Aneurysmal Bone Cyst
An aneurysmal bone cyst is a highly destructive benign bone tumor, representing 1 to 6 percent of all solid bone tumors.
What is an Aneurysmal Bone Cyst?
Aneurysmal bone cyst (ABC) is a highly destructive benign bone tumor, representing 1 to 6 percent of all solid bone tumors. The term "aneurysmal" refers to the explosive, expansile nature of the bone containing the aneurysmal bone cyst, similar to dilation and expansion seen with heart aneurysms. The majority of aneurysmal bone cysts are a large network of blood-filled cystic spaces. However, 3 to 7.5 percent of aneurysmal bone cysts are predominantly solid tumors with small vascular spaces.
Approximately 70 percent of aneurysmal bone cysts are primary lesions meaning they are directly related to the diagnosis of the cyst and not another medical reason. The remaining 30 percent occur coincidentally with other bone lesions, such as giant cell tumor, osteoblastoma, chondroblastoma, hemangioma, fibrous dysplasia and telangiectatic osteosarcoma. These tumors most often appear in the first two decades of life, with the most common locations including the humerus, tibia, fibula, skull, femur and spine. Approximately 8 to 30 percent are in the spine, most often involving the posterior aspects of the spine.
What are the Symptoms of an Aneurysmal Bone Cyst?Most often the symptom that causes patients to realize that they have an aneurysmal bone cyst is pain in the bone with the cyst. In other patients, the bone is so thin the patients discover it when the bone breaks (fractures) through the cyst, even with little or no trauma.
What Causes an Aneurysmal Bone Cyst?
Previously considered to be an idiopathic (uncertain cause) bone cyst consisting of multiple honeycomb blood-filled spaces, aneurysmal bone cyst is now known to be a benign neoplasm (tumor) of bone. Most often, it is the result of translocations (criss-crossing) of the #16 and #17 chromosomes, resulting in the formation of highly destructive tumor tissue. The science of the aneurysmal bone cyst is explained by the chromosomal translocation that develops what is known as an "oncogene". Scientifically, the oncogene triggers the development of destructive solid tissue, giant cell-like osteoclasts (other cells that destroy bone) and vascular spaces. In addition, the oncogene triggers expression of an enzyme called "matrix metalloproteinase" that attacks and destroys the underlying structural matrix of bone. Furthermore, the translocation oncogene triggers the expression of "Vascular Endothelial Growth Factor" (VEGF) that recruits blood supply for this destructive tumor.
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How is an Aneurysmal Bone Cyst Diagnosed?
Most often, an aneurysmal bone cyst is diagnosed with an X-ray or MRI examination of the damaged bone. Diagnostic imaging has traditionally relied on a combination of plain X-ray studies, CT scan, nuclear medicine bone scan and MRI. Of all these procedures, MRI is the imaging choice for a complete assessment of the aneurysmal bone cyst, especially in the spine, to determine the extent of spinal cord and nerve compression. MRI routinely detects the multiple blood-filled spaces and walls (septae) separating the spaces. Research investigations confirmed with pathologic proof that the septae (seen on ultrasound and MRI) separating the blood filled spaces indeed represent the "solid" elements of the destructive tumor requiring treatment. After the cyst is identified on the X-ray or MRI examination, a biopsy (procedure to take a small sample of tissue) will be performed either by an interventional radiologist or by a surgeon.
Aneurysmal Bone Cyst Treatment Options
Aneurysmal bone cysts have unique surgical challenges, often with large amounts of blood loss during surgery, and recurrence following surgical management in 12 to 75 percent of cases (75 percent in children under age 5 years). These therapeutic challenges led our Radiology Team to develop minimally-invasive diagnostic and treatment solutions, in conjunction with the Department of Orthopedic Oncology in The Ohio State University Wexner Medical Center. In the past, the treatment for these cysts relied on surgical curettage (scraping) of the bone cysts with bone graft placement, or amputation if there is recurrence after the scraping.
Aneurysmal Bone Cyst Procedure at Nationwide Children's Hospital
When designing therapy for aneurysmal bone cysts, our radiologists took the following into consideration. The ideal therapy would kill the solid tumor (fibroproliferative stromal) cells, inhibit or kill the giant cell-like osteoclasts, inhibit angiogenesis (VEGF activity), inhibit the destructive enzymes known as MMP (matrix metalloproteinase), and trigger the body to heal the affected bone with new bone. The interventional radiology treatment of aneurysmal bone cyst involves a series (one every 3 months) of treatment injections of a drug known as doxycycline (injected as a foam). The therapy is usually performed an outpatient procedure with minimal recovery time and often also relieves the bone pain produced by the cyst. The treatment injections are precisely guided with either ultrasound "cameras", live X-ray machines (fluoroscopy), or CT scan. The doxycycline is injected in a sustained-released form that prolongs the therapeutic effect of treatment and prevents rapid washout of the drug in the aneurysmal bone cyst tissue and vascular spaces. After precise injection of the doxycycline foam, the openings of the bones are sealed as the needles are removed. Finally, numbing medicine (a local anesthetic) is injected in the tissues surrounding the needle entry sites to reduce pain from the procedure.
Above: patient undergoing aneurysmal bone cyst treatment at Nationwide Children's Hospital
Frequently Asked Questions About Aneurysmal Bone Cyst Treatment
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?
Each aneurysmal bone cyst treatment session lasts approximately 1 hour.
Are there any risks to the procedure?
Risks are possible with any treatment but are extremely rare. In over 300 treatments at Nationwide Children’s Hospital, there have been no complications of infection, excessive bleeding, or injury to muscles, nerves, or other nearby body parts. The possibility of skin injury at the injection site is minimized by precise pressure control during the treatment injection procedure.
What happens after the procedure?
Once the patient is awake from anesthesia, the patient is discharged as an outpatient and sent home. Patients are able to move normally the same day following each treatment without special recovery time. Patients are given a prescription for pain medication if the treatment site hurts for a day or two.
When can my child bathe?
Patients may shower immediately following treatment but are asked not to submerge the treatment parts in a bathtub for a few days.
Are there any activity restrictions?
There are no specific activity restrictions (other than those prescribed by your orthopedic surgeon or neurosurgeon prior to 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.
Will the aneurysmal bone cyst come back after the procedure?
Since the cyst contains many small and large spaces with tumor cells, patients are followed for 5 years after treatment is completed. 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 initial treatment. If small areas of residual tumor are detected, with small enlarging areas of bone loss, the interventional radiologists precisely target treatment of these remaining areas of tumor tissue. This type of residual tumor detection is considered recurrence and occurs in approximately 5% of patients. Once these final islands of tumor cells are treated, no cases of recurrence have occurred in the 8 years of treatment at Nationwide Children's Hospital.
What can my child expect after treatment is complete? Any long-term effects?
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, 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. No other negative long-term effects have been identified in 8 years of ABC treatment at Nationwide Children's Hospital. None of the patients (some treated after surgical recurrence) have required surgery for further treatment. All of the patients have normal use of the affected bones, including normal motion and activity, including the spine after treatment of spinal aneurysmal bone cyst. None have had a spinal fusion, which is permanent immobilization using metal rods, screws and a bone graft.
What happens if an aneurysmal bone cyst is left untreated?
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.
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.