Recognizing Atelectasis

Chapter 5 Recognizing Atelectasis



What is Atelectasis?



image Common to all forms of atelectasis is a loss of volume in some or all of the lung, usually leading to increased density of the lung involved.
• The lung normally appears “black” on a chest radiograph because it contains air. When something of fluid or soft tissue density is substituted for that air or when the air in the lung is resorbed (as it can be in atelectasis), that part of the lung becomes whiter (more dense or more opaque).

image Unless mentioned otherwise, statements in this chapter that refer to “atelectasis” are referring to obstructive atelectasis. This might be a good time to review the chart from Chapter 4 (see Table 4-1) highlighting the markedly different appearances of the thorax in a large pneumothorax and atelectasis of the entire lung (see Fig. 4-2).


Signs of Atelectasis



image Displacement (shift) of the interlobar fissures (major and minor) toward the area of atelectasis.

image Increase in the density of the affected lung (Fig. 5-1).

image Displacement (shift) of the mobile structures of the thorax.
• The mobile structures are those capable of movement due to changes in lung volume.
• Trachea
• Normally midline in location and centered on the spinous processes of the vertebral bodies (also midline structures) on a nonrotated, frontal chest x-ray. A slight rightward deviation of the trachea is always present at the site of the left-sided aortic knob.

• With atelectasis, especially of the upper lobes, the trachea may shift toward the side of the volume loss (Fig. 5-2).

• Heart
• At least 1 cm of the right heart border normally projects to the right of the spine on a nonrotated, frontal radiograph.

• With atelectasis, especially of the lower lobes, the heart may shift to one side or the other.
image When the heart shifts toward the left, the right heart border will overlap the spine (Fig. 5-3).

image When the heart shifts toward the right, the left heart border will approach the midline (Fig. 5-4).

• Hemidiaphragm
image The right hemidiaphragm is almost always higher than the left by about half the interspace distance between two adjacent ribs. In about 10% of normal people, the left hemidiaphragm is higher than the right.

image In the presence of atelectasis, especially of the lower lobes, the hemidiaphragm on the affected side will usually be displaced upward (Fig. 5-5).

image Overinflation of the unaffected ipsilateral lobes or the contralateral lung.
• The greater the volume loss and the more chronic its presence, the more the lung on the side opposite the atelectasis or the unaffected lobe(s) in the ipsilateral lung will attempt to overinflate to compensate for the volume loss.

• This may be noticeable on the lateral projection by an increase in the size of the retrosternal clear space and on the frontal projection by extension of the overinflated contralateral lung across the midline (Fig. 5-6).

image The signs of atelectasis are summarized in Box 5-1.

image

Figure 5-1 Right middle lobe atelectasis.


Frontal (A) and lateral (B) views of the chest show an area of increased density (solid white arrow), which is silhouetting the normal right heart border (solid black arrow) indicating its anterior location in the right middle lobe. On the lateral view (B), the minor fissure is displaced downward (dotted white arrow) and the major fissure is displaced slightly upward (dotted black arrow). Note the anterior location of the middle lobe.


image

Figure 5-2 Right upper lobe atelectasis.


A fan-shaped area of increased density is seen on the frontal projection (A) representing the airless right upper lobe. The minor fissure is displaced upward (solid white arrow). The trachea is shifted to the right (solid black arrow). The lateral (B) demonstrates a similar wedge-shaped density near the apex of the lung. The minor fissure (solid white arrow) is pulled upward and the major fissure is pulled forward (solid black arrow). This is a child who had asthma leading to formation of a mucous plug, which obstructed the right upper lobe bronchus.


image

Figure 5-3 Atelectasis of the left lung.


There is complete opacification of the left hemithorax with shift of the trachea (solid black arrow) and the esophagus (marked here by a nasogastric tube, dotted black arrow) toward the side of the atelectasis. The right heart border, which should project about a centimeter to the right of the spine, has been pulled to the left side and is no longer visible. The patient had an obstructing bronchogenic carcinoma in the left main bronchus.


image

Figure 5-4 Atelectasis of the right lung.


There is complete opacification of the right hemithorax with shift of the trachea (solid black arrow) toward the side of the atelectasis. The left heart border is displaced far to the right and now almost overlaps the spine (solid white arrow). This patient had an endobronchial metastasis in the right main bronchus from her left-sided breast cancer. Did you notice the left breast was surgically absent?


image

Figure 5-5 Left upper lobe atelectasis.


On the frontal projection (A), there is a hazy density surrounding the left hilum (solid white arrow) and there is a soft tissue mass in the left hilum (solid black arrow). Notice how the left hemidiaphragm has been pulled up to the same level as the right. The lateral projection (B) shows a bandlike zone of increased density (solid white arrows) representing the atelectatic left upper lobe sharply demarcated by the major fissure, which has been pulled anteriorly. The patient had a squamous cell carcinoma of the left upper lobe bronchus that was producing complete obstruction of that bronchus.


image

Figure 5-6 Left-sided pneumonectomy.


Complete opacification of the left hemithorax (A) is most likely from a fibrothorax produced following complete removal of the lung. There is associated marked volume loss with shift of the trachea to the left (solid white arrow). The left 5th rib was surgically removed during the pneumonectomy (solid black arrow). The right lung has herniated across the midline in an attempt to “fill-up” the left hemithorax, which is seen by the increased lucency behind the sternum in (B) (solid white arrow). Notice that because only the right hemithorax has an aerated lung remaining, only the right hemidiaphragm is visible on the lateral projection (solid black arrow). The left hemidiaphragm has been silhouetted by the airless hemithorax above it.



Box 5-1 Signs of Atelectasis



Displacement of the major or minor fissure*

Increased density of the atelectatic portion of lung

Shift of the mobile structures in the thorax, i.e., the heart, trachea, and/or hemidiaphragms*

Compensatory overinflation of the unaffected segments, lobes, or lung


* Toward the atelectasis.



Types of Atelectasis



image Subsegmental atelectasis (also called discoid atelectasis or platelike atelectasis) (Fig. 5-7)
• Subsegmental atelectasis produces linear densities of varying thickness usually parallel to the diaphragm, most commonly at the lung bases.
• It does not produce a sufficient amount of volume loss to cause a shift of the mobile thoracic structures.

• It occurs mostly in patients who are “splinting,” i.e., not taking a deep breath, such as postoperative patients or patients with pleuritic chest pain.

• Subsegmental atelectasis is not due to bronchial obstruction

Related posts:

Recognizing Pneumonia Recognizing a Pleural Effusion Recognizing the Normal Abdomen Computed Tomography Recognizing Some Common Causes of Neck and Back Pain Ultrasonography

Stay updated, free articles. Join our Telegram channel
Tags:
Mar 2, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on Recognizing Atelectasis

Full access? Get Clinical Tree
Get Clinical Tree app for offline access