Radiologic diagnosis of extrathoracic metastases to the lung.

Because many types of cancers metastasize to the lungs, early detection may affect both tumor staging and treatment planning. On the other hand, it is also important to refrain from subjecting patients to procedures that are unnecessary because of the low likelihood of positive yield. The radiologic modalities of greatest benefit in screening for pulmonary metastases are the standard chest radiograph and thoracic computed tomography (CT). Other modalities that may be of value in answering specific questions are positron emission tomography (PET) and magnetic resonance imaging (MRI). Factors that help determine which tests will be most useful in demonstrating pulmonary metastasis from extrathoracic primary tumors include the mechanisms of hematogenous tumor spread, the likelihood of distant metastasis vs spread to nearby nodal groups, and the probability of distant metastasis in the absence of local invasion.