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ABCMD definition of Exostosis:

Exostosis is an abnormal outgrowth of bone projecting from the surface of a bone.

What is Exostosis?  

Exostosis is a bony outgrowth on the surface of a bone or a tooth. These outgrowths are benign and do not spread to other body parts (they do not metastasize). Usually they are asymptomatic (do not cause any pain) but they may become painful depending on their size and location.

Exostosis is also known as 'Osteocartilaginous exostosis' named after its contents. Osteon is the basic cell element of bones. Bone tissues are formed through a process known as Osteosis. Exostoses occur when something goes wrong with this process. Basically, exostosis is a benign connective tissue tumor with proliferation of bone tissue. Usually it appears like a round or oval mass of bone.

What causes Exostoses?

Environmental stress is said to be one of the more common reasons for exostosis to develop.  A common example is “surfer’s ear.” It happens when bone grows within the ear canal. It is believed that this happens due to frequent flooding of the ear canal with cold water.

Other causes of exostoses may include damage to joints.  In such cases strain on the joints causes a small accumulation of mass of bone on or near the joint. These minor tumors may be removed or left in place depending on whether or not they affect the movement of joints. 

What are the symptoms of Exostoses?

·         Asymptomatic (no symptoms)

·         Bone lump

·         Painful bone lump

How is Exostosis diagnosed?

Abnormal growths of bone are usually easily noticeable. If found, such abnormal growths should be brought to your doctor’s attention as soon as possible to ensure proper work-up and to rule out serious disease.  A swelling characterized by an immovable character, hard and firm texture may most likely be exostosis, other means of diagnosis should also be used and you should see your doctor for an evaluation.  It is usually best to get an x-ray, computed tomography (CT) scan or a  magnetic resonance imaging (MRI) scan.  In some very rare cases biopsy may be needed to diagnose exostoses.  The condition is confirmed as exostoses if a lamellar pattern with fibro cartilaginous covering is found on biopsy.  It is important to rule out other cancerous tumors and malignancies.

How is Exostosis treated?

Generally exostosis is left untreated if it is assessed that it is benign (harmless) by your doctor and you have no symptoms or pain.  In such cases it is usually followed with regular observation.  When exostoses begins to disturb the functionality and the quality of life in someone, it can be removed with surgery.  In these surgical procedures the outgrowth is shaved off from the surface of bone. If shaving off the growth is not possible, it can be excised completely with the surrounding bone tissues. This treatment does not guarantee that exostosis will not re-occur in the same place or at another part of body.

Precautionary measures which may help in avoiding development of  exostosis includes avoiding calcium supplements, avoiding tight fitting shoes and avoiding repeated stress and strain at the same spot.  

This information has been reviewed by Matthew C Niesen MD, a resident at the University of Wisconsin Hospital and Clinics in order to help ensure the accuracy and completeness of information written.  However, this information may not be entirely complete and should be discussed with your physician prior to making any medical decisions or changes in your medical care.