Trichilemmal cysts, also known as pilar cysts or tricholemmal cysts, are derived from the outer root sheath of the deeper parts of a hair follicle and consist of a well-keratinized epidermal wall surrounding semisolid hair keratin. They occur predominantly on the scalp, are easily enucleated, and appear as a firm, smooth, white-walled cyst without a punctum (McGavran and Binnington, 1966; Pinkus, 1969; Leppard and Sanderson, 1976). [from
OMIM]