Common anorectal disorders: fissure = linear anoderm tear with sentinel skin tag; fistula = epithelialized tract from anal gland to skin.
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Question 1GastrointestinalMedium
A 35-year-old man with Crohn disease maintained on adalimumab presents with 4 days of worsening anal pain. He is afebrile with stable vital signs. Perianal examination shows an external fistula opening with purulent discharge, and palpation reveals an exquisitely tender, fluctuant swelling adjacent to the anal verge. Which of the following is the most appropriate next step in management?
- ASurgical drainage with seton placement
- BEscalation of adalimumab to weekly dosing
- CSubstitution of azathioprine for adalimumab
- DIntravenous broad-spectrum antibiotics
Reveal answer & full explanation
Correct answer: A — Surgical drainage with seton placement
- ASurgical drainage with seton placement✓
- BEscalation of adalimumab to weekly dosing
- CSubstitution of azathioprine for adalimumab
- DIntravenous broad-spectrum antibiotics
Why Surgical drainage with seton placement is correct
- A tender, fluctuant perianal swelling with a purulently draining fistula in Crohn disease is a perianal abscess complicating fistulizing disease
- A fluctuant abscess is a closed-space infection that requires prompt incision and drainage; a draining (non-cutting) seton is placed through the fistula tract at the same sitting to keep it open and prevent recurrent abscess
- Source control comes first: biologic therapy should not be started or escalated over undrained perianal sepsis
- The accepted sequence, per current AGA and ACG guidance on perianal fistulizing Crohn disease, is examination under anesthesia with drainage and seton placement, pelvic MRI to map the tract, then optimization of anti-tumor necrosis factor (anti-TNF) therapy with adjunctive antibiotics
Why the others are wrong
- Escalation of adalimumab to weekly dosing — anti-TNF optimization is appropriate for fistulizing disease, but escalating a biologic over an undrained collection can worsen the infection; the step is premature until source control is achieved (right-diagnosis-wrong-step)
- Substitution of azathioprine for adalimumab — a maintenance immunosuppression change does nothing for the acute abscess, and thiopurines are less effective than anti-TNF therapy for fistulizing perianal disease (premature closure on a medication change)
- Intravenous broad-spectrum antibiotics — antibiotics are an adjunct, but a fluctuant collection cannot be cleared without drainage; this catches the learner who anchors on the signs of infection and skips source control (anchoring)
Question 2GastrointestinalMedium
A 32-year-old man reports 3 months of sharp pain with defecation and bright red blood on the toilet paper. He has a history of chronic constipation and strains during bowel movements. On exam, gentle external traction reveals a longitudinal tear in the posterior midline of the anal canal with a small sentinel skin tag. He has been managing with sitz baths, increased fiber, and topical nifedipine, but symptoms have not resolved. Which of the following is the most likely diagnosis?
- AAcute anal fissure
- BAnal fistula
- CChronic anal fissure
- DCrohn-associated anal fissure
Reveal answer & full explanation
Correct answer: C — Chronic anal fissure
- AAcute anal fissure
- BAnal fistula
- CChronic anal fissure✓
- DCrohn-associated anal fissure
Why Chronic anal fissure is correct
- An acute anal fissure that persists beyond 6–8 weeks despite conservative therapy progresses to a chronic fissure.
- Chronic fissure is characterized by a sentinel skin tag externally, a hypertrophied anal papilla internally, and exposure of internal sphincter fibers at the base.
- Chronicity results from a hypertonic internal anal sphincter that perpetuates ischemia of the fissure bed.
Why the others are wrong
- Acute anal fissure — an acute fissure lasts less than 6–8 weeks, has no sentinel skin tag, and heals with the fiber, sitz baths, and topical nifedipine that have already failed over 3 months here.
- Anal fistula — typically follows drainage of a cryptoglandular abscess and presents with chronic purulent drainage, not pain with defecation.
- Crohn-associated anal fissure — Crohn fissures are typically lateral, multiple, deep, or relatively painless and travel with diarrhea, weight loss, or perianal fistulizing disease, rather than an isolated posterior-midline tear from chronic straining.
Additional high-yield points
- When chronic fissure fails medical therapy, lateral internal sphincterotomy is the surgical gold standard.
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Risk factors
- Anal fissure: constipation with hard, large stools; prolonged diarrhea; childbirth; receptive anal intercourse; Crohn disease (multiple, lateral, or atypical fissures); HIV; TB; syphilis; anal cancer
- Anal fistula: prior perianal abscess (most common); Crohn disease; tuberculosis; hidradenitis suppurativa; trauma; pelvic radiation; malignancy
- Common to both: chronic constipation, diarrhea, smoking, IBD
Pathophysiology
Fissure: forceful passage of hard stool tears the anoderm; resulting hypertonia of the internal anal sphincter reduces blood flow to the posterior midline (a watershed) → ischemia prevents healing → chronic fissure with sentinel skin tag and hypertrophied anal papilla. Fistula: cryptoglandular theory — obstruction of an anal gland at the dentate line leads to abscess in the intersphincteric space; abscess decompresses through one of several anatomic planes, leaving an epithelialized tract (Parks classification: intersphincteric, transsphincteric, suprasphincteric, extrasphincteric).
