Anal Fissure

Overview

Anal fissure is a split in the skin of the distal anal canal. It presents with severe pain on defecation, like passing “glass shards”, and rectal bleeding. It is more frequently diagnosed in younger and middle-aged individuals. Anal fissures are mostly caused by passage of hard stool but can also be a result of other conditions, like Crohn’s disease.^1,2

Anorectal Anatomy

Anal canal – channel connecting the rectum to the anus, located within the anal triangle of the perineum, between the two ischioanal fossae.

Anal Sphincters

• Internal sphincter
  • Involuntary control – continuation of circular fibers of the colon so it receives autonomic supply
  • Surrounds upper 3/4 of anal canal
• External sphincter
  • Voluntary control
  • Surrounds entire length of anal canal
  • Consists of three parts – subcutaneous, superficial and deep

Intersphincteric plane

• Between external sphincter muscle laterally and the longitudinal muscle (inner sphincteric muscle) medially
• Contains anal glands
• Can be opened up surgically to provide access for operations on the sphincter muscles

Anal glands

• Apocrine glands
• Occasionally infected and act as a source of anal fistula

Dentate (pectinate) line

• Junction of the proximal and distal segments of the anal canal
• Divides the anus into proximal 2/3 and distal 1/3
• Situated at the middle of internal sphincter

Aetiology and Risk Factors

• Primary fissures: due to trauma
  • Constipation
  • Diarrhea
  • Vaginal delivery
  • Anal sex
• Secondary fissures: due to another condition
  • Crohn’s disease
  • Malignancy
  • Communicable disease (eg. HIV, syphillis, chlamydia)
  • Granulomatous disease (eg. extrapulmonary tuberculosis, sarcoidosis)

Pathophysiology

Acute trauma or another disease

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Internal anal sphincter spasm

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Local ischaemia

↓

Impaired healing

↓

Hard stool passage causing a skin tear that cannot heal

Classification

Based on aetiology:

• Primary: caused by local trauma in the context of anal spasm or high anal pressure; mostly located at posterior midline and sometimes at anterior midline
• Secondary: caused by another disease; occur at locations other than midline; if you see atypical location investigate for other diseases

Based on timeframe:

• Acute: less than 6 weeks; longitudinal tear in skin of distal anal canal
• Chronic: more than 6 weeks; often with stigmata of chronicity (hypertrophied anal papilla, skin tag, exposed internal sphincter fibers)

Clinical Manifestation

• Anal pain during and for one to two hours after defecation (due to persistent internal anal sphincter hypertonia) – distinguishing feature to other anal pain differentials
• Tearing sensation: described as “passing glass shards”
• Bright red blood: on stool or toilet paper
• Fear of defecation: due to severe pain

Examination

General inspection

• Visible fissure (90% posterior, 10% anterior; sometimes both are present “kissing fissures”).
• Stigmata of chronicity (in chronic fissures): exposed internal anal sphincter muscle fibers, skin tags, hypertrophied anal papillae.

Palpation: to reproduce anal pain if fissure cannot be visualised – performed to confirm diagnosis.

Differential Diagnosis

• Haemorrhoids
• Perianal ulcers or sores
• Anal fistula
• Solitary rectal ulcer syndrome

Investigations

Not usually indicated, unless diagnosis is uncertain or secondary fissure suspected 

Treatment

Medical management:

• Topical analgesia
• Stool softeners
• High fibre diet
• Sitz bath
• Topical vasodilators: nifedipine or glyceryl trinitrate (GTN)

Surgical management:

• Botulinum toxin (BOTOX): relaxes muscle and improves healing
• Lateral internal sphincterotomy: gold standard due to highest healing rate (>90%); sphincter muscle fibers are cut to reduce pressure and improve blood flow; can lead to incontinence in high-risk patients
• Anal advancement flap: skin flap created from skin around anus and used to cover fissure
• Fissurectomy: excision of anal fissure

Complications and Prognosis

Complication

• Sentinel skin tag (hypertrophied external skin margin)
• Hypertrophied anal papilla (internal end)
• Subcutaneous fistula or abscess (rare; due to secondary infection)
• Anal stenosis (from fibrosis and repeated scarring)
• Sphincter spasm and fibrosis → perpetuates pain and poor healing
• Incontinence (potential postoperative complication if sphincterotomy is excessive)

Prognosis

• Acute fissures
  • 90% heal with conservative management (stool softeners, topical nitrates, sitz baths)
  • Good prognosis if treated early
    
• Chronic fissures
  • Often recur or persist due to internal sphincter hypertonia
  • Require pharmacologic relaxation (nitrates, calcium-channel blockers) or lateral internal sphincterotomy for definitive cure
  • Excellent long-term outcomes (>90% success) with surgery, but minor incontinence may occur in 1–5%

References

1. Paluvoi N. Anal fissure: BMJ Best Practice; 2023 [updated 2023 Dec 22; cited 2025 Sep 28]. Available from: https://bestpractice.bmj.com/topics/en-gb/563. 

2. Gerbasi L, Ashurst JV. Anal Fissures: National Library of Medicine; 2025 [updated 2025 Sep 15; cited 2025 Sep 28]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK526063/. 

3. Davids JS, Hawkins AT, Bhama AR, Feinberg AE, Grieco MJ, Lightner AL, et al. The American Society of Colon and Rectal Surgeons Clinical Practice Guidelines for the Management of Anal Fissures. Disease of the Colon & Rectum. 2022;66(2):190-9. Doi: 10.1097/DCR.0000000000002664 

4. Madalinski MH. Identifying the best therapy for chronic anal fissure. World Journal of Gastrointestinal Pharmacology and Therapeutics. 2011;2(2):9-16. Doi: 10.4292/wjgpt.v2.i2.9 

5. Bleday R. Anal fissure: Medical management. Up To Date [updated 2023 May 19; cited 2025 Sep 28]. Available from: https://www.uptodate.com/contents/anal-fissure-medical-management. 

6. Stewart DB. Anal fissure: Clinical manifestations, diagnosis, prevention. Up To Date [updated 2025 Mar 19; cited 2025 Sep 28]. Available from: https://www.uptodate.com/contents/anal-fissure-clinical-manifestations-diagnosis-prevention.