Aneurysmal Bone Cyst
Aneurysmal bone cysts are filled with blood. They can expand or grow in the bone and are most commonly found in the upper arm bone, leg, pelvis or spine.
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What Is an Aneurysmal Bone Cyst?
An Aneurysmal bone cyst (ABC) is a highly destructive benign bone tumor, occurring in less than 1 in 100,000 people per year. The term "aneurysmal" refers to the explosive, expansile nature of the bone containing the aneurysmal bone cyst, similar to the enlargement seen with blood vessel or heart aneurysms. The majority of ABCs are hollow and filled with different sized liquid or blood filled sacs called cysts. Because ABCs usually are filled with these blood-filled cysts, they are fragile and prone to fracture. Approximately 5% of aneurysmal bone cysts are solid tumors rather than being hollow.
Approximately 70 percent of aneurysmal bone cysts are primary lesions, meaning that they occur by themselves in patients who have no other diseases. The remaining 30 percent occur along side of other bone lesions, such as giant cell tumors, osteoblastomas, chondroblastomas, hemangiomas, fibrous dysplasia and telangiectatic osteosarcomas. ABCs usually appear in the first two decades of life, with the most common locations being the arm (humerus), leg (tibia, fibula, femur), pelvis and spine. Approximately 15 to 20 percent are in the spine.
What Are the Symptoms of an Aneurysmal Bone Cyst? Are ABCs Dangerous?
Most often the symptom that causes patients to realize that they have an ABC is pain in the affected bone. In other patients, the bone is so thin and fragile that the ABC is discovered when the bone breaks (fractures) through the cyst, commonly with only minimal trauma.
If left untreated, ABCs can be dangerous, especially if they are in a bone near a critical structure that might be injured should the bone break. This is especially true of ABCs in the skull or spine.
What Causes an Aneurysmal Bone Cyst? Are ABCs Hereditary?
While there have been rare reports of more than one family member being diagnosed with this problem, aneurysmal bone cysts are not felt to be hereditary. Previously considered to be idiopathic (uncertain cause) bone cysts consisting of multiple honeycomb blood-filled spaces, aneurysmal bone cysts are now known to be benign tumors of bone.
Most often, they result from spontaneous translocations (criss-crossings) of small parts of the #16 and #17 chromosomes, resulting in the formation of highly destructive tumor tissue. Scientifically, the chromosomal translocation activates an oncogene, which is a tumor-causing gene. This oncogene triggers the development of destructive tumor tissue that, in part, is made of giant cell-like osteoclasts (cells that destroy bone) and vascular spaces. The oncogene also triggers production of an enzyme called matrix metalloproteinase (MMP), a protein that attacks and destroys the underlying structural matrix of bone. Furthermore, the oncogene triggers the expression of Vascular Endothelial Growth Factor (VEGF) a protein signal in the body that recruits blood supply for this destructive tumor allowing it to grow more rapidly.
How Is an Aneurysmal Bone Cyst Diagnosed?
Most often, an aneurysmal bone cyst is diagnosed with an X-ray, computed tomography (CT) scan, or magnetic resonance imaging (MRI) examination of the painful damaged bone.
Of all these procedures, MRI is often the best imaging choice for a complete assessment of the aneurysmal bone cyst and the surrounding structures, especially for ABCs in the spine. MRI routinely detects the multiple blood-filled cystic spaces and walls (septae) separating the cysts. These septae, together with the internal lining of the cyst walls, represent the "solid" elements of the destructive tumor requiring treatment. After the ABC is seen on the X-ray or MRI, a biopsy (procedure to take a small sample of tissue) will be performed to confirm the diagnosis.
Often, if the diagnosis based upon the imaging is clear enough, the biopsy can be performed during the initial treatment.
How Are Aneurysmal Bone Cysts Traditionally Treated?
