An epidermoid cyst (sometimes called an “epidermal inclusion cyst”, “epidermal cyst”, or “follicular infundibular cyst”) is a benign (non-cancerous) cystic lesion of the skin. It consists of a sac or cavity lined by stratified squamous epithelium including a granular layer, which produces keratin inside the lumen. Despite older names such as “sebaceous cyst,” epidermoid cysts do not originate from sebaceous glands nor do they contain sebum.
Why Do Epidermoid Cysts Develop?
Epidermoid cysts form through several mechanisms. The most common is via the infundibulum of hair follicles: blockage, irritation, or damage leads to invagination or inward growth of epidermal (skin surface) cells into the dermis (deep skin layer). Those cells continue to keratinize (produce keratin) and the accumulated keratin forms the cyst lumen.
Other less common causes include traumatic or surgical implantation of epidermal elements into deeper layers, embryonic sequestration of epidermal rests during development, and in some cases human papillomavirus (HPV) infection, particularly in areas such as the palms or soles. Genetic syndromes are occasionally involved when multiple cysts are present.
Where and in Whom Do Epidermoid Cysts Occur?
Epidermoid cysts may occur in people of all ages, though they are more common in adults; they are less frequent in children. There is a slight male predominance in many clinical series, though ratios vary.
They tend to appear most often on skin that has hair follicles: face, neck, scalp, trunk. In one large series of 432 excised cysts, about 65% were on the face, around 11% on the trunk, and the rest on scalp, neck, or extremities. Occasionally they occur in hairless skin areas via trauma or other unusual mechanisms.
What Are the Clinical Features?
Clinically, an epidermoid cyst presents as a slow-growing, painless (or mildly tender if inflamed) subcutaneous or dermal mass. It is usually mobile over underlying structures, with a discrete border. The overlying skin may show a central, small pore or “punctum” — this represents the connection to the follicular infundibulum or blocked follicle.
If the cyst ruptures or becomes inflamed, there may be redness, swelling, and pain. Sometimes it is mistaken for an abscess. Rarely, very large cysts or cysts in certain locations cause discomfort from mass effect, for example pressure on adjacent structures.
What does an epidermoid cyst look like under a dermatoscope?
Under dermoscopy, epidermoid cysts often show a central punctum (sometimes called the “pore sign”), which corresponds to the follicular opening. This feature is very helpful, especially when the punctum is not visible to the naked eye.
Other characteristic dermoscopic findings include homogeneous areas of white, yellow or blue coloration. The white areas reflect compact keratin; yellow often arises when layered keratin mass produces a mass effect; bluish hues are attributed to light scattering (Tyndall effect) in deeper keratin material.
In non-ruptured cysts, vessels tend to be less prominent or fine; in ruptured or inflamed cysts dermoscopy may show more vascular features (branched linear vessels, erythema) and sometimes red lacunae.
Are Epidermoid Cysts Dangerous?
For the most part, they are benign and pose minimal risk. However, there are some potential complications:
·Inflammation or rupture: if the cyst wall breaks, its contents leak and provoke a foreign body inflammatory response. This may cause pain, swelling, or infection.
·Cosmetic disfigurement: especially for cysts on visible skin areas.
·Rare malignant transformation: there are case reports of squamous cell carcinoma and other skin cancers arising from epidermoid cysts, but these are very rare.
·Recurrence: if treatment does not fully remove the cyst wall (capsule), the cyst may recur.
·In special locations, such as the central nervous system or skull bone, there may be more risk depending on mass effect or surgical complications.
How Are Epidermoid Cysts Treated?
The definitive treatment is complete surgical excision. That means removal of the entire cyst including its wall (capsule) to prevent recurrence. If there is active infection or inflammation, that is treated first with antibiotics or anti-inflammatory drugs, and excision is delayed until inflammation subsides.
In some cases, minimal excision techniques are used for small cysts or those in cosmetically sensitive areas; these aim to reduce scarring. But risk of recurrence can be higher if the capsule is left behind. For deep or intracranial epidermoid cysts, neurosurgical removal is performed, often guided by imaging, with the goal of gross total resection.
What Should Be Expected After Treatment?
Once a cyst is fully excised, prognosis is excellent. Healing is usually good; there may be a scar, whose appearance depends on size and location. Risk of recurrence is low if the entire wall was removed. If removal was partial and the capsule left behind, recurrence rates rise substantially.
In cases of intracranial or bone cysts, outcome depends on how completely the cyst was removed and whether there is damage to adjacent structures. Long-term follow-up is often required. And dermoscopy can be highly effective for this.