Epidermal Inclusion Cyst

Epidermal inclusion cysts are the most common cutaneous cysts. Numerous synonyms for epidermal inclusion cysts exist, including epidermoid cyst, epidermal cyst, infundibular cyst, inclusion cyst, and keratin cyst. These cysts can occur anywhere on the body, typically present as nodules directly underneath the patient's skin, and often have a visible central punctum. They are usually freely moveable. The size of these cysts can range from a few millimeters to several centimeters in diameter. Lesions may remain stable or progressively enlarge over time. There are no reliable predictive factors to tell if an epidermal inclusion cyst will enlarge, become inflamed, or remain quiescent. Infected and/or fluctuant cysts tend to be larger, erythematous, and more noticeable to the patient. Due to the inflammatory response, the cyst will often become painful to the patient and may present as a fluctuant filled nodule below the patient's skin. The center of epidermoid cysts almost always contains keratin and not sebum. This keratin often has a "cheesy" appearance. They also do not originate from sebaceous glands; therefore, epidermal inclusion cysts are not sebaceous cysts. The term "sebaceous" cyst should not be used when describing an "epidermoid" cyst. Unfortunately, in practice, the terms are often used interchangeably.