pract Res Clin Gastroenterol. 2009;23(4):575-592. doi:10.1016/j.bpg.2009.05.006

44. Eke N. Fournier's gangrene: a review of 1726 cases. Br J Surg. 2000;87(6):718-728. doi:10.1046/j.1365-2168.2000.01497.x

45. Sandborn WJ, Fazio VW, Feagan BG, Hanauer SB. AGA technical review on perianal Crohn's disease. Gastroenterology. 2003;125(5):1508-1530. doi:10.1016/j.gastro.2003.08.025

46. Milsom JW, Mazier WP. Classification and management of postsurgical anal stenosis. Surg Gynecol Obstet. 1986;163(1):60-64. PMID: 3715992

47. Sorensen MD, Krieger JN, Rivara FP, et al. Fournier's gangrene: population based epidemiology and outcomes. J Urol. 2009;181(5):2120-2126. doi:10.1016/j.juro.2009.01.034

48. Seow-Choen F, Nicholls RJ. Anal fistula. Br J Surg. 1992;79(3):197-205. doi:10.1002/bjs.1800790305

49. Nunoo-Mensah JW, Balasubramaniam S, Wasserberg N, et al. Fistula-in-ano: do antibiotics make a difference? Int J Colorectal Dis. 2006;21(5):441-443. doi:10.1007/s00384-005-0026-3

50. D'Haens G, Sandborn WJ, Feagan BG, et al. A review of activity indices and efficacy end points for clinical trials of medical therapy in adults with ulcerative colitis. Gastroenterology. 2007;132(2):763-786. doi:10.1053/j.gastro.2006.12.038

51. Buchanan GN, Halligan S, Bartram CI, et al. Clinical examination, endosonography, and MR imaging in preoperative assessment of fistula in ano. Lancet. 2003;361(9360):1653-1657. doi:10.1016/S0140-6736(03)13185-3

52. Halligan S, Stoker J. Imaging of fistula in ano. Radiology. 2006;239(1):18-33. doi:10.1148/radiol.2391041043

53. Buchanan G, Bishop N, Marti-Obiol R, et al. Effect of MRI on clinical outcome of recurrent fistula-in-ano. Lancet. 2002;360(9346):1661-1662. doi:10.1016/S0140-6736(02)11605-9

54. Van Assche G, Vanbeckevoort D, Bielen D, et al. Magnetic resonance imaging of the effects of infliximab on perianal fistulizing Crohn's disease. Am J Gastroenterol. 2003;98(2):332-339. doi:10.1111/j.1572-0241.2003.07241.x

55. Dohan A, Hoeffel C, Soyer P, et al. Evaluation of MRI criteria for the diagnosis of anal fistula. Eur Radiol. 2015;25(1):259-267. doi:10.1007/s00330-014-3387-6

56. Kruskal JB, Kane RA, Sentovich SM, Longmaid HE 3rd. Pitfalls and sources of error in staging rectal cancer with endorectal US. Radiographics. 1997;17(3):609-626. doi:10.1148/radiographics.17.3.9153700

57. Schaefer O, Lohrmann C, Langer M. Assessment of anal fistulas with high-resolution subtraction MR-fistulography: comparison with surgical findings. J Magn Reson Imaging. 2004;19(1):91-98. doi:10.1002/jmri.10427

58. Sahni VA, Ahmad R, Burling D. Which method is best for imaging of perianal fistula? Abdom Imaging. 2008;33(1):26-30. doi:10.1007/s00261-007-9309-y

59. Kuijpers HC, Schulpen T. Fistulography for fistula-in-ano. Is it useful? Dis Colon Rectum. 1985;28(2):103-104. doi:10.1007/BF02553900

60. Lunniss PJ, Phillips RK. Surgical assessment of acute anorectal sepsis is a better predictor of fistula than microbiological analysis. Br J Surg. 1994;81(3):368-369. doi:10.1002/bjs.1800810316

61. Quality of Life in Crohn's disease. Guyatt G, Mitchell A, Irvine EJ, et al. A new measure of health status for clinical trials in inflammatory bowel disease. Gastroenterology. 1989;96(3):804-810. PMID: 2644154

62. Whiteford MH, Kilkenny J 3rd, Hyman N, et al. Practice parameters for the treatment of perianal abscess and fistula-in-ano (revised). Dis Colon Rectum. 2005;48(7):1337-1342. doi:10.1007/s10350-005-0055-3

