What Is an Osteoid Osteoma?

Medically Reviewed by Jabeen Begum, MD on October 10, 2022
5 min read

An osteoid osteoma is a bone condition that often affects children and young adults aged 5 to 25 years. Boys are three times more likely to experience it than girls. 

An osteoid osteoma is a non-cancerous bone tumor. It can grow in any bone but usually affects the long bones of your legs, including your femur (thigh bone) and your tibia (shin bone). In other cases, an osteoma can form in your spine, which can lead to an abnormal spinal curve called scoliosis

A tumor is a mass of tumor cells, bone cells, and blood vessels. Over time, bone cells may form around the tumor and create a bony shell. The center of the tumor is called a nidus and is usually less than 2 centimeters in size. 

While an osteoma can grow, it doesn’t spread to other bones or tissues.

The most common symptom of an osteoid osteoma is bone pain, which is often described as a deep, intense, and ongoing ache. The pain usually:

  • Gets worse at night
  • Comes and goes during the day
  • Isn’t linked to activity
  • Can be managed over-the-counter pain relievers, though not always
  • Worsens after consumption of alcohol 

Other osteoid osteoma symptoms include:

  • Swelling
  • Joint stiffness
  • Limping 
  • Misshapen bones
  • Muscle loss
  • Contractures (hardened muscles and tissues that cause rigid joints)
  • Scoliosis

An osteoid osteoma in your femur or tibia can also produce a longer leg, which is likely related to blood flow. The tumor attracts extra blood flow to fuel its growth, which then brings in nutrients that help the surrounding tissue grow. If the tumor is near an open growth plate, the extra blood flow will encourage bone growth, leading to a longer bone. 

The growth plate closes after puberty, though, usually between age 13 to 15 in girls and age 15 to 17 in boys, so it’s unlikely that a tumor that grows in adulthood will affect your limb length.

The exact cause of osteoid osteoma is unclear. Some experts believe it occurs if cells don’t die when they should or because they grow and divide more than they should. A close look at the osteoma cells shows that they’re a little different from bone cells, which supports the idea that they grow from irregular cells.

Still, other experts think the tumor specifically grows as a reaction to inflammation in the bone. The tumor is usually small and self-limiting, so it doesn’t spread the way a cancerous mass does. Both of these features suggest it grows in response to inflammation. 

These tumors also contain high levels of chemicals called prostaglandins that seem to make them grow and cause pain. Even though there’s lots of inflammation, there’s usually no history of injury or infection, so it’s not clear exactly why these happen. 

Your doctor will first go over your symptoms and medical history and conduct a physical examination of the area. They’ll ask you to describe your pain, whether you’ve had an accident or injury to that area before, and whether pain relievers like ibuprofen help. Once they have this information, they’ll order additional tests. 

Imaging tests. Your doctor will order one or more imaging tests to get a picture of your bone and surrounding tissues. These tests may include:

In an X-ray image, an osteoid osteoma looks like a circle with a white outer ring and a dark center, which is the nidus. They can often look like other conditions, such as bone cancer, bone infections, or other cysts, so your doctor might order MRI or CT tests for more detailed images and to rule out other problems.

Other tests. Your doctor might also order blood tests and a bone biopsy to confirm their diagnosis. To perform a biopsy, they will insert a needle through your skin into the tumor and draw out some of the fluid and cells. A lab technician then looks at these cells under a microscope to determine the type. 

Lots of osteomas get better on their own, though it can take time. Typically, the main focus of osteoid osteoma treatment is to ease pain and reduce inflammation, which doctors will attempt to do by using the following treatments:

Over-the-counter NSAIDs. In most cases, you can take over-the-counter non-steroidal anti-inflammatory drugs, known as NSAIDs. These include:

Prescription NSAIDs. Osteomas can cause severe pain, so you may need something stronger than over-the-counter medications. Prescription NSAIDs can help ease pain and shrink the tumor faster. 

That being said, some people don’t find relief after taking NSAIDs, and these drugs can also cause side effects (especially if you’re on them for a long time), including:

You also might have to avoid these medications if you have a bowel disease that puts you at high risk for ulcers and bleeding. In these cases where NSAIDs don’t help the pain or may cause side effects, your doctor might suggest surgery or other surgical procedures. 

CT-guided ablation. The gold standard for surgical osteoid osteoma treatment is called a CT-guided radiofrequency ablation. Your doctor will use a CT scan to find the tumor, then insert a probe into it and burn it. 

The procedure takes about 2 hours, and you usually only need one treatment. It’s minimally invasive and precise, which means there’s less risk of damage to the surrounding bone tissue.  

CT-guided drill resection. This procedure is like a CT-guided ablation, but your doctor will use a drill to remove the tumor instead of a heated probe. 

Intralesional curettage. This procedure is an open surgery where your doctor scrapes the tumor out of the bone and then fills the space with a bone graft. It’s much more invasive but is sometimes necessary. 

The outlook for osteoid osteoma is good. While you might experience pain or see changes to your spinal curve, the tumor is noncancerous and can be managed with NSAIDs in most cases. Even if you don’t respond to the medications, surgery can totally remove the tumor, and recurrence is rare.

If you experience any bone pain, talk to your doctor. You may have an osteoma.