Horizontal fissure

Dr Jeremy Jones et al.

The horizontal fissure (also called the minor fissure) is a unilateral structure in the right lung that separates the right middle lobe from the right upper lobe.

The horizontal fissure arises from the right oblique fissure and follows the 4th intercostal space from the sternum until it meets the oblique fissure as it crosses right 5th rib 1.

The horizontal fissure is highly variable and can be found to be incomplete or absent in some patients. According to different postmortem dissection studies, the prevalence of incomplete horizontal fissures can vary between 8-35% and may be absent in 3-50% of the patients' right-sided lungs 2,3,4.

A minority of individuals have a horizontal fissure in the left lung, independently of the right horizontal fissure.

The horizontal fissure can be visualised on both conventional radiography and computed tomography (CT) scans.

Plain radiograph
  • seen on ~65% (range 5-80%) of normal frontal chest radiographs as a thin line running horizontally from the edge of right lung towards the right hilum, at approximately the level of the anterior 4th rib 5
Chest x-ray
Thoracic anatomy
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Article Information

rID: 13561
System: Chest
Section: Anatomy
Synonyms or Alternate Spellings:
  • Minor fissure

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Cases and Figures

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    Figure 1
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    RUL consolidation
    Case 1: Right upper lobe consolidation
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    Case 2: Right upper lobe pneumonia
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