Aneurysmal Bone Cyst: What It Is, Symptoms, and How It Is Treated
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
TL;DR
An aneurysmal bone cyst (ABC) is a rare, benign (noncancerous) bone tumor filled with tiny blood-filled cysts. It typically affects children and young adults under 20, most often in the long bones of the arms and legs — the femur, tibia, and humerus — as well as the spine and pelvis. The classic warning signs are a lump you can see and feel, swelling, and pain that may worsen very quickly. The condition is highly treatable, most often with surgery called curettage, but it comes back in 1 in 5 people, usually within the first year after treatment. The most reassuring fact for worried parents: an ABC is not a type of bone cancer.
Quick Answer
What it is: A rare, benign (noncancerous) bone tumor containing tiny cysts filled with blood, most common in children and young adults under 20.
Where it forms: Any bone can be affected, but most often the femur (thighbone), tibia (shin bone), humerus (upper arm bone), spine, and pelvis.
Main symptoms: A visible, feelable lump, swelling around it, and pain that may get worse very quickly; spinal cysts can cause numbness, tingling, weakness, or paralysis.
Treatment and outlook: Highly treatable — most often curettage (surgical removal of the cysts and lining) — but recurs in 1 in 5 people, typically within the first year.
What Is an Aneurysmal Bone Cyst?
An aneurysmal bone cyst (ABC) is a benign (noncancerous) tumor in your bones. The tumor contains tiny cysts filled with blood.
The name describes its structure. "Aneurysmal" (pronounced "an-yuh-riz-mahl") refers to a bulge in a blood vessel wall. "Cyst" refers to fluid-filled cavities.
Aneurysmal bone cysts are rare. They make up just a small percentage of all bone tumors — and bone tumors themselves are uncommon. The condition usually affects children and young adults under 20.
Key Fact | Detail |
Type | Benign (noncancerous) bone tumor |
Contents | Tiny cysts filled with blood |
Who is affected | Typically children and young adults under 20 |
Growth behavior | Can grow quickly and become large |
Cancer risk | Not cancerous, but must be checked to confirm |
Where Do Aneurysmal Bone Cysts Develop?
The tumors can develop in any bone. But the most common locations are in the long bones of the arms and legs and in the spine:
Location | Common Name |
Femur | Thighbone |
Tibia | Shin bone |
Humerus | Upper arm bone |
Vertebrae | Bones in your spine |
Pelvis | Bones in your pelvis |
What Are the Types of Aneurysmal Bone Cysts?
There are two types of aneurysmal bone cysts: primary and secondary. A primary cyst develops on its own. A secondary cyst forms when a different type of bone tumor leads to an aneurysmal bone cyst.
Type | How It Develops | Associated Conditions |
Primary | Develops on its own | None — arises independently |
Secondary | Caused by another bone tumor or condition | Fibrous dysplasia, giant cell tumor, osteoblastoma, chondrosarcoma, osteosarcoma |
What Are the Symptoms of an Aneurysmal Bone Cyst?
Common symptoms are changes in your arm, leg, pelvis, or spine. Those changes include a lump that you can see and feel, pain that may get worse very quickly, and swelling around the lump.
An ABC on your spine that presses on your spinal nerves may cause additional symptoms: numbness, paresthesia (tingling sensation), muscle weakness, and in severe cases, paralysis.
Symptom | Notes |
Lump | Visible and feelable; does not go away and may grow |
Pain | May get worse very quickly |
Swelling | Around the lump |
Numbness | When a spinal ABC presses on spinal nerves |
Tingling (paresthesia) | When a spinal ABC presses on spinal nerves |
Muscle weakness | When a spinal ABC presses on spinal nerves |
Paralysis | When a spinal ABC presses on spinal nerves |
What Causes an Aneurysmal Bone Cyst?
Experts do not know the exact cause of aneurysmal bone cysts. Possible causes could be issues with blood vessels in your bones, or variations in the genes that control how your cells grow and divide.
What Are the Complications?
The condition may keep your child's bones from growing as they should. That may mean your child's arm or leg bones are shorter than their other arm or leg.
An aneurysmal bone cyst can also cause a bone fracture if the tumor grows large enough to weaken your bones.
How Is an Aneurysmal Bone Cyst Diagnosed?
A healthcare provider will do a physical examination, checking any noticeable lumps on your bones. They may then order imaging tests, including bone scans, CT scans, MRI scans, and X-rays.
Your provider may also do a biopsy to get tissue samples from the tumor. A medical pathologist will look at the tissue under a microscope and check for signs that the tumor is cancerous.
Diagnostic Step | What It Involves |
Physical examination | A provider examines any noticeable lump on your bones |
X-ray | Images of the affected bone |
CT scan | Detailed cross-sectional images |
MRI scan | Detailed images of soft tissue and bone |
Bone scan | Whole-body or regional scan of bone activity |
Biopsy | Tissue samples checked under a microscope to confirm the tumor is not cancerous |
How Is an Aneurysmal Bone Cyst Treated?
The most common treatment is curettage. In curettage, an orthopaedic surgeon makes an incision in the area where the tumor is located. They open the tumor and remove the cysts and the lining of the tumor. They may use a bone graft from a donor or from another area of your body to refill the area where the tumor was.
