Lung fissures

Last revised by Ciléin Kearns on 10 Oct 2023

Lung fissures are double-folds of visceral pleura that either completely or incompletely invaginate lung parenchyma to form the lung lobes. 

Each lung has an oblique fissure separating the upper lobes from the lower lobes and the right lung has a horizontal fissure that separates the right upper lobe from the middle lobe

There are numerous accessory fissures that are common anatomical variants


The oblique fissure (also known as the major fissure) is similar for both lungs. It extends from the level of the T4/T5 vertebrae posterosuperiorly to the hemidiaphragms anteroinferiorly and is gently undulating in nature. The left oblique fissure has a more vertical course compared to the right oblique fissure 2.

The horizontal fissure (also known as the minor fissure or transverse fissure) is found in the right lung where it separates the upper and middle lobes. It runs horizontally at the level of the right 4th costal cartilage from the hilum to the anterior and lateral surfaces of the right lung. The horizontal fissure is complete in only one-third of people and is absent in 10% of people 2. A less common normal variant of the left upper lobe is a left horizontal fissure.

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