Dermoid vs. Epidermal Cyst: Key Differences
The fundamental difference between dermoid and epidermal cysts is histopathologic: dermoid cysts contain skin appendages (hair follicles, sebaceous glands, sweat glands) within their wall, while epidermal cysts are lined only by keratinized stratified squamous epithelium without these adnexal structures 1, 2, 3.
Histopathologic Distinction
The distinction between these two entities can only be definitively made by histopathologic examination after excision 1. This is the gold standard for diagnosis:
Epidermal (epidermoid) cysts: Lined by keratinized stratified squamous epithelium composed of an ectodermic layer alone, containing desquamated squamous epithelium and keratin in the lumen 1, 3
Dermoid cysts: Lined by stratified epithelium (dermis) with skin adnexa including sebaceous glands, sweat glands, and hair follicles 1, 3
Clinical and Radiologic Features
While clinically these lesions are often indistinguishable 4, some patterns emerge:
Location patterns:
- Congenital epidermal cysts: Tend to grow at the upper part of structures (e.g., upper auricle) 3
- Dermoid cysts: More commonly at lower and posterior locations (e.g., lower/posterior auricle) 3
- Both can occur in the oral cavity (1.6% of cases), predominantly in the sublingual region 1
Radiologic differences (when orbital):
- Epidermal cysts: Average radiodensity of 18.9 ± 56.2 HU on CT 5
- Dermoid cysts: Average radiodensity of -67.9 ± 63.3 HU on CT (lower density attributed to sebaceous gland activity) 5
- Dermoid cysts show more frequent focal bony notching, bone remodeling, and dumbbell-shaped bony changes 5
Management Implications
The distinction is largely academic since both types have identical management 4:
- Incision and drainage is recommended for inflamed epidermal cysts 6
- Complete surgical excision (including entire cyst wall) is the definitive treatment for both types to minimize recurrence 7
- Gram stain and culture of pus from inflamed epidermal cysts are not recommended 6
- Antibiotics are only indicated if systemic inflammatory response syndrome (SIRS) is present 6
Clinical Pitfall
Do not attempt to distinguish these lesions clinically or base treatment decisions on the presumed type—both require the same surgical approach, and only histopathology provides definitive classification 1, 4, 2.