Clinical presentation
Symptoms
- Fissure: severe sharp pain with defecation lasting minutes to hours after passing stool; bright red blood on toilet paper or coating stool; pain often leads to stool withholding, worsening constipation
- Fistula: persistent or intermittent drainage of pus, mucus, or stool from a perianal opening; recurrent perianal abscesses; perianal itching or irritation; usually NOT severely painful unless an abscess is reaccumulating
Signs / physical exam
- Fissure: linear tear in the posterior (90% in men, 75% in women) or anterior (10-25%, more common in women, especially postpartum) midline. Lateral fissures suggest secondary cause (Crohn, HIV, TB, malignancy)
- Chronic fissure: sentinel skin tag externally, hypertrophied anal papilla internally, visible internal sphincter fibers at the base
- Fistula: external skin opening with drainage, palpable cord-like tract; Goodsall rule predicts internal opening location
- Exam typically requires only inspection and gentle digital exam; anoscopy may be deferred for acute fissures due to pain
Classic findings
Goodsall rule: external openings anterior to a transverse line through the anus connect to the internal opening via a straight radial tract; posterior external openings curve to the posterior midline.
Differential diagnosis
- Hemorrhoid (thrombosed external) — Tender bluish mass at anal verge; not a linear tear
- Perianal abscess — Tender fluctuant mass with erythema and fever; precedes fistula
- Anal cancer (squamous cell carcinoma) — Indurated ulcer, lymphadenopathy; biopsy any nonhealing 'fissure'
- Crohn perianal disease — Multiple complex fistulae, lateral or large 'elephant ear' fissures, edematous skin tags
- Hidradenitis suppurativa — Recurrent skin abscesses with sinus tracts in apocrine areas (groin, axilla, buttocks)
- Pilonidal disease — Located in natal cleft above coccyx, not at anal verge; midline pits with hair
- Sexually transmitted infections (syphilis, herpes, LGV) — Multiple ulcers, painful or painless; lymphadenopathy; serologies/swab
Diagnostic workup
Diagnostic criteria
Both are clinical diagnoses based on inspection. Atypical features (lateral, multiple, painless, indurated, or nonhealing) require biopsy to exclude malignancy or Crohn disease.
Labs
- Usually not required for typical fissure
- Consider CBC, CRP, ESR, fecal calprotectin, IBD serologies if Crohn suspected (atypical, multiple, recurrent, or lateral fissures; complex fistulae)
- HIV, RPR, gonorrhea/chlamydia, HSV PCR if STI risk factors
Imaging
- Fissure: clinical diagnosis; no imaging required
- Fistula: MRI pelvis (preferred) or endoanal ultrasound for complex, recurrent, or Crohn-associated fistulae to map the tract and identify additional collections
- Examination under anesthesia (EUA) ± fistulography for surgical planning
- Colonoscopy if Crohn disease suspected
Complications
- Anal fissure: chronic fissure with stenosis, chronic pain, fecal impaction from withholding
- Anal fistula: recurrent abscesses, sepsis (especially diabetic or immunocompromised), persistent drainage, fecal incontinence (treatment-related)
- Fournier gangrene (rare necrotizing perineal infection)
- Sphincter injury and incontinence after sphincterotomy or aggressive fistulotomy
- Anal stenosis after over-aggressive surgery
- Malignant transformation (rare; suspect with chronic nonhealing lesions or long-standing Crohn fistulae)
PANCE pearls
- Posterior midline fissure with pain after defecation in a young adult — classic; treat conservatively with fiber, sitz baths, and topical CCB.
- Lateral or multiple fissures should prompt evaluation for Crohn, HIV, TB, syphilis, or malignancy.
- Drain perianal abscesses immediately — antibiotics alone are not enough.
- Goodsall rule: anterior external openings track radially; posterior openings curve to the posterior midline.
- Avoid lateral internal sphincterotomy in women with prior obstetric injury, patients with IBD, and patients with baseline incontinence — botulinum toxin is a safer first-line surgical alternative.
References
- ASCRS 2017 — American Society of Colon and Rectal Surgeons Clinical Practice Guidelines for the Management of Anal Fissures (Stewart et al., Dis Colon Rectum 2017)
- ASCRS 2016 — ASCRS Clinical Practice Guideline for the Management of Anorectal Abscess, Fistula-in-Ano, and Rectovaginal Fistula (Vogel et al., Dis Colon Rectum 2016)
- ACG 2018 — ACG Clinical Guideline: Management of Crohn's Disease in Adults (Lichtenstein et al., Am J Gastroenterol 2018) — perianal Crohn section