Pilonidal Disease & Anorectal Disorders
Surgery · General Surgery · lean revision notes
Pilonidal Disease & Anorectal Disorders
A high-frequency cluster in General Surgery covering pilonidal sinus, perianal abscess, anal fissure, haemorrhoids and pruritus ani. Questions hinge on anal canal anatomy (dentate line, sphincters, blood supply), clinical recognition, and the operation of choice for each lesion.
Surgical Anatomy of the Anal Canal (the foundation of every question)
The anal canal is ~4 cm long, extending from the anorectal ring to the anal verge. The dentate (pectinate) line is the single most examined landmark — it represents the embryological junction of endoderm (hindgut) and ectoderm (proctodeum).
| Feature | Above dentate line | Below dentate line |
|---|---|---|
| Origin | Endoderm (hindgut) | Ectoderm (proctodeum) |
| Epithelium | Columnar/transitional | Stratified squamous |
| Arterial supply | Superior rectal a. (from IMA) | Inferior rectal a. (from internal pudendal) |
| Venous drainage | Superior rectal → portal | Inferior rectal → systemic (IVC) |
| Lymphatics | Internal iliac nodes | Superficial inguinal nodes |
| Nerve supply | Autonomic (insensate) | Inferior rectal n. (somatic, painful) |
| Cancer type | Adenocarcinoma | Squamous cell carcinoma |
High-yield: Internal haemorrhoids (above dentate line) are painless and bleed; external haemorrhoids and fissures (below dentate line) are painful. The dentate line is the watershed for pain, lymphatic spread and tumour histology.
The internal anal sphincter is involuntary smooth muscle (continuation of circular rectal muscle, autonomic) — responsible for ~80% of resting tone. The external anal sphincter is voluntary striated muscle (inferior rectal nerve, S2–S4) — responsible for squeeze pressure. The anorectal ring (puborectalis + top of internal/external sphincters) is the surgically critical structure: division causes incontinence.
Anal columns of Morgagni contain the anal glands, which open into the anal crypts (of Morgagni) at the dentate line. Obstruction of these glands is the origin of cryptoglandular abscess and fistula — the unifying pathophysiology of anorectal sepsis.
Pilonidal Disease
Definition & pathophysiology
A pilonidal sinus is an acquired subcutaneous sinus containing hair and granulation tissue, classically in the natal (intergluteal) cleft about 5 cm posterior to the anus. "Pilonidal" = pilus (hair) + nidus (nest). It is now regarded as an acquired condition: loose hair drills into the skin through enlarged hair follicles, a foreign-body reaction forms, and a midline pit (the primary opening) develops, often with lateral secondary tracks.
Risk factors (the "Jeep disease" demographic):
- Young adult males (20–30 yrs), hirsute, dark, obese
- Sedentary occupation / prolonged sitting (drivers — hence "Jeep driver's disease", WWII)
- Deep natal cleft, poor hygiene, excessive sweating
- Family history
High-yield: Pilonidal sinus can also occur in the web spaces between fingers of barbers and dog groomers (interdigital pilonidal sinus) — classic exam trick proving it is acquired from external hair, not congenital.
Clinical features
Ranges from an asymptomatic midline pit → recurrent discharging sinus → acute pilonidal abscess (painful, tender, fluctuant swelling lateral to midline with surrounding cellulitis). Look for the tell-tale midline pits with hair tufts protruding.
Management
Acute abscess → incision and drainage (off-midline incision preferred), no primary closure.
Chronic disease — the menu of options:
- Conservative: hygiene, shaving/laser depilation, phenol injection into the tract (for limited disease).
- Excision + healing by secondary intention (lay open) — low recurrence but slow healing (weeks).
- Excision + primary midline closure — fast healing but highest recurrence and wound breakdown (wound under tension in the cleft).
- Off-midline / flattening-the-cleft flaps — preferred for recurrent/extensive disease:
- Karydakis flap (asymmetric, flattens cleft, moves scar off midline)
- Limberg (rhomboid) transposition flap
- Bascom procedure (cleft lift)
High-yield: The principle that reduces recurrence is keeping the scar OFF the midline and flattening the natal cleft. Midline primary closure has the worst recurrence.
