Lung atelectasis

Lung atelectasis (plural: atelectases) refers to collapse or incomplete expansion of pulmonary parenchyma. Note that the term "atelectasis" is typically used when there is partial collapse, whereas the term "collapsed lung" is typically reserved for when the entire lung is totally collapsed.


Atelectasis is a radiopathological sign which can be classified in many ways. The aim of each classification approach is to help identify possible underlying causes together with other accompanying radiological and clinical findings.

Atelectasis can be subcategorised based on underlying mechanism, as follows:

  • resorptive (obstructive) atelectasis
    • occurs as a result of complete obstruction of an airway
    • no new air can enter the portion of the lung distal to the obstruction and any air that is already there is eventually absorbed into the pulmonary capillary system, leaving a collapsed section of the affected lung
    • because the visceral and parietal pleura do not separate in resorptive atelectasis, traction is created, and if the loss of volume is considerable, mobile thoracic structures may be pulled toward the side of volume loss ("mediastinal shift")
    • potential causes of resorptive atelectasis include obstructing neoplasms, mucus plugging in asthmatics or critically ill patients and foreign body aspiration
    • resorptive atelectasis of an entire lung ("collapsed lung") can result from complete obstruction of the right or left main bronchus
  • passive (relaxation) atelectasis
    • occurs when contact between the parietal and visceral pleura is disrupted
    • the three most common specific etiologies of passive atelectasis are pleural effusionpneumothorax and diaphragmatic abnormality
  • compressive atelectasis
    • occurs as a result of any thoracic space-occupying lesion compressing the lung and forcing air out of the alveoli
  • cicatrisation atelectasis
  • adhesive atelectasis
    • occurs from surfactant deficiency 2
    • depending on etiology, this deficiency may either be diffuse throughout the lungs or localized 
  • gravity dependent atelectasis (dependent atelectasis)
    • in the most dependent portions of the lungs due to the weight of the lungs

Atelectasis can also be subcategorised by morphology as follows: 

Vary depending on the underlying mechanism and type of atelectasis

  • displacement of interlobar fissures
  • crowding together of pulmonary vessels
  • crowded air bronchograms (does not apply to all types of atelectasis; can be seen in subsegmental atelectasis due to small peripheral bronchi obstruction, usually by secretions; if the cause of the atelectasis is central bronchial obstruction, there will usually be no air bronchograms.)
  • pulmonary opacification
  • shifting granuloma (or any other previously documented lesion, used as a reference for comparison).
  • compensatory hyperexpansion of the surrounding or contralateral lung
  • displacement of the heart, mediastinum, trachea, hilum
  • elevation of the diaphragm
  • propinquity of the ribs
  • increased density (opacity) of the atelectatic portion of lung
  • displacement of the fissures toward the area of atelectasis
  • upward displacement of hemidiaphragm ipsilateral to the side of atelectasis
  • crowding of pulmonary vessels and bronchi in region of atelectasis
  • +/- compensatory overinflation of unaffected lung
  • +/- displacement of thoracic structures (if atelectasis is substantial)
  • relatively thin, linear densities in the lung bases oriented parallel to the diaphragm (known as Fleischner lines

Atelectasis comes from the greek words ateles and ektasis translating to 'incomplete stretching or expansion'.

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Article information

rID: 19437
System: Chest
Section: Gamuts
Synonyms or Alternate Spellings:
  • Pulmonary atelectases
  • Lung atelectases
  • Atelectasis
  • Pulmonary atelectasis
  • Atelectasis of lung
  • Atelectatic lung
  • Atelectatic lungs
  • Atelectasis of lungs
  • Atelectasis of the lung
  • Atelectasis of the lungs
  • Atelectatic changes
  • Atelectatic change

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Cases and figures

  • Case 1: segmental atelectasis
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  • Case 2: round atelectasis - left lower lobe
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  • Case 3: bilateral atelectasis
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  • Right middle lobe collapse
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  • Right middle lobe collapse
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  • Shifting granuloma sign
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