An epidermoid cyst, also known as an epidermal inclusion cyst, is a semi-solid cyst. The cyst wall is stratified squamous epithelium, and the contents consist of macerated keratin and lipid-rich debris. The epidermoid cyst is a common lesion that can arise on the face, trunk, extremities, in the mouth, or on the genitals at any age. They are more common in men. Several etiologic factors have been implicated in the formation of epidermoid cysts, including traumatic or iatrogenic implantation of epidermal elements, sequestration of epidermal rests, occlusion of the eccrine duct or pilosebaceous unit, and human papillomavirus (HPV) infection. Epidermoid cysts are a feature of several hereditary syndromes, such as Gardner syndrome, pachyonychia congenita, and the basal cell nevus syndrome. It is rare to see an epidermoid cyst in a pre-pubertal patient; in such cases, other diagnoses should be carefully considered.
Epidermoid cysts are benign and usually asymptomatic, but they may be painful if ruptured or infected. Rarely, malignancies such as basal cell carcinoma, squamous cell carcinoma, and mycosis fungoides have developed within these cysts.
ICD10CM: L72.0 – Epidermal cyst
SNOMEDCT: 419893006 – Epidermoid cyst
Differential Diagnosis & Pitfalls
Pilar cyst (trichilemmal cyst) – most commonly located on the scalp; usually has a firmer consistency on palpation
Epidermoid cysts, sometimes known as sebaceous cysts (a misnomer), contain a soft "cheesy" material composed of keratin, a protein component of skin, hair, and nails.
Epidermoid cysts form when the top layer of skin (epidermis) grows into the middle layer of the skin (dermis). This may occur due to injury or blocked hair follicles.
The lesion may be asymptomatic, but rupture of the epidermoid cyst can result in significant discomfort.
Who’s At Risk
Epidermoid cysts are a common lesion that affect people of all ages.
Signs & Symptoms
Epidermoid cysts can be located almost anywhere but are most common on the face, neck, scalp, or trunk.
A cyst appears as a dome-shaped, skin-colored growth that usually moves when touched and pressed upon. It may have a small opening in the center.
The cyst can be well-defined or irregular due to prior rupture, scarring, and regrowth.
If manipulated or infected, the cyst can become red and may be tender.
None necessary. It is advised not to try to express the material within cysts as further inflammation and even infection may result.
When to Seek Medical Care
See your primary care physician or a dermatologist if a cyst becomes inflamed or painful.
Inflamed, non-infected cysts may be injected with steroids to reduce inflammation.
Incision and drainage can provide immediate reduction in the cyst. However, this is a temporary measure. After this treatment, a cyst will refill with the cheesy contents because the lining of the cyst has not been removed.
Cysts may be removed (excised) surgically.
Bolognia, Jean L., ed. Dermatology, pp.1721-1723. New York: Mosby, 2003.