Mnemonic — "Karydakis Keeps it off the Kleft."
Anorectal Abscess
Pathophysiology
~90% arise from cryptoglandular infection — obstruction and infection of an anal gland at the dentate line, with pus tracking along planes of least resistance. Other causes: Crohn's disease, trauma, malignancy, TB, immunosuppression (diabetes, HIV).
Classification by anatomical space (commonest → rarest)
| Type | Location | Frequency | Notes |
|---|---|---|---|
| Perianal | Subcutaneous, at anal verge | Most common (~60%) | Superficial, "pointing" red swelling |
| Ischiorectal (ischioanal) | Ischiorectal fossa | ~20% | Larger, may cross to form horseshoe abscess |
| Intersphincteric | Between internal & external sphincter | ~5% | Pain ++, often no external swelling; PR tenderness |
| Supralevator | Above levator ani | Rare | Pelvic source; deep, serious |
Clinical features
Severe, constant throbbing perianal pain, worse on sitting/defecation, with fever and a tender fluctuant swelling. Intersphincteric/supralevator abscesses may have no visible swelling — only severe pain and tenderness on PR examination.
Management
High-yield: Treatment of an anorectal abscess is prompt incision and drainage — NOT antibiotics. Antibiotics alone are inadequate and risk progression to Fournier's gangrene (necrotising fasciitis of the perineum, especially in diabetics).
Antibiotics are adjuncts when there is cellulitis, systemic sepsis, diabetes, immunosuppression or valvular heart disease. After drainage, ~30–50% develop a fistula-in-ano.
Flow: Severe perianal pain + fever → examine (EUA if intersphincteric suspected) → incision & drainage → send pus for culture/histology → look for/manage fistula at follow-up.
Fistula-in-Ano (closely linked)
An abnormal track lined by granulation tissue connecting the anal canal (internal opening, usually at dentate line crypt) to perianal skin (external opening). Usually the sequel of a drained abscess.
Goodsall's rule (predicts internal opening from external opening position, patient prone):
- External opening anterior to a transverse anal line → tract runs radially/straight to nearest crypt.
- External opening posterior → tract is curved, opening in the posterior midline.
High-yield mnemonic — "anterior = straight, posterior = curved" (think of a dog: nose straight ahead, tail curls).
Park's classification: intersphincteric (commonest) → transsphincteric → suprasphincteric → extrasphincteric.
Management: MRI / endoanal ultrasound to map the tract.
- Low fistula (below anorectal ring) → fistulotomy (lay open) — gold standard.
- High / complex fistula (involves significant sphincter) → seton placement (to preserve continence), LIFT procedure, or advancement flap. Fistulotomy of a high tract risks incontinence.
Anal Fissure
Definition
A longitudinal tear/ulcer in the anoderm distal to the dentate line. 90% lie in the posterior midline (least vascular, "watershed" zone supplied poorly by inferior rectal artery). Anterior fissures are more common in women (post-partum).
High-yield: Fissures off the midline (lateral/multiple) suggest secondary causes — Crohn's disease, TB, syphilis, HIV, leukaemia, anal cancer — and warrant biopsy.
Pathophysiology
A vicious cycle: hard stool tears anoderm → pain → internal anal sphincter spasm → reduced anodermal blood flow / ischaemia → impaired healing → chronicity. High resting anal pressure is central.
Clinical features
- Acute: intense, knife-like/tearing pain on defecation lasting minutes–hours, with bright red blood on the paper.
- Chronic (>6 weeks) triad: fissure + sentinel pile (skin tag) + hypertrophied anal papilla, with visible exposed internal sphincter fibres at the base. Patient often too tender for digital examination.
Management (stepwise)
First line (conservative, ~50% heal): high-fibre diet, stool softeners, sitz baths, adequate fluids.
Medical sphincter relaxation ("chemical sphincterotomy"):
- Topical GTN (0.2–0.4% glyceryl trinitrate) ointment — main side effect headache.
- Topical diltiazem / nifedipine (calcium channel blockers) — fewer headaches, now often preferred.
