CHAPTER 2 Localizing lesions
2.1 The lungs
As well as knowing what a lesion is it is often important to know its position within the lung. To accurately localize a lesion on a chest X-ray you need to look at both the PA and lateral films. First look at the PA film:
1. The position of the lesion can be described in terms of zones. The upper zone lies above the right anterior border of the 2nd rib, the middle zone between the right anterior borders of the 2nd and 4th ribs, and the lower zone between the right anterior border of the 4th rib and the diaphragm. Although this is useful descriptively it does not give any information about the lobes of the lung.
2. Look at the borders of the lesion. If the lesion is next to a dense (white) structure then the border between the lesion and that structure will be lost – this is called the silhouette sign. Therefore if the lesion is in the right lung and obscures part of the heart border it must be in the right middle lobe. If it obscures the border of the diaphragm it is in the right lower lobe.
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