Overview of Bone and Joint Tumors
Bone tumors may be benign or malignant. Malignant tumors may be primary or metastatic.
In children, most bone tumors are primary and benign; some are malignant primary tumors (eg, osteosarcoma, Ewing sarcoma). Very few are metastatic tumors (eg, neuroblastoma, Wilms tumor). Bone marrow 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 (PVNS and also known as tenosynovial giant cell tumor) 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 of a bone tumor. Some pelvic bone tumors can cause pelvic or proximal buttock pain, mimic sciatica or, rarely, cause true sciatica by compressing the sciatic nerve.
Plain x-rays are the first test to identify and characterize a bone tumor. Lesions suggestive of tumors, including those found incidentally on x-rays done for other reasons, usually require further assessment, often with additional imaging studies (eg, CT or MRI) and a biopsy. However, tumors with x-ray findings classic for benign lesions do not require bone scan, CT, or MRI. Whole body bone scan in general, rather than just a scan of a selected area, should be done routinely to identify other areas of abnormality, especially if multicentric or metastatic tumors are suspected. Whole body scan is usually preferred to ensure that other skeletal lesions are identified, particularly because the patient has already received the full dose of radionucleotide, and the whole body component only takes some limited additional time. There are times where gadolinium contrasted MRI is necessary and other times where contrast is not necessary. Adequacy of renal function should be documented before adding MRI contrast, because there may be renal toxicity in patients with reduced renal capacity. The MRI radiologist should make the final decision whether a contrasted MRI should follow the noncontrasted MRI study and what additional MRI sequences are needed.
Some tumors (eg, nonossifying fibroma, fibrous dysplasia, enchondromas) and tumor-like conditions (eg, Paget disease of bone) 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 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. For example, Ewing sarcoma typically shows permeative-type bone destruction, including a large soft-tissue mass with aggressive periosteal onion-skin reactive bone often before there is an extensive, lytic, destructive appearance, and a 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. For example, Ewing 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, and a 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, multiple bone islands) is an asymptomatic condition of no clinical consequence but can mimic osteoblastic bone metastases of breast or prostate 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.
Bone infection can manifest with pain and a destructive lesion on x-rays.
The primary cancer location can be identified over 85% of the time with a quality history and physical examination, CT of the chest/abdomen/pelvis, mammography in females, and prostate-specific antigen (PSA) in males. 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-99 whole body bone scanning should be done to search for additional tumors. Positron emission tomography (PET) imaging may be done, often combined with CT (PET-CT). For possibly metastatic tumors, mammography in females and PSA in males may help identify the primary cancer.
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.
Biopsy may be needed to confirm the diagnosis of suspected metastatic disease in an isolated, single lesion. However, biopsy may not be needed if there are multiple metastatic lesions in a patient with a confirmed primary cancer.
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 (eg, from breast, lung, prostate, or renal cancer) 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.