Nonsurgical treatments are also available for tumors that are difficult to reach surgically or as supporting therapy:
Treatment | How It Works |
Curettage (surgery) | The tumor is opened; the cysts and tumor lining are removed; the area is often refilled with a bone graft |
Arterial embolization | Blocks the blood vessels that feed the tumor |
Doxycycline injection | Shrinks the tumor and keeps it from growing |
Denosumab (Prolia) | A medication that strengthens your bones |
Radiation therapy | Destroys tumor cells |
Sclerotherapy | An injected medication that makes the tumor collapse |
What Is the Recovery Time?
Recovery time for you or your child will depend on the treatment your provider uses. For example, it may take three to six months for your bone to heal after curettage. Ask your provider what you can expect as you or your child recover from surgery.
What Is the Prognosis?
Aneurysmal bone cysts are highly treatable. But they come back in 1 in 5 people. Recurrence is most common within the first year after treatment.
Because an ABC can recur after treatment, you should contact your provider if you notice changes like a new lump or pain in the area where you had treatment.
When Should You See a Healthcare Provider?
Lumps are common. You or your child can get one from bumping into a door or running into any hard object. But a lump that does not go away and gets bigger may be a symptom of an aneurysmal bone cyst.
This is a rare disease that affects kids and young adults. You may be relieved to learn that an ABC is not a type of bone cancer. But the condition can lead to serious issues like a broken bone. Talk to a healthcare provider if you or your child have a lump that lingers or grows.
Conclusion
An aneurysmal bone cyst is an uncommon but highly treatable condition. It is a benign, blood-filled bone tumor that usually appears in children and young adults under 20, most often in the femur, tibia, humerus, spine, or pelvis. The telltale signs are a persistent, growing lump with swelling and pain that can worsen quickly — and when the cyst sits on the spine, numbness, tingling, weakness, or paralysis can follow.
The most important facts for families are reassuring: an ABC is not bone cancer, and the standard treatment — curettage, often with a bone graft — is effective in most cases. The honest caveats are just as important: the tumor can weaken the bone and cause a fracture, and it returns in 1 in 5 people, usually within the first year. That is why follow-up matters as much as treatment.
If you or your child has a lump on a bone that does not go away — especially one that grows, becomes painful, or comes with swelling — schedule an evaluation with a healthcare provider. Early imaging and, if needed, a biopsy confirm the diagnosis, and treatment is far simpler before the tumor weakens the bone or causes a fracture.
FAQ
What is an aneurysmal bone cyst?
An aneurysmal bone cyst (ABC) is a rare, benign (noncancerous) bone tumor containing tiny cysts filled with blood. "Aneurysmal" refers to a bulge in a blood vessel wall, and "cyst" refers to fluid-filled cavities.
Is an aneurysmal bone cyst cancer?
No. An ABC is a benign, noncancerous tumor. However, a biopsy is usually performed to confirm the tumor is not cancerous, because a secondary ABC can develop from other bone tumors — some of which are malignant.
Who gets aneurysmal bone cysts?
They typically affect children and young adults under 20. The condition is rare, making up just a small percentage of all bone tumors.
Where do aneurysmal bone cysts most often occur?
Any bone can be affected, but the most common locations are the femur (thighbone), tibia (shin bone), humerus (upper arm bone), the vertebrae of the spine, and the bones of the pelvis.
What are the symptoms?
The most common symptoms are a lump you can see and feel, swelling around the lump, and pain that may worsen very quickly. A spinal ABC pressing on spinal nerves can also cause numbness, tingling, muscle weakness, or paralysis.
How is it diagnosed?
A provider examines the lump and may order X-rays, CT scans, MRI scans, or bone scans. A biopsy removes tissue samples that a pathologist examines under a microscope to confirm the tumor is benign.
How is an aneurysmal bone cyst treated?
The most common treatment is curettage: surgery in which the tumor is opened, the cysts and lining are removed, and the area is often refilled with a bone graft. Nonsurgical options include embolization, doxycycline injections, denosumab, radiation therapy, and sclerotherapy.
Can it come back after treatment?
Yes. Aneurysmal bone cysts come back in 1 in 5 people, most often within the first year after treatment. Contact your provider if a new lump or pain appears in the treated area.
References
American Academy of Orthopaedic Surgeons. "Giant cell tumor of bone." OrthoInfo. orthoinfo.aaos.org/en/diseases--conditions/giant-cell-tumor-of-bone
American Academy of Orthopaedic Surgeons. "Osteosarcoma." OrthoInfo. orthoinfo.aaos.org/en/diseases--conditions/osteosarcoma
American Academy of Orthopaedic Surgeons. "Unicameral bone cysts." OrthoInfo. orthoinfo.aaos.org/en/diseases--conditions/unicameral-bone-cysts
Park HY, Yang SK, Sheppard WL, et al. "Current management of aneurysmal bone cysts." Current Reviews in Musculoskeletal Medicine. 2016;9(4):435-444. ncbi.nlm.nih.gov/pmc/articles/PMC5127951
Stevens K, Stevens J. "Aneurysmal Bone Cysts." StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021. Updated 2021 Aug 8. statpearls.com/ArticleLibrary/viewarticle/17552
Disclaimer: This article is for general educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider for guidance specific to your situation.
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