Epidermoid Cyst

An epidermoid cyst, also called an epidermal inclusion cyst and often loosely referred to as a sebaceous cyst even though it does not actually arise from the sebaceous glands, is a benign cyst of the skin lined by a thin layer of squamous epithelium and most commonly forms from the infundibular portion of a hair follicle. It may cause no symptoms at all, or it may be tender or painful to the touch, and it can release a thick, cheese-like material called macerated keratin if it ruptures or is opened; it typically appears on areas of the body with relatively little hair, which helps distinguish it from a related growth called a pilar cyst. It is the most commonly surgically removed type of skin cyst, accounting for an estimated eighty-five to ninety-five percent of all excised cutaneous cysts. Malignant change within an epidermoid cyst is exceedingly rare, with squamous cell carcinoma developing in only an estimated 0.011 to 0.045 percent of cases.