Chest x-ray anatomy
Lung lobes and fissures
The surface of the visceral pleura that covers the lung, is continuous with the visceral pleura that covers the fissures.
The left lung is divided into two lobes, upper and lower. These lobes have their own pleural covering and these lie together to form the oblique (major) fissure.
In the right lung there is an oblique fissure and a horizontal fissure, separating the lung into three lobes - upper, middle, and lower. Each lobe again has its own visceral pleural covering.
Lateral chest x-rays are helpful in demonstrating the oblique fissures (also known as the major fissures).
Key points
- The left lung has two lobes and the right has three
- Each lobe has its own pleural covering
- The horizontal fissure (right) is often seen on a normal frontal view
- The oblique fissures are often seen on a normal lateral view
Hover over image to show findings
Lobes and fissures
This cut-out of a lateral chest x-ray shows the positions of the lobes of the right lung (roll over the image).
On the left the oblique fissure is in a similar position but there is usually no horizontal fissure, and so there are only two lobes on the left.
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Hover over image to show findings
Horizontal fissure
The horizontal fissure separates the right upper lobe from the right middle lobe. It can be seen on normal chest x-rays as a thin line running roughly horizontally from the edge of the lung towards the right hilum.
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Hover over image to show findings
Oblique fissures
The oblique fissures overlie each other on a lateral view and are not always seen in entirety. If seen at all, the lower end is usually seen most clearly, as on this x-ray.
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Hover over image to show findings
Azygous fissure
The most common accessory fissure you will see on a chest x-ray is an azygous fissure. This occurs in approximately 1-2% of individuals.
The azygous vein usually runs horizontally along the right side of the mediastinum. It hooks forwards over the right main bronchus, draining the azygous system into the superior vena cava.
If there is an azygous fissure, the vein appears to run within the lung, but is actually surrounded by both parietal and visceral pleura. The azygous fissure therefore consists of four layers of pleura, two parietal layers and two visceral layers, which wrap around the vein giving the appearance of a tadpole.
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Assessing the fissures
Occasionally diseases in the lung are limited in extent by a fissure. This can help locate a disease process more specifically to a lobe. For most cases this degree of accuracy is not clinically important - unless further action such as biopsy or surgery is required, in which case other imaging such as CT would probably be performed. In most cases it is still best to refer to the location of abnormalities in terms of lung zones.