Left horizontal fissure

The left horizontal (or minor) fissure is an accessory fissure. In a prospective study of 2,000 consecutive normal chest X-rays (AP and lateral), a definite left horizontal fissure was identified in 1.6% of the subjects 1.

The left horizontal fissure separates the lingula from the rest of the left upper lobe (anterior-apicoposterior segments). The segmental anatomy of the left lung is preserved, despite the accessory fissure, with the lingula retaining its superior and inferior segments rather than assuming the lateral and medial arrangement of the right middle lobe segments 2.

Plain film

On frontal radiographs, the fissure resembles the right horizontal fissure, except that it may be higher (more common) or lower. The fissure usually slopes caudally from its medial to its lateral margin 2. It tends to be dome-shaped on at least one projection. The fissure infrequently has a horizontal course 1.

Like the right horizontal fissure, it can become conspicuous on plain film by air space opacification on either side or pleural effusion involving it.


  • pleural-parenchymal scarring
Thoracic anatomy
Chest x-ray
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Article Information

rID: 28138
System: Chest
Section: Anatomy
Synonyms or Alternate Spellings:
  • Left minor fissure
  • Left minor accessory lung fissure

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