- Botulinum toxin injection into internal sphincter (temporary chemical denervation) for refractory cases.
Surgical (gold standard for chronic refractory fissure):
High-yield: Lateral internal sphincterotomy (LIS) is the surgical treatment of choice and the most effective treatment for chronic anal fissure. The main complication is flatus/minor faecal incontinence. Anal dilatation (Lord's procedure) is abandoned — uncontrolled, high incontinence.
| Treatment | Mechanism | Key point |
|---|---|---|
| GTN ointment | NO donor → smooth muscle relaxation | Headache; ~50–60% heal |
| Diltiazem/nifedipine | Ca²⁺ channel blocker | Fewer side effects |
| Botulinum toxin | Blocks ACh at sphincter | Reversible, for refractory |
| Lateral internal sphincterotomy | Divides distal internal sphincter | Most effective; risk of incontinence |
Haemorrhoids (Piles)
Definition & anatomy
Haemorrhoids are symptomatic enlargement and distal displacement of the normal anal cushions (vascular submucosal tissue aiding continence). Internal haemorrhoids classically lie at 3, 7 and 11 o'clock positions (lithotomy) — the "right anterior, right posterior, left lateral" primary cushions.
High-yield: Haemorrhoids are NOT varicose veins — they are arteriovenous sinusoids/cushions. Hence bleeding is bright red and arterial in nature.
Internal (above dentate line, painless, columnar) vs external (below dentate line, painful, squamous, somatic innervation). A thrombosed external haemorrhoid (perianal haematoma) presents as an acutely painful blue-purple lump.
Causes / risk factors
Constipation and straining, low-fibre diet, pregnancy, raised intra-abdominal pressure, portal hypertension (anorectal varices distinct from haemorrhoids), ageing.
Goligher grading of internal haemorrhoids (must memorise)
| Grade | Description |
|---|---|
| I | Project into lumen, bleed but do NOT prolapse |
| II | Prolapse on straining, reduce spontaneously |
| III | Prolapse on straining, require manual reduction |
| IV | Permanently prolapsed / irreducible (± thrombosis) |
Clinical features
Painless bright red rectal bleeding (on stool surface/dripping after defaecation), pruritus, mucus discharge, prolapse, sensation of lump. Pain implies thrombosis, fissure or external component.
High-yield: Never attribute rectal bleeding to haemorrhoids without excluding colorectal cancer. Patients >40 yrs, with altered bowel habit, weight loss or anaemia need colonoscopy/proctoscopy first.
Management by grade (stepwise)
Diagnosis tool: Proctoscopy is the investigation of choice to visualise internal haemorrhoids.
Flow: Grade I–II → conservative + office procedure → Grade III–IV / failed → surgery.
- Conservative (all grades, esp. I): high-fibre diet, fluids, stool softeners, avoid straining.
- Office / outpatient procedures (Grade I–II, some III):
- Rubber band ligation (Barron's bands) — most effective non-operative procedure; band placed on the base above the dentate line (insensate) — placing it too low causes severe pain.
- Sclerotherapy — injection of 5% phenol in almond/arachis oil into the submucosa above the haemorrhoid (good for grade I bleeding).
- Infrared coagulation / cryotherapy.
- Surgery (Grade III–IV, recurrent, large external component):
- Open haemorrhoidectomy (Milligan–Morgan) — gold standard, leaves skin bridges open.
- Closed haemorrhoidectomy (Ferguson).
- Stapled haemorrhoidopexy (MIPH / Longo) — for circumferential prolapse; less pain, but risk of recurrence/rectovaginal complications.
- Doppler-guided haemorrhoidal artery ligation (HAL/THD).
High-yield: Thrombosed external haemorrhoid within 48–72 hours of onset → surgical excision for rapid relief; if presenting late → conservative (analgesia, sitz baths) as pain is already settling.
Mnemonic for band complication danger: bands must go above the dentate line — "No pain above, pain below."
Pruritus Ani
Intense perianal itching, worse at night. Often a vicious itch–scratch cycle.
- Idiopathic (50–90%) — most common; faecal soiling/moisture, over-cleaning, dietary irritants (coffee, citrus, spicy food, tomatoes, chocolate, beer).
