Epidermoid/Epidermal Inclusion Cyst
Elsa F. Velazquez, MD
Key Facts
Etiology/Pathogenesis
Infundibular cyst variant
Implantation (inclusion) cyst variant
Clinical Issues
Very common lesions
Usually affecting face, neck, and trunk
Microscopic Pathology
Unilocular cyst
Lined by squamous epithelium with granular layer
Contains laminated (“basket weave”) keratin
May rupture and become inflamed
Keratin granuloma
Top Differential Diagnoses
Tricholemmal (pilar) cyst
Vellus hair cyst
Dermoid cyst
HPV-related epidermoid cyst
 A solitary epidermoid cyst is appreciated in the dermis. Note the thin squamous epithelium  and abundant keratin contents  . The punctum is not represented in this section. |
 The contents of the epidermoid cyst consist of laminated orthokeratotic material. The cyst lining is composed of a bland squamous epithelium  similar to the epidermis. |
TERMINOLOGY
Abbreviations
Epidermoid/epidermal inclusion cyst (EIC)
Synonyms
Infundibular cyst
Definitions
Unilocular cysts lined by epidermis-like epithelium
ETIOLOGY/PATHOGENESIS
Etiology
Damage to the pilosebaceous unit
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