Epidermoid & Pilar Cysts
Summary
Epidermoid and pilar cysts are the most common cutaneous cysts, often incorrectly called "sebaceous cysts." They are lined by epithelium and contain keratin (not sebum), which gives them their characteristic "cheesy" foul-smelling contents. Epidermoid cysts have a visible central punctum and occur on the face, trunk, and neck. Pilar (trichilemmal) cysts lack a punctum, occur predominantly on the scalp (90%), and are often familial. Both are benign and usually asymptomatic unless they become infected. Treatment is surgical excision of the entire cyst wall to prevent recurrence.
Key Facts
- Contents: Keratin (NOT sebum - "sebaceous cyst" is a misnomer)
- Epidermoid Cyst: Has central PUNCTUM; Face/Trunk
- Pilar Cyst: NO punctum; Scalp (90%); Often familial
- Sign: Attached to skin (punctum/scar), mobile over deeper tissues
- Treatment: Complete excision of cyst wall (capsule)
- Infection: Common; I&D provides drainage but cyst recurs
Clinical Pearls
"Sebaceous Cyst is Wrong": These cysts contain keratin, not sebum. The term "sebaceous cyst" is a misnomer but still commonly used.
"Punctum = Epidermoid": The central punctum is diagnostic of epidermoid cysts. Pilar cysts don't have one.
"Scalp + No Punctum = Pilar": 90% of pilar cysts are on the scalp and they're often familial (autosomal dominant).
"Remove the Whole Capsule": If any of the cyst wall remains, it will recur. Complete excision is essential.
Incidence
- Very common
- Most common cutaneous cysts
Demographics
- Peak age: 20-40 years
- Equal M:F (slight male predominance for epidermoid)
- Pilar cysts: Familial (autosomal dominant)
Distribution
| Cyst Type | Common Sites |
|---|---|
| Epidermoid | Face, Neck, Trunk, Scrotum |
| Pilar | Scalp (90%) |
Associations
- Multiple epidermoid cysts: Consider Gardner syndrome (FAP variant)
- Pilar cysts: Familial clustering (AD inheritance)
Origin
| Type | Origin | Lining |
|---|---|---|
| Epidermoid | Infundibulum of hair follicle or implanted epidermis | Stratified squamous epithelium with granular layer |
| Pilar | Isthmus of hair follicle | Stratified squamous epithelium WITHOUT granular layer |
Contents
- Keratin (lamellar, "cheesy")
- NOT sebum
- Foul-smelling when ruptured
Mechanism of Formation
- Keratin accumulates within epithelial-lined cyst
- Slow growth over years
- Rupture causes intense inflammatory reaction
Epidermoid Cyst
| Feature | Description |
|---|---|
| Size | Usually 1-5 cm |
| Shape | Dome-shaped, smooth |
| Surface | Central punctum (blackhead-like) |
| Consistency | Firm, compressible |
| Mobility | Attached to skin, mobile over deeper tissues |
| Contents | Keratin (cheesy, foul-smelling if expressed) |
Pilar Cyst
| Feature | Description |
|---|---|
| Size | Usually 1-5 cm; can be large |
| Shape | Dome-shaped |
| Surface | NO punctum; smooth skin over surface |
| Location | Scalp (90%) |
| Number | Often multiple |
| Heredity | Autosomal dominant pattern |
Infected Cyst
| Feature | Description |
|---|---|
| Pain | Tender |
| Erythema | Red, hot |
| Swelling | Rapid increase in size |
| Abscess | Fluctuant if pus formed |
Inspection
- Smooth, dome-shaped nodule
- Look for punctum (epidermoid)
- Overlying skin usually normal
Palpation
- Firm, rubbery
- May be compressible
- Tethered to skin (can't move skin separately from cyst)
- Mobile over underlying fascia
- May express cheesy material if squeezed (not recommended)
Signs of Infection
- Tenderness
- Warmth
- Erythema
- Fluctuance (abscess)
Clinical Diagnosis
- Usually clinical - no investigation needed
When to Investigate
| Indication | Test |
|---|---|
| Uncertain diagnosis | Ultrasound |
| Suspected deep extension | MRI |
| Multiple cysts | Consider Gardner syndrome (colonoscopy) |
Histology (After Excision)
- Epidermoid: Stratified squamous epithelium with distinct granular layer
- Pilar: Similar but lacks granular layer
Non-Infected Cyst
┌──────────────────────────────────────────────────────────┐
│ EPIDERMOID/PILAR CYST MANAGEMENT │
├──────────────────────────────────────────────────────────┤
│ │
│ ASYMPTOMATIC CYST: │
│ • Reassurance (benign) │
│ • No treatment if not troublesome │
│ │
│ SYMPTOMATIC/COSMETIC: │
│ • Surgical excision under local anaesthetic │
│ • MUST remove entire cyst wall (capsule) │
│ • Elliptical incision including punctum │
│ • Dissect around capsule intact if possible │
│ • Closure with sutures │
│ │
│ INFECTED CYST: │
│ • Antibiotics (Flucloxacillin 500mg QDS for 7 days) │
│ • Warm compresses │
│ • If abscess: Incision and drainage │
│ • Definitive excision 4-6 weeks after infection settles │
│ (I&D alone = high recurrence) │
│ │
└──────────────────────────────────────────────────────────┘
Surgical Technique
- Local anaesthetic infiltration
- Elliptical incision including punctum
- Dissect around capsule (try to keep intact)
- Remove entire cyst wall
- Haemostasis, closure
- Send for histology
Recurrence Prevention
- Complete capsule removal is key
- If capsule ruptures during surgery, curette remnants
Of Cyst
- Infection/Abscess
- Rupture (intense inflammatory reaction)
- Cosmetic concern
- Rarely: Malignant transformation (very rare, squamous cell carcinoma)
Of Treatment
- Recurrence (if capsule not fully removed)
- Scarring
- Infection
- Haematoma
With Complete Excision
- Cure rate very high
- Low recurrence if entire capsule removed
Without Treatment
- May slowly enlarge
- Risk of infection/rupture
Key Guidelines
- British Association of Dermatologists: Patient Information
- Minor Surgery Guidelines (Primary Care)
Key Evidence
Excision
- Complete excision has lowest recurrence
What Are These Cysts?
Epidermoid and pilar cysts are harmless lumps under the skin. They're filled with a cheesy material called keratin (not fat or oil). They're sometimes incorrectly called "sebaceous cysts."
What's the Difference?
- Epidermoid cysts usually appear on the face or body and have a tiny dark spot on top (punctum)
- Pilar cysts are usually on the scalp and run in families
Are They Dangerous?
No. They're benign and usually cause no problems. Sometimes they can become infected, causing pain and swelling.
Do They Need Treatment?
If they're not bothering you, no treatment is needed. If you want them removed (for cosmetic reasons or discomfort), a minor operation can remove them.
What Happens If They Get Infected?
You may need antibiotics and sometimes the cyst needs to be drained. After the infection settles, the cyst can be properly removed to prevent it coming back.
Primary Guidelines
- British Association of Dermatologists. Patient Information: Epidermoid and Pilar Cysts.
Key Studies
- Zuber TJ. Minimal excision technique for epidermoid (sebaceous) cysts. Am Fam Physician. 2002;65(7):1409-1412. PMID: 11996422