The pathways of tumor spread through the lung are described and their significance for radiographic interpretation is illustrated. A key to understanding the spread of bronchogenic carcinoma is the realization that although the normal flow of lymph in the pulmonary lymphatics is centripetal, lymphatic obstruction can cause reversal of flow. As a result, tumor cells are commonly carried centrifugally to the periphery in lymphatics or the connective tissue around them, and remote pleural involvement, secondary parenchymal masses, or satellite nodules may develop. Failure to appreciate peripheral spread of tumor has negative consequences for tumor staging, surgery, and radiotherapy. In the absence of hilar node involvement causing obstruction, long line shadows more than 0.5 inch (1.25 cm) in length proximal to a peripheral mass very infrequently represent tumor.

Calcification was demonstrated radiographically within newly diagnosed lymphoma of the mediastinum in two patients. These patients and those in other isolated reports show that radiographic examinations may, rarely, reveal calcification in lymphomatous tissue prior to treatment.

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The epicardial fat pad sign (EFPS) has been useful in the diagnosis of pericardial effusion on plain frontal and lateral chest radiographs. In this series of 100 cases, including patients with small pericardial effusions, it was positive in 52% of cases, being seen on the lateral view in 41%, on the frontal view in 23%, and on both views in 12%. The authors consider this sign to be the most reliable plain-radiograph finding in the diagnosis of pericardial effusion.

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