Aneurysmal bone cysts are rare but can grow rapidly and cause bone pain, deformities, and other symptoms. They are most common in adolescents and can occur in any bone, but are more likely to grow in the limbs, knee bones, and spinal vertebrae. The cause is unknown, and treatment usually involves surgery to remove the cyst and repair the affected bone. Curettage is the most common treatment, but it has a high potential for recurrence. Complete removal of the cyst reduces the risk of recurrence. If the cyst does not grow or grows slowly, it may not require treatment, but the patient should be monitored for signs of growth.
An aneurysmal bone cyst is a bone lesion that, although benign, can grow rapidly and potentially destroy bone tissue. Cysts can cause bone pain, bone deformities, and other symptoms that depend on their location. These cysts are called an aneurysm because when seen on an X-ray, the cysts look like aneurysms. Aneurysmal bone cysts are rare; between 1% and 6% of all bone cancers are of this variety.
Although these cysts can grow into any bone in the body, the most likely locations for an aneurysmal bone cyst to grow are the limbs, knee bones, and spinal vertebrae. They’re more common in adolescents than other age groups, with as many as 86 percent of cysts developing in people younger than 20. The average age of these patients is 13-17 years, but cysts can develop in people of any age.
The underlying cause of aneurysmal bone cysts is unknown. Some develop in areas where bone trauma has previously occurred, and others occur in combination with other types of benign or malignant bone tumors. Still others develop in the absence of other disease or trauma.
Developing an aneurysmal bone cyst doesn’t always cause symptoms. In some people, the cysts stay small and no symptoms ever develop. In such cases, the cysts are only discovered when an x-ray is taken for an unrelated reason.
When symptoms appear, they commonly include pain, swelling, and lump formation at the site of the cyst. When the cyst is near a joint, it could cause a decreased range of motion or joint stiffness or weakness. Some cysts grow rapidly and cause bone tissue to weaken, increasing the risk of fracture. If the cyst grows into the spinal bones, it could cause neurological symptoms.
When needed, treatment of aneurysmal bone cysts usually includes surgery to remove the cyst and repair the affected bone. The most common treatment is curettage of the cyst followed by bone grafting. Curettage means that the cyst is opened and the contents are scraped off with a hollowed-out instrument called a curette. Once the cyst has been drained, it is filled in with a bone graft or synthetic filler.
Although curettage is the most common treatment, it has the highest potential for recurrence, due to the difficulty of removing all of the cyst’s contents. Cryotherapy, which is cold therapy, is sometimes done after curettage to reduce the likelihood of recurrence, but this procedure can cause bone fractures or nerve damage and is therefore not a common treatment. When an aneurysmal bone cyst is in non-weight-bearing bone, it can be removed by complete excision rather than curettage of the interior. Complete removal of the cyst also reduces the risk of recurrence.
Surgical treatment is not always necessary. Typically, if a cyst does not grow or grows very slowly, it is not treated. In these cases, the patient is monitored for signs that the growth rate of the cysts is increasing. This could include regular CT scans or MRI scans to assess the size of the aneurysmal bone cyst.
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