Chapter 42: Epidermal Inclusion Cyst

INTRODUCTION

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.

EPIDEMIOLOGY

Incidence: very common

Age: adults

Race: none

Sex: equal

Precipitating factors: develop spontaneously or as a result of trauma

PATHOGENESIS

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.

PATHOLOGY

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.

PHYSICAL LESIONS

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.

DIFFERENTIAL DIAGNOSIS

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.

LABORATORY EXAMINATION

In the event of uncertainty of diagnosis, a biopsy can be performed to rule out neoplasm.

COURSE

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?

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