Chest X-ray Anatomy
Lung lobes and 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

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).

Lobes and fissures

Hover on/off image to show/hide findings

Tap on/off image to show/hide findings

Click image to align with top of page

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.

Horizontal fissure

Hover on/off image to show/hide findings

Tap on/off image to show/hide findings

Click image to align with top of page

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.

Oblique fissures

Hover on/off image to show/hide findings

Tap on/off image to show/hide findings

Click image to align with top of page

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.

Accessory fissures

Hover on/off image to show/hide findings

Tap on/off image to show/hide findings

Click image to align with top of page

Accessory fissures

  • The most common accessory fissure you will see on a chest X-ray is an azygos fissure. This occurs in approximately 1-2% of individuals.
  • The azygos vein usually runs horizontally along the right side of the mediastinum. It hooks forwards over the right main bronchus, draining the azygos system into the superior vena cava.
  • If there is an azygos fissure, the vein appears to run within the lung, but is actually surrounded by both parietal and visceral pleura. The azygos 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.

Assessing the fissures

Occasionally lung disease is 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 lung abnormalities seen on a chest X-ray in terms of lung zones rather than lobes.