Aneurysmal Bone Cyst

What is an aneurysmal bone cyst?

Bones naturally grow and change as your child gets older. However, throughout a long process, abnormalities can sometimes occur. An aneurysmal bone cyst (which is often abbreviated ABC) is one such abnormality. ABCs are blood-filled, fibrous cysts that expand the bone and can cause pain, swelling, and fractures. They are benign cysts (non-cancerous) that don’t spread.

ABCs are most common during a child’s teenage years. They can occur in virtually any bone in the arms, legs, trunk, or skull as well as the vertebrae and knee. While it’s benign, it can be quite destructive, because it deforms the bone and can cause fractures. ABC’s don’t spread but can be quite damaging to the bone and can come back after they are removed.

With surgery, these cysts are highly curable, although they do grow back in some cases.

What are the types of aneurysmal bone cysts?

An aneurysmal bone cyst usually falls into one of two categories: active and aggressive.

An active ABC is one that could deform the bone it’s growing in, but remains contained in the bone, while an aggressive ABC extends beyond the bone to the nearby soft connective tissues. Rarely will aggressive cysts go away without treatment.

Both types can cause pain and swelling and, in rare cases, fractures in the involved bone. Aneurysmal bone cysts do not generally go away on their own.

What are the symptoms of an aneurysmal bone cyst?

  • swelling
  • mild to severe neurological problems (if the cyst is in your child's spine)
  • a fracture caused by the cyst (rarely)

It’s important to understand that the symptoms of aneurysmal bone cyst may resemble other medical problems, some of them which are very common and easy to treat, others which could be more serious.

Your child may experience symptoms differently. Therefore, it is important to be evaluated by a physician to get an accurate diagnosis. Always consult your child's physician if you have concerns.

What causes an aneurysmal bone cyst?

The cause of these cysts is unknown and controversial. They’re believed to grow in response to a disturbance of the blood vessels in the involved bone. They may grow because of a pre-existing tumor. In half of all cases, a pre-existing tumor, such as fibrous dysplasia, non-ossifying fibroma, a solitary bone cyst, or osteosarcoma also exists.

Abnormalities in the chromosomes (karyotype) of the tumor cells have been described, but the significance of these findings is unclear.

There is no definitive explanation for why these cysts occur. It’s important to know that there’s nothing that you could have done (or not done) that would have prevented your child’s cyst from developing.

How we care for aneurysmal bone cysts

Experts in Boston Children's Hospital's Bone and Soft Tissue Tumors Program within our Orthopedic Center provide comprehensive medical and surgical care for children with aneurysmal bone cysts and other bone and soft tissue disorders.

Our multidisciplinary approach to care ensures that your child’s case receives input from experts in several fields before your care team develops a personalized treatment plan.