What do you mean by zones of the lungs?

What do you mean by zones of the lungs? Can’t we describe lung pathologies according to the lobes of lungs?

The zones of the lungs are described based on looking at the lower margins of the anterior ribs, and classified as follows:

  • From the apex of lung to a horizontal line drawn through lower border of 2nd anterior rib- Upper zone. 
  • From the lower border of the 2nd anterior rib to a horizontal line drawn through lower border of 4th anterior rib- Middle zone.
  • From the lower border of the 4th anterior rib to a horizontal line drawn through lower border of 6th anterior rib- Lower zone.

Note the lungs divided into 3 zones from the descriptions mentioned above. Also, note the ribs counting.

On the right side of the X-ray, the ribs are counted according to the anterior part of the ribs, also called the ‘anterior ribs’ in short.

On the left side of the X-ray, the ribs are counted according to the posterior part of the ribs, also called the ‘ posterior ribs’ in short.

Always, you should know that the zones are named according to the anterior ribs and not the posterior ribs.

Lung pathologies should always be described based on the zones. This is because the lobes of lung overlap with each other.

Look at this image.

Image courtesy of - https://www.researchgate.net/figure/Chest-X-ray-shows-an-836-cm-mass-lesion-on-right-middle-and-lower-zone_fig1_274660499

This mass lies predominantly in the right middle zone. In normal anatomy this mass may lie in the upper lobe, middle lobe, or lower lobe, we can’t say. This is because of the anatomy of the lung, which we can appreciate down.

The first diagram shows the PA view of the lungs, and also contains a mass, as in the Chest Xray. The rest of the three images are of the lateral view. Since parts of the upper, middle and lower lobes overlap in different areas, the mass can’t be said to lie in a certain lobe, just on the basis of a single PA or AP view.

From the diagram given above, note how the mass in the mid-zone can fall into either the upper, middle or lower lobe on the lateral view.

To better localize a mass lesion to a particular lobe, we should perform a ‘ Lateral view’ Xray.

Nowadays, whenever a mass is seen in a PA view, clinicians recommend a CT scan. CT scan can not only confirm the location of the mass but can also characterize the mass and come to a provisional diagnosis of the case.

 

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