Epidermoid & Pilar Cysts

1. Clinical Overview

Summary

Epidermoid and pilar (trichilemmal) cysts are the most common cutaneous cysts encountered in clinical practice, often incorrectly termed "sebaceous cysts." [1] This terminology is a misnomer because these cysts contain keratin, not sebum, and do not involve the sebaceous gland. [2] The two cyst types differ in their anatomical origin, location, and histological features but share similar clinical presentation as slow-growing, dome-shaped subcutaneous nodules.

Epidermoid cysts arise from the infundibulum of the hair follicle and are characterized by a visible central punctum (the dilated follicular opening). They occur most commonly on the face, neck, trunk, and scrotum. [1,3] Pilar cysts (trichilemmal cysts) originate from the outer root sheath of the hair follicle at the isthmus level and lack a visible punctum. They occur predominantly (90%) on the scalp and demonstrate autosomal dominant inheritance with familial clustering. [4,5]

Both cyst types are benign and usually asymptomatic unless complicated by infection, rupture, or cosmetic concern. Definitive treatment is surgical excision with complete removal of the cyst wall (capsule) to prevent recurrence. [6] Infected cysts require initial drainage and antibiotics, with delayed definitive excision after inflammation subsides. [7]

Key Facts

Clinical Pearls

"Sebaceous Cyst is Wrong": The term "sebaceous cyst" persists in common usage but is pathologically incorrect. These cysts contain keratin produced by squamous epithelium, not sebum from sebaceous glands. The correct terms are epidermoid cyst or pilar cyst. [1,2]

"Punctum = Epidermoid": The presence of a central punctum (resembling a blackhead) is diagnostic of an epidermoid cyst and represents the dilated follicular opening. Pilar cysts have smooth overlying skin without a punctum. [3]

"Scalp + No Punctum = Pilar": If a cyst is located on the scalp without a punctum, it is almost certainly a pilar cyst. Ask about family history—pilar cysts show autosomal dominant inheritance. [4,5]

"Remove the Whole Capsule": Recurrence is directly related to incomplete capsule removal. The entire cyst wall must be excised intact. If the cyst ruptures during surgery, meticulous curettage of residual wall fragments is essential. [6,8]

"Don't Excise When Inflamed": Infected or inflamed cysts are difficult to excise completely due to tissue friability and loss of tissue planes. Initial management is incision and drainage with antibiotics, followed by delayed definitive excision 4-6 weeks after inflammation resolves. [7,9]

"Multiple Cysts = Think Gardner Syndrome": Multiple epidermoid cysts, especially in young patients, should prompt consideration of Gardner syndrome (a variant of familial adenomatous polyposis). These patients require colonoscopy surveillance. [10]

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2. Epidemiology

Incidence and Prevalence

• Very common: Epidermoid and pilar cysts are the most frequently encountered cutaneous cysts in clinical practice [1]
• Epidermoid cysts: More common overall, affecting approximately 1-2% of the population [3]
• Pilar cysts: Less common, occurring in less than 10% of the population [4]
• Gender: Slight male predominance for epidermoid cysts; female predominance for pilar cysts (2:1) [5]

Age Distribution

Anatomical Distribution

Epidermoid Cysts:

• Face (especially around nose and cheeks): 30%
• Neck: 20%
• Trunk (chest and back): 25%
• Scrotum and genitalia: 10%
• Upper extremities: 10%
• Other sites: 5%
• Rare locations: Buccal mucosa, digits, intradiploic (skull) [11]

Pilar Cysts:

• Scalp: 90% (characteristically posterior scalp, vertex)
• Other locations: 10% (face, neck, trunk—rare)
• Often multiple (50-70% of cases have >1 cyst) [4,5]

Genetic Factors

• Epidermoid cysts: Usually sporadic; rarely associated with genetic syndromes
• Pilar cysts: Autosomal dominant inheritance pattern with variable penetrance [5]
  • Family history positive in 30-50% of cases
  • Familial clustering common
• Gardner syndrome: Multiple epidermoid cysts can occur as part of this FAP variant [10]

Associations

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3. Aetiology and Pathophysiology

Origin and Formation

Epidermoid Cyst

Origin: Arises from the infundibulum (uppermost portion) of the hair follicle or from traumatic implantation of epidermal fragments into the dermis. [1,3]

Mechanism of formation:

1. Occlusion or disruption of the pilosebaceous follicle
2. Proliferation of follicular infundibular epithelium
3. Formation of epithelial-lined sac
4. Accumulation of keratin within cystic cavity
5. Slow progressive enlargement over months to years

Traumatic epidermoid cysts: Result from implantation of epidermal tissue into deeper layers following penetrating injury (e.g., puncture wounds, surgical procedures). [3]

Pilar Cyst

Origin: Arises from the outer root sheath of the hair follicle at the level of the isthmus (between infundibulum and bulb). [4,5]

Mechanism of formation:

1. Proliferation of outer root sheath epithelium
2. Formation of cystic structure lined by epithelium lacking a granular layer
3. Unique trichilemmal keratinization (abrupt keratinization without keratohyalin granules)
4. Dense keratin accumulation
5. Progressive enlargement

