General and Systemic Histopathology, C601&C602
    Slide 152: Ruptured Epidermal Inclusion Cyst of Skin
    OK, there isn't much to this one, but it's pretty common for us in the clinical lab to receive a specimen that looks like this.  Generally the surgeon just pulls out fragments of the wall of the cyst and bits of its contents.  Take note of the lining and keratotic matter.

    See this slide with the virtual microscope.

    These are very common lesions of the skin, and may result from the implantation of a small fragment of viable epidermis into the deeper layers of the dermis or subcutaneous tissues. The lesion is just as it sounds, a cyst composed of epidermal elements. The cyst lining is composed of benign squamous epithelium, and the lumen eventually fills with shed keratotic matter. If these rupture, the keratin debris is considered "non-self" by the immune system, and there follows a significant and often rather painful foreign body type inflammatory reaction. Because of the swelling associated with the reaction to the keratin from a ruptured epidermal inclusion cyst, the person considers the lesion to have "grown" dramatically almost overnight. As you can guess, this is very worrisome, and most folks come right in to have it looked at, thinking it must be cancer because of the rapid "growth."

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