Anus and anal canal: haemorrhoids, fissure, fistula, abscess, pilonidal sinus

Overview

Anal complaints (bleeding, pain, lumps, discharge, itching) are among the commonest reasons to see a surgeon. Most have benign causes, but rectal and anal cancer must be excluded before blaming piles.

Careful inspection, digital examination, proctoscopy and sigmoidoscopy diagnose most conditions. Painful conditions (fissure, abscess) may need examination under anaesthesia (EUA).

Surgical anatomy

• The anal canal is about 4 cm long, from the anorectal ring (puborectalis level, felt as a ridge on PR) to the anal verge.
• Internal sphincter: thickened circular smooth muscle, involuntary, autonomic; keeps resting tone; relaxed by nitric oxide. Pearly-white at surgery.
• External sphincter: striated, voluntary, supplied by the pudendal nerve (inferior rectal branch); red at surgery.
• Puborectalis keeps the anorectal angle, a key part of continence.
• Intersphincteric plane between them contains anal glands, the source of most abscesses and fistulas.
• Anal cushions: three vascular cushions (left lateral, right posterior, right anterior) that help seal the canal.

The dentate (pectinate) line

The line of anal crypts (of Morgagni) lies at the dentate line; anal glands open into these crypts.

Haemorrhoids (piles)

What they are

Symptomatic anal cushions that have slid down because their supporting tissue has weakened. Not simple varicose veins.

• Primary positions: 3, 7 and 11 o'clock with the patient in the lithotomy position.
• Internal haemorrhoids: above the dentate line, covered by mucosa.
• External "haemorrhoids": venous channels below the dentate line, usually noticed only when they thrombose (perianal haematoma).
• Interno-external: an internal pile extending below the line.

Predisposing factors: straining, low-fibre diet, constipation, pregnancy, obesity, prolonged sitting on the toilet, raised intra-abdominal pressure, ageing. Secondary causes include rectal carcinoma and pelvic masses.

Clinical features

• Bright red, painless bleeding, separate from the stool: on the paper or splashing in the pan. The earliest symptom.
• Prolapse, mucus discharge, itching, a feeling of incomplete emptying.
• Pain is unusual unless they prolapse and thrombose.
• Anaemia occasionally.

Management

Always exclude colon and rectal cancer (sigmoidoscopy; colonoscopy if over about 50, change in habit, anaemia or family history).

• Injection too deep can cause prostatitis, pelvic sepsis or rectovaginal fistula; pain on injection means the needle is too low.
• Banding can cause pain (if placed too near the dentate line), bleeding when the pile sloughs and, rarely, pelvic sepsis.

Complications of haemorrhoidectomy

Complications of haemorrhoids

• Strangulation and thrombosis of prolapsed piles: very painful, swollen, dark; treat with analgesia, rest, ice or warm baths, stool softeners; most settle in a few days; urgent haemorrhoidectomy is an option in experienced hands.
• Ulceration, gangrene, fibrosis; rarely portal pyaemia; anaemia.

Perianal haematoma (thrombosed external haemorrhoid)

• Sudden painful blue lump at the anal margin after straining or lifting.
• Within about 48 hours: incise under local anaesthetic and remove the clot.
• Later: conservative; it settles ("a painful, self-curing lesion" over about 5 days), may leave a skin tag.

Anal fissure

A longitudinal split in the anoderm below the dentate line.

• Site: posterior midline in most patients. Anterior fissures occur more in women (often after childbirth). Off-midline or multiple fissures suggest Crohn disease, TB, syphilis, HIV, herpes or carcinoma → biopsy.
• Cause: passage of a hard stool (or diarrhoea) tears the anoderm; internal sphincter spasm reduces blood flow to the posterior midline, so it fails to heal (an ischaemic ulcer).

Features

• Severe, sharp pain during and after defaecation, lasting minutes to hours. Patients fear opening their bowels → constipation → worse fissure.
• Bright red blood on the paper.
• On gentle parting of the buttocks the fissure is seen; PR is often impossible because of pain and spasm.
• Acute: shallow split, under about 6 weeks.
• Chronic: sentinel tag (pile) externally, indurated ulcer with internal sphincter fibres visible in the base, and a hypertrophied anal papilla internally.

Treatment

1. Conservative: fibre, fluids, stool softeners, warm baths, topical local anaesthetic.
2. Chemical sphincterotomy (relaxes the internal sphincter): GTN 0.2% ointment (headache is common) or diltiazem 2% (fewer side effects); botulinum toxin injection is an alternative.
3. Surgery if these fail: lateral internal sphincterotomy (divide the distal internal sphincter, up to the height of the fissure, at the lateral position, away from the fissure). Very effective but carries a risk of minor incontinence, especially in women.
4. Anal advancement flap for women or patients with low sphincter pressures.

