Epidermoid cyst

Epidermoid cyst (previously called an epidermal inclusion cyst or sebaceous cyst) is a common benign, slow-growing cystic lesion that develops from the epidermis. It is lined by stratified squamous epithelium and contains keratinous material rather than sebum. Epidermoid cysts may occur anywhere on the body but are most common on the face, neck, trunk, and back.

Most epidermoid cysts are asymptomatic, but they may become inflamed, rupture, or become secondarily infected. Complete surgical excision is curative.

Pathophysiology (Brief)

Epidermoid cysts develop when epidermal cells become implanted into the dermis or when the hair follicle becomes obstructed.

The cyst wall continues producing keratin, leading to gradual enlargement of the cyst.

Risk factors include:

• Trauma

• Acne

• Hair follicle obstruction

• Previous surgery

• Genetic disorders (rare)

Signs & Symptoms

Typical lesions include:

• Slow-growing skin-colored nodule

• Round, firm, mobile cyst

• Central punctum

• Usually painless

Common sites:

• Face

• Neck

• Scalp

• Back

• Chest

Inflamed or infected cysts may present with:

• Pain

• Redness

• Swelling

• Purulent discharge

• Rupture with foul-smelling keratin material

Diagnostic Criteria

Diagnosis is usually clinical and based on:

• Slowly enlarging subcutaneous cyst

• Characteristic central punctum

• Soft to firm consistency

• Mobile lesion

Investigations

Diagnosis is usually clinical.

Special investigations

• Ultrasound if diagnosis is uncertain.

• Histopathological examination following excision confirms the diagnosis.

Treatment

Non-pharmacological Treatment

• Observe asymptomatic small cysts.

• Avoid squeezing or puncturing the cyst.

• Treat secondary infection if present before definitive surgery.

Surgical Treatment

• Complete surgical excision of the cyst with its wall intact to prevent recurrence.

Complications

• Secondary bacterial infection

• Rupture

• Abscess formation

• Recurrence following incomplete excision

• Cosmetic concerns

Prevention

There is no proven method of prevention.

Early treatment of inflamed lesions may reduce complications.

Patient counselling (Important)

• Epidermoid cysts are benign and are not cancerous.

• They usually grow slowly over several years.

• Do not squeeze or puncture the cyst.

• Complete surgical removal usually provides permanent cure.