Exostosis

What is an exostosis?

An exostosis is a benign (noncancerous) bone tumor. The plural form of exostosis is exostoses.

Exostoses are benign bone tumors that form on top of your existing bone tissue. In other words, they’re bumps of bone that grow out of one of your bones. They’re not cancerous. This means they’re not a symptom of cancer, and they don’t cause it. An exostosis also won’t spread to other parts of your body (metastasize).

Many exostoses don’t cause symptoms, and you might never know you have one. But — depending on where an exostosis develops — it might be painful when you move or use the affected bone.

Which treatments you’ll need for an exostosis depends on where it forms. Which bone it’s on will affect which symptoms you’ll experience and how a healthcare provider will treat the exostosis.

How does an exostosis affect my body?

An exostosis can form on any bone in your body. Some of the most common types of exostoses form on bones in your:

• Ankles and feet.
• Ear canals.
• Sinus cavities.
• Jaw.
• Fingers.
• Toes.

A healthcare provider might diagnose some types of exostoses with a specific name, including:

• Surfer’s ear: An exostosis that forms on the bones in your ear canal. It can make you more likely to experience ear infections. Surfer’s ear can sometimes lead to hearing loss.
• Haglund’s deformity: Haglund’s deformity is an exostosis that grows on your heel bone (calcaneus) where your Achilles tendon connects to your ankle. Haglund’s deformity can cause heel pain, especially when you wear shoes that press tightly against the back of your heel.
• Subungual exostosis: Subungual exostoses form on the bones in your fingers or toes under your nail bed — the layer of tissue directly under a fingernail or toenail.
• Paranasal sinus exostosis: Exostoses that form on bones in your nasal cavities (the narrow spaces around your nose) are called paranasal sinus exostoses.
• Bone spurs: Bone spurs are a type of exostosis called osteophytes. Bone spurs develop over long periods of time, usually near joints (where two or more bones meet).

Who is affected by exostoses?

Anyone can develop an exostosis. They’re more common in children and teens because their bones are still rapidly growing and developing.

What are the symptoms of an exostosis?

Some exostoses hurt. Many don’t cause symptoms. You might never know you have an exostosis until a healthcare provider discovers it accidentally during an imaging test or physical examination. Symptoms of an exostosis can include:

• Pain in the area around the exostosis.
• Stiffness or pain when you move, caused by exostoses that form on or near a joint (like your hip, knee, ankle, finger or toe).
• A stuffy or blocked nose if an exostosis forms in your sinus cavities.
• Difficulty hearing if you have surfer’s ear. You might be more likely to experience ear infections because the exostosis makes it easier for water to get trapped inside your ear canal.

What causes exostoses?

Some exostoses occur with no known cause (idiopathically).

The most common causes of exostoses include:

• Injuries: Damage to a bone can make it regrow incorrectly and form an exostosis.
• Health conditions: Some conditions like osteoarthritis and spinal stenosis cause extra wear and tear on your bones. This stress can lead to an exostosis growing near that irritation.
• Family history: You might be more likely to develop exostoses if your biological parents have them.

How is an exostosis diagnosed?

A healthcare provider will diagnose an exostosis with a physical exam and imaging tests.

They’ll look at the growth and ask you about any symptoms you’re experiencing.

You’ll need one of a few types of imaging test to take pictures of your bone and the area around it, including:

• X-rays.
• A computed tomography (CT) scan.
• Magnetic resonance imaging (MRI).

How are exostoses treated?

Treatment for an exostosis depends on where in your body it forms and if it’s causing you any symptoms.

Some exostoses don’t need any treatment. You might be able to relieve symptoms like pain and inflammation with over-the-counter (OTC) NSAIDs. Talk to a healthcare provider before taking NSAIDs for more than 10 days in a row.

Exostoses like Haglund’s deformity can be treated by wearing different shoes that don’t put as much pressure on your heel.

Some types of exostoses must be surgically removed. Your provider or surgeon will tell you what to expect and how long it will take to recover.

How can I prevent an exostosis?

You can’t prevent an exostosis from forming.

Talk to a healthcare provider if you have arthritis or spinal stenosis. Managing your symptoms might reduce the chances that your bones are irritated enough to form an exostosis.

What can I expect if I have an exostosis?

You should expect to make a full recovery after having an exostosis. Even if you need surgery to remove it, you shouldn’t experience any long-term symptoms.

Some types of exostoses — especially surfer’s ear — can regrow after they’re removed. Visit a healthcare provider if you notice another growth.

When should I see my healthcare provider?

Visit a healthcare provider as soon as you notice a new growth or bump on or near a bone. A provider needs to examine the growth to make sure it’s an exostosis and not something more serious (like a sarcoma).

Even though exostoses aren’t cancerous, you should get any new growth examined as soon as possible.

What questions should I ask my doctor?

• Do I have an exostosis or another type of growth?
• Which type of exostosis do I have?
• What caused the exostosis?
• Will I need surgery to remove the exostosis?
• What can I do to treat my symptoms at home?

What is the difference between an exostosis and a sarcoma?

Exostosis and sarcomas are both tumors. The biggest difference is that exostoses are never cancerous.

Sarcomas are a rare type of cancerous (malignant) tumor that develops in bones and the connective tissue around them. Sarcomas form when immature bone or tissue cells experience a DNA mutation. Some mutations make them develop into cancer cells.

Visit a healthcare provider right away if you notice a new growth on or near one of your bones, especially if it’s painful. Even though exostoses aren’t cancerous, they can develop in similar locations — and share early symptoms — with sarcomas.

What is the difference between an exostosis and an osteoma?

Osteoid osteomas are another type of benign bone tumor. You might see them referred to as just osteomas.

Osteoid osteomas are very similar to exostoses. They typically grow on long bones in people between 5 and 25 years old. They usually cause aching, dull pain that gets noticeably worse at night.

What is the difference between an exostosis and an osteochondroma?

If an exostosis forms on an area of bone that’s covered by cartilage, it’s called an osteochondroma. They’re both benign bone tumors. Osteochondromas usually grow out of the end of long bones in kids and teens. They commonly affect kids’ growth plates — disks of developing cartilage that eventually harden into bone.

Osteochondromas that develop one at a time are called solitary osteochondroma. Some children develop multiple osteochondromas at the same time. This is usually caused by a condition called multiple hereditary osteochondroma.

Visit a healthcare provider if your child has a new bump on or near one of their bones, especially if the growth is painful.

A note from Cleveland Clinic

Finding out you have a tumor is always scary. Fortunately, exostoses aren’t cancerous. In fact, you might not need any treatment at all if the exostosis isn’t causing pain or making it difficult to move. Even if you do need an exostosis surgically removed, you should make a full recovery with no long-term effects.

Visit a healthcare provider as soon as you notice a new bump on or near a bone. It’s important to have a provider diagnose a growth as soon as possible to make sure it’s an exostosis and not a different, more dangerous type of tumor.