Slide 65: Ruptured Epidermal Inclusion Cyst
 
 
 

Here it's easy to understand the nature of this lesion.  We have a benign cyst, lined by stratified squamous epithelium, present in the dermis.  This probably came into being as a puncture wound in the skin which drove a small piece of epidermis down into the dermis.  Rather than dying and being removed, it survived and formed the cyst.  In this case we even see a little sinus tract communicating to the skin surface. See this slide with the virtual microscope.

Note the cyst lining composed of keratinized squamous epithelium. You should be able to find the foreign body reaction at the edge of the cyst, and may even be able to discern the site of rupture of the cyst wall. What are the giant cells reacting to? How would a cyst of this type form? Try slide 152 for another example, and answers to these questions.

Mark Braun, MD braunm@indiana.edu
Copyright 1998, the Trustees of Indiana University