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OverviewAetiologyPathophysiologyClinical features and red flagsInvestigationsDifferential diagnosisManagementComplicationsMonitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Anal fissure

Gastroenterology and hepatology · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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Time-critical presentation

A fissure itself rarely causes physiological instability. Fever, spreading erythema, fluctuance, immunocompromise with severe pain, necrosis, inability to examine because pain is disproportionate, or a suspicious indurated ulcer requires urgent assessment for abscess, Fournier gangrene or malignancy.

Overview

Recognise a typical anal fissure, identify atypical secondary causes, and sequence bowel regulation, topical sphincter relaxation and continence-preserving specialist intervention.

A fissure is a linear tear in the anoderm, usually initiated by mechanical trauma. Internal sphincter spasm reduces local perfusion and maintains pain and non-healing, creating a cycle in which fear of defaecation worsens constipation.

The central decision is whether this is a typical primary midline fissure that can begin conservative care, or an atypical ulcer signalling Crohn disease, infection, trauma or cancer. Pain pattern and inspection matter more than the label attached by the patient.

Treatment should heal the tear while preserving continence. Chemical sphincter relaxation precedes irreversible division in most chronic cases, and specialist assessment should be individualised for pregnancy, breastfeeding, previous anorectal surgery, low resting pressure or pre-existing leakage.

Key points

  • The classic symptom is sharp tearing pain during defaecation followed by burning or spasm lasting minutes to hours, often with a small amount of bright blood.
  • Most primary fissures are posterior midline; an anterior fissure can occur, particularly after childbirth, but lateral or multiple fissures require investigation for secondary disease.
  • Chronic fissures show exposed sphincter fibres, a sentinel skin tag or hypertrophied anal papilla and persist despite basic bowel measures.

Aetiology

01

Local mucosal trauma

Hard stool, constipation, childbirth or repeated diarrhoea can split the anoderm, usually in the posterior midline.

02

Sphincter hypertonia

Raised internal anal sphincter tone and impaired local perfusion promote persistence after the initial tear, particularly in chronic primary fissure.

03

Secondary fissuring

Crohn disease, infection, malignancy, trauma or inflammatory dermatosis should be considered when fissures are multiple, lateral, painless or otherwise atypical.

Pathophysiology

  1. 1
    Anodermal tear

    Passage of stool disrupts the sensitive distal anal lining, exposing fibres and producing sharp defaecation-related pain and bright bleeding.

  2. 2
    Reflex sphincter spasm

    Pain triggers internal sphincter contraction, increasing resting pressure and making subsequent stool passage more traumatic and delays healing.

  3. 3
    Ischaemic non-healing cycle

    Sustained spasm reduces anodermal blood flow, preventing healing and producing chronic induration, a sentinel tag and recurrent tearing.

Clinical features and red flags

Acute primary fissure

A fresh posterior midline tear accompanies sharp defaecatory pain and scant bright blood, often after a hard stool. The surrounding tissue lacks chronic fibrotic features.

Chronic hypertonic fissure

Persistent pain with a deep ulcer, visible internal sphincter fibres, sentinel pile or hypertrophied papilla suggests non-healing maintained by sphincter spasm and reduced perfusion.

Atypical location or numberRed flag

Lateral, multiple, painless, irregular or broad ulcers raise Crohn disease, HIV-related or sexually transmitted infection, tuberculosis, haematological disease, trauma or anal cancer and warrant specialist assessment.

Abscess rather than fissureRed flag

Constant throbbing pain, fever, swelling, fluctuance or systemic illness is not explained by a simple fissure and requires urgent search for occult perianal sepsis.

Low-pressure fissure

A patient with previous obstetric sphincter injury, anorectal surgery, older age or baseline leakage may have reduced sphincter pressure; dividing muscle can worsen continence and alternative repair may be safer.

Child or postpartum context

Constipation is common in children, while pregnancy and birth injury influence medicine and procedure choices. Use age-specific or maternity guidance rather than copying an adult surgical pathway.

Investigations

  1. 01
    Gentle perianal inspectionFirst step
    Why
    Confirm site, chronic features and competing visible pathology.
    Interpretation and limitations
    A linear midline tear with concordant pain supports primary fissure. Document sentinel tag, exposed fibres, multiple ulcers, induration, discharge or pigmentation; suspicious tissue needs specialist biopsy planning.
  2. 02
    Digital rectal examination when tolerable
    Why
    Assess a mass, sphincter tone and another rectal source.
    Interpretation and limitations
    Defer in a very painful obvious acute fissure if it will not change immediate care. Under anaesthesia or specialist conditions, low tone influences whether sphincterotomy is safe.
  3. 03
    Anoscopy, proctoscopy or examination under anaesthesia
    Why
    Inspect when diagnosis is uncertain or treatment has failed.
    Interpretation and limitations
    This can reveal internal sepsis, proctitis, Crohn changes, a tumour or another lesion. Examination under anaesthesia permits biopsy or treatment without forcing an intolerable clinic examination.
  4. 04
    Targeted infection testing
    Why
    Investigate secondary fissure according to exposure and appearance.
    Interpretation and limitations
    Use sexual-health testing for syphilis, herpes, HIV or other infection when indicated; consider tuberculosis tests with epidemiological risk. Avoid indiscriminate swabs that

Differential diagnosis

01

Thrombosed external haemorrhoid

A sudden tender blue perianal lump causes constant pain rather than the characteristic cutting pain during and after defaecation.

