Recognizing Normal Pulmonary Anatomy

In this chapter, you’ll learn how to evaluate the normal anatomy ( Fig. 2.1 ) and the technical adequacy ( Fig. 2.2 ) of the lungs on conventional radiography as well as on computed tomography. To become more proficient interpreting images of the chest, you should first be able to recognize fundamental, normal anatomy in order to differentiate it from what is abnormal.

Case Quiz 2 Question

This is a 52-year-old male with a debilitating disease. Is this patient’s heart really on the wrong side of the body or is there another explanation for the appearance of this image? The “L” marker ( at top right ) is in the correct location. The explanation appears in this chapter and the answer box is at the end of this chapter.

The Normal Frontal Chest Radiograph

Fig. 2.1 displays some of the normal anatomic features visible on the frontal chest radiograph.
Vessels and bronchi—normal lung markings
- Virtually all of the branching white lines you see in the lungs on a chest radiograph are blood vessels. Blood vessels characteristically branch and taper gradually from the hila to the periphery of the lung. You cannot accurately differentiate between pulmonary arteries and pulmonary veins on a conventional radiograph ( Fig. 2.3 ).
- Bronchi are mostly invisible on a normal chest radiograph because they are normally very thin-walled , they contain air and are surrounded by air.

Pleura: Normal Anatomy

The pleura is composed of two layers, the outer parietal and inner visceral layer with the pleural space between them. The visceral pleura is adherent to the lung and enfolds to form the major (oblique) and minor (horizontal) fissures .
Normally there are several milliliters of fluid, but no air, in the pleural space.
Neither the parietal pleura nor the visceral pleura is routinely visible on a conventional chest radiograph, except where the two layers of visceral pleura enfold to form the fissures. Even then, they are usually no thicker than a line you could draw with the point of a sharpened pencil ( Fig. 2.4 ).

Normal Pulmonary Vasculature

Important Points

In the upright position, the blood flow to the bases is normally greater than the flow to the apices because of the effect of gravity. Therefore, the vessels at the base are normally larger in size than the vessels at the apex of the lung.

Changes in pressure or flow can alter the normal dynamics of the pulmonary vasculature, some of which are described in Chapter 11 .
Online extra: For more on recognizing normal pulmonary vasculature and an imaging approach to diagnosing heart disease in adults from the chest x-ray, see e-Appendix B. The ABCs of Heart Disease .

The Normal Lateral Chest Radiograph ( FIG. 2.5 )

As part of the standard two-view chest examination, patients usually have an upright, frontal chest radiograph and an upright, left lateral view of the chest. A left lateral chest x-ray (the patient’s left side is against the detector) is of great diagnostic value but is sometimes ignored by beginners because of their lack of familiarity with the findings visible in that projection ( Box 2.1 , Fig. 2.5 ).
BOX 2.1

Why Look at the Lateral Chest?
- It can help you define the location of disease you already identified as being present on the frontal image.
- It can confirm the presence of disease you may be unsure of on the basis of the frontal image alone, such as a mass or pneumonia.
- It can demonstrate the existence of disease not visible on the frontal image ( Fig. 2.6 ).