63. Quah HM, Tang CL, Eu KW, et al. Meta-analysis of randomized clinical trials comparing drainage alone vs primary sphincter-cutting procedures for anorectal abscess-fistula. Int J Colorectal Dis. 2006;21(6):602-609. doi:10.1007/s00384-005-0060-9

64. Tonkin DM, Murphy E, Brooke-Smith M, et al. Perianal abscess: a pilot study comparing packing with nonpacking of the abscess cavity. Dis Colon Rectum. 2004;47(9):1510-1514. doi:10.1007/s10350-004-0645-1

65. Tang CL, Chew SP, Seow-Choen F. Prospective randomized trial of drainage alone vs. drainage and fistulotomy for acute perianal abscesses with proven internal opening. Dis Colon Rectum. 1996;39(12):1415-1417. doi:10.1007/BF02054224

66. Malik AI, Nelson RL, Tou S. Incision and drainage of perianal abscess with or without treatment of anal fistula. Cochrane Database Syst Rev. 2010;(7):CD006827. doi:10.1002/14651858.CD006827.pub2

67. Jorge JM, Wexner SD. Etiology and management of fecal incontinence. Dis Colon Rectum. 1993;36(1):77-97. doi:10.1007/BF02050307

68. Kronborg O. To lay open or excise a fistula-in-ano: a randomized trial. Br J Surg. 1985;72(12):970. doi:10.1002/bjs.1800721214

69. García-Aguilar J, Belmonte C, Wong DW, et al. Cutting seton versus two-stage seton fistulotomy in the surgical management of high anal fistula. Br J Surg. 1998;85(2):243-245. doi:10.1046/j.1365-2168.1998.00504.x

70. Cavanaugh M, Hyman N, Osler T. Fecal incontinence severity index after fistulotomy: a predictor of quality of life. Dis Colon Rectum. 2002;45(3):349-353. doi:10.1007/s10350-004-6182-5

71. Williams JG, Farrands PA, Williams AB, et al. The treatment of anal fistula: ACPGBI position statement. Colorectal Dis. 2007;9 Suppl 4:18-50. doi:10.1111/j.1463-1318.2007.01372.x

72. Ritchie RD, Sackier JM, Hodde JP. Incontinence rates after cutting seton treatment for anal fistula. Colorectal Dis. 2009;11(6):564-571. doi:10.1111/j.1463-1318.2008.01713.x

73. Pearl RK, Andrews JR, Orsay CP, et al. Role of the seton in the management of anorectal fistulas. Dis Colon Rectum. 1993;36(6):573-577. doi:10.1007/BF02049863

74. Mentes BB, Oktemer S, Tezcaner T, et al. Long-term results of bedside fistulotomy with anal dilatation for recurrent and complex perianal fistulas. Tech Coloproctol. 2006;10(3):197-200. doi:10.1007/s10151-006-0281-1

75. Rojanasakul A, Pattanaarun J, Sahakitrungruang C, Tantiphlachiva K. Total anal sphincter saving technique for fistula-in-ano; the ligation of intersphincteric fistula tract. J Med Assoc Thai. 2007;90(3):581-586. PMID: 17427539

76. Yassin NA, Hammond TM, Lunniss PJ, Phillips RK. Ligation of the intersphincteric fistula tract in the management of anal fistula. A systematic review. Colorectal Dis. 2013;15(5):527-535. doi:10.1111/codi.12107

77. Tan KK, Tan IJ, Lim FS, et al. The anatomy of failures following the ligation of intersphincteric tract technique for anal fistula: a review of 93 patients over 4 years. Dis Colon Rectum. 2011;54(11):1368-1372. doi:10.1097/DCR.0b013e31822bb55e

78. Aguilar PS, Plasencia G, Hardy TG Jr, et al. Mucosal advancement in the treatment of anal fistula. Dis Colon Rectum. 1985;28(7):496-498. doi:10.1007/BF02560228

79. Balciscueta Z, Uribe N, Balciscueta I, et al. Rectal advancement flap for the treatment of complex cryptoglandular anal fistulas: a systematic review and meta-analysis. Int J Colorectal Dis. 2017;32(5):599-609. doi:10.1007/s00384-017-2779-7

