Common anorectal disorders: fissure = linear anoderm tear with sentinel skin tag; fistula = epithelialized tract from anal gland to skin.
Also known as: anal fissure, anal fistula, fistula-in-ano, perianal fistula
Overview
Anal fissure: a longitudinal tear in the squamous lining (anoderm) of the distal anal canal, typically along the posterior midline. Anal fistula (fistula-in-ano): an abnormal epithelialized tract connecting the anal canal (internal opening at a crypt) with the perianal skin (external opening), almost always developing from a prior cryptoglandular abscess.
Epidemiology
Fissure: peak ages 15-40, equal sex distribution; estimated lifetime risk ~10%. Fistula: incidence ~1-2 per 10,000; male predominance (2:1); commonly follows perianal abscess — about 30-50% of abscesses develop into fistulae.
Try two board-style Anal Fissure and Anal Fistula questions
Real questions from the FirstPassPA bank, with the full explanation. Pick an answer — no signup, no email.
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
BSubstitution of azathioprine for adalimumab
CEscalation of adalimumab to weekly dosing
DIntravenous broad-spectrum antibiotics
EAddition of oral prednisone to adalimumab
Reveal answer & full explanation
Correct answer: A — Surgical drainage with seton placement
ASurgical drainage with seton placement✓
BSubstitution of azathioprine for adalimumab
CEscalation of adalimumab to weekly dosing
DIntravenous broad-spectrum antibiotics
EAddition of oral prednisone to adalimumab
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)
Addition of oral prednisone to adalimumab — systemic corticosteroids are a common reflex for a Crohn flare, but they do not heal fistulizing perianal disease and, given over an undrained collection, can worsen the perianal sepsis; source control must come first (reflex-steroids-for-a-flare)
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?
AInternal hemorrhoids
BCrohn-associated anal fissure
CChronic anal fissure
DAcute anal fissure
EAnal fistula
Reveal answer & full explanation
Correct answer: C — Chronic anal fissure
AInternal hemorrhoids
BCrohn-associated anal fissure
CChronic anal fissure✓
DAcute anal fissure
EAnal fistula
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.
Internal hemorrhoids — shares the constipation, straining, and bright red blood on the toilet paper, and the sentinel tag can be mistaken for hemorrhoidal tissue, but uncomplicated internal hemorrhoids arise above the dentate line and bleed painlessly; sharp pain with defecation and a visible posterior-midline tear identify a fissure.
Additional high-yield points
When chronic fissure fails medical therapy, lateral internal sphincterotomy is the surgical gold standard.
That's 2. Get 7,700+ more.
Unlock the full FirstPassPA bank: 7,700+ board-style questions, flashcards, and an AI tutor that explains every answer. Your 7-day free trial includes everything, and there's no credit card required.
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, 7,700+ board-style questions, flashcards, and an AI tutor. Your 7-day free trial includes everything, and there's no credit card required.
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
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
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
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 2023 — The American Society of Colon and Rectal Surgeons Clinical Practice Guidelines for the Management of Anal Fissures (Davids JS et al., Dis Colon Rectum 2023;66:190-199)
ASCRS 2022 — The American Society of Colon and Rectal Surgeons Clinical Practice Guidelines for the Management of Anorectal Abscess, Fistula-in-Ano, and Rectovaginal Fistula (Gaertner WB et al., Dis Colon Rectum 2022;65:964-985)
ACG 2025 — ACG Clinical Guideline: Management of Crohn's Disease in Adults (Lichtenstein GR et al., Am J Gastroenterol 2025;120:1225-1264) — perianal Crohn section
Practice Gastrointestinal questions on FirstPassPA
Turn this outline into retention. 7,700+ board-style questions with an AI tutor that explains every answer — free to start, no card required.
Educational use only. This outline is a study aid for PA students and is not medical advice or a substitute for clinical judgment. FirstPassPA is an independent study tool and is not affiliated with, endorsed by, or sponsored by NCCPA or PAEA. PANCE® and PANRE® are registered trademarks of the National Commission on Certification of Physician Assistants; End of Rotation™ is a program of the Physician Assistant Education Association.