The epidermal inclusion cyst (EIC), also known as sebaceous cyst and epidermoid cyst, is the most common cyst of the skin. It ranges in size from a few millimeters to a few centimeters and originates from the follicular infundibulum. Its contents are a cheesy, malodorous mixture of degraded lipid and keratin. It often ruptures, with associated pain and inflammation.
Precipitating factors: develop spontaneously or as a result of trauma
Arise from epidermal cells in the dermis. These cells may be implanted as a result of trauma or arise from follicular infundibular cells. These cells may proliferate as a result of pilosebaceous occlusion. Multiple lesions have associated with Gardner syndrome and basal cell nevus syndrome.
Within the dermis or subcutaneous fat, there is a well-demarcated cyst containing laminated keratin debris. The cyst wall is lined by stratified squamous epithelium featuring a granular cell layer. In ruptured cysts, there is a foreign body granulomatous reaction with multinucleated giant cells.
An EIC is a dome-shaped, smooth, firm, well-circumscribed mobile nodule frequently protruding above the skin surface with a central pore (Fig. 42.1). They range in size from a few millimeters to a few centimeters. They typically present on hair-bearing skin, such as the upper trunk, neck, earlobes, and face. After rupture, these cysts develop a strong inflammatory reaction as a result of the spillage of cyst contents into the dermis. In this setting, the cysts become red, inflamed, tender, and enlarged. Perilesional fibrosis may develop with chronic inflammation.
(A) Elliptical excision around epidermal inclusion cyst punctum. (B) Cyst sac being “delivered” from excision site.
Pilars cyst, dermoid cyst, branchial cleft cyst, nodular fibroma, and dermal tumors may cause confusion with EICs. Of these lesions, only EICs feature central pores.
In the event of uncertainty of diagnosis, a biopsy can be performed to rule out neoplasm.
EICs may increase in size over time, especially with physical manipulation. These lesions frequently become inflamed, resulting in discomfort. Frank purulence may arise, requiring incision and drainage.
KEY CONSULTATIVE QUESTIONS
Is the lesion recurrently inflamed and painful?
Is the lesion symptomatic?
Is the lesion increasing in size?
Has the lesion been inflamed before?
Has the lesion been drained or excised in the past?
Would the patient prefer a surgical scar rather than keeping the cyst?