Many noncancerous (benign) bone abnormalities may resemble bone tumors but are not.
(See also Overview of Bone Tumors.)
Aneurysmal bone cysts usually develop before people reach age 25, and the cause is not known. These cysts are made up of multiple blood-filled sacs that are packed together. These cysts usually occur near the inside edges of the long bones (upper arm and thigh bones), but almost any bone may be affected. The cysts tend to grow slowly. Pain and swelling are common. The cyst may be present for a few weeks to a year before diagnosis.
Surgical removal of the entire cyst is the most successful treatment, but sometimes the cysts return, particularly if they are not removed completely. Radiation should be avoided when possible because cancerous tumors occasionally develop later. However, radiation may be the treatment of choice for cysts in the spine that cannot be treated surgically and are putting pressure on the spinal cord.
Unicameral bone cysts occur near the growth plates in the arms or legs in children. Growth plates are what enable children to grow.
The cysts often cause nearby bones to thin, which can lead to a break (fracture). Cysts that are less than 2 inches (about 5 centimeters) long or wide may heal and may disappear as the fracture heals. Cysts that are more than 2 inches long or wide, particularly in children, may require treatment.
To diagnose unicameral bone cysts, doctors usually do x-rays. Most of the time, x-rays are enough to make the diagnosis, but sometimes other imaging tests, such as magnetic resonance imaging (MRI) or occasionally computed tomography (CT), are done.
Most often, these cysts are treated with injections of corticosteroids (often repeatedly), with processed bone putty, or with synthetic bone substitutes. Sometimes treatment is surgery to remove the contents of the cyst from the bone by scraping it with a scoop-shaped instrument (curettage) and transplantation of bone from one site to another (bone grafting). Regardless of treatment, the cyst remains or returns in about 10 to 15% of people.