Histopathology of Epidermoid Cysts
Epidermoid cysts are characterized histologically by a cyst wall lined with stratified squamous epithelium containing keratin material, without skin appendages. 1, 2, 3
Key Histopathological Features
Epithelial Lining
- Thin layer of keratinizing stratified squamous epithelium similar to epidermis 4
- Complete cyst wall that must be entirely removed during excision to prevent recurrence 1
- No skin appendages (distinguishing feature from dermoid cysts) 4, 3
Cyst Contents
- Filled with keratin material 5
- Nucleate and anucleate squames visible on cytology 2
- Keratinous debris in varying amounts 2
Surrounding Tissue
- Fibrous connective tissue surrounding the epithelial lining 4
- May show inflammatory infiltrate, especially in infected cysts 2, 4
Histopathological Differential Diagnosis
Dermoid Cysts
- Unlike epidermoid cysts, dermoid cysts contain skin appendages (sebaceous glands, hair follicles) within the cyst wall 4, 3
- Part of the spectrum of cystic teratomas 3
Other Squamous-Containing Lesions
- Branchial cysts
- Thyroglossal cysts
- Pilomatricoma
- Sebaceous cysts 2
Histopathological Variations
Uncomplicated Epidermoid Cysts
- Clear background with high cellularity on cytology 2
- Abundant squamous cells (both nucleate and anucleate) 2
Infected/Complicated Epidermoid Cysts
- Dense inflammatory infiltrate in addition to squamous elements 2
- May show areas of focal ulceration in the cyst wall 3
- Chronic inflammatory changes may be present 3
Clinical-Pathological Correlation
Histopathological examination is recommended when cysts have suspicious features such as:
- Size greater than 1.5 cm
- Rapid growth
- Nodular mass
- Ulceration
- Extensive scarring
- Fixation to surrounding tissues 1
Histopathology is essential to rule out potential malignant transformation, which is rare but possible 1, 6
Diagnostic Approach
Fine needle aspiration cytology may show:
- Clear background
- High cellularity
- Nucleate and anucleate squames
- Keratinous material (though less than cellular elements) 2
Definitive diagnosis requires histopathological examination of the excised specimen 1, 4
Importance of Complete Excision
- Incomplete removal of the cyst wall is associated with recurrence rates of 2.2-8.3% 1
- The entire cyst wall must be removed to prevent recurrence 1
Understanding these histopathological features is crucial for accurate diagnosis and appropriate management of epidermoid cysts, particularly to distinguish them from other cystic lesions and to ensure complete excision to prevent recurrence.