Aneurysmal bone cysts historically were treated with surgical removal and this is still a good option for many ABCs. Either the entire bone containing the tumor is removed or just the tumor can be scraped out of the bone. Surgery sometimes requires that the weakened bone be supported by metal or bone graft/cement implants. Orthopedic surgeons and neurological surgeons perform these procedures at most institutions. Sometimes ABCs can be made smaller with radiation therapy or medical therapy, but usually this does not cure the tumor completely.
Aneurysmal bone cysts have unique surgical challenges, sometimes with significant blood loss during surgery, risks of injury to surrounding normal structures, and risks of recurrence in the years after surgery. Risk of tumor recurrence following surgical management varies in different reports but ranges between 12 and 75 percent of cases (recurrence is especially high in children under the age of 5 years).
These therapeutic challenges led our Interventional Radiology Team to develop minimally invasive diagnostic and treatment solutions, in conjunction with the Department of Orthopedic Oncology at The Ohio State University Wexner Medical Center.
How are Aneurysmal Bone Cysts Treated by Interventional Radiology at Nationwide Children's?
When designing our alternative therapy for ABCs, our interventional radiologists thoughtfully took the most up-to-date scientific information into account. The ideal therapy needs to kill the solid tumor cells, inhibit or kill the giant cell-like osteoclasts, inhibit blood vessel growth called angiogenesis (VEGF activity), inhibit the destructive enzymes (MMPs) that destroy bone, and trigger the body to heal the weakened bone by stimulating the growth of healthy bone building cells called osteoblasts.
The interventional radiology treatment of aneurysmal bone cyst involves a series (one every 3 months) of minimally invasive treatment injections of a drug called doxycycline.
The therapy is performed as an outpatient procedure with minimal recovery time. Much of the bone pain caused by the ABC is usually relieved within one or two treatments. The injections are precisely guided with ultrasound cameras, live X-ray machines (fluoroscopy), or CT scans. The doxycycline is injected in a sustained-released thick fluid or foam that prolongs the therapeutic effect of treatment and prevents rapid washout of the drug from the aneurysmal bone cyst into the bloodstream. After precise injection of the doxycycline foam, the openings of the bones are sealed as the needles are removed to minimize any bleeding. Finally, numbing medicine (a local anesthetic) is injected in the tissues surrounding the needle entry sites to reduce post-procedure pain.
Frequently Asked Questions About Aneurysmal Bone Cyst Treatment in Interventional Radiology
Will my child be awake during the procedure?
Since the treatment involves placing needles precisely into the bone with the aneurysmal bone cyst, the procedure is performed while the patient is asleep with general anesthesia.
How long will the procedure take?
It usually takes the interventional radiologist 1 to 2 hours to perform each ABC treatment session.
Are there any risks to the procedure?
Risks are possible with any treatment but serious complications with each treatment session are very rare. In over 1000 treatments performed so far at Nationwide Children’s Hospital, there have been no serious infections or episodes of bleeding requiring blood transfusion. Doxycyline, the injected medication is itself an antibiotic, which minimizes infection risks, and the needles used are small limiting any bleeding risks. Injury to muscles, nerves, or other nearby body parts has occurred in less than 1% of the treatments and is usually temporary. The possibility of skin injury at the needle entry sites is minimized by careful control of injection pressures during the treatments.
What happens after each procedure?
Once the patient is fully awake after anesthesia, the patient is discharged from the Nationwide Children’s Hospital’s outpatient procedure center and sent home. Patients are able to move normally the same day following each treatment without special recovery time. Care must be taken to keep the dressing clean and dry for 2 days after treatment. If needed, patients are given a prescription for pain medication to be used for a day or two after treatment if there is injection site pain.
When can my child bathe?
Patients may shower immediately following treatment but are asked not to submerge the treatment area and the dressing in a bathtub for a few days.
Are there any activity restrictions after each procedure?
