Abstract

A cyst is a closed sac, having a distinct membrane and division compared with the nearby tissue. Hence, it is a cluster of cells that has grouped together to form a sac (not unlike the manner in which water molecules group together, forming a bubble); however, the distinguishing aspect of a cyst is that the cells forming the "shell" of such a sac are distinctly abnormal (in both appearance and behaviour) when compared with all surrounding cells for that given location. It may contain air, fluids, or semi-solid material. A collection of pus is called an abscess, not a cyst. Once formed, sometimes a cyst may resolve on its own. When a cyst fails to resolve, it may need to be removed surgically, but that would depend upon its type and location.

Cancer-related cysts are formed as a defense mechanism for the body, following the development of mutations that lead to an uncontrolled cellular division. Once that mutation has occurred, the affected cells divide incessantly (and become known as cancerous), forming a tumour. The body encapsulates those cells to try to prevent them from continuing their division and to try to contain the tumour, which becomes known as a cyst. That said, the cancerous cells still may mutate further and gain the ability to form their own blood vessels, from which they received nourishment before being contained. Once that happens, the capsule becomes useless and the tumour may advance from benign to a cancer.

Some cysts are neoplastic and thus, are called cystic tumors; many types are not neoplastic. Some are dysplastic or metaplastic. Pseudocysts are similar to cysts (having a sac filled with fluid), but lack an epithelial lining.

Terminology

A small cyst that requires magnification to be seen, may be called a microcyst. Similarly, a cyst that is larger than usual or compared to others, may be called a macrocyst.

Types

The aneurysmal bone cyst is a neoplastic cyst, more specifically, an aggressive lesion with radiographic cystic appearance.

Types | Cystic fibrosis

Despite being described in 1938 as the microscopic appearance of cysts in the pancreas, cystic fibrosis is an example of a genetic disorder whose name is related to fibrosis of the cystic duct (which serves the gallbladder) and does not involve cysts.

This is just one example of how the Greek root "cyst-", which simply means a fluid-filled sac, also is found in medical terms that relate to the urinary bladder and the gallbladder, neither of which involve cysts.

Cystic neoplasm

Examples of neoplastic cysts include:

- Dermoid cyst

- Keratocystic odontogenic tumor

- Calcifying odontogenic cyst

Treatment

Treatment ranges from simple enucleation of the cyst to curettage to resection. There are cysts—e.g., buccal bifurcation cyst—that resolve on their own, in which just close observation may be employed, unless it is infected and symptomatic.

Related structures

A pseudocyst is similar collection without a distinct membrane.

A syrinx in the spinal cord or brainstem is sometimes inaccurately referred to as a cyst.