02

Perianal abscess

Progressive throbbing pain, fever, focal swelling or deep tenderness suggests sepsis requiring drainage rather than sphincter-relaxing therapy.

03

Crohn disease or anal cancer

Multiple lateral ulcers, fistulae, induration, a mass or systemic bowel features require biopsy or specialist assessment for secondary disease.

Management

01InitialTypical acute fissure careFirst stepA concordant painful midline tear without secondary-disease features.+
  1. 1Explain the pain–spasm–constipation cycle, provide gentle hygiene advice and offer warm shallow bathing and non-constipating analgesia for symptom relief.
  2. 2Make stool consistently soft using gradual dietary fibre, adequate fluids and a formulary laxative; address diarrhoea as actively as constipation when it is the trigger.
  3. 3Avoid repeated traumatic examinations and review within an agreed interval to confirm pain and bleeding are settling and the patient is passing stool without fear.
  4. 4EscalationEscalate earlier for atypical site, persistent bleeding, systemic symptoms, immune compromise, inflammatory bowel symptoms or a suspicious indurated edge.
02ChronicChemical sphincter relaxationPersistent typical fissure despite stool optimisation or chronic examination features.

Complications

01

Chronic non-healing fissure

Persistent ischaemia produces exposed sphincter fibres, hypertrophied anal papilla and a sentinel skin tag, making simple bowel regulation less effective.

02

Pain-constipation cycle

Fear of defaecation leads to withholding and harder stool, amplifying trauma, functional impairment and reduced food or fluid intake.

03

Treatment-related continence harm

Over-aggressive sphincter division can cause flatus or stool leakage, so baseline continence and obstetric or surgical injury should shape intervention.

Monitoring and follow-up

  • Ask about pain during and after defaecation, bleeding, stool form, avoidance behaviour and adherence rather than judging success from one visual check.
  • During topical vasodilator therapy, monitor headache, postural symptoms, skin reaction and concurrent vasoactive medicines, adjusting through the current prescribing guidance.
  • Confirm sustained symptom improvement and clinical healing after the planned course; recurrence should trigger reassessment of bowel drivers and secondary causes.
  • Before and after a procedure, document flatus, liquid and solid-stool continence so new dysfunction is recognised and managed promptly.
  • For atypical fissure, track the underlying Crohn, infectious or malignant diagnosis through the relevant specialist service rather than treating only the tear.

Special situations

Pain continues after stool

Internal sphincter spasm explains the characteristic burning that persists after defaecation; painless bleeding alone is less typical and needs another explanation.

A tag is not a haemorrhoid

The sentinel skin tag of a chronic fissure may be mistaken for an external haemorrhoid. The associated linear ulcer and pain pattern identify the process.

Location tests the diagnosis

Posterior midline disease is common. A lateral or multiple ulcer should slow the clinician down and prompt investigation for inflammatory, infectious or neoplastic disease.

Diltiazem counselling matters

Topical diltiazem is familiar in UK colorectal practice but remains an off-label use; name that fact, explain alternatives and follow the local formulary.

Healing and symptoms can diverge

A patient may become nearly asymptomatic before complete epithelial healing, while a visible scar may persist after clinical recovery. Review the whole clinical course.

Pressure directs surgery

Sphincterotomy can be highly effective in hypertonic fissure but is poorly matched to a patient with low resting pressure or an occult obstetric defect.

Common pitfalls

  1. 01

    Forcing a digital rectal examination through a clearly visible acutely painful fissure.

  2. 02

    Calling a lateral indurated ulcer an ordinary primary fissure.

  3. 03

    Prescribing topical diltiazem without explaining that the use is off-label.

  4. 04

    Stopping stool-softening measures as soon as pain improves.

  5. 05

    Repeating topical therapy indefinitely while missing Crohn disease, infection or cancer.

  6. 06

    Offering sphincterotomy without documenting continence and obstetric or surgical history.

Practice

Two practice questions

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Question 1 of 2
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Gastroenterology and hepatologyOriginal SBA

Atypical fissure location

A 42-year-old has recurrent diarrhoea, weight loss and a painful broad lateral anal ulcer. There is no typical posterior midline tear. What is the most appropriate clinical interpretation?