For most patients, there are no specific activity restrictions after each treatment. Patients are instructed to be careful not to engage in strenuous activity with the affected bone to avoid fracture of the bone while it is healing. Occasionally, if the ABC is in an especially critical area, such as the neck or spine, there may be additional activity restrictions until it is clear that strong healthy bone healing has begun.
What happens after all the treatments are complete?
Most aneurysmal bone cysts require 3-5 treatments. If the ABC is very large, more treatments may be needed. Once all the symptoms from the ABC are gone and the bone appears to be healing well on imaging tests the patient will enter the surveillance phase of care.
Aneurysmal bone cysts are well-known to recur or regrow after treatment of any kind. Therefore, we follow all patients with periodic imaging tests for 5 years after the last treatment. During this 5-year period, the radiologists at Nationwide Children's Hospital monitor for evidence of small islands of tumor cells that did not get killed during the initial treatments. If small areas of growing tumor are detected and are causing new areas of bone destruction, the interventional radiologists may need to retreat these areas. Tumors detected in this way is considered a recurrence and occurs in approximately 5% of patients. If 5 years of surveillance reveals no recurrence, no additional imaging or clinical follow-up is needed unless new symptoms arise.
What can my child expect after all the treatments are complete? Any long-term effects?
After completion of all treatments the treated area should be strong and healthy allowing a return to full activity. A special concern in ABCs given that they usually occur in children is bone growth. All children with aneurysmal bone cysts next to their growth plates have demonstrated healing of the cysts and normal growth of adjacent bone, with no injury to the bone growth plate. In a small number of patients (2%), when the cyst invades the growth plate of the bone before the lesion is discovered, the treatment and healing process results in a bone scar in this area that can result in a growth disturbance of the bone and mild shortening of the affected bone.
Rarely, between the first few treatments and following a traumatic accident, an ABC can still cause a fracture that might require surgical care of the fracture. To minimize the risk of such a fracture, we look for strong healthy bone regrowth in the treated areas before advising return to full physical activity such as athletics. Once treatment is complete, nearly all patients resume all their normal physical act ivies including athletics.
What happens if an aneurysmal bone cyst is left untreated? Do ABCs go away?
If an aneurysmal bone cyst is left untreated, the destructive tumor processes in the bone continues. Further bone destruction will cause pain, fracture of the bone, immobility of the patient, and if the cyst involves the spine, further destruction can result in nerve damage or paralysis. ABCs are not known to go away without treatment.
Can patients be treated at Nationwide Children’s Hospital even if they do not live in Ohio or even in the United States?
Nationwide Children’s Hospital takes care of patients from all over the world for many different diseases and conditions including ABCs. We have staff available to discuss the needs of families traveling to Columbus, Ohio, from other cities in the United States and other countries around the world. We realize that travel to Nationwide Children’s Hospital is a large undertaking for any family and we welcome inquiries from any families who want to know if this option is right for their child.
Patient Outcomes
A 17-year-old girl, who was succeeding in high school both socially and academically, began suffering with frequent neck pain and headaches. She was able to push through her pain until it became increasingly worse when she tilted her head to the left.
A CT scan showed an aneurysmal bone cyst with complete destruction of the left half of her second cervical vertebra and no bony protection over the spinal cord in this dangerous location. A neurosurgeon described the most optimistic surgical option, which included extensive surgery, to remove the diseased bony segment in this highly sensitive location, and permanent spinal fusion, with hope for no recurrence. The neurosurgeon recommended a second opinion consultation at Nationwide Children’s Hospital.
After considering the interventional radiology plan for definitive biopsy and treatment, and evaluating prior results at Nationwide Children’s Hospital, the neurosurgeon, patient and her parents elected to proceed with the minimally-invasive interventional radiology biopsy and treatment. Four years following a series of 4 outpatient treatments, the patient’s neck has fully healed with strong bone fully protecting her spinal cord. She has full mobility and use of her neck, without recurrence of her aneurysmal bone cyst tumor.