Introduction of bone cysts

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. This can lead to symptoms such as pain, swelling or not being able to move or put weight on a body part.

Read more about the symptoms of bone cysts.

It is not known exactly what causes the build up of fluid that leads to a bone cyst, but several theories have been suggested, including damage to the blood vessels in the bone.

Read more about the causes of bone cysts.

Types of bone cysts

There are two main types of bone cysts.

Unicameral bone cysts

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. They often do not need treatment.

Most cases affect younger children 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

Aneurysmal bone cysts can also develop anywhere in the body. However, most cysts develop inside:

  • the bone of the thigh, lower leg or upper arm 
  • the vertebral bones (in the spine)

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.

Treating bone cysts

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 fracture, several treatment options are available. For example, steroids may be injected into the bone to encourage the cyst to heal. If the bone is still not healing, surgery may be needed to treat the cyst.

However, there is a one in three chance that a bone cyst will reoccur in the future, usually within two years.

Read more about how bone cysts are treated.

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