Epidermal Cyst

Aka: Epidermal Cyst, Epidermoid Cyst, Epidermal Inclusion Cyst, Epithelial Inclusion Cyst, Sebaceous Cyst, Epithelial Cyst, Keratin Cyst

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II. Epidemiology

  1. Most common skin cyst

III. Causes

  1. Ruptured Pilosebaceous Follicle (acne comedone)
  2. Local Trauma buries surface epithelium under skin

IV. Pathophysiology

  1. Previously known as Sebaceous Cysts, but not derived from sebaceous tissue
    1. Do not contain sebaceous cells or their material
  2. Lesion
    1. Implanted epidermal elements into deeper dermal layers
    2. Cyst wall: stratified squamous epithelium
      1. Proliferates, resulting in dermal keratin accumulation
    3. Central punctum is typically present on close exam (hallmark finding of Sebaceous Cyst)
    4. Cyst contents (Does NOT contain Sebaceous Glands)
      1. Keratin and lipid
      2. Breakdown products
      3. Bacterial Infection
  3. Cyst rupture effect (keratin spills into Dermis)
    1. Significant inflammation
    2. Lesion may scar or become infected

V. Symptoms

  1. Usually asymptomatic
  2. Soft, yellow keratin discharge may have foul odor

VI. Signs

  1. Round, mobile, smooth surfaced, discrete firm Nodule
  2. Slow growing lesion from 5 mm to 5 cm in diameter
  3. Visible pore (central punctum) may be present at center of lesions
  4. May be inflamed if cyst has ruptured
  5. Distribution
    1. Head and Neck (Face, Ears)
    2. Trunk (Chest, Back)

VII. Differential Diagnosis

  1. See Soft Tissue Mass
  2. See site specific (e.g. Neck Masses in Children)
  3. Lipoma
  4. Milia (1-2 mm lesion)
    1. Puncture with needle, express with comedone extractor
  5. Dermoid Cyst
    1. May extend intracranially (CT Head before excision)
    2. Locations
      1. Follow Cleavage Lines
      2. Sublingual
      3. Periorbital
      4. Base of nose

VIII. Types: Variations with Multiple Lesions

  1. Gardner's Syndrome
    1. Autosomal Dominant condition associated with Colonic Polyps and Colon Cancer
    2. Children with Sebaceous Cysts
    3. Adults with Sebaceous Cysts in rare location (fingers, toes)
    4. Multiple Lipomas, fibromas, osteomas
  2. Steatocystoma Multiplex
    1. Numerous 2-3mm lesions on trunk, arm, axilla, thigh
  3. Favre-Racouchot Syndrome
    1. Multiple facial lesions due to sun damage

IX. Management

  1. Non-inflamed cyst
    1. Small to moderate sized cysts
      1. See Minimal Epidermal Cyst Excision
    2. Large Cysts (2 cm or larger)
      1. Complete excision in standard fashion
      2. Remove cyst intact via Blunt Dissection
  2. Inflamed cyst
    1. Warm compresses
    2. Intralesional Corticosteroid may be considered
  3. Infected cyst
    1. Incision and Drainage

X. Complications

  1. Cyst rupture
  2. Cyst inflammation or infection
  3. Malignancies may develop adjacent to or within Sebaceous Cysts (very rare)

XI. References

  1. Habif (1996) Clinical Dermatology, p. 644
  2. White (1994) Regional Dermatology, p. 27
  3. Higgins (2015) Am Fam Physician 92(7): 601-7 [PubMed]
  4. Wagner (2024) Am Fam Physician 110(4): 353-61 [PubMed]
  5. Zuber (2002) Am Fam Physician 65(7):1409-12 [PubMed]

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