Common anorectal disorders: fissure = linear anoderm tear with sentinel skin tag; fistula = epithelialized tract from anal gland to skin.
🔒 Free preview limit reached
Keep reading — start your free trial
You've read your 2 free diagnosis previews. Create your free account to unlock the full Anal Fissure and Anal Fistula outline — plus all 514 diagnoses, 3,500+ board-style questions, flashcards, and an AI tutor. Your 7-day free trial includes everything, and there's no credit card required.
Free to start · No credit card · Cancel anytime
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
Practice Gastrointestinal questions on FirstPassPA
Turn this outline into retention. 3,500+ board-style questions with an AI tutor that explains every answer — free to start, no card required.
Start studying free →
Browse all 514 diagnoses