Unicameral (Simple) Bone Cyst

A unicameral bone cyst is a benign tumor that is more common in children. It develops as a cyst (fluid-filled cavity) near the end of the thigh bone or upper arm bone, near the joint. It doesn't spread to other parts of the body, but can weaken the bone, causing it to fracture.

Unicameral bone cysts are thought to arise from a growth plate (growing ends of long bones in children) or from synovial tissue around joints. When the growth plate is involved, the cyst is termed active and can grow leading to deformity, decreased bone length or fracture. Cysts that do not involve the growth plate are termed latent. Once your child is fully grown, a unicameral bone cyst will usually stop growing, fill in with bone and disappear.

Unicameral cysts are often not painful and may be discovered incidentally on X-rays or when a bone fractures with the least amount of force. Rarely, the growing cyst may produce pain or visible deformity.

To diagnose a unicameral bone cyst, your child's doctor will order an X-ray. Other imaging studies such as a CT or MRI may sometimes be necessary to help differentiate it from other types of cysts. To confirm the diagnosis, a sample of cavity fluid may be obtained with the help of a needle (biopsy) and examined in the laboratory.

Treatment depends on the location, size and growth of the bone cyst. If the cyst is small, has no symptoms and the likelihood of fracture is minimal, your doctor may just observe it with periodic X-rays and recommend moderating your child's activities until bone's grow to their full capacity. If the bone fractures, it is allowed to heal normally. A fracture along the cyst may sometimes resolve the cyst as well. A painful or persistent cyst may need surgical treatment. A needle may be used to aspirate cyst fluid and inject medications that inhibit reformation. Alternatively, the cyst may be scraped out and bone graft is placed within the cavity to encourage bone growth.