Epidermoid epidermal inclusion cyst
An epidermoid (epidermal inclusion) cyst is a benign, keratin-filled, epithelium-lined dermal or subcutaneous sac that presents as a mobile nodule, often with a central punctum; sebaceous cyst is an inaccurate synonym because the contents are keratin rather than sebum. Most are diagnosed clinically and simply observed, and management is elective excision of the cyst wall and contents for pain, recurrent inflammation, or patient preference, with incision and drainage reserved for a fluctuant abscess.
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What this article covers
- Overview
Definition: an epidermoid cyst, also called an epidermal inclusion cyst, is a benign epithelium-lined dermal or subcutaneous sac filled with keratin, often centered on a hair follicle.
- Epidemiology
A common benign skin lesion: epidermoid cysts are among the benign lesions of the skin encountered in routine practice.
- Risk factors
Follicular origin: cysts often surround a hair follicle, which is why they are dome-shaped and can develop anywhere hair-bearing skin is present.
- Pathophysiology
Epithelium-lined keratin sac: the cyst wall is lined by epithelium that continues to produce keratin, which accumulates within the sac rather than being shed at the skin surface.
- Clinical features
Mobile nodule with a central punctum: the characteristic finding is a mobile dermal or subcutaneous nodule, often with a visible central punctum.
- Differential diagnosis
Dermatofibroma: a firm, brown-pink nodule that dimples or buttonholes when pinched, unlike an epidermoid cyst, which does not dimple.
- Diagnosis
Clinical diagnosis: a mobile dermal or subcutaneous nodule with a central punctum is characteristic and is usually sufficient to establish the diagnosis on examination alone.
- Management
First, observe an asymptomatic typical cyst, since most epidermoid cysts require no intervention.
- Complications
Recurrence: an incompletely excised cyst, with epithelial lining left behind, tends to recur.
- Prognosis
Excellent for a typical cyst: most epidermoid cysts are benign and stable, and observation alone is sufficient.
- Prevention
No specific prevention exists for a sporadic cyst, since it arises from a follicle-associated epithelial sac rather than a modifiable exposure.
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