80. Ellis CN, Clark S. Effect of tobacco smoking on advancement flap repair of complex anal fistulas. Dis Colon Rectum. 2007;50(4):459-463. doi:10.1007/s10350-006-0839-6

81. Meinero P, Mori L. Video-assisted anal fistula treatment (VAAFT): a novel sphincter-saving procedure for treating complex anal fistulas. Tech Coloproctol. 2011;15(4):417-422. doi:10.1007/s10151-011-0769-2

82. Emile SH, Elfeki H, Shalaby M, Sakr A. A Systematic review and meta-analysis of the efficacy and safety of video-assisted anal fistula treatment (VAAFT). Surg Endosc. 2018;32(4):2084-2093. doi:10.1007/s00464-017-5905-2

83. Mendes CR, Ferreira LS, Sapucaia RA, Lima MA. Video-assisted anal fistula treatment: technical considerations and results of the first Brazilian experience. Arq Bras Cir Dig. 2014;27(1):77-81. doi:10.1590/s0102-67202014000100018

84. Sentovich SM. Fibrin glue for all anal fistulas. J Gastrointest Surg. 2001;5(2):158-161. doi:10.1016/s1091-255x(01)80329-x

85. Champagne BJ, O'Connor LM, Ferguson M, et al. Efficacy of anal fistula plug in closure of cryptoglandular fistulas: long-term follow-up. Dis Colon Rectum. 2006;49(12):1817-1821. doi:10.1007/s10350-006-0755-9

86. Panes J, Garcia-Olmo D, Van Assche G, et al. Expanded allogeneic adipose-derived mesenchymal stem cells (Cx601) for complex perianal fistulas in Crohn's disease: a phase 3 randomised, double-blind controlled trial. Lancet. 2016;388(10051):1281-1290. doi:10.1016/S0140-6736(16)31203-X

87. Present DH, Rutgeerts P, Targan S, et al. Infliximab for the treatment of fistulas in patients with Crohn's disease. N Engl J Med. 1999;340(18):1398-1405. doi:10.1056/NEJM199905063401804

88. Gionchetti P, Dignass A, Danese S, et al. 3rd European Evidence-based Consensus on the Diagnosis and Management of Crohn's Disease 2016: Part 2: Surgical Management and Special Situations. J Crohns Colitis. 2017;11(2):135-149. doi:10.1093/ecco-jcc/jjw169

89. Lowry AC, Thorson AG, Rothenberger DA, Goldberg SM. Repair of simple rectovaginal fistulas. Influence of previous repairs. Dis Colon Rectum. 1988;31(9):676-678. doi:10.1007/BF02552585

90. Seow-Choen F, Nicholls RJ. Anal fistula. Br J Surg. 1992;79(3):197-205. doi:10.1002/bjs.1800790305

91. Londono-Schimmer EE, Garcia-Duperly R, Nicholls RJ, et al. Overlapping anal sphincter repair for faecal incontinence due to sphincter trauma: five year follow-up functional results. Int J Colorectal Dis. 1994;9(2):110-113. doi:10.1007/BF00699423

92. Tjandra JJ, Chan MK, Yeh CH, Murray-Green C. Sacral nerve stimulation is more effective than optimal medical therapy for severe fecal incontinence: a randomized, controlled study. Dis Colon Rectum. 2008;51(5):494-502. doi:10.1007/s10350-007-9103-5

93. Banerjee AK. Sexual problems after surgery for rectal cancer. Aust N Z J Surg. 1999;69(8):562-566. doi:10.1046/j.1440-1622.1999.01642.x

94. D'Haens G, Baert F, van Assche G, et al. Early combined immunosuppression or conventional management in patients with newly diagnosed Crohn's disease: an open randomised trial. Lancet. 2008;371(9613):660-667. doi:10.1016/S0140-6736(08)60304-9

95. Williams AB, Steele SR, Hyman N, et al. Practice parameters for the treatment of perianal abscess and fistula-in-ano. Dis Colon Rectum. 2016;59(12):1117-1133. doi:10.1097/DCR.0000000000000733

---

Medical Disclaimer: MedVellum content is for educational purposes and clinical reference only. Clinical decisions must be individualized based on patient-specific circumstances, local guidelines, and consultation with appropriate specialists. This content does not replace clinical judgment or formal medical training.