Choose one answer, then submit
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Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • ACPGBI anal fissure guidelineCurrent specialist guidance including special circumstances.
  • BNF anal fissure treatment summaryLicensed treatment and prescribing cautions.
  • NICE topical diltiazem evidence summaryEvidence and off-label status for two percent topical diltiazem.
  • NHS anal fissure overviewSymptoms, self-care and procedural overview for UK patients.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom
  • Constipation and hard stool are common triggers, but recurrent diarrhoea, postpartum injury, Crohn disease, sexually transmitted infection, tuberculosis and malignancy also matter.
  • A gentle visual diagnosis is often enough; forcing digital rectal examination or proctoscopy through severe acute pain adds little and can worsen spasm.
  • First make stool soft and easy to pass, optimise fibre and fluid, avoid straining and use warm bathing and simple analgesia for comfort.
  • Topical glyceryl trinitrate is licensed for chronic fissure; topical diltiazem is used off-label in UK practice and requires explicit counselling and local-formulary confirmation.
  • Botulinum toxin or lateral internal sphincterotomy may help refractory hypertonic fissure, but baseline continence, obstetric injury and a hypotensive sphincter change the safest procedure.
    • do not
    answer a clinical question.
  • 05
    Lower gastrointestinal assessment
    Why
    Look for inflammatory bowel disease or colorectal neoplasia when red flags exist.
    Interpretation and limitations
    Faecal calprotectin, colonoscopy and imaging are selected by gastroenterology or colorectal teams; persistent diarrhoea, weight loss, anaemia or lateral ulceration makes a simple primary fissure less likely.
  • 06
    Anorectal manometry and endoanal ultrasound
    Why
    Define resting pressure and sphincter integrity before irreversible surgery in selected patients.
    Interpretation and limitations
    Low pressure or a structural defect argues against standard sphincter division and supports a continence-preserving strategy. These tests are not required for every straightforward acute fissure.
    • +
    1. 1Reconfirm the diagnosis, adherence and stool consistency, and assess blood pressure, headache susceptibility, interacting vasodilators, pregnancy status and baseline continence.
    2. 2Offer licensed topical glyceryl trinitrate according to the current BNF, or locally approved off-label topical diltiazem after explaining its licensing status and skin adverse effects.
    3. 3Continue bowel regulation throughout the full prescribed course and review both symptom resolution and clinical healing; stopping as soon as pain eases may permit relapse.
    4. 4Refer persistent, recurrent, atypical or low-pressure disease to colorectal specialists rather than repeating topical courses indefinitely without reconsidering the diagnosis.
    03RefractoryContinence-preserving procedural choiceConfirmed chronic fissure failing adequate medical treatment or causing unacceptable recurrent symptoms.+
    1. 1Document flatus and stool continence, obstetric history, previous pelvic or anal operations and examination findings; obtain physiology or endoanal imaging when it will alter the procedure.
    2. 2Discuss botulinum toxin as a temporary chemical sphincter treatment, including variable healing and possible repeat treatment, through the specialist pathway.
    3. 3For selected hypertonic primary fissure, consider tailored lateral internal sphincterotomy after explicit counselling about healing, recurrence and permanent continence risk.
    4. 4Prefer alternatives such as advancement flap in a hypotensive fissure or high-risk sphincter, guided by an experienced colorectal surgeon and current ACPGBI recommendations.
    Key medicines and prescribing safety4 treatments · regimens, roles and cautions+
    Removes recurrent mechanical trauma and supports healing throughout every treatment stage.

    Macrogol or another suitable laxative

    Titrate the locally preferred product until stool is soft and easily passed.

    Avoid indiscriminate escalation in diarrhoea, obstruction or impaction; counsel about fluid intake, bloating and dose adjustment, and use age-specific prescribing for children.

    Relaxes the internal sphincter and improves perfusion in chronic fissure.

    Glyceryl trinitrate rectal ointment

    Apply the licensed preparation according to current BNF instructions for the full course.

    Headache and dizziness are common; assess hypotension and nitrate interactions, avoid phosphodiesterase-5 combinations, and check pregnancy or breastfeeding advice before prescribing.

    Provides chemical sphincter relaxation with similar efficacy and fewer headaches for some patients.

    Topical diltiazem two percent

    Apply under the locally approved off-label regimen, commonly twice daily for several weeks.

    This use is unlicensed and requires informed discussion. Local irritation or dermatitis can occur; confirm formulation, duration and pregnancy or breastfeeding suitability with the current formulary.

    May reduce pain while bowel regulation and healing treatment take effect.

    Topical local anaesthetic

    Use a small amount for only a short symptom-relief course.

    It does not heal the fissure; prolonged use can cause sensitisation or obscure worsening pathology, so avoid repeated unsupervised courses and reassess persistent pain.