Bone cyst - Causes

The cause or causes of both unicameral and aneurysmal bone cysts are unclear, although several theories have been suggested.

These are described below.

Unicameral bone cyst

A leading theory is that unicameral bone cysts are caused by a build-up of fluid, resulting in high pressure and obstruction. This is thought to happen when rapid bone growth during childhood occasionally disrupts the workings of the cells.

There is some limited evidence to suggest there may be certain genetic mutations that can make a person more likely to develop a unicameral bone cyst.

A genetic mutation occurs when the normal instructions carried in certain genes (single units of genetic material) become scrambled. This means some of the functions and processes of the body will not work in the normal way.

Aneurysmal bone cyst

Blood is the fluid that forms inside an aneurysmal bone cyst. This suggests that an underlying abnormality with the blood vessels inside an affected bone causes the problem. However, it is unclear exactly what type of abnormality is involved or what causes it.

One theory is that a previous injury to the bone may damage the blood vessels, leading to a build-up of blood inside the bone. Another theory is that other non-cancerous growths (benign tumours) inside the bone may disrupt the blood supply, resulting in the formation of an aneurysmal bone cyst.