Description

• 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.

Epidemiology

• 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
• Spontaneous
• Damage to hair follicle
• Ruptured sebaceous gland
• Congenital trauma (translocation of surface epithelial cells deep to the dermis) (3)

Genetics
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)

General Prevention

Avoid significant sun exposure.