Broadly speaking, cysts are defined as pathological cavities, lined with epithelium (the kind of tissue that covers the body’s various surfaces) and filled with fluid, air or semi-solids. Figure 1 schematically illustrates such an epithelium-lined cavity.

Figure 1: Schematic view of a cyst, lined with epithelium cells.

A wide variety of cysts (of different origins) occur all over the body, affecting soft and hard tissues. Cysts can be further classified according to their type of epithelial lining. There are different theories about their formation.

To confuse matters a little further, there are some kinds of fluid-filled cavities in bones that are not lined by epithelium; these cavities are referred to as nonepithelial cysts (somewhat of a misnomer) or pseudo-cysts.

The head and neck region is home to a fair variety of cysts. For example, the most common cause of chronic swelling of the jaw is a cyst. There is much overlap with other benign lumps, occasionally infections of cysts occur that may lead to abscesses. Cysts, or pseudo-cysts, affecting the bones overlap with several other bone lesions.

Cysts of the head and neck can be identified by clinical examination , distinct history and some other diagnostic tests, particularly X-rays and other scan, in some cases a biopsy.