An epidermoid cyst is the growth of normal tissue in an abnormal place in the body. It contains skin and nail tissue. An epidermoid cyst is also called an epidermoid tumor. The cyst is benign, meaning it is not cancer. But in rare cases, an epidermoid cyst may turn into skin cancer.
An epidermoid cyst grows very slowly. A brain or spinal cord cyst usually first appears when a person is an adult. It's most often found in one of these places:
- An area where the brain meets the brain stem
- On the pituitary gland
- Along the inside of the skull
- Growing through the skull bone