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Enchondromas can occur in anyone but are most common in middle-aged patients. They are most often found in the small bones of the hand. In fact, enchondroma is the most common bone tumor of the hand. Enchondomas can also develop in the body's long bones, such as the femur (thighbone), tibia (shinbone), and humerus (upper arm bone).

Enchondromas are most often solitary tumors. In rare cases, however, multiple tumors can appear as part of a condition such as Ollier disease or Maffucci syndrome.

Single enchondromas rarely become cancerous, though the chances are a little higher in patients with Ollier disease and Maffucci syndrome. When enchondromas do become cancerous, they usually become a type of malignant cartilage tumor called a chondrosarcoma.

Distinguishing between a noncancerous enchondroma and the very low-grade form of a cancerous tumor can be difficult, even for orthopaedic tumor surgeons.

The exact cause of enchondromas is unknown. Some research indicates that they may result when cells turn into cartilage instead of bone.

It is not believed that the tumors are caused by radiation or chemical exposure, or by any specific activity.

In most cases, enchondromas are not painful and do not cause any symptoms. However, if the tumors appear in the hands or feet, or if there are multiple lesions, the bone can weaken and become deformed. This can lead to pathologic bone fractures or enlargement of the affected fingers.

In patients with Ollier disease and Maffucci syndrome, bone deformities can be quite severe. If pain from other sources has been excluded, your doctor will carefully study the tumor to determine whether it could actually be a low-grade chondrosarcoma. Pain at night or at rest is more likely to indicate a malignant tumor. However, because pain is a common symptom of many conditions and injuries, your doctor will conduct a thorough evaluation.

Because they do not often cause symptoms, most enchondromas are found when routine X-rays are taken for another reason such as an injury or arthritis. When this occurs, your doctor will conduct an examination and may order a number of tests to confirm that your tumor is actually an enchondroma — and not a more aggressive or cancerous tumor.

Tests

X-rays. X-rays provide images of dense structures such as bone. On X-rays, enchondromas appear as small (less than 5 cm), lobe-shaped, darkened tumors in the middle of the bone. They usually contain white spots or calcification within. The white areas of the tumor show a pattern of rings and arcs that indicates the tumor contains cartilage.

X-rays, taken from the front (left) and side (right) showing a benign enchondroma. The tumor was discovered when X-rays were done after a knee injury.

An X-ray (left) and MRI scan (right) showing a large enchondroma of the fifth metacarpal of the hand.

Other imaging tests. Your doctor may order a computerized tomography (CT) or magnetic resonance imaging (MRI) scan to help further evaluate your tumor. These scans give a more complete picture of the bone around the tumor. If the tumor has turned into a malignancy, the scans may show bone erosion, bone inflammation, or a mass growing outside the bone.

Coronal (left) and axial (right) MRI scans showing a painful enchondroma in the upper arm.

 In some cases, your doctor may order a bone scan. During this test, a very small amount of radioactive dye is injected into the body by vein. Both benign and malignant tumors can cause an increased uptake of the radioactive material in the bone due to bone activity. Enchondromas are typically active on bone scans.

Bone scan shows an uptake of radioactive dye near the end of the thigh bone.

Biopsy. A biopsy may be necessary to exclude a more aggressive tumor than an enchondroma. In a biopsy, a tissue sample of the tumor is taken and examined under a microscope.

A biopsy can be performed under local anesthesia with a needle or as a small open operation.

Grading. The grade, or aggressiveness, of the tumor is determined by imaging studies and how the tumor looks under a microscope.

Under the microscope, enchondromas have islands of cartilage that are easy to tell apart from the normal bone that surrounds them. Usually, cartilage is not found in the center of bones. Enchondromas in the hand and foot or in patients with Ollier disease or Maffucci syndrome may contain more odd-looking cartilage. It may be difficult to distinguish these tumors from low-grade chondrosarcomas.

Low-grade chondrosarcomas look more cellular than enchondromas under a microscope, and there is less normal bone in the tumor. Because low-grade chondrosarcomas and enchondromas look similar, experienced surgeons, radiologists, and pathologists will work together to get the best interpretation of the tumor.

Characteristics of a more aggressive tumor or a malignant chondrosarcoma include:

• Thickening of the bone's outer cortex
• Reactive bone growth on the outer surface of the bone
• Destruction of the bone by the tumor
• Soft-tissue mass expanding from the tumor
• Large amounts of bone erosion
• Bone erosion that is growing
• Erosion surrounded by reactive bone

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Some tumors may look like simple enchondromas on X-ray — but are painful. Treatment of these lesions can be controversial. Some doctors recommend surgical curettage. Others think that the tumors are not likely to be the cause of the pain in the area — so they recommend monitoring with regular X-rays.

Unfortunately, biopsies are not often helpful in these cases. Even for specialized bone pathologists, it can be difficult to differentiate between a benign enchondroma and a low-grade chondrosarcoma. In this setting, needle biopsies are not recommended.

More aggressive tumors with bone destruction or with a mass growing outside the bone are usually chondrosarcomas. These malignant tumors need to be removed in their entirety. The specific procedure used depends upon the grade of the tumor; however, the vast majority of patients will be treated with surgery alone.

There is rarely a role for chemotherapy or radiation in the treatment of chondrosarcomas.

There is a great deal of ongoing research on enchondromas and chondrosarcomas. Current studies are trying to identify chemical markers that may help doctors tell the difference between benign and malignant cartilage tumors.

Other studies are looking at the different characteristics of tumors on specialized imaging studies such as MRI, CT, or positron emission tomography (PET) scans.