A trichilemmal cyst is a cyst derived from the outer root sheath of the deeper parts of a hair follicle. It consists of a well-keratinized epidermal wall surrounding semi-solid hair keratin.
Epidemiologically, they are more common in women and in middle age. There is an autosomal dominant association. Often patients have multiple lesions.
The most common sites for trichilemmal cysts are hair-bearing areas, typically the scalp. Clinically, they present as smooth and mobile cysts within the dermis. The cyst may marsupialize by fusing with surrounding surface epidermis. Patients may complain of discharge. Rupture may exacerbate local inflammation. Complications include rarely extensive local invasion - proliferating trichilemmal cyst - or malignancy.
Treatment is by excision.
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