This document discusses atelectasis, which is the loss of air in the alveoli. There are several types of atelectasis described, including absorption, relaxation, compression, adhesive, cicatricial, and round atelectasis. Signs of atelectasis on imaging include shifts of mediastinal structures, changes in fissure positions, loss of lung volumes, and compensatory hyperinflation of the remaining lung. Specific radiographic findings are outlined for different types of lobar and segmental atelectasis. CT further aids in characterization of atelectatic regions and any associated abnormalities.

2. Atelectasis
Gamal Rabie Agmy ,MD ,FCCP
Professor of Chest Diseases, Assiut University

3. Atelectasis
The definition of atelectasis is loss of air in the alveoli;
alveoli devoid of air (not replaced).
A diagnosis of atelectasis requires the following:
1-A density, representing lung devoid of air
2-Signs indicating loss of lung volume

4. Types of Atelectasis:
1-Absorption Atelectasis
When airways are obstructed there is no further
ventilation to the lungs and beyond. In the early
stages, blood flow continues and gradually the
oxygen and nitrogen get absorbed, resulting in
atelectasis.

5. Types of Atelectasis:
2-Relaxation Atelectasis
The lung is held close to the chest wall because of the
negative pressure in the pleural space. Once the
negative pressure is lost the lung tends to recoil due
to elastic properties and becomes atelectatic. This
occurs in patients with pneumothorax and pleural
effusion. In this instance, the loss of negative
pressure in the pleura permits the lung to relax, due
to elastic recoil. There is common misconception that
atelectasis is due to compression.

6. Types of Atelectasis:
3-Comression Atelectasis
Collapse secondary to bullae or large tumour

7. Types of Atelectasis:
4-Adhesive Atelectasis :
Surfactant reduces surface tension and keeps the
alveoli open. In conditions where there is loss of
surfactant, the alveoli collapse and become
atelectatic. In ARDS this occurs diffusely to both
lungs. In pulmonary embolism due to loss of blood
flow and lack of CO2, the integrity of surfactant
gets impaired.

8. Types of Atelectasis:
5-Cicatricial Atelectasis
– Alveoli gets trapped in scar and
becomes atelectatic in fibrotic
disorders

9. Types of Atelectasis:
.
6-Round Atelectasis
An instance where the lung gets trapped by
pleural disease and is devoid of air.
Classically encountered in asbestosis.

10. Signs of Loss of Lung Volume:
Generalized
1-Shift of mediastinum: The trachea and heart gets shifted
towards the atelectatic lung.
2-Elevation of diaphragm: The diaphragm moves up and
the normal relationship between left and right side gets
altered.
3-Drooping of shoulder.
4-Crowding of ribs: The interspace between the ribs is
narrower compared to the opposite side.

11. Signs of Loss of Lung Volume:
Movement of Fissures
You need a lateral view to appreciate the movement of
oblique fissures. Forward movement of oblique fissure in
LUL atelectasis. Backward movement in lower lobe
atelectasis.
Movement of transverse fissure can be recognized in the
PA film.

12. Signs of Loss of Lung Volume:
Movement of Hilum
The right hilum is normally slightly lower than the left.
This relationship will change with lobar atelectasis.

13. Signs of Loss of Lung Volume:
Compensatory Hyperinflation
Compensatory hyperinflation as evidenced by increased
radiolucency and splaying of vessels can be seen with the
normal lobe or opposite lung.

14. Signs of Loss of Lung Volume:
Alterations in Proportion of Left and
Right Lung
