Anterior junction line

Last revised by Dr Henry Knipe on 31 Mar 2022

The anterior junction (or junctional) line is a feature of frontal chest radiographs and chest CTs. It is a result of the parietal and visceral pleura meeting anteromedially. It normally contains a small amount of fat in between but can form a stripe of variable thickness if there is a lot of fat present or by the presence of the thymus in young patients 1.

Anterior mediastinal masses can cause obliteration of the anterior junction line 3

Occasionally the anterior junction line may mimic pneumomediastinum, so-called pseudopneumomediastinum 4.

Radiological appearance

Plain radiograph
  • seen on ~40% (range 25-57%) of frontal chest x-rays 1
  • oblique course crossing the upper two-thirds of the sternum from the upper right to lower left 1,2 and does not extend above the manubriosternal joint 3
CT
  • seen as a thin, dense line separating the two lungs in the anterosuperior portion of the chest 2

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Cases and figures

  • Case 1: anterior and posterior junctional lines
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  • Case 1: blue line represents anterior junctional line
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  • Case 2: visible anterior to heart
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