Cyst, Sebaceous (Epidermal Cyst)
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- The term “sebaceous cyst” is a misnomer.
- The correct nomenclature is “epidermoid cyst” because these structures have no sebaceous gland component (1).
- Also known as epidermal inclusion cyst and infundibular cyst
- A benign, encapsulated, subepidermal nodule filled with keratinaceous material produced by the stratified squamous epithelium lining the cyst wall
- Most commonly located on face, neck, trunk
- Synonym(s): epidermal inclusion cysts; epidermal cysts; infundibular cysts; keratin cysts; inclusion cysts
- “True sebaceous cysts” that originate from the sebaceous gland are known as steatocystoma simplex. These are rare.
- Most common cutaneous cyst
- Predominant sex: male > female (2:1)
- Predominant age: most common in 3rd to 4th decades
- Rare before puberty
- An estimated 1% of epidermoid cysts are found to have malignant transformation (2).
- Squamous cell carcinomas are the most common (70%), followed by basal cell carcinoma (10%).
Etiology and Pathophysiology
- Result from plugging of the follicular orifice
- May occur by epidermal implantation through deep penetrating injuries
- Often result from rupture or occlusion of pilosebaceous follicles resulting in the accumulation of keratin in the subepidermal or dermal layer of the skin
- Damage to hair follicle
- Ruptured sebaceous gland
- Congenital trauma (translocation of surface epithelial cells deep to the dermis) (3)
Most cases are sporadic and nonfamilial. Epidermoid cysts are also noted in the following:
- Gardner syndrome (autosomal dominant)
- Consider when encountering epidermoid cysts unusual in number or location (e.g., multiple digits or legs) (4), especially if found in conjunction with osteomas.
- Other genetic syndromes with cystic structures resembling epidermoid cysts such as Gorlin syndrome (autosomal dominant)
- Pachyonychia congenita type II (autosomal dominant)
Avoid significant sun exposure.