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Overview of Bone and Joint Tumors
Bone tumors may be primary or metastatic and benign or malignant.
In children, most bone tumors are primary and benign; some are malignant primary tumors (eg, osteosarcoma, Ewing’s sarcoma). Very few are metastatic tumors (eg, neuroblastoma, Wilms’ tumor). Bone also can be affected by childhood leukemia and lymphomas.
In adults, especially those over age 40, metastatic tumors are about 100 times more common than primary malignant tumors. Excluding marrow cell tumors (eg, multiple myeloma), there are only about 2500 cases of primary malignant bone tumors in the US each year among children and adults.
Synovial tumors are extremely rare in both children and adults. Pigmented villonodular synovitis is a benign but at times destructive tumor of synovial cells. Synovial sarcoma (often with both spindle cell and glandular–like components) is a malignant soft-tissue tumor not of synovial origin, which seldom occurs inside of a joint.
The most common reason that diagnosis of bone tumors is delayed is that physicians fail to suspect the tumor and order appropriate imaging studies. Bone tumors should be considered in patients who have unexplained bone pain, particularly pain at night or at rest. Persistent or progressive unexplained pain of the trunk or extremities, particularly if associated with a mass, is suggestive. Plain x-rays are the first test. Tumors should also be suspected if an imaging study shows an unexplained abnormality consistent with a tumor. Lesions suggestive of tumors usually require further assessment, often with additional imaging studies and a biopsy.
Some tumors (eg, Paget’s disease of bone, nonossifying fibroma, fibrous dysplasia, enchondromas) may have characteristic radiographic findings and can be diagnosed without biopsy.
Radiographic findings that suggest cancer include the following:
A lytic appearance is characterized by clear areas of bone destruction that are sharply demarcated. A permeative appearance is characterized by a faint, gradual loss of bone or an infiltrating pattern without clear borders. Certain tumors have a characteristic appearance (eg, Ewing’s sarcoma typically shows permeative-type bone destruction, including a large soft-tissue mass with periosteal onion-skin reactive bone often before there is an extensive, lytic, destructive appearance; giant cell tumor has a cystic appearance without a sclerotic interface between the tumor and normal bone). The tumor’s location may narrow diagnostic possibilities (eg, Ewing’s sarcoma commonly appears in the shaft of a long bone; osteosarcoma usually appears in the metaphyseal-diaphyseal region toward the end of a long bone; giant cell tumor usually occurs in the epiphysis).
Some benign conditions, however, can mimic a malignant tumor:
Heterotopic ossification (myositis ossificans) and exuberant callus formation after fracture can cause mineralization around bony cortices and in adjacent soft tissues, mimicking malignant tumors.
Langerhans’ cell histiocytosis (histiocytosis X, Letterer-Siwe disease, Hand-Schüller-Christian disease, eosinophilic granuloma) can cause solitary or multiple bone lesions that are usually distinguishable on x-ray. In solitary lesions, there may be periosteal new bone formation, suggesting a malignant bone tumor.
Osteopoikilosis (spotted bones) is an asymptomatic condition of no clinical consequence but can simulate osteoblastic bone metastases of breast cancer. It is characterized by multiple small, round, or oval foci of bony sclerosis, usually in the tarsal, carpal, or pelvic bones or the metaphyseal-epiphyseal regions of tubular bones.
CT and MRI may help define the location and extent of a bone tumor and sometimes suggest a specific diagnosis. MRI is usually done if cancer is suspected. If tumors are suspected of being metastatic or involving multiple foci (multicentric), then radioisotopic technetium bone scanning should be done to search for additional tumors.
Biopsy is usually essential for diagnosis of malignant tumors, unless the imaging studies have a classically benign appearance. The pathologist should be given pertinent details of the clinical history and should review imaging studies. Histopathologic diagnosis may be difficult and requires sufficient viable tissue from a representative portion of the tumor (usually the soft portion). The best results are obtained in centers with extensive experience in bone biopsies. Immediate, accurate, definitive diagnosis is possible in > 90% of cases. If a malignant diagnosis is suspected on frozen section histology, often the surgeon will wait for the results of permanent histology before treating definitively. Mistakes occur more frequently in hospitals that infrequently encounter patients with malignant primary bone tumors.
In children, most bone tumors are primary and benign, some are primary and malignant, and very few are metastatic.
In adults, especially those age > 40, metastatic tumors are about 100 times more common than primary malignant tumors.
Assessment begins with plain x-rays but typically requires MRI and often other studies.
General radiographic findings suggesting cancer include a destructive appearance (particularly with multiple foci), irregular borders, cortical destruction, soft-tissue extension, and pathologic fracture.
Biopsy is required for diagnosis of malignant tumors.
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