Aneurysmal Bone Cyst

Aneurysmal bone cysts (ABC) (only found in pediatric patients) are rare skeletal tumors affecting fewer than 1 in 100,000 people per year and accounting for 1 to 2 percent of all primary bone tumors. It’s a blood-filled, fibrous cyst that expands the bone. They can occur in any bone in the arms, legs, trunk or skull, as well as the vertebrae and knee. While they are usually benign (non-cancerous) and don’t spread, they can cause pain, swelling and fractures if they deform the bone.

Types & Stages

There are two types of aneurysmal bone cysts: 

• Active or primary. An active ABC could deform the bone it’s growing in but remains contained in the bone. It’s called a primary cyst because it develops on its own.
   
• Aggressive or secondary. An aggressive ABC extends beyond the bone to the nearby soft connective tissues. It’s called a secondary cyst because it occurs in conjunction with another existing bone tumor or condition. Bone conditions and bone cancer that can cause secondary aneurysmal bone cysts include:
   
  • Fibrous dysplasia. A chronic disorder of the skeleton in which scar-like tissue grows in place of normal bone. 
     
  • Giant cell tumor. Also called GCT, a rare, aggressive non-cancerous tumor that generally occurs in adults between the ages 20 and 40.
     
  • Osteoblastoma. A rare, non-cancerous, aggressive bone tumor. It tends to form in any of the bones in the hands and feet, but it can also occur in the spine where it can lead to scoliosis and neurological symptoms. 
     
  • Chondrosarcoma. A type of bone cancer that develops in cartilage cells—the gristly connective tissue from which most bones develop. 
     
  • Osteosarcoma. Cancer that begins in your bones, usually in the arms or legs. Limited movement, bone pain, a lump and an unexplained broken bone are the most common symptoms. It is most often found in pediatric patients.

Signs & Symptoms

ABCs may cause:

• pain and swelling in a bone or joint
• stiffness or decreased range of motion in the arm, leg, hand or foot
• a broken bone could be the first sign that a person has an ABC
• back or neck pain, nerve pain radiating (spreading) into the hands or feet, or difficulty using the bathroom if the ABC is in the spine
• may be discovered incidentally, such as during a routine doctor's visit or on an X-ray taken to confirm an injury

Diagnosis

Tests and procedures used to diagnose ABCs include:

• Examination. Your doctor will do a physical examination to look for any noticeable lumps on your bones. 
   
• Imaging tests. These may include: 
   
  • Bone scans. A whole-body bone scan is a nuclear medicine test to check your bones for issues or changes. You receive an injection of a substance called a radiotracer. The radiotracer collects in areas of irregular activity and highlights these areas on an imaging scan. 
     
  • Computerized tomography scan (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. 
     
  • Magnetic resonance imaging (MRI). A diagnostic procedure that uses a combination of large magnets, radiofrequencies and a computer to produce detailed images of organs and structures within the body. 
     
• Biopsy. A procedure to remove some cells for testing. The sample might be removed with a needle put through the skin. Or the sample might be taken during surgery to remove the cancer. The type of biopsy depends on the cancer's location.

Treatment

Because ABCs rarely go away without removing them surgically—and in some cases they do grow back—treatment options include: 

• Surgery. Most patients undergo surgical removal of the tumor. The options include: 
   
  • Curettage and bone grafting. The most common treatment is curettage in which an orthopedic 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 bone graft from a donor or another area of your body to refill the area where the tumor was.
     
  • Wide Resection. Surgery with a wide resection, or en bloc resection, involves removing a large segment of bone where the cyst is located. Surgery with a wide resection is usually reserved for ABCs that have caused severe bone destruction or have recurred multiple times. It usually requires the bone to be reconstructed or rebuilt with a large piece of donor bone (allograft) or a metal bone or joint replacement.
     
• Nonsurgical treatments. Options for large, difficult-to-access tumors that are challenging to remove safely during surgery include:
   
  • Arterial embolization. A procedure that blocks the blood vessels that feed the tumor. Treatment works by placing a substance like tiny balloons, gelatin foam or particulate agents in the vessel to prevent blood from flowing through it. 
     
  • Radiation therapy. Radiotherapy uses a type of radiation to target the tumor cells. These high doses of radiation usually will kill the tumor and prevent it from coming back. 
     
  • Sclerotherapy. This minimally invasive procedure involves directly injecting a solution into the tumor or blood vessels near the tumor.  

Causes & Risk Factors

Doctors don’t know what causes aneurysmal bone cysts. Some causes and risks include: 

• Age. ABCs affect children more frequently than adults.
   
• Gender. There is a slightly higher incidence in females.
   
• Growth factors. Most ABCs are formed near growth plates (the areas at the ends of long bones in children and teens that allow the bones to grow longer).

Screening

There is no standard screening for ABCs.