Epidermal inclusion cysts are common benign intradermal cysts lined by stratified squamous epithelium and filled with keratin. They present as slow-growing, firm, dome-shaped nodules with a central punctum, most often on the face, neck, upper back, and trunk. They may become inflamed or rupture, causing pain, erythema, and drainage of malodorous keratin. Diagnosis is clinical; treatment options include intralesional corticosteroids for inflamed cysts and definitive complete excision of the entire cyst wall to prevent recurrence.
Epidemiology and Risk Factors
- Occur in adolescents and adults; more common in men.
- Risk factors: acne-prone/oily skin, trauma or procedures that implant epidermis into dermis, genetic syndromes (Gardner syndrome—multiple EICs with osteomas and colon polyps; Gorlin syndrome).
Clinical Features
- Firm, freely movable dermal nodule 0.5–5 cm; visible central punctum.
- Non-inflamed cysts are asymptomatic; inflamed/ruptured cysts become tender, red, and may drain cheesy keratin.
- Common sites: head/neck, upper back, chest, posterior ears.
Differential Diagnosis
- Pilar (trichilemmal) cysts (scalp; lack punctum; thicker wall), lipoma, abscess, furuncle, dermoid cyst (congenital, periorbital/nasal), steatocystoma, metastatic nodules (rare), cystic BCC/SCC in atypical presentations.
Diagnosis
- Clinical; ultrasound may show well-defined hypoechoic to isoechoic lesion with posterior enhancement and punctum.
- Pathology (if excised): cyst lined by keratinizing squamous epithelium with granular layer; central lamellated keratin.
Management
- Non-inflamed cyst
- Observation if asymptomatic.
- Elective excision with complete removal of cyst wall to prevent recurrence; best performed when not inflamed.
- Techniques: elliptical excision, punch excision with expression of sac, minimal excision technique through 3–5 mm incision; close dead space to reduce seroma.
- Inflamed or ruptured cyst
- Do not attempt full excision during acute inflammation; cyst wall friable and recurrence risk high.
- Options:
- Intralesional triamcinolone (10–20 mg/mL) to reduce inflammation.
- Incision and drainage (I&D) if fluctuant abscess forms; express keratin/debris; culture if purulent; short antibiotic course if cellulitis/systemic signs (cover MSSA; consider MRSA risk).
- Plan interval complete excision after inflammation resolves (typically 4–6 weeks).
- Antibiotics
- Not needed for noninfected inflamed cysts (sterile keratin granulomas); reserve for secondary bacterial infection.
- Complications and Recurrence
- Recurrence if cyst wall not fully removed; scar formation; PIH.
- Rare malignant transformation to SCC reported within long-standing cysts—biopsy atypical or rapidly changing lesions.
- Counseling
- Explain benign nature and recurrence risk if excision incomplete.
- For facial cysts, discuss scar location and tension lines; schedule surgery when inflammation quiet.
References (recent guidelines and key reviews)
- Best practices for EIC excision and minimal excision techniques, 2021–2024.
- Management of inflamed vs infected epidermoid cysts and antibiotic stewardship, 2022–2024.
- Distinguishing pilar cysts and syndromic associations (Gardner syndrome), 2021–2024.