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 may be seen on a normal lateral view

The visceral pleura covers the lung surfaces and is continuous with the visceral pleura that covers the fissures.

The left lung is divided into two lobes, upper and lower, by the oblique (major) fissure.

The right lung has two fissures, oblique fissure and horizontal fissure, which separate the lung into three lobes - upper, middle, and lower. Each lobe has its own visceral pleural covering.

Only the horizontal fissure is commonly seen on a frontal chest X-ray. The oblique fissures (also known as the major fissures) may be visible on lateral images.

Lobes and fissures (right lung)

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Lobes and fissures (right lung)

  • This cut-out of a lateral chest X-ray shows the positions of the three lobes of the right lung (roll over image) separated by the horizontal and oblique (or major) fissures

Lobes and fissures (left lung)

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Lobes and fissures (left lung)

  • There are two lobes on the left
  • There is usually no horizontal fissure on the left

Horizontal fissure

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Horizontal fissure

  • The horizontal fissure separates the right upper lobe from the right middle lobe
  • It may be seen on a normal chest X-ray as a thin line running roughly horizontally from the edge of the lung towards the right hilum

Oblique fissures

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Oblique fissures

  • The oblique (major) 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 (dotted lines = predicted positions)
  • The horizontal fissure is not seen at all on this lateral image (white dotted line = predicted position)

Accessory fissures

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Accessory fissures

  • The azygos fissure is the most common accessory fissure visible on a chest X-ray (1-2% of individuals)
  • In most people the azygos vein passes horizontally along the right side of the mediastinum
  • In those with an azygos fissure a small section of the right upper lobe (an azygos lobe) develops medial to the vein which is pushed away from the mediastinum
  • The azygos vein appears to pass through the lung and is surrounded by both parietal and visceral pleura
  • The azygos fissure therefore consists of four layers of pleura, two parietal layers and two visceral layers
  • The appearance resembles a tadpole - the head is the azygos vein and the tail the azygos fissure
  • Note that the azygos lobe is not a separate lobe - it is part of the right upper lobe

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.

Page author: Salisbury NHS Foundation Trust UK (Read bio)

Last reviewed: February 2020