Atelectasis

What is atelectasis?

• Alveoli devoid of air with loss of lung volume.
• If alveoli are filled with material (inflammatory fluid, blood etc) displacing air, it is not considered atelectasis.

What are the types of atelectasis?

• Resorptive
  • When there is endobronchial obstruction, there is no more ventilation and air gets absorbed from alveoli. Alveoli collapse with significant loss of lung volume. Example: Lobar atelectasis from endobronchial lung cancer.
• Relaxation
  • Normally lungs are held close to chest wall by the negative pressure in pleura. In pneumothorax or pleural effusion the negative pressure in pleura is lost. Lung relaxes to its resting position.
• Adhesive
  • Surfactant is necessary for keeping the alveoli open. In ARDS and Pulmonary embolism there is loss of surfactant and alveoli collapse.

What are the radiological findings of resorptive atelectasis?

• Density corresponding to the atelectatic lung
• Signs of loss of lung volume
• Compensatory hyperinflation 

Resorptive Atelectasis / Cancer Lung LUL atelectasis due to endobronchial obstruction. Once the bronchus is obstructed, there is no ventilation and the air gets absorbed. The distal lung is now devoid of air and becomes atelectatic.

What are the signs of volume loss?

• Global shift of structures towards atelectatic lung
  • Mediastinum
  • Diaphragm
  • Crowding of ribs
• Movement of fissures
• Movement of hilum
• Compensatory hyperinflation of the rest of the lun

What are the radiological findings of relaxation atelectasis?

• The primary finding is in pleura [Pneumothorax or Pleural effusion]
• Lung relaxes to its resting position
• Mediastinum is pushed to the opposite side due to pleural disease.

Relaxation Atelectasis / Pneumothorax Right lung atelectasis due to pneumothorax. There is loss of negative pressure in the right pleural cavity and the lung relaxes to its resting position. The right lung is now devoid of air and is atelectatic.

What are the radiological findings of adhesive atelectasis?

• Focal:
  • Plate like atelectasis
    • Pulmonary embolism
    • Post op hypo ventilation
• Diffuse alveolar atelectasis [ARDS]
  • White out of lungs
  • Small lungs

Adhesive Atelectasis / ARDS Diffuse bilateral lung atelectasis due to ARDS. There is loss of surfactant with resultant atelectasis of alveoli.