What is pilonidal sinus
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Pilonidal Sinus
Definition
A pilonidal sinus is a small hole or tunnel in the skin located in the natal cleft (the crease between the buttocks), overlying the sacrococcygeal region. The name comes from Latin: pilus (hair) and nidus (nest) - essentially a "nest of hair." It consists of one or more midline openings that communicate with a fibrous track lined by granulation tissue, with hair lying loosely within the lumen.
- Bailey and Love's Short Practice of Surgery, 28th Ed.
Clinical Photo
Pilonidal sinus showing the midline pit and a lateral sinus tract with granulation tissue. (Sabiston Textbook of Surgery)
Pathophysiology / How It Forms
The condition is acquired, not congenital. Evidence supporting the acquired origin:
- Interdigital pilonidal sinus is an occupational disease of hairdressers (hair puncturing the skin between fingers)
- The age of appearance is older than expected for a congenital lesion
- Hair follicles are rarely present in the walls of the sinus
- The pointed ends of hairs are directed toward the blind end of the sinus (indicating external penetration)
- The disease mostly affects hirsute men
Mechanism: Buttock friction and shearing forces allow shed or broken hairs that collect in the natal cleft to drill through the midline skin. Movement of the buttocks creates a vacuum effect, forcing loose hair into the skin through small cutaneous pits. The trapped hair triggers a foreign body reaction, causing local inflammation. This may become superinfected, forming a hair-filled abscess cavity. Secondary tracks may spread laterally, emerging at the skin as discharging openings.
- Sabiston Textbook of Surgery; Bailey and Love's
Who Gets It?
- Predominantly young people (typically late teens to mid-20s); rarely after age 40
- Males much more commonly than females (more hirsute)
- Dark-haired individuals more than blond
- Associated with: obesity, sedentary occupation (truck drivers, office workers), local irritation or trauma
- Affects approximately 70,000 patients annually in the United States
Clinical Presentations
Pilonidal disease exists on a spectrum:
| Presentation | Features |
|---|---|
| Asymptomatic pit | Incidental midline pit found without inflammation |
| Acute abscess | Painful, swollen, fluctuant swelling in the natal cleft; may have pus |
| Chronic sinus | Intermittent pain, swelling, and purulent or bloody discharge; history of recurrent abscesses |
All primary sinus openings are strictly in the midline, between the level of the sacrococcygeal joint and the tip of the coccyx. Lateral openings suggest secondary tracks from a midline primary pit.
Differential diagnosis if no midline pits: hidradenitis suppurativa, complex anal fistula, osteomyelitis, tuberculosis, actinomycosis.
Histology
The cyst/sinus is lined by stratified squamous epithelium (like normal epidermis or follicular infundibulum). Some pilonidal cysts are composed of epithelium that keratinizes without a granular cell layer - analogous to the outer root sheath.
- Andrews' Diseases of the Skin
Treatment
Treatment is tailored to severity:
1. Conservative (Minimal/No Symptoms)
- Regular cleaning of the tracks and removal of all hair
- Strict hygiene; regular hair exfoliation of the area
- Laser or depilatory hair removal reduces recurrence rates
- Silver nitrate or laser coagulation to cauterize simple tracks
2. Acute Abscess
- Incision and drainage (I&D) - the standard of care
- A lateral incision (avoiding the midline) should be made over the most fluctuant area
- The cavity is thoroughly curetted - all embedded hair and devitalized tissue removed
- Antibiotics as adjunct (bacterial colonization 50-70%; common isolates: Staphylococcus aureus, Bacteroides)
3. Recurrent or Chronic Disease (Surgical Excision)
Several techniques exist:
| Procedure | Description |
|---|---|
| Gips procedure | Excision of midline pits + debridement of abscess cavity and sinus tracts (minimally invasive) |
| Bascom procedure | Lateral incision over sinus cavity + excision of midline pits; avoids midline closure |
| Wide excision + open healing | Complete excision left to heal by secondary intention |
| Excision + flap closure | Bascom cleft lift, Limberg flap, Z-plasty, V-to-Y advancement flap for complex disease |
| Phenol injection | Chemical ablation of tracts; useful for both chronic and post-I&D cases |
| EPSiT / SiLaC | Newer minimally invasive endoscopic/laser techniques (recent 2026 meta-analysis comparing these) |
Key principle: avoid midline wound closure - midline scars in the natal cleft have higher breakdown and recurrence rates.
- Sabiston Textbook of Surgery; Bailey and Love's
Complications
- Recurrence - the most common problem; even after adequate excision
- Chronic wound healing problems
- Squamous cell carcinoma (SCC) - rare but reported in longstanding, neglected pilonidal disease
Association with Other Conditions
Pilonidal sinus may occur alongside the acne tetrad: nodulocystic acne, dissecting cellulitis of the scalp, hidradenitis suppurativa, and pilonidal sinus - all sharing a follicular occlusion mechanism.
Recent evidence note: A 2026 systematic review and meta-analysis (PMID: 41964736) compared newer minimally invasive techniques - Sinus Laser Closure (SiLaC) vs. Endoscopic Pilonidal Sinus Treatment (EPSiT) - suggesting these are effective alternatives to traditional open surgery, particularly for recurrence rates and healing time.
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