The Role of CT and MRI in Staging of the Mediastinum

¹ From the University of Colorado Health Sciences Center, Denver VA Medical Center

Lung Cancer Study Group (LCSG) Protocol 883, the comparative study of the results of magnetic resonance imaging (MRI) and computerized tomography (CT) for staging of tumor, nodal, and selected metastatic sights in patients with surgically staged lung cancer was activated in August 1988 but was not completed because of termination of LCSG funding. A literature review was therefore undertaken to determine the results of other studies that were performed to evaluate the relative efficacy of MRI and CT in the staging of patients with lung cancer. These studies determined that CT and MRI are approximately equal in the staging of N2 disease with a sensitivity of 70 to 90%, a specificity of 60 to 90%, and an accuracy of 66 to 90% depending on the criteria used for determining positive nodes and the compulsiveness of surgical staging. Magnetic resonance imaging is probably better in the assessment of superior sulcus tumors, tumors involving the aorta-pulmonary window, hilar nodes, in assessing chest wall or diaphragmatic invasion, and in evaluating patients whose CT findings are equivocal. Computed tomography and MRI reveal adrenal abnormalities in 10 to 20% of patients but only one third of these have metastases. Mediastinoscopy has a sensitivity of 85 to 90%, a specificity of 100%, and an accuracy of about 95% and is therefore the gold standard for N2 staging. If the CT examination reveals no N2 disease, one can proceed directly to thoracotomy with approximately a 15% chance of finding N2 disease. It was concluded that because CT is much cheaper, it should therefore be used for the noninvasive staging of patients with lung cancer unless the above-noted special circumstances are present that have been shown to favor MRI. Because of the limited accuracy of CT and MRI, however, positive findings must be confirmed by biopsy specimens and pathologic study.