A bone cyst is a fluid-filled hole that develops inside a bone. They mostly occur in children and young adults.
Bone cysts do not usually cause any symptoms, they are not cancerous and they do not usually pose a serious threat to health. However, larger cysts can cause a bone to weaken, making it more vulnerable to fracture.
It is not known what causes bone cysts.
Outlook
Most bone cysts heal within six months to a year without the need for treatment.
If a bone cyst does not get better, or if treatment is recommended to help reduce the risk of a bone fracture, several effective treatment options are available. For example, steroids may be injected into the bone to encourage the cyst to heal. See Bone cyst - treatment for more information.
However, there is a one in three chance that a bone cyst will reoccur in the future, usually within two years.
Types of bone cysts
There are two main types of bone cysts. They are:
- unicameral bone cysts, which are thought to be relatively common and often do not require treatment
- aneurysmal bone cysts, which are thought to be very rare and can quickly spread through the bone, meaning treatment is necessary
These are described in more detail below.
Unicameral bone cyst
Unicameral bone cysts can develop anywhere in the body, although 90% of cases involve either the bone of the upper arm or the thigh bone.
Most cases affect younger children who are between five and fifteen years of age, with the average age at diagnosis being nine years. Boys are twice as likely to be affected by a unicameral bone cyst as girls.
Aneurysmal bone cyst
As with unicameral bone cysts, aneurysmal bone cysts can develop anywhere in the body. However, most cysts develop inside:
- the bone of the lower leg
- the spine
- flat bones, such as the vertebrae (the horseshoe shaped bones that make up the spine) or the bones of the pelvis (hipbone)
Aneurysmal bone cysts are thought to be very rare, affecting about one in every million people in any given year. They are not cancerous, but they can grow quickly and disrupt the normal workings of the affected bone.
Most cases of aneurysmal bone cysts affect young people who are between 10 and 20 years of age. It is thought that aneurysmal bone cysts are slightly more common in females.
