INTRODUCTION The epidermoid cyst is also referred to as infundibular cyst, epidermal inclusion cyst, keratinous cyst, or frequently and erroneously sebaceous cyst. The sebaceous cyst is similar clinically but arises from obstruction in the hair follicle and is referred to as a pilar or trichilemmal cyst. The epidermoid cyst is a very common skin lesion that arises from traumatic entrapment of surface epithelium or from aberrant healing of the infundibular epithelium of the hair follicle following episodes of follicular inflammation. They can also be seen following any injury to the skin, including surgery. When congenital, they likely arise from sequestration of epidermal rests along embryonic fusion planes. Epidermoid cysts are not of sebaceous origin, but rather produce normal keratin rather than sebum. These cysts may present anytime from adolescence through adulthood, but commonly in the third and fourth decades.
CLINICAL PRESENTATION On the eyelid epidermoid cysts present as a slow-growing round, firm flesh-colored to yellow or white lesion within the dermis or subcutaneous tissue. On the face they may be associated and causally related to the obstructing effects of acne vulgaris and seborrhea. Epidermoid cysts are usually solitary, fluctuant, and freely movable, and are generally less than 1 to 2 cm in diameter. Sometimes a central pore or depression is seen, but this is an inconsistent finding. The cyst can be pigmented in darker skinned individuals. A foul-smelling cheese-like material may discharge from the lesion. Rupture of the cyst wall may cause an inflammatory foreign body reaction, with associated tenderness or pain. Less frequently the cyst can become infected. Rarely carcinomas, such as basal cell carcinoma, may arise within an epidermoid cyst.
HISTOPATHOLOGY Epidermoid cysts are lined by keratinized, stratified squamous epithelium nearly identical to the epidermis. Keratohyaline granules are often prominent in the epithelial cells nearer the cyst lumen. Adnexal structures are absent from the cyst wall. Laminated keratin fills the cyst lumen.
TREATMENT Asymptomatic epidermoid cysts may respond to injections of intralesional tiramcinolone, particularly when they are inflamed. Incision and drainage is a fast and easy method, but the keratin-producing lining remains and recurrence is common. Dissection of the overlying epithelium and shelling out of the cyst is very effective. However, after inflammation the cyst may be more firmly adherent to surrounding tissues so that a full-thickness elliptical excision including the entire cyst wall may be required.
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