Atelectasis , Lung Collapse

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
Right upper lobe Lung collapse

The ‘Golden S sign’ – collapse of the right upper lobe with a well demarcated lateral border formed by the elevated horizontal fissure (arrows), and a focal convex bulge at the apex due to the centrally located bronchogenic carcinoma (arrowheads).
The abnormalities that can you see on this CXR : - Opacity with a sharp well-demarcated lateral border (arrows) in right upper zone with lack of air within the abnormality. Focal convex bulge at the apex of the abnormality.Hyperinflation of the right lower lobe.Elevated right hemidiaphragm.
radiological diagnosis: Lung collapse
- The lack of air within collapsed right upper lobe accounts for the increase in radiographic density.The well-demarcated lateral border represents the elevated horizontal fissure.
- The focal bulge at the apex of the collapsed right upper lobe corresponds to the centrally located bronchogenic carcinoma causing the lobar collapse. The combined radiologic appearance on frontal radiograph is known as ‘Golden S sign’.
- The hyperinflation and elevated right hemidiaphragm are due to volume loss.
* Other radiologic features of right upper lobe collapse not seen on this chest radiograph include:
1. Crowding of ribs in right upper chest wall – due to underlying lung volume loss
2. Tracheal deviation to the right – due to traction from the collapsed lung
* Recognition of lobar collapse is important, especially in elderly patients, as this may be the only radiologic feature of primary lung carcinoma. Further evaluation by sputum cytology, bronchoscopy or CT scan is necessary.

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
o Mediastinum
o Diaphragm
o 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:
o Plate like atelectasis
 Pulmonary embolism
 Post op hypo ventilation
• Diffuse alveolar atelectasis [ARDS]
o White out of lungs
o Small lungs
Adhesive Atelectasis / ARDS
Diffuse bilateral lung atelectasis due to ARDS. There is loss of surfactant with resultant atelectasis of alveoli.