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Benign Bone Tumors

by Michael J. Joyce, MD

Osteochondroma

Osteochondromas (osteocartilaginous exostoses), the most common benign bone tumors, may arise from any bone but tend to occur near the ends of long bones. These tumors manifest most often in people aged 10 to 20 and may be single or multiple. Multiple osteochondromas tend to run in families. Secondary malignant chondrosarcoma develops in well under 1% of patients with single osteochondromas, but in about 10% of patients with multiple osteochondromas. Patients with multiple hereditary osteochondromas have more tumors and are more likely to develop a chondrosarcoma than patients with a single osteochondroma. Osteochondromas rarely cause the bone to fracture.

On imaging studies, the lesion appears as a bony prominence with a cartilage cap (< 2 cm) off the surface of the bone with no underlying cortex under the prominence. The medullary canal is in continuity with the base of the exostosis. The medullary canal and exostosis are confluent, and there is no true underlying cortex at the base of the exostosis.

Excision is needed if the tumor is compressing a large nerve; causes pain (especially when impinging on muscle and creating an inflammatory bursa); disturbs growth; or on imaging study has a destructive appearance, soft-tissue mass, or thickened cartilaginous cap (> 2 cm) suggesting transformation into malignant chondrosarcoma. An enlarging tumor in an adult should raise concern of chondrosarcoma and the possible need for excision or biopsy.

Enchondroma

Enchondromas may occur at any age but tend to manifest in people aged 10 to 40. They are usually located within the medullary bone metaphyseal-diaphyseal region. These tumors are usually asymptomatic but may enlarge and become painful. They are often found when x-rays are taken for another reason.

On x-ray, the tumor may appear as a lobulated calcified area within bone; some lesions are less calcified, with areas of stippled calcification on either plain films or CT. If adjacent to the cortex, enchondromas show minor endosteal scalloping. Almost all enchondromas have increased uptake on a bone scan and thus create concern of cancer. X-ray findings, including MRI and CT, may be diagnostic; if they are not, and especially if the tumor (not the associated joint) is painful, the diagnosis should be confirmed by biopsy. To help differentiate bone pain from joint pain, the joint can be injected, usually with a long-lasting anesthetic (eg, bupivacaine); if pain persists, it may be caused by the bone lesion.

An asymptomatic enchondroma does not need biopsy, excision, or other treatment (usually curettage); however, follow-up imaging studies are indicated to rule out the rare disease progression to chondrosarcoma. These studies are done at 6 mo and again at 1 yr or whenever symptoms develop.

Patients with multiple enchondromas (Ollier's disease) and especially multiple enchondromatosis with soft-tissue hemangiomas (Maffucci's syndrome) have a much higher risk of chondrosarcoma.

Chondroblastoma

Chondroblastoma is rare and occurs most commonly among people aged 10 to 20. Arising in the epiphysis, this tumor may continue to grow and destroy bone and the joint. It appears on imaging studies as a sclerotic marginated cyst containing spots of punctate calcification. MRI can help diagnostically by showing characteristic changes well away from the lesion.

The tumor must be surgically removed by curettage, and the cavity must be bone grafted. Local recurrence rate is about 10 to 20%, and recurrent lesions often resolve with repeat bone curettage and bone grafting.

Chondromyxofibroma

Chondromyxofibroma is very rare and usually occurs before age 30. The appearance on imaging studies, which is usually eccentric, sharply circumscribed, lytic, and located near the end of long bones, suggests the diagnosis. Treatment after biopsy is surgical excision or curettage.

Osteoid osteoma

Osteoid osteoma, which tends to affect young people (commonly aged 10 to 35), can occur in any bone but is most common among long bones. It can cause pain (usually worse at night, reflecting increased nocturnal prostaglandin-mediated inflammation). Pain is typically relieved by mild analgesics (particularly aspirin or other NSAIDs) that target prostaglandins. In growing children, the inflammatory response and associated hyperemia, if close to the open growth plate, may cause overgrowth and limb length discrepancy. Physical examination may reveal atrophy of regional muscles because the pain causes muscle disuse.

Characteristic appearance on imaging studies is a small radiolucent zone surrounded by a larger sclerotic zone. If a tumor is suspected, a technetium-99m bone scan should be done; an osteoid osteoma appears as an area of increased uptake. CT with fine image sequences is also done and is most helpful in distinguishing the lesion.

Removal of the small radiolucent zone with percutaneous radiofrequency ablation provides permanent relief. Most osteoid osteomas are treated by an interventional musculoskeletal radiologist using percutaneous techniques and anesthesia. Less often, osteoid osteomas are surgically curetted or excised. Surgical removal may be preferred when the osteoid osteoma is near a nerve or close to the skin (eg, spine, hands, feet) because the heat produced by radiofrequency ablation may cause damage.

Nonossifying fibroma (fibrous cortical defect)

Nonossifying fibroma (fibrous cortical defect, fibroxanthoma) is a benign fibrous lesion of bone that appears as a well-defined lucent cortical defect on x-ray. A very small nonossifying fibroma is called a fibrous cortical defect. These lesions are developmental defects in which parts of bone that normally ossify are instead filled with fibrous tissue. They commonly affect the metaphyses, and the most commonly affected sites are, in order, the distal femur, distal tibia, and proximal tibia. They can progressively enlarge and become multiloculated. Nonossifying fibromas are common among children. Most lesions eventually ossify and undergo remodeling, often resulting in dense, sclerotic areas. However, some lesions enlarge.

Small nonossifying fibromas are asymptomatic. However, lesions that involve nearly 50% of the bone diameter tend to cause pain and increase the risk of pathologic fracture.

Nonossifying fibromas are generally first noted incidentally on imaging studies (eg, after trauma). They typically are radiolucent, single, < 2 cm in diameter, and have an oblong lucent appearance with a well-defined sclerotic border in the cortex. They can also be mutiloculated.

Small nonossifying fibromas require no treatment and limited follow-up. Lesions that cause pain or are close to 50% of the bone diameter may warrant curettage and bone grafting to decrease risk of a pathologic fracture through the lesion.

Benign giant cell tumor of bone

Benign giant cell tumors of bone, which most commonly affect people in their 20s and 30s, occur in the epiphyses. These tumors are considered locally aggressive. They tend to continue to enlarge, destroy bone, and may eventually erode the rest of the bone and extend into the soft tissues. They may cause pain. These tumors are notorious for their tendency to recur. Rarely, a giant cell tumor of bone may metastasize to the lung, even though it remains histologically benign.

Benign giant cell tumors of bone appear as expansile lytic lesions on imaging. On imaging studies, there is a margin without a sclerotic rim where the tumor ends and normal trabecular bone begins.

Most benign giant cell tumors of bone are treated by curettage and packing with methyl methacrylate or by bone graft. To reduce recurrence rate, surgeons often prefer using an adjuvant such as thermal heat (provided by the hardening of methyl methacrylate) or treating the tumors chemically with phenol or freezing with liquid nitrogen. If a tumor is very large and destructive to the joint, complete excision with joint reconstruction may be necessary.

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