Anorectal abscess

Most arise from infection of an intersphincteric anal gland (the cryptoglandular theory). Pus tracks:

• Down → perianal abscess (commonest, about 60%).
• Across the external sphincter → ischiorectal (ischioanal) abscess (about 30%).
• Up → intersphincteric or supralevator (pelvirectal) abscess.
• Around the canal → horseshoe abscess (usually posterior).

Other sources: infected skin (boils), Crohn disease, TB, cancer, trauma, pelvic sepsis spreading down. Diabetes and immunosuppression make abscesses aggressive.

Treatment: incision and drainage promptly (do not wait for fluctuation), usually under anaesthesia with EUA and sigmoidoscopy. Deroof with a cruciate incision, curette, send pus for culture and wall for histology. Antibiotics alone are not enough; add them for cellulitis, diabetes or immunosuppression. Do not probe forcefully for a fistula in the acute stage.

Fistula-in-ano

A chronic abnormal track lined by granulation tissue, from an internal opening in the anal canal (usually at the dentate line) to an external opening on the perianal skin.

• Most are cryptoglandular, following an abscess.
• Specific causes: Crohn disease, tuberculosis (common in Pakistan), lymphogranuloma venereum, actinomycosis, carcinoma, trauma, foreign body.
• Symptoms: recurrent discharge of pus or blood, itching, intermittent pain relieved when it drains; history of abscess.

Parks classification

"Low" fistulas cross little or no external sphincter; "high" fistulas cross most of it.

Goodsall rule

Draw a transverse line across the middle of the anus (patient in lithotomy):

• External opening anterior to the line → a short, straight, radial track to the nearest crypt.
• External opening posterior to the line → a curved track opening in the posterior midline (often a horseshoe).
• Exception: anterior openings more than about 3 cm from the anus may still curve to the posterior midline.

Investigations

• EUA with probing and hydrogen peroxide injected through the external opening to show the internal opening.
• Endoanal ultrasound shows sphincter integrity.
• MRI pelvis: gold standard for complex and recurrent fistulas (secondary tracks, horseshoe extensions).
• Sigmoidoscopy; biopsy; test for Crohn and TB where suspected.

Treatment

Pilonidal sinus

• A sinus in the natal cleft over the sacrum and coccyx containing loose hairs; "jeep disease".
• Acquired: shed hairs are drilled into the midline skin by friction and suction of the buttocks.
• Young adults (late teens to 20s), men, dark and hairy, sedentary jobs; interdigital form in barbers.
• One or more midline pits between the sacrococcygeal joint and the coccyx tip; lateral openings from secondary tracks; tracks usually run upwards (cephalad).
• Presents as recurrent abscess or chronic discharge.

Other conditions in brief

• Pruritus ani: poor hygiene, piles, fissure, threadworms, fungal infection, skin disease, diabetes; treat the cause, keep the area dry; avoid strong creams.
• Anal incontinence: obstetric sphincter injury (commonest in women), pudendal neuropathy, surgery (sphincterotomy, fistulotomy), neurological disease; endoanal ultrasound and manometry; treatment with diet, loperamide, biofeedback, sphincter repair.
• Anal stenosis: mostly after haemorrhoidectomy; dilators or anoplasty.
• Anal warts (HPV 6, 11): topical treatment or excision; associated with anal intraepithelial neoplasia.
• Proctalgia fugax: brief, severe night-time rectal cramps; harmless.

Anal cancer

• Usually squamous cell carcinoma, linked to HPV 16 and 18, HIV, immunosuppression and anal intraepithelial neoplasia.
• Presents with pain, bleeding, a mass or an ulcer, often mistaken for piles or fissure.
• Lymph spread to inguinal nodes (below the dentate line).
• First-line treatment: chemoradiotherapy (5-FU and mitomycin C; the Nigro regimen). Abdominoperineal resection is kept for persistent or recurrent disease. Small anal margin lesions may be excised locally.
• Adenocarcinoma of the canal is treated like low rectal cancer; anal melanoma is rare and has a very poor outlook.

Quick revision

• Dentate line: above painless, portal, internal iliac nodes; below painful, systemic, inguinal nodes.
• Piles: 3, 7, 11 o'clock; bright red painless bleeding; degrees 1–4.
• 1st–2nd: diet, injection, banding; 3rd–4th: haemorrhoidectomy with skin bridges.
• Perianal haematoma: evacuate if seen within 48 hours.
• Fissure: posterior midline; GTN/diltiazem → lateral internal sphincterotomy.
• Abscess: drain promptly; perianal commonest.
• Fistula: intersphincteric commonest; Goodsall; low → lay open, high → seton/LIFT/flap; MRI for complex.
• Pilonidal: natal cleft hair; drain off midline; excise with off-midline closure.
• Anal SCC: HPV; inguinal nodes; Nigro chemoradiotherapy.

Written by The House Job from standard references (Bailey & Love).

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