Bone and Soft Tissue Tumors: Benign Tumors
Bone Cyst (Aneurysmal)
On this page:
What is an aneurysmal bone cyst?
What causes an aneurysmal bone cyst?
What are the symptoms of an aneurysmal bone cyst?
How is an aneurysmal bone cyst diagnosed?
Treatment for an aneurysmal bone cyst
What is the long-term outlook for a patient with an aneurysmal bone cyst?
What is an aneurysmal bone cyst?
An aneurysmal bone cyst is a blood-filled fibrous tumor-like cyst that expands the bone, giving it a "blow-out" appearance. It typically occurs in the second decade of life and can emerge in virtually any bone in the arms, legs, trunk or skull. The vertebrae and knee are the most common sites of occurrence.
An aneurysmal bone cyst is a benign bone tumor, meaning that it does not metastasize (spread) to other regions of the body. It can however be quite destructive locally and has a high propensity for recurrence.
When it occurs in bones of a limb, it typically involves any of the following areas of the bone:
- Metaphysis – the transitional zone where the shaft of the bone joins the end of the bone
- Diaphysis (shaft) – bone near the growth plate (the area of the bone in which growth occurs)
When it occurs in the spine, the cyst can grow to involve the entire vertebral body where it arose or it can involve the adjacent vertebrae.
Generally, those cysts considered "active" could deform the host bone but remain contained in the bone, while others, considered "aggressive" extend beyond the bone to the adjacent soft connective tissues. Rarely will these types of cysts resolve on their own without treatment.
What causes an aneurysmal bone cyst?
The cause of these tumors is unknown. However, they are believed to emerge in response to a disturbance of the rich capillary network in the host bone. Controversy exists as to whether or not aneurysmal bone cysts emerge secondary to a pre-existing tumor. In about half of all cases, a preexisting tumor, such as fibrous dysplasia, nonossifying fibroma, solitary bone cyst or osteosarcoma can be identified. Recently, abnormalities in the chromosomes (karyotype) of the tumor cells have been described, but the significance of these findings is unclear.
What are the symptoms of an aneurysmal bone cyst?
The following are the most common symptoms of an aneurysmal bone cyst. Keep in mind that every child experiences symptoms differently. Symptoms include:
- pain
- swelling
- a mass that can be felt (sometimes)
- mild to severe neurological problems (if cyst is in spine)
- fracture caused by the cyst (rarely)
The symptoms of an aneurysmal bone cyst resemble symptoms of other conditions or medical problems. Always consult a physician for a diagnosis.
How is an aneurysmal bone cyst diagnosed?
When making a diagnosis, your child's doctor will also want to know how aggressive the tumor is. In addition to performing a physical examination and taking a medical history, the doctor will want your child to undergo one or more of the following diagnostic tests:
- X-ray – a diagnostic test that uses invisible electromagnetic energy beams to produce images of internal tissues, bones, and organs onto film.
- Magnetic resonance imaging (MRI) – a diagnostic procedure that uses a combination of large magnets, radio frequencies and a computer to produce detailed images of organs and structures within the body. This test is particularly useful to confirm the diagnosis by demonstrating the characteristic fluid levels within the cyst.
- Computerized tomography scan (also called CT or CAT scan) – a diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce cross-sectional images (often called slices) both horizontally and vertically, of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat and organs. CT scans are more detailed that general X-rays. This test is also particularly useful in confirming the diagnosis by demonstrating the characteristic fluid levels within the cyst.
- Bone scan – a test that uses an injection of an isotope (small dose of radioactive material) that seeks out all bones of the skeleton. It tells the doctor whether there are other tumor sites (although this would be unusual in aneurysmal bone cyst).
Additional tests may include:
- Complete blood count (CBC) – a measurement of size, number and maturity of different blood cells in a specific volume of blood
- Blood tests – (including blood chemistries)
Treatment for an aneurysmal bone cyst
Specific treatment for an aneurysmal bone cyst will be determined by your child's physician based on:
- your child's age, overall health, and medical history
- extent of the disease (especially the location in the bone, the potential risk for fracture and the relationship to the growth plate)
- your child's tolerance for specific medications, procedures, or therapies
- how your child's physician expects the disease may progress
- your opinion or preference
Due to the vascular nature of this cyst, there is some potential for excessive blood loss during an operation to treat it. Therefore, treatment for an aneurysmal bone cyst involves careful planning. In some cases, in preparation to treat the cyst, a radiologist may perform a procedure that essentially blocks the blood flow in the abnormal vessels that are involved with the cyst. This procedure, known as arterial embolization, is not needed for everyone. To determine whether your child can undergo arterial embolization without complications, an angiography may be used. This is a special X-ray that enables doctors to visualize the blood vessels. The X-ray is taken after the patient is injected with a radiopaque substance that demonstrates the blood vessels.
Treatment for the cyst will likely involve one or a combination of the following surgical procedures performed by a pediatric orthopedic surgeon:
- Curettage/bone grafting: This is the most common form of treatment for an aneurysmal bone cyst. Curettage is an operation during which the cyst is scraped out of the bone with a special instrument called a curette that has a scoop, loop or ring at its tip. For this procedure, surgeons make an incision in the bone to create a window. The fluid in the cyst is aspirated and the lining tissue is completely curetted. Particularly in the case of an aneurysmal bone cyst where the chance for recurrence is high, surgeons must scrape aggressively so that there are no remaining remnants of the tumor. The remaining cavity is then packed with donor bone tissue (allograft), bone chips taken from another bone (autograft), or other materials depending on the preference of the surgeon.
- Marginal or wide excision of the host bone: Sometimes an operation to remove the part of the bone involving the cysts at its margins (marginal excision) or beyond its margins (wide excision) is the surgical procedure of choice. Wide excision is recommended when the cyst is located in bones considered expendable, such as the ribs or fibula.
- Biopsy: During the operation, doctors will take a tissue sample of the cyst so the diagnosis can be confirmed under a microscope.
- Cryotherapy: Due to the high risk of recurrence associated with these cysts, adjuvant therapies, such as cryotherapy, a surgical freezing of the cyst, are sometimes considered. Cryotherapy is associated with complications such as fracture of the bone, nerve injury and others, so is not widely accepted as standard treatment in many institutions.
- Radiation therapy: Radiation, which uses high-energy rays from a specialized machine to damage or kill tumor cells, is sometimes used as an adjuvant therapy. Because of risks associated with high doses of radiation in young children, radiation is used only if other means of treatment have failed.
What is the long-term outlook for a patient with an aneurysmal bone cyst?
Patients may become frustrated, because this benign cyst can recur after curettage. It may require two or three operations to eventually cure the cyst, but ultimately, this is a benign tumor and it does not spread, so a cure is obtained in almost all cases eventually. Resection of the tumor almost always ensures cure, but curettage is frequently attempted first to avoid the consequences of removing a part of an otherwise normal bone. Prompt medical attention and aggressive therapy are important for the best prognosis. Continuous follow-up care is essential for a child diagnosed with an aneurysmal bone cyst.
