Arcot J Chandrasekhar, M.D.
Objectives: You will learn
Types of atelectasis
Genesis of each type of atelectasis
Image criteria for each type of atelectasis
Appearance of atelectasis of various lobes
This type of atelectasis can be lobar, segmental or one lung left or right based on the site of endobronchial obstruction.
Resorptive Atelectasis of LUL
Relaxation Atelectasis / Pneumothorax
The CXR on the left reveals a right pneumothorax.
In this instance, the loss of negative pressure in the pleura permits the lung to relax and become atelectatic due to elastic recoil. The right lung is now devoid of air and is atelectatic. Note the atelectatic lung adjacent to the right heart silhouette.
Black arrow is pointing to deep sulcus sign. The loss of negative pressure in pleural space releases the chest wall to TLC position. Diaphragm is part of the chest wall and moves downwards creating the deep sulcus sign.
Black arrowhead is pointing to trachea.
There is a common misconception that atelectasis is due to compression. I disagree with that concept as is given in textbooks. Lung relaxes to the atelectatic position due to elastic recoil and not due to external compression.
Adhesive Atelectasis / ARDS
Diffuse bilateral lung atelectasis due to ARDS. There is loss of surfactant with resultant atelectasis of alveoli.
There is diffuse white out of lungs.
The lungs are small.
Plate like atelectasis
Plate like atelectasis (sub segmental atelectasis) is an example of focal loss of surfactant.
Note the bilateral basal plate like atelectasis.
This is an example of plate like atelectasis in a patient with pulmonary embolism.
You can also encounter plate like atelectasis whenever there is basal hypo ventilation.
This is resorptive atelectasis due to bronchial obstruction (cancer lung).
The adjacent CXR shows density in the projection of the right lower lung field. The right heart border is seen clearly while the diaphragm is indistinct, indicating that it is lower lobe disease (silhouette sign).
The shadow is triangular with narrow end near the hilum, suggesting that it is lobar density.
The right hilum and transverse fissure are pulled down (loss of lung volume). Arrows are pointing to the hila position on both sides.
In complete RLL atelectasis you will not see the right inter lobar artery because it is surrounded by airless lung (silhouette sign).
This is an example of right lower lobe resorptive atelectasis. Bronchial obstruction is due to endobronchial lung cancer.
Vague density in the right lower lung field. It can easily be missed in PA view.
Minor loss of right heart silhouette.
Triangular density in the lateral chest with narrow end towards hilum.
Loss of lung volume:
This is a case of RML resorptive atelectasis due to obstruction of the RML.
Haziness in the projection of the left upper lung field in PA view. Band of increased density in the retrosternal space in lateral chest (airless lung).
Loss of left heart silhouette indicating that the lingula is abnormal.
Loss of lung volume:
Note the compensatory hyper inflation of left lower lobe behind the oblique fissure in the lateral chest. See the lower lobe creep up all the way up to the apical region (luft sichel sign)
This is a case of resorptive atelectasis due to endobronchial obstruction of the LUL.
Atelectatic LL moves to retro cardiac location and projects as a triangular density seen through heart. Lateral decubitus film shows clearly the triangular atelectatic left lower lobe behind the heart.
Left hilum moves down (sign of loss of lung volume).
In the lateral chest (not shown), atelectatic LL projects over lower thoracic vertebra. Instead of uniform density of thoracic vertebra from top to bottom you will see lower thoracic vertebra appear denser than upper thoracic vertebra.
As with other lobar atelectasis you will not see the lower lobe vessels.
The medial portion of left diaphragm will become indistinct (silhouette sign).
Total atelectasis of Lung
The right hemi thorax is whited out (no air).
Signs of loss of lung volume include:
The silhouette of the right heart and right hemi diaphragm are lost.
Vessels in right lung not seen due to loss of air in alveoli
|When you are considering resorptive
atelectasis make the following statements to support it.
Most of the time you will not see anything obvious to account for obstruction. You have to suspect the etiology of obstruction based on the history and the clinical setting.
When you are considering relaxation atelectasis make the following
statements to support it.
When you are considering adhesive atelectasis make the following
statements to support it. This occurs when there is no surfactant.
When it is plate like atelectasis it is either due to loss of CO2 or oxygen. CO2 and oxygen maintain the integrity of surfactant.
Basal hypo ventilation can be seen in
Look at the clinical setting to determine the etiology of adhesive atelectasis.