- Secondary: anorectal disease (fissure, fistula, haemorrhoids, skin tags), infection (threadworm/Enterobius in children — Sellotape/scotch-tape test, candida, tinea), dermatoses (psoriasis, lichen sclerosus, contact dermatitis), systemic (diabetes, jaundice), and anal/perianal neoplasia (Bowen's, Paget's, SCC) — biopsy persistent/atypical lesions.
Management: treat the underlying cause; meticulous hygiene without over-washing, keep area dry, avoid scented soaps and irritant foods, short-course low-potency topical steroid for inflammation.
High-yield: In a child with perianal itching, think threadworm (Enterobius vermicularis) → tape test → treat with albendazole/mebendazole and treat the whole family.
Key Differentials & Pitfalls
- Painless bright red bleeding: internal haemorrhoids — but rule out colorectal carcinoma in older patients.
- Painful defaecation + bleeding: anal fissure (most likely) vs thrombosed external pile.
- Recurrent perianal discharge: fistula-in-ano vs pilonidal sinus (location distinguishes — natal cleft vs anal verge) vs hidradenitis suppurativa vs Crohn's.
- Off-midline / atypical fissures: Crohn's, TB, malignancy.
- Perianal swelling with severe pain & fever: abscess (drain it; beware Fournier's gangrene in diabetics).
Recently asked / exam angle
- Dentate line significance: pain, blood supply, venous drainage (portal vs systemic), lymphatic spread (inguinal vs internal iliac), cancer type — a perennial single-best-answer.
- Goligher grading matched to management (e.g. "Grade I bleeding piles → sclerotherapy/banding"; "Grade IV → haemorrhoidectomy").
- Operation of choice for chronic anal fissure = lateral internal sphincterotomy; commonest site of fissure = posterior midline.
- Drug of choice / first medical line for fissure = topical GTN or diltiazem; complication of GTN = headache.
- Pilonidal sinus is acquired, occurs in barbers' web spaces, "Jeep disease"; flap procedures (Karydakis, Limberg) reduce recurrence by moving scar off midline.
- Goodsall's rule for fistula internal opening; MRI is investigation of choice for complex/high fistula.
- Anorectal abscess → incision and drainage (not antibiotics); Fournier's gangrene as a feared complication in diabetics.
- Phenol in almond oil (5%) for sclerotherapy; rubber band placed above dentate line to avoid pain.
- Child + perianal itch → threadworm, tape test.
Rapid revision
- Dentate line = endoderm/ectoderm junction → above it painless (autonomic, portal drainage, internal iliac nodes, adenocarcinoma); below it painful (somatic, systemic drainage, inguinal nodes, SCC).
- Internal sphincter = involuntary, 80% of resting tone; anorectal ring division = incontinence.
- Pilonidal sinus is acquired, mid-natal-cleft, young hirsute males; also occurs in barbers' interdigital web spaces.
- Recurrent/extensive pilonidal disease → off-midline flap (Karydakis/Limberg/Bascom); midline primary closure has the worst recurrence.
- Anorectal abscess → prompt incision & drainage; antibiotics are adjuncts; beware Fournier's gangrene.
- ~30–50% of drained abscesses → fistula-in-ano; map with MRI; low fistula → fistulotomy, high fistula → seton/LIFT.
- Goodsall's rule: anterior external opening → straight tract; posterior → curved to posterior midline.
- Anal fissure: 90% posterior midline; off-midline fissures → think Crohn's/TB/malignancy.
- Fissure treatment ladder: fibre/sitz baths → GTN/diltiazem → botulinum toxin → lateral internal sphincterotomy (most effective; risk of incontinence).
- Haemorrhoids are vascular cushions at 3, 7, 11 o'clock, not varicose veins; bleeding is bright red.
- Goligher grading I–IV: I bleed only, II reduce spontaneously, III need manual reduction, IV irreducible; treat by grade (sclerotherapy/banding for I–II, haemorrhoidectomy for III–IV).
- Proctoscopy diagnoses internal haemorrhoids; always exclude colorectal cancer in older patients with rectal bleeding; child with perianal itch = threadworm.