What is a keratinous cyst?

Updated: Jan 30, 2020
  • Author: Ginard I Henry, MD; Chief Editor: Gregory Gary Caputy, MD, PhD, FICS  more...
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Benign subdermal cysts that pathologically collect normally skin surface secreted materials have long had a number of labels and resultant confusion in the terminology. Descriptors such as keratinous cysts, sebaceous cyst, [23] wen, atheroma, steatoma, epidermoid/epidermal inclusion cyst [EIC], pilar cyst, and trichilemmal cyst have been previously used interchangeably but not always correctly. Essentially, the two most common types of subdermal cysts are keratinous cysts and sebaceous cysts. Keratinous cysts trap keratin within a pseudo-epithelium sack whereas sebaceous cysts trap sebum produced from apocrine glands. Keratinous cysts are more common and have also been described as epidermoid or epidermal inclusion cysts. Cornified epithelium, a very well demarcated granular layer, and multiple lamellae of keratin without calcification characterize these epidermoid cysts. (See the image of keratinous cyst, below.)

Subepidermal lesion: Keratinous cyst (epidermal in Subepidermal lesion: Keratinous cyst (epidermal inclusion cyst).

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