Epidermal Inclusion Cysts (EIC) are also referred to as Epidermoid Cysts, Epidermal Cysts, Infundibular Cysts or Keratin Cysts. They are probably the most common benign skin tumor, estimated to be found in 20% of adult individuals. EICs most commonly are found on the face, neck, and trunk, areas where there is little hair, but may be found in almost any location except the scalp (scalp cysts are pilar cysts). Most cysts arise during adult life.
They frequently result from plugging of the folicullar orifice and may be associated with cystic acne. Deep penetrating injuries such as sewing machine needles or staples or nail injuries may result in EICs. Penetrating injuries into bone may result in the formation of an intraosseus epidermoid cyst (Samlaska CP, Hansen MF. Intraosseous epidermoid cysts J Am Acad Dermatol 1992;27:454-455). They are more than twice as common in men as in women.
They present as compressible but not fluctuant cystic masses. The overlying skin may be smooth or shiny and there may be a central punctum. If the cyst ruptures it induces a vigorous foreign body reaction, inducing an intense inflammatory response…giving the impression that the cyst is infected, but it is not (see above). There is often redness, pain, swelling and local heat. They are frequently misdiagnosed as being an infection.
TREATMENT: I rarely surgically excise EICs anymore. One reason is that few insurance companies cover the cost. The surgical scar is three times as large as the cyst and if any fragment is left behind the whole procedure is a waste…the cyst comes back and now it is buried in scar. Ruptured cysts need to be drained and the material that comes out is pasty, macerated and cheesy material that has a very pungent odor. The easiest and least scarring procedure is a simple incision and drainage. I numb the area over the center of the cyst, stab it with an 11 blade and use a closed curette to remove the cheesy content. If I am lucky and the cyst is not scarred down, I can hook the cyst wall and remove the cyst like turning a pillow case inside out…and the cyst is permanently removed without scarring. Otherwise the cyst is dramatically reduced and heals with flat, normal appearing skin. If the cyst inflates again with time…months to years…the procedure can be performed again. If the cyst is not ruptured it does not need to be treated. To read more about EICs click HERE and HERE. To read about Dermoid Cysts click HERE.