Localizing lesions

Published on 23/05/2015 by admin

Filed under Internal Medicine

Last modified 22/04/2025

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CHAPTER 2 Localizing lesions

2.1 The lungs 18
2.2 The heart 21

2.1 The lungs

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This pair of films shows a right upper zone mass lesion. The PA film shows that it lies above the horizontal fissure (1) and the lateral film that it lies in front of the oblique fissure, as well as above the horizontal fissure (2), so the mass lies in the right upper lobe.

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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.

If the lesion is not going to be localized by CT, then a lateral film will be needed.

Using the lateral, if the lesion is in the right lung:

1. Identify the oblique fissure (see p. 14). If the lesion lies posterior to the oblique fissure it must lie within the lower lobe no matter how high it appears on the PA film.
2. If the lesion lies anterior to the oblique fissure it may be in the upper or middle lobe. Identify the horizontal fissure (see p. 14). If the lesion is below the horizontal fissure it is in the middle lobe. If it is above it is in the upper lobe.

If the lesion is in the left lung:

1. Identify the oblique fissure. If it is behind the oblique fissure it must be in the lower lobe. If it is anterior to the oblique fissure it is within the upper lobe – there is no middle lobe on the left!

See Chapter 3, which describes localizing using CT scanning.

2.2 The heart

In order to fully assess any abnormalities of the shape of the heart it is important to understand the composition of the heart shadow. Look at the following four films on pages 22–25.

1. Look at the right heart border and follow it up from the diaphragm. From the diaphragm to the hilum the heart border is formed by the edge of the right atrium (1). From the hilum upwards it is formed by the superior vena cava (2).
2. Follow the left heart border up from the diaphragm. From the diaphragm up to the left hilum it consists of the left ventricle (3). The left border is then concave at the lower level of the left hilum and here it is made up of the left atrial appendage (4). This concavity is lost when the left atrium is enlarged leading to a straightening of the left heart border and sometimes the development of a convexity at this point. At the level of the hilum the border is made up of the pulmonary artery (5) and above this the aortic knuckle (6).

The lateral film is useful. The posterior border of the heart shadow is made up of the left ventricle (7) and the anterior border the right ventricle (8). For example, to identify whether a valve replacement is mitral or aortic, draw an imaginary line from the apex of the heart to the hilum. If the replacement valve lies above this line it is aortic and if it lies below or on, it is mitral.

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This film is of a patient with an atrial (A) and ventricular (V) pacing wire, with the pacemaker box over the left anterior chest. The atrial wire attaches in the right atrial appendage, and the ventricular wire lies across the tricuspid valve and attaches to the wall of the right ventricle. The numbers are explained in the text on page 21.

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This film is of a patient with prosthetic aortic (A) and mitral (M) valves showing their position in the AP and lateral films.

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Abnormal ribs The abnormal hilum The hidden abnormality The abnormal heart shadow The black lung field The white lung field