Trichilemmal cyst

**Definition:** A trichilemmal (pilar) cyst is a common, typically non-tender, intradermal or subcutaneous cyst. The cysts are typically confined to the scalp and are often multiple. They usually occur sporadically but may be inherited in an autosomal dominant manner. They are derived from the outer root sheath of the hair follicle and as such contain keratin or keratin degradation products. Rarely, they may undergo malignant transformation.

**Inclusions:** - Pilar cyst