Left lower lobe collapse

Last revised by Mostafa Elfeky on 3 May 2024

Left lower lobe collapse has distinctive features, and can be readily identified on frontal chest radiographs, provided attention is paid to the normal cardiomediastinal contours. However, the shadow cast by the heart does make it more difficult to see than the right lower lobe collapse.

Some of the findings of right lower lobe collapse can be grouped together as they are almost identical on both sides.

For a general discussion please refer to the article on lobar collapse.

Left lower lobe collapse is readily identified on a well-penetrated radiograph of a patient with a normal sized heart but can be challenging in the typical patient with collapse, namely unwell patients, with portable (AP) often underpenetrated films, or with concomitant cardiomegaly. Features include 1-3:

  • triangular opacity in the posteromedial aspect of the left lung (retrocardiac sail sign)
    • left lower zone opacification (usually medially) with the apex pointing towards the left hilum
  • edge of the collapsed lung may create a 'double cardiac contour'
  • inferior displacement of the left hilum
  • flat waist sign: flattening of the left heart border
  • obscuration of the left hemidiaphragm
  • obscuration of the descending aorta
  • preservation of a clear left heart border, which is contacted by the lingular segments of the left upper lobe (cf. obscuration seen left upper lobe consolidation)
  • inferior displacement of the oblique fissure
  • descending interlobar pulmonary artery is not visible

Non-specific signs found in left-sided atelectasis are usually also present including:

  • elevation of the left hemidiaphragm
  • crowding of the left ribs
  • shift of the mediastinum to the left

On the lateral projection the findings are usually obvious:

  • triangular opacification in the lower posterior chest
  • left hemidiaphragm is obscured posteriorly and the lower thoracic vertebrae appear denser than normal (they are usually more radiolucent than the upper vertebrae) 3
  • oblique fissure displaced posteroinferiorly but may be invisible with a severe collapse of the left lower lobe as it fissure rotates posteromedially becoming non-tangential to the x-ray beam 2
  • inferior displacement of the left hilum
  • triangular opacification in axial images, thinner at the hilum, against the posterior mediastinum and medial hemidiaphragm 2
  • oblique fissure rotates posteromedially or posteriorly 2
  • compensatory hyperinflation of the left upper lobe 2

The characteristic shape associated with volume loss usually does not allow for any significant differential diagnosis. As always one should consider:

ADVERTISEMENT: Supporters see fewer/no ads

Updating… Please wait.

 Unable to process the form. Check for errors and try again.

 Thank you for updating your details.