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Left lower lobe collapse

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. The shadow cast by the heart does however make it harder to see than the right lower lobe collapse.

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

Radiographic features

Chest radiograph

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

  • triangular opacity in the posteromedial aspect of the left lung
  • edge of collapsed lung may create a 'double cardiac contour'
  • left hilum with be depressed
  • loss of the normal left hemidaphgragmatic outline
  • loss of the outline of the descending aorta

Non-specific signs indicating left sided atelectasis are usually also be present including:

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

On lateral projection the left hemidiaphragmatic outline is lost posteriorly and the lower thoracic vertebrae appear denser than normal (they are usually more radiolucent than the upper vertebrae) 3.

Differential diagnosis

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

  • consolidation (of the medial basal segment of the right lower lobe)
  • a pulmonary or posterior mediastinal mass

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