Small skin tumour that results when skin cells are pushed under the skin by an injury. The wound heals normally and is usually forgotten, but the cells under the skin become a cavity (cyst), formed by tiny sweat and sebaceous glands which have also been pushed under the skin, in which fluid accumulates. A few months after the healing of the wound the cyst may be large enough to be noticed; it may be several millimetres in diameter, and positioned on the site of the wound. A distinction should be made between a sebaceous cyst and a ganglion. Epidermoid cysts can easily be removed by surgery, because they are loosely bedded in tissue.