by Baram » Wed Aug 23, 2017 1:01 am
The first diagnostic test to arouse suspicion for a primary bone tumor is generally a plain radiograph of the affected area [51] . Characteristic features of conventional osteosarcomas (which account for the majority of cases, see below) include destruction of the normal trabecular bone pattern, indistinct margins, and no endosteal bone response. The affected bone is characterized by a mixture of radiodense and radiolucent areas, with periosteal new bone formation, lifting of the cortex, and formation of Codman's triangle (show radiograph 1). The associated soft tissue mass is variably ossified in a radial or "sunburst" pattern. (See "Bone tumors: Diagnosis and biopsy techniques").
Differential diagnosis ? The correct histologic diagnosis of osteosarcoma may be predicted in up to two-thirds of patients who have a characteristic radiographic appearance, clinical features, and tumor location [52] . However, no radiographic finding is pathognomonic, and biopsy is required for definitive diagnosis. The differential diagnosis includes other malignant bone tumors (ie, Ewing's sarcoma, lymphoma, and metastases), benign bone tumors (eg, osteoid osteoma, chondroblastoma, osteochondroma), and nonneoplastic conditions, such as osteomyelitis, eosinophilic granuloma, and aneurysmal bone cysts. (See "Langerhans cell histiocytosis (Eosinophilic granuloma) of bone" and see "Overview of osteomyelitis in adults" and see "Approach to imaging modalities in the setting of suspected osteomyelitis").
Occasionally, no abnormalities will be evident on plain radiographs. In such cases, magnetic resonance imaging (MRI) should be obtained if clinical suspicion for a bone tumor is high. Even for patients with characteristic plain radiographic findings, MRI is indicated for surgical planning (see "Staging system" below).
Staging work-up ? Patients with overt metastatic disease at presentation have a significantly worse outcome than those with localized disease. Because a significant proportion of patients with metastases (including up to one-half of those with limited pulmonary involvement) may be amenable to cure, a thorough staging workup is imperative to facilitate surgical planning.
Imaging studies ? The staging work-up should include the following: MRI of the entire length of the involved long bone. MRI is superior to computed tomography (CT) for defining soft tissue extension, particularly to the neurovascular bundle, joint and marrow involvement, and the presence of skip lesions (ie, medullary disease within the same bone, but not in direct contiguity with the primary lesion) [53] . CT scans are best suited to evaluate the thorax for metastatic disease, which is essential because approximately 80 percent of osteosarcoma metastases involve the lungs [49,54] . Because of the possibility of false-positive results, histologic confirmation is indicated for suspected sites of metastatic disease, particularly if a given lesion was not detected on plain films.
CT may also underestimate the extent of pulmonary involvement by metastatic tumor [55,56] . In one study, metastases would have been missed in more than one-third of cases by any tactic other than manual palpation of the lung during open thoracotomy [55] . These data raise doubt as to the advisability of minimal access procedures (eg, thoracoscopic metastasectomy) when the goal is resection of all pulmonary metastases [57-59] .
The role of PET and integrated PET/CT imaging in patients with osteosarcoma is incompletely characterized [60,61] . Radionuclide bone scanning with technetium is the preferred method for evaluating the entire skeleton for the presence of multiple lesions. Although a positron emission tomography (PET) scan may have greater utility for assessing the response to preoperative chemotherapy, at least one study suggests it is inferior to radionuclide bone scanning for the detection of osseous metastases from osteosarcoma [62] and to spiral CT for detecting pulmonary metastases [60] .
Biopsy ? Once the diagnosis of a primary bone tumor is suspected, referral should be made to a facility with expertise in pediatric oncology for further management, including a diagnostic biopsy. The biopsy should be carried out by an orthopedic surgeon who is experienced in the management of osteosarcoma and ideally by the same surgeon who will perform the definitive surgery. Proper planning of the biopsy with careful consideration of the future definitive surgery is important so as not to jeopardize the subsequent treatment, particularly a limb salvage procedure [63] . This topic is discussed in detail elsewhere.