The classic features of six common pulmonary developmental anomalies have been presented. In addition, several overlap cases, each demonstrating features of more than one anomaly, have been illustrated. Such cases serve to emphasize that pulmonary developmental anomalies exist as a continuum, often frustrating our attempts at discrete classification. Future advances in pulmonary embryology may further elucidate the pathogenesis of these entities.
Perception of a roentgen image is greatly influenced by the production of Mach bands by the retinal neural networks. The mechanism of their production and contributing factors such as lateral inhibition, projection, contour, film density, object density, and background are discussed. Although Mach bands often facilitate perception of roentgen density, misinterpretation of their significance may lead to errors in diagnosis.
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.
The superior intercostal veins define the pleural reflections of the caudad extent of the posterior junction line. They are paired structures which drain the first three intercostal spaces and join the azygous on the right and the accessory hemiazygous on the left. Because of their location posterior and lateral to the esophagus and trachea, their pleural reflections may be altered early in the course of a focal nodal disease of the posterior mediastinum.
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