What is an epidermoid cyst?
An epidermoid cyst is a benign cyst derived from the infundibulum or upper portion of a hair follicle, encapsulated in a thin layer of epidermis-like epithelium. Epidermoid cysts are typically filled with keratin and lipid-rich debris [1,2].
Synonyms for an epidermoid cyst include:
- Epidermal cyst
- Epidermal inclusion cyst
- Epithelial cyst
- Follicular infundibular cyst
- Infundibular cyst
- Keratin cyst
- Sebaceous cyst (this is a common misnomer, as these cysts do not involve sebaceous glands, nor do they contain sebum).
Who gets an epidermoid cyst?
Epidermoid cysts most commonly occur in adults, particularly when young-to-middle aged. They occur twice as frequently in men than in women .
Genetic disorders which may increase the risk of developing multiple epidermoid cysts include :
Syndromes associated with epidermoid cysts
What causes an epidermoid cyst?
An epidermoid cyst generally results from an occluded pilosebaceous unit.
On non-hair-bearing areas of the body, such as the buttock, palm of the hand, or sole of the foot, an epidermoid cyst may be due to traumatic implantation of epidermal cells into the dermis where keratin accumulates within an epithelium-lined sac .
What are the clinical features of an epidermoid cyst?
The clinical features of an epidermoid cyst include :
- A firm, flesh-coloured or yellowish round papule or nodule fixed to the skin surface but typically mobile over deeper layers
- Diameter 1–3 cm
- A central punctum
- Foul-smelling cheesy debris can be expressed from the central punctum.
Epidermoid cysts are most common on the central trunk (eg, chest and shoulders) and face but can occur almost anywhere on the body. Epidermoid cysts are common the scrotum and vulva. They may be solitary or multiple, and are generally asymptomatic.
What are the complications of an epidermoid cyst?
Rupture of the cyst contents into the dermis results in swelling, redness, and tenderness. This can be due to trauma or bacterial infection, commonly by Staphylococcus aureus, Escherichia coli, and group A streptococcus .
Cutaneous squamous cell carcinoma may very rarely arise within an epidermoid cyst .
How is an epidermoid cyst diagnosed?
The diagnosis of an epidermoid cyst is usually made clinically.
- A cystic structure in the dermis
- A single cavity (unilocular)
- An epithelial lining without rete ridges and with a granular layer with keratinohyaline granules.
Ultrasound can be used in the initial evaluation of a soft tissue mass but is not usually required for a typical epidermoid cyst.
What is the differential diagnosis for an epidermoid cyst?
Differential diagnoses for an epidermoid cyst include:
- Lipoma — a mobile 2–10 cm dome or egg-shaped subcutaneous lump with a rubbery or soft and smooth consistency
- Trichilemmal cyst — a firm, mobile, 0.5–5 cm subcutaneous nodule without a central punctum, usually presenting on the scalp; it has a thick capsule and is not typically prone to rupture
- Acne pseudocyst — this lacks a capsule and is associated with other signs of acne such as comedones, inflammatory papules, pustules, and nodules
- Myxoid pseudocyst — a shiny papule arising at the end of a digit
- Dermoid cyst — this has epidermal and dermal components and arises in early childhood
- Human papillomavirus (HPV)-related epidermal cyst — a lesion with a hard, keratinous surface.
What is the treatment for an epidermoid cyst?
Most small uncomplicated epidermoid cysts will not require treatment.
The most effective treatment for an epidermoid cyst is complete surgical excision with an intact cyst capsule. Removal of the entire cyst lining decreases rates of recurrence . This can be difficult to achieve following cyst rupture. Histological examination of the surgical specimen is recommended due to the small risk of malignant transformation and misdiagnosis .
In cases of infection, initial antibiotics, incision and drainage may be indicated.
What is the outcome for an epidermoid cyst?
Epidermoid cysts are typically benign and slow growing, rarely undergoing malignant transformation. Occasionally, they resolve spontaneously without intervention .