A dermal nodule 0.5-2.0 cm in diameter is typical. A central pore is usually visible. The patient often relates being able to squeeze out a foul-smelling material.

EPIDERMAL INCLUSION CYST

The epidermal inclusion cyst (EIC)--formerly known as the sebaceous cyst--is a sphere of skin within the skin. The cyst wall constantly flakes into the center of the cyst causing it to enlarge over time.

• The EIC may form from occlusion of a pore and subsequent dilatation of the underlying follicle. Alternatively, penetrating injuries may cause dermal implantation of epidermis, leading to EIC formation.

Clinical

A dermal nodule 0.5-2.0 cm in diameter is typical. A central pore is usually visible. The patient often relates being able to squeeze out a foul-smelling material. If left alone, the lesion may at some point become acutely inflamed. This is usually is a result of rupture of the cyst wall and release of the cyst contents into the surrounding dermis. A foreign body response results. The patient then presents with an acutely inflamed and painful nodule where the asymptomatic bump used to be. Initially, the lesion is firm, but later it becomes fluctuant and may ultimately drain. The skin heals having extruded the cyst. Alternatively, the inflammation may subside and the lesion returns to an asymptomatic bump. When patients present this way, the clinician often assumes the lesion is "infected". Cultures usually show it is not.

Differential Diagnosis

• Benign adnexal neoplasm (e.g. pilomatricoma, neurofibroma, cylindroma, chondroid syringoma, poroma)
• Lipoma
• Dermatofibroma
• Scar
• Calcinosis cutis
• Nevus
• Squamous cell carcinoma, basal cell carcinoma or melanoma
• Granulomatous inflammation

Malignancy?

In one review of 13,746 EICs, 48 contained a malignancy, for an incidence of 0.3% and with the most common malignancy being squamous cell carcinoma

Treatment

• Complete surgical excision.
  
• Observe (But make sure you are certain of the diagnosis. Rarely, a tumor or metastatic disease presents as a dermal/subcutaneous nodule.)
• If acutely inflamed and fluctuant, drain. If acutely inflamed but not fluctuant, use intralesional steroids.

If the diagnosis is assured (e.g., pore is visible, drains white, smelly material), the EIC may be ignored as it is entirely benign. If the diagnosis is in question, removal is desired by the patient, or the lesion constantly gets inflamed, surgical excision is the treatment of choice. Usually, the lesion needs to be removed in its entirety. If any portion of the wall is left behind, recurrence is common.

If the lesion becomes acutely inflamed and is fluctuant, it should be incised and drained. If not, warm compresses and an oral antibiotic are in order. If there is a suspicion of infection, an antibiotic should be prescribed.

Any inflammatory episode may cause resolution of the lesion. If not, the lesion may be surgically excised after the inflammation has subsided (e.g., wait 4-6 weeks). Surgery acutely will be very difficult with much intraoperative bleeding and pain.

Additional Pictures

An EIC of the ear.

RegionalDerm

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