Osteochondroma (Extosis)

Osteochondroma is the most common type of non-cancerous (benign) bone tumor. An osteochondroma is a hard mass of cartilage and bone that generally appears near the growth plate (a layer of cartilage at the ends of a child’s long bones). The majority of children with an osteochondroma only have a single tumor. Less commonly, osteochondromas will occur as multiple tumors.

Although osteochondromas do not spread beyond the affected bone, they may grow in size as your child grows. An osteochondroma ordinarily stops growing when a child reaches full height (around age 14 in girls and 16 in boys).

In most cases, osteochondromas don’t create problems and treatment isn’t needed. Surgery is only necessary if the tumor is causing significant pain, putting pressure on blood vessels or nerves, or is very large in size.

Very rarely, an osteochondroma can transform into a malignant condition later in adulthood. Your child’s doctor will probably want to keep an eye on the condition for this reason. It is extremely unusual and is therefore not a reason to remove all osteochondromas.

In general, osteochondromas are hard masses that grow on top of the bone and only cause pain when nerves, muscles, or tendons rub against them.

Keep in mind that each child can experience symptoms of osteochondroma differently, depending on the size and location of the tumor or tumors.

Because the symptoms may also be caused by other, more serious health conditions, it is important to be evaluated by a physician to get an accurate diagnosis. Always consult your child's physician if you have concerns.

The following are the most common symptoms of osteochondromas:

• A hard, painless mass; the mass can be painful if nearby muscles or tissues rub over the osteochondroma and become inflamed 
• Different limb lengths
• Shorter than average height for age
• Joint and muscle pains

The cause of osteochondroma is unknown, but the tumor is thought to be related to an abnormality in the growth plate, causing a bony prominence to grow away from the bone.

If a child has several osteochondromas, they are usually the result of a genetic disorder known as multiple hereditary exostoses (MHE) or multiple osteochondromas. However, there is also a non-heredity form of MHE in which multiple osteochondromas occur by chance (sporadically).

In addition to a complete medical history and a full physical examination, the procedures for diagnosing osteochondroma in children may include:

• X-ray: In almost all cases, an osteochondroma can be diagnosed using an X-ray. An X-ray uses a small amount of radiation to produce pictures of a child’s bones and organs. This helps to determine where the growth is located. Osteochondromas show up on the X-ray as a hard mass near the growth plate on a normal bone, which makes most easy to detect.

The following diagnostic tests are usually not required, except if the tumor is found in an unusual location, such as the pelvis:

• Magnetic resonance imaging (MRI): a diagnostic procedure that uses a combination of large magnets, radio frequencies, and a computer to produce detailed images of organs and structures within the body. This test is particularly useful in identifying tumors in areas that are difficult to image on a plain X-ray. It also helps confirm the size of the tumor and distinguish it from other types of bone tumors.
• Computerized tomography scan (also called a CT or CAT scan): a diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce images, both horizontally and vertically, of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, and organs. CT scans are more detailed than general X-rays.
• Bone scans: a nuclear imaging method to detect bone diseases, tumors, and inflammation. In rare cases, this is used to check for other osteochondromas in children with multiple hereditary exostoses (MHE).

Osteochondromas that are not painful or likely to cause a fracture don't require treatment.

Complications that can occur with surgery to remove this kind of tumor (or tumors) factor in to a decision to leave the tumor alone. For example, if an osteochondroma occurs in close proximity to the bone's growth plate, surgical interference in the area could affect how the bone grows.

The child should continue to be seen by a doctor, since a very small number of osteochondromas (1 percent) can develop into cancerous (malignant) tumors. In the rare circumstance that this occurs, it is almost always in adulthood and is usually notable for growth in size of a lump or pain in a previously painless lump.

Your child's physician may recommend surgery if your child is experiencing pain, a fracture, or nerve irritation, or if the tumor is large or bothersome.

In cases where surgery is necessary, the treatment of choice is complete removal of the tumor. This involves opening the skin over the tumor, locating the osteochondroma, and cutting it off of the normal bone. Depending on the location of the osteochondroma, surgical removal of the lesion is usually successful. However, if the tumor is close to nerves and blood vessels, the operation can be more difficult.

In cases where the genetic disorder, multiple hereditary exostoses (MHE), causes multiple lesions, and in very young children, there is a very small chance (5 percent) that new tumors may form in the same area after they are removed with surgery.

Experts in the Bone and Soft Tissue Tumors Program at Boston Children’s are devoted to caring for children and teenagers with osteochondromas and other bone and soft tissue disorders.

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

Our care is informed by our research. We have a long history of research and innovation in treating conditions like osteochondromas.

Boston Children's is a world leader in opening new avenues of "translational research," bringing laboratory advances to the bedside and doctor's office as quickly as possible. All of our senior medical staff members of the Bone and Soft Tissue Tumors Program participate in clinical research activities. Our Translational Research Program aims to dramatically improve translational research in pediatric hematology and oncology.

In addition to a variety of clinical trials, Boston Children’s also conducts extensive laboratory research to identify new treatments and improve therapies for bone and soft tissue tumors.

For more information about current research, visit our Bone and Soft Tissue Tumors Program page.