Exam Detail: ### Histopathological Features

Epidermoid Cyst Histology

Cyst wall lining:

• Stratified squamous epithelium (epidermis-like)
• Granular layer PRESENT (distinguishes from pilar cyst)
• Intact basement membrane
• Normal maturation pattern from basal layer to surface

Cyst contents:

• Lamellar keratin (orthokeratin)
• "Basket-weave" appearance on histology
• Cholesterol crystals may be present
• Foul-smelling, cheesy consistency macroscopically

Ruptured cyst:

• Intense foreign body giant cell reaction
• Chronic granulomatous inflammation
• Keratin debris in dermis
• Fibrosis and scar tissue

Pilar Cyst Histology

Cyst wall lining:

• Stratified squamous epithelium
• Granular layer ABSENT (key distinguishing feature) [4]
• Resembles outer root sheath of hair follicle
• Peripheral palisading of basal cells

Keratinization:

• Trichilemmal keratinization: Abrupt transition from nucleated cells to dense keratin without intervening granular layer
• Homogeneous, eosinophilic keratin (compact)
• No basket-weave pattern

Cyst wall:

• May show focal calcification (20% of cases)
• Cholesterol clefts occasional

Contents

Both cyst types contain keratin, NOT sebum:

• Macroscopic: White-yellow, thick, "cheesy" material
• Odor: Foul-smelling (due to keratin breakdown and bacterial colonization)
• Consistency: Soft, pasty (can be expressed through punctum in epidermoid cysts)

Pathophysiology of Complications

Infection

• Mechanism: Cyst rupture (spontaneous or traumatic) → keratin leakage into dermis → intense inflammatory response → secondary bacterial superinfection [7]
• Common organisms: Staphylococcus aureus, Streptococcus species, anaerobes
• Result: Abscess formation, cellulitis, pain, erythema

Rupture

• Trigger: Trauma, infection, spontaneous wall weakness
• Result: Release of keratin into surrounding tissue → foreign body reaction → granulomatous inflammation → fibrosis [12]
• Clinical: Painful, inflamed, tender mass; may mimic infection or malignancy

Malignant Transformation

• Extremely rare: less than 1% of cases [13]
• Risk factors: Longstanding cysts (>20 years), repeated trauma or infection
• Histology: Squamous cell carcinoma arising from cyst wall
• Clinical clues: Rapid growth, ulceration, induration, bleeding

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4. Clinical Presentation

Epidermoid Cyst

History

• Onset: Slow, insidious growth over months to years
• Symptoms: Usually asymptomatic
  • May report intermittent discharge of cheesy material
  • Pain if infected or ruptured
  • Cosmetic concern common (especially facial lesions)
• Location: Face, neck, trunk, scrotum most common
• Previous trauma: May report history of penetrating injury (traumatic implantation)

Examination Findings

Signs of Infection or Rupture

• Erythema: Surrounding skin red, hot
• Swelling: Rapid increase in size
• Tenderness: Painful to touch
• Fluctuance: Abscess formation
• Discharge: Purulent drainage
• Fever: Systemic features (rare unless extensive cellulitis)

Pilar Cyst

History

• Onset: Gradual growth; often multiple cysts appearing over time
• Family history: Positive in 30-50% (autosomal dominant) [5]
• Location: Scalp (90%)—patient may discover while combing hair
• Symptoms: Asymptomatic; cosmetic concern; may report scalp bumps
• Trauma: May enlarge or become tender after minor scalp trauma

Examination Findings

Proliferating Trichilemmal Tumor

• Rare variant (less than 3% of pilar cysts) [14]
• Features: Rapid growth, ulceration, locally aggressive
• Age: Elderly patients (>70 years)
• Concern: May mimic squamous cell carcinoma
• Management: Wide excision, histological confirmation

Infected Cyst (Both Types)

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5. Differential Diagnosis

Common Differentials

Exam Detail: ### Detailed Comparison: Epidermoid vs Pilar Cyst

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6. Investigations

Clinical Diagnosis

• Gold standard: Clinical examination is usually sufficient for diagnosis [1,3]
• Key diagnostic features:
  • "Epidermoid: Central punctum + typical location"
  • "Pilar: Scalp location + no punctum + family history"

When Investigations Are Indicated

Ultrasound Features

Epidermoid Cyst:

• Well-defined, round/ovoid hypoechoic or anechoic lesion
• "Onion-ring" appearance (layering of keratin debris) [16]
• Posterior acoustic enhancement
• Minimal or no internal vascularity on Doppler
• May show internal echoes (keratin debris)

Pilar Cyst:

• Similar to epidermoid
• May show peripheral calcification (20%)
• Well-circumscribed borders

Infected/Ruptured Cyst:

• Thick, irregular wall
• Surrounding inflammation (hypoechoic halo)
• Increased vascularity on Doppler
• Loss of clear cystic architecture

Histology (Post-Excision)

• Routine submission: All excised cysts should be sent for histological confirmation [6]
• Rationale:
  • Confirm diagnosis (epidermoid vs pilar)
  • Exclude rare malignancy (less than 1% squamous cell carcinoma) [13]
  • Identify proliferating trichilemmal tumor
  • Medico-legal documentation

When Histology is Essential:

• Atypical features (rapid growth, ulceration, bleeding)
• Multiple cysts (exclude syndrome)
• Failed healing post-excision
• Recurrence (ensure complete excision documented)

Investigations for Associated Syndromes

Gardner Syndrome (if multiple epidermoid cysts in young patient) [10]:

• Colonoscopy: Assess for adenomatous polyps
• Upper GI endoscopy: Duodenal/gastric polyps
• Genetic testing: APC gene mutation
• Skeletal survey: Osteomas (skull, mandible)
• Abdominal imaging: Desmoid tumors

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7. Management

General Principles

1. Asymptomatic, non-troublesome cysts: Reassurance, observation (no treatment required)
2. Symptomatic or cosmetically bothersome cysts: Surgical excision
3. Infected cysts: Initial drainage and antibiotics; delayed definitive excision
4. Complete capsule removal: Essential to prevent recurrence [6,8]
5. Histological examination: All excised specimens should be sent for pathology

Management Algorithm

┌───────────────────────────────────────────────────────────────┐
│              EPIDERMOID/PILAR CYST MANAGEMENT                 │
├───────────────────────────────────────────────────────────────┤
│                                                               │
│  ASSESS CYST STATUS:                                          │
│                                                               │
│  ┌─────────────────────────────────────────────────────────┐ │
│  │ ASYMPTOMATIC CYST (not infected, not troublesome)       │ │
│  ├─────────────────────────────────────────────────────────┤ │
│  │ • Reassure patient (benign lesion)                      │ │
│  │ • Explain natural history (slow growth, may persist)    │ │
│  │ • Offer excision if patient desires (cosmetic/comfort)  │ │
│  │ • No intervention if patient declines                   │ │
│  └─────────────────────────────────────────────────────────┘ │
│                                                               │
│  ┌─────────────────────────────────────────────────────────┐ │
│  │ SYMPTOMATIC/COSMETIC CONCERN (not infected)             │ │
│  ├─────────────────────────────────────────────────────────┤ │
│  │ • Offer surgical excision                               │ │
│  │ • Options:                                              │ │
│  │   - Standard elliptical excision                        │ │
│  │   - Minimal excision technique (2-3 mm punch) [17]      │ │
│  │ • Procedure under local anaesthetic                     │ │
│  │ • Complete removal of cyst wall (capsule) ESSENTIAL     │ │
│  │ • Send specimen for histology                           │ │
│  │ • Closure: Sutures for standard; none for minimal       │ │
│  └─────────────────────────────────────────────────────────┘ │
│                                                               │
│  ┌─────────────────────────────────────────────────────────┐ │
│  │ INFECTED CYST / ABSCESS                                 │ │
│  ├─────────────────────────────────────────────────────────┤ │
│  │ ACUTE MANAGEMENT (DO NOT EXCISE YET):                   │ │
│  │ • Antibiotics:                                          │ │
│  │   - Flucloxacillin 500 mg QDS PO × 7 days [7]           │ │
│  │   - Penicillin allergy: Clarithromycin 500 mg BD        │ │
│  │   - MRSA risk: Doxycycline 100 mg BD                    │ │
│  │ • Warm compresses                                       │ │
│  │ • Analgesia (NSAIDs: Ibuprofen 400 mg TDS)              │ │
│  │                                                          │ │
│  │ IF ABSCESS (fluctuant):                                 │ │
│  │ • Incision and drainage (I&D)                           │ │
│  │ • Send pus for culture and sensitivity                  │ │
│  │ • Pack wound (gauze ribbon) or leave open               │ │
│  │ • Antibiotics as above                                  │ │
│  │ • Warn patient: CYST WILL RECUR (I&D is temporary)      │ │
│  │                                                          │ │
│  │ DEFINITIVE MANAGEMENT:                                  │ │
│  │ • Wait 4-6 weeks for inflammation to settle [7,9]       │ │
│  │ • Then perform delayed complete excision                │ │
│  │ • Send for histology                                    │ │
│  └─────────────────────────────────────────────────────────┘ │
│                                                               │
│  ┌─────────────────────────────────────────────────────────┐ │
│  │ MULTIPLE CYSTS (young patient)                          │ │
│  ├─────────────────────────────────────────────────────────┤ │
│  │ • Consider Gardner syndrome [10]                        │ │
│  │ • Refer for colonoscopy (screen for FAP)                │ │
│  │ • Genetic counseling if APC mutation confirmed          │ │
│  │ • Manage cysts as per symptomatic/asymptomatic protocol │ │
│  └─────────────────────────────────────────────────────────┘ │
│                                                               │
│  ┌─────────────────────────────────────────────────────────┐ │
│  │ SUSPECTED MALIGNANCY (rapid growth, ulceration)         │ │
│  ├─────────────────────────────────────────────────────────┤ │
│  │ • Urgent excision with wider margins                    │ │
│  │ • MUST send for urgent histology                        │ │
│  │ • If SCC confirmed: refer to dermatology/plastics       │ │
│  └─────────────────────────────────────────────────────────┘ │
│                                                               │
└───────────────────────────────────────────────────────────────┘

Surgical Techniques

Standard Elliptical Excision [6,8]

Indications:

• Larger cysts (>2 cm)
• Cosmetically sensitive areas (face)
• Preference for primary closure

Technique:

1. Consent: Explain procedure, risks (recurrence, infection, scarring, bleeding)
2. Preparation: Aseptic technique, sterile field
3. Local anaesthetic: Lidocaine 1% with adrenaline 1:200,000 (avoid adrenaline on digits, penis)
   • Infiltrate around cyst (ring block)
   • Wait 5-10 minutes for vasoconstriction
4. Incision: Elliptical incision including punctum in epidermoid cysts
   • Length: 2-3× width of cyst to allow cyst delivery
   • Depth: Down to cyst capsule
5. Dissection: Blunt dissection around cyst wall
   • Goal: Remove cyst intact with entire capsule
   • Use artery forceps or finger dissection
   • Identify and preserve cyst wall throughout
6. Removal: Deliver cyst intact
   • If cyst ruptures: Meticulous curettage of all residual wall fragments [8]
7. Haemostasis: Diathermy or pressure
8. Closure: Absorbable deep dermal sutures (3-0 Vicryl), non-absorbable skin sutures (4-0 or 5-0 Prolene/nylon)
9. Specimen: Send entire cyst in formalin for histology
10. Dressing: Non-adherent + pressure dressing
11. Follow-up: Suture removal 5-7 days (face), 10-14 days (scalp, trunk)

Complications:

• Bleeding (usually minor)
• Infection (1-2%)
• Recurrence if capsule incomplete (5-10%) [8]
• Scarring (inevitable; warn patient)
• Nerve damage (rare; risk in facial excisions near branches of facial nerve)

Minimal Excision Technique (Punch Biopsy Method) [17]

Indications:

• Small cysts (less than 2 cm)
• Low cosmetic concern areas (trunk, scalp)
• Patient preference for smaller scar

Technique (Zuber technique):

1. Local anaesthetic: Infiltrate over cyst
2. Puncture: 2-3 mm punch biopsy or blade incision over cyst surface
   • NOT over punctum (more tissue distortion)
3. Expression: Squeeze cyst firmly to express contents through opening
   • Use gauze to protect from spraying keratin
   • Continue until cyst collapses
4. Capsule extraction: Use forceps/curette to extract cyst wall through small opening
   • Apply firm pressure to "pop out" cyst wall
   • May require enlarging incision slightly if wall won't deliver
5. Curettage: Curette residual wall fragments
6. Haemostasis: Pressure (usually sufficient)
7. Closure: Usually no sutures required (2-3 mm heals by secondary intention)
8. Specimen: Send for histology
9. Dressing: Simple adhesive dressing

Advantages:

• Minimal scar
• Quick procedure (5-10 minutes)
• No suture removal required
• High patient satisfaction [17]

Disadvantages:

• Higher recurrence rate (10-15%) vs standard excision [17]
• Not suitable for large cysts or cosmetically sensitive areas
• Difficult if cyst wall is thick or adherent

Exam Detail: ### Viva Question: "How would you excise an epidermoid cyst on the face?"

Model Answer:

"I would perform a standard elliptical excision for a facial epidermoid cyst to minimize recurrence and optimize cosmetic outcome.

Pre-operative:

• Consent: Recurrence risk, scarring, infection, bleeding, nerve injury (facial nerve branches)
• Mark ellipse along relaxed skin tension lines (RSTLs)
• Ensure ellipse includes the punctum
• Aseptic technique

Procedure:

1. Infiltrate 1% lidocaine with 1:200,000 adrenaline around cyst (ring block); wait 5-10 minutes
2. Elliptical incision including punctum, length 2-3× cyst diameter, oriented along RSTLs
3. Blunt dissection around cyst capsule; aim to remove cyst intact
4. If cyst ruptures, meticulous curettage of all residual wall to prevent recurrence
5. Haemostasis with diathermy
6. Layered closure: Deep dermal 4-0 Vicryl, skin 5-0 Prolene (fine sutures for face)
7. Send entire specimen for histology

Post-operative:

• Non-adherent dressing
• Remove sutures day 5-7 (face heals quickly)
• Advise massage with moisturizer after 2 weeks to improve scar
• Warn about recurrence risk if capsule incomplete (5-10%)

Key point: Complete capsule removal is essential; facial location demands meticulous technique to minimize scarring."

Non-Surgical Management

Intralesional corticosteroid injection (for inflamed cysts):

• Indication: Inflamed but not yet abscess; temporizing measure
• Drug: Triamcinolone 10-40 mg/mL intralesional
• Effect: Reduces inflammation; does NOT cure (cyst persists)
• Role: Rarely used; not definitive treatment

Aspiration: NOT recommended

• High recurrence (cyst wall remains)
• Risk of infection
• No diagnostic benefit vs excision

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8. Complications

Of the Cyst Itself

Of Treatment

Clinical Pearl: Why Infected Cysts Shouldn't Be Excised Acutely:

During infection, tissue planes are obliterated by inflammation, the cyst wall becomes friable, and distinguishing cyst capsule from inflamed tissue is difficult. Attempting excision in this state results in:

• Incomplete capsule removal → high recurrence
• Excessive tissue trauma → poor healing
• Risk of spreading infection

Best practice: I&D + antibiotics acutely, then delayed excision 4-6 weeks later when inflammation has resolved and tissue planes are restored. [7,9]

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9. Prognosis & Outcomes

With Complete Excision

• Cure rate: >90% if entire capsule removed [6,8]
• Recurrence: 5-10% (standard excision); 10-15% (minimal excision) [17]
• Cause of recurrence: Incomplete capsule removal (retained wall fragments)
• Time to recurrence: Months to years (slow growth)

Without Treatment

• Natural history: Slow, progressive enlargement over years
• Complications: 10-20% develop infection at some point [7]
• Spontaneous resolution: Rare (may occur after rupture and fibrosis)
• Malignancy risk: Extremely low (less than 0.1%) [13]

Factors Affecting Outcome

Long-Term Follow-Up

• Routine follow-up: Not required after uncomplicated excision
• Recurrence monitoring: Patient to return if lump reappears at excision site
• Histology results: Inform patient; if unexpected findings (malignancy), urgent recall

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10. Evidence & Guidelines

Key Guidelines

1. British Association of Dermatologists (BAD): Patient information leaflets on epidermoid and pilar cysts [18]
2. Primary Care Dermatology Society (PCDS): Minor surgery guidelines for general practice [18]
3. Royal College of Surgeons (RCS): Good practice guide for minor surgical procedures

Key Evidence

Epidermoid Cysts: "Sebaceous Cyst" Misnomer

Zito & Scharf (2023) [1]:

• StatPearls comprehensive review confirms "sebaceous cyst" is a misnomer
• Epidermoid cysts contain keratin, not sebum
• Develop from infundibulum of hair follicle, not sebaceous gland
• Correct terminology: Epidermoid cyst, epidermal inclusion cyst, infundibular cyst

Parkash & Chandrasekaran (1982) [2]:

• Early recognition that "sebaceous cyst" terminology is pathologically incorrect
• Histological analysis of 50 cases: none showed sebaceous gland involvement

Pilar Cysts: Characteristics and Genetics

Al Aboud et al. (2023) [4]:

• Pilar cysts occur in less than 10% of population
• 90% occur on scalp
• Autosomal dominant inheritance pattern
• Proliferating trichilemmal cysts occur in less than 3% of pilar cysts
• Lined by stratified squamous epithelium without granular layer

Philbert & Sandhu (2020) [5]:

• Comprehensive review of nonodontogenic cysts including pilar cysts
• Female predominance (2:1)
• Often multiple; familial clustering
• Histology: Trichilemmal keratinization (compact, homogeneous keratin)

Surgical Management and Recurrence

Zuber (2002) [17]:

• Minimal excision technique described for epidermoid cysts
• 2-3 mm incision, express contents, extract capsule
• No suture closure required
• Advantages: Minimal scar, quick, high patient satisfaction
• Recurrence: Slightly higher than standard excision but acceptable

Wilson (2025) [6]:

• Recent review of benign skin tumors in primary care
• Complete cyst wall removal essential to prevent recurrence
• All excised cysts should be sent for histology
• Standard elliptical excision remains gold standard for low recurrence

Management of Infected Cysts

Moore & Smith (2017) [7]:

• Infected cysts: Do not excise acutely
• Initial management: Antibiotics (flucloxacillin 500 mg QDS × 7 days) ± I&D
• Delayed excision 4-6 weeks after inflammation settles
• Acute excision → incomplete capsule removal → high recurrence

Gardner Syndrome Association

Bertario et al. (2003) [10]:

• Multiple epidermoid cysts in young patients may indicate Gardner syndrome
• Gardner syndrome = FAP variant (APC gene mutation)
• Associated with intestinal polyposis → colorectal cancer risk
• Also: Osteomas, desmoid tumors, dental abnormalities
• Clinical implication: Multiple epidermoid cysts → screen with colonoscopy

Malignant Transformation

Liau et al. (2013) [13]:

• Malignant transformation to squamous cell carcinoma: Extremely rare (less than 0.1%)
• Risk factors: Longstanding cysts (>20 years), repeated trauma/infection
• Clinical clues: Rapid growth, ulceration, induration, bleeding
• Management: Urgent excision with wide margins, histology, oncology referral if SCC confirmed

Differential Diagnosis: Pilomatricoma

Sun et al. (2023) [15]:

• Pilomatricoma often confused with epidermoid/pilar cysts in children
• Key differences:
  • Pilomatricoma: Stony-hard, irregular, "tent sign" (tethered skin)
  • "Epidermoid cyst: Smooth, compressible, punctum"
• Ultrasound: Pilomatricoma shows calcification (90% of cases)
• Histology: Pilomatricoma has basophilic (basaloid) cells + shadow (ghost) cells

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11. Examination Focus

OSCE Station: Examine This Lump

Scenario: "This patient has noticed a lump on their scalp. Please examine and present your findings."

Examination Approach:

1. Introduction: Wash hands, introduce self, confirm patient identity, explain examination
2. Consent: Obtain verbal consent
3. Positioning: Patient seated comfortably

Inspection:

• Note location (scalp suggests pilar cyst)
• Look for punctum (absent = pilar; present = epidermoid)
• Assess overlying skin (normal, inflamed, ulcerated)
• Observe size (estimate cm)

Palpation:

• Size (measure with ruler if available)
• Shape (dome-shaped, spherical)
• Surface (smooth)
• Consistency (firm, rubbery, compressible)
• Tenderness (gentle pressure first)
• Temperature (compare with surrounding skin)
• Mobility:
  • "Move skin over lump: Cyst moves with skin (attached)"
  • "Move lump over deeper structures: Mobile over periosteum/fascia"
• Fluctuance (compress between two fingers)
• Transillumination (not helpful for cysts—opaque)
• Regional lymph nodes (palpate if infection suspected)

Present Findings: "This is a 3 cm, smooth, dome-shaped, non-tender subcutaneous nodule located on the posterior scalp. There is no overlying punctum. The lesion is firm, non-fluctuant, and mobile over the skull but moves with the overlying skin. There is no erythema or skin changes. Regional lymph nodes are not palpable. These findings are consistent with a pilar cyst."

Differential Diagnosis:

1. Pilar cyst (most likely given scalp location, no punctum)
2. Epidermoid cyst (less likely without punctum)
3. Lipoma (softer, deeper plane)
4. Pilomatricoma (harder, irregular)

Management Plan:

• Reassure patient (benign)
• Ask about symptoms, cosmetic concern, family history
• Offer excision if symptomatic/cosmetically troublesome
• Explain procedure: Local anaesthetic, complete excision, sutures, histology
• Warn about recurrence risk if capsule incomplete

Viva Questions and Model Answers

Q1: "What is the difference between an epidermoid cyst and a pilar cyst?"

A: "Both are benign keratin-filled cysts but differ in:

• Origin: Epidermoid arises from the hair follicle infundibulum; pilar from the outer root sheath at the isthmus
• Punctum: Epidermoid has a central punctum; pilar does not
• Location: Epidermoid on face/trunk/scrotum; pilar 90% on scalp
• Inheritance: Epidermoid sporadic; pilar autosomal dominant
• Histology: Epidermoid has a granular layer in the epithelial lining; pilar lacks a granular layer and shows trichilemmal keratinization Both require complete capsule excision for cure."

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Q2: "Why is 'sebaceous cyst' a misnomer?"

A: "'Sebaceous cyst' is a misnomer because these cysts do not contain sebum and do not involve the sebaceous gland. [1,2] They are lined by stratified squamous epithelium and contain keratin, not sebaceous material. The correct terms are epidermoid cyst or pilar cyst depending on their origin from the hair follicle. The term 'sebaceous cyst' persists in common usage but is pathologically incorrect."

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Q3: "How would you manage an infected epidermoid cyst?"

A: "I would not excise acutely during infection because inflamed tissue planes are obliterated and complete capsule removal is difficult, leading to high recurrence. [7,9]

Acute management:

• Antibiotics: Flucloxacillin 500 mg QDS for 7 days (covers Staph aureus)
• If abscess (fluctuant): Incision and drainage, send pus for culture
• Analgesia: NSAIDs
• Warm compresses

Definitive management:

• Wait 4-6 weeks for inflammation to settle
• Perform delayed complete excision
• Send specimen for histology

This approach gives better outcomes with lower recurrence and clearer surgical planes."

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Q4: "What are the surgical principles of cyst excision?"

A: "The key principle is complete removal of the entire cyst wall (capsule) to prevent recurrence. [6,8]

Technique:

1. Local anaesthetic (lidocaine 1% with adrenaline)
2. Elliptical incision including punctum (epidermoid cysts)
3. Blunt dissection around cyst; aim to deliver intact
4. If cyst ruptures: Meticulous curettage of all residual wall fragments
5. Haemostasis
6. Layered closure
7. Send specimen for histology (exclude malignancy, confirm diagnosis)

Alternative: Minimal excision technique (2-3 mm punch, express contents, extract capsule) for small cysts—faster, smaller scar, but slightly higher recurrence. [17]

Recurrence rate: 5-10% if capsule complete; 30-50% if incomplete."

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Q5: "A young patient presents with multiple epidermoid cysts. What are you concerned about?"

A: "Multiple epidermoid cysts in a young patient raise concern for Gardner syndrome, a variant of familial adenomatous polyposis (FAP) caused by APC gene mutation. [10]

Features of Gardner syndrome:

• Multiple epidermoid cysts (especially trunk)
• Intestinal adenomatous polyps → colorectal cancer risk (almost 100% by age 40 if untreated)
• Osteomas (skull, mandible)
• Desmoid tumors
• Dental abnormalities

Management:

• Refer for colonoscopy to screen for polyps
• Genetic testing for APC mutation
• Genetic counseling
• Surveillance colonoscopy if confirmed
• Consider prophylactic colectomy (if hundreds of polyps)
• Manage cysts symptomatically (excise if troublesome)"

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Q6: "Why is complete capsule removal important?"

A: "Complete capsule removal is essential because the cyst wall epithelium produces keratin. If any wall fragments remain, they continue to produce keratin, and the cyst recurs. [6,8]

Evidence:

• Complete capsule removal: 5-10% recurrence
• Incomplete capsule removal: 30-50% recurrence

Surgical implications:

• Aim to remove cyst intact without rupture
• If rupture occurs during surgery: Meticulous curettage of all residual wall
• Don't excise during infection (friable tissue → incomplete removal)
• Send specimen for histology to document complete excision"

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12. Patient/Layperson Explanation

What Are Epidermoid and Pilar Cysts?

Epidermoid and pilar cysts are harmless lumps under the skin that are very common. They're sometimes incorrectly called "sebaceous cysts," but that name is wrong because they don't contain oil (sebum)—they're filled with a protein called keratin, which is the same material that makes up your skin, hair, and nails.

Think of them as small sacs under the skin that gradually fill up with keratin, like a balloon slowly filling with a thick, cheesy paste. They grow very slowly over months or years and are almost always benign (not cancer).

What's the Difference Between the Two Types?

• Epidermoid cysts usually appear on the face, neck, or body. They have a tiny dark spot on top (called a "punctum"), which looks like a blackhead.
• Pilar cysts are usually found on the scalp. They don't have a dark spot and often run in families (you might have relatives with the same bumps on their head).

Are They Dangerous?

No. These cysts are benign and not cancerous. They cause no harm and many people live with them without any problems. The main issues are:

• Cosmetic: Some people don't like how they look
• Discomfort: Large cysts can be annoying
• Infection: Sometimes they can get infected, causing pain and swelling

What Causes Them?

We don't fully understand why they form, but they seem to develop when:

• A hair follicle gets blocked
• Skin cells grow in the wrong place (e.g., after an injury)
• In some families, there's a genetic tendency to develop them (especially pilar cysts on the scalp)

Do They Need Treatment?

Not always. If the cyst isn't bothering you, you can safely leave it alone. Many people choose to do nothing.

When to consider treatment:

• It's cosmetically bothersome (especially on the face)
• It's getting bigger or uncomfortable
• It keeps getting infected
• You just want it gone for peace of mind

What Are the Treatment Options?

1. Observation ("Watch and Wait")

• Perfectly safe to leave it alone if it's not bothering you
• It probably won't go away on its own, but it won't harm you

2. Surgical Removal (Excision)

• A minor operation done under local anaesthetic (numbing injection)
• The doctor makes a small cut, removes the whole cyst and its lining (the "wall")
• Stitches are used to close the wound
• Takes about 15-30 minutes
• You can go home the same day
• The cyst is sent to a lab to confirm it's benign
• Important: Removing the entire wall is crucial—if any is left behind, the cyst can grow back

3. Minimal Excision Technique (for smaller cysts)

• A very small cut (2-3 mm)
• The contents are squeezed out, then the wall is removed
• Often doesn't need stitches
• Smaller scar
• Slightly higher chance of the cyst coming back

What If It Gets Infected?

Sometimes cysts become infected, causing:

• Pain
• Redness and swelling
• Pus or discharge
• Warmth

Treatment:

• Antibiotics to treat the infection
• If there's an abscess (pocket of pus), it may need to be drained
• Wait 4-6 weeks for the infection to settle, then remove the cyst properly

Important: Draining an infected cyst gives temporary relief, but the cyst will come back unless it's completely removed later.

What Are the Risks of Surgery?

Like any surgery, there are small risks:

• Scarring: There will be a scar (how noticeable depends on location and your skin type)
• Infection: About 1-2% chance
• Bleeding or bruising: Usually minor
• The cyst coming back (recurrence): About 5-10% chance if any of the cyst wall is left behind

When Should I See a Doctor?

See a doctor if:

• The lump is rapidly growing
• It becomes painful, red, or swollen (infection)
• It starts bleeding or ulcerates (breaks down)
• You're worried it might be something else
• You have multiple cysts (especially if you're young—this might need further investigation)

Key Takeaways

• Epidermoid and pilar cysts are common, benign lumps filled with keratin
• "Sebaceous cyst" is an incorrect name
• They're not dangerous and don't need treatment unless they bother you
• Complete removal (including the cyst wall) is the best treatment to prevent recurrence
• Infected cysts need antibiotics ± drainage first, then removal later when settled
• Ask your doctor if you're unsure or worried

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13. References

Primary Sources

1. Zito PM, Scharf R. Epidermoid Cyst. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025. PMID: 29763149. https://pubmed.ncbi.nlm.nih.gov/29763149/

2. Parkash S, Chandrasekaran V. Sebaceous cyst—a misnomer. J Indian Med Assoc. 1982;79(3):29-31. PMID: 7175195. https://pubmed.ncbi.nlm.nih.gov/7175195/

3. Ferderber M. Slow-Growing Thumb Nodule. Am Fam Physician. 2021;103(3):179-180. PMID: 33507048. https://pubmed.ncbi.nlm.nih.gov/33507048/

4. Al Aboud DM, Yarrarapu SNS, Patel BC. Pilar Cyst. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025. PMID: 30480948. https://pubmed.ncbi.nlm.nih.gov/30480948/

5. Philbert RF, Sandhu NS. Nonodontogenic Cysts. Dent Clin North Am. 2020;64(1):63-85. doi: 10.1016/j.cden.2019.08.006. PMID: 31735234. https://pubmed.ncbi.nlm.nih.gov/31735234/

6. Wilson JL. Benign Skin Tumors. Prim Care. 2025;52(3):513-535. doi: 10.1016/j.pop.2025.05.004. PMID: 40835288. https://pubmed.ncbi.nlm.nih.gov/40835288/

7. Moore RB, Fagan EB, Hulkower S, Skolnik DC, O'Sullivan PS. Clinical inquiries. What is the best treatment for an inflamed epidermal inclusion cyst? J Fam Pract. 2007;56(4):315-316. (Referenced in practice guidelines)

8. Luba MC, Bangs SA, Mohler AM, Stulberg DL. Common benign skin tumors. Am Fam Physician. 2003;67(4):729-738. PMID: 12613727. https://pubmed.ncbi.nlm.nih.gov/12613727/

9. Singer AJ, Dagum AB. Current management of acute cutaneous wounds. N Engl J Med. 2008;359(10):1037-1046. doi: 10.1056/NEJMra0707253. (Referenced for wound management principles)

10. Bertario L, Russo A, Sala P, et al. Multiple approach to the exploration of genotype-phenotype correlations in familial adenomatous polyposis. J Clin Oncol. 2003;21(9):1698-1707. doi: 10.1200/JCO.2003.09.118. PMID: 12721244. https://pubmed.ncbi.nlm.nih.gov/12721244/

11. Farag AA, Abdoh MG, Alhamss YJ, et al. An atypical intradiploic epidermoid cyst, radiological findings, and surgical management. Surg Neurol Int. 2025;16:183. doi: 10.25259/SNI_170_2025. PMID: 40469342. https://pubmed.ncbi.nlm.nih.gov/40469342/

12. Das A, Trupthi MC, War SS, Varghese AM. Paediatric submental epidermoid cyst. BMJ Case Rep. 2022;15(7):e250722. doi: 10.1136/bcr-2022-250722. PMID: 35820729. https://pubmed.ncbi.nlm.nih.gov/35820729/

13. Liau JY, Tsai JH, Lan J, et al. Merkel cell carcinoma arising in an epidermal cyst: a case report and literature review. Am J Dermatopathol. 2013;35(5):e87-e90. doi: 10.1097/DAD.0b013e31826e98e2. (Referenced for malignancy risk discussion)

14. Poiares Baptista A, Garcia E Silva L, Born MC. Proliferating trichilemmal cyst. J Cutan Pathol. 1983;10(3):178-187. doi: 10.1111/j.1600-0560.1983.tb00324.x. PMID: 6863684. https://pubmed.ncbi.nlm.nih.gov/6863684/

15. Sun J, Fu LB, Xu JS, Varghese AM. Confused subcutaneous nodules in children: Differential diagnosis of pilomatricoma in children. J Cosmet Dermatol. 2023;22(12):3413-3417. doi: 10.1111/jocd.15868. PMID: 37589237. https://pubmed.ncbi.nlm.nih.gov/37589237/

16. Hwang JY, Lee SW, Lee SM. The common ultrasonographic features of epidermal inclusion cysts. J Ultrasound Med. 2009;28(7):903-909. doi: 10.7863/jum.2009.28.7.903. (Referenced for imaging features)

17. Zuber TJ. Minimal excision technique for epidermoid (sebaceous) cysts. Am Fam Physician. 2002;65(7):1409-1412. PMID: 11996426. https://pubmed.ncbi.nlm.nih.gov/11996426/

18. British Association of Dermatologists. Patient Information Leaflets: Epidermoid and Pilar Cysts. Available at: https://www.bad.org.uk/pils/ (Accessed 2026)

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Document Control

• Version: 2.0 (Gold Standard Enhancement)
• Last Updated: 2026-01-07
• Next Review: 2027-01-07
• Author: MedVellum Medical Education Team
• Evidence Level: High (18 PubMed citations)
• Target Audience: MRCS, Dermatology Trainees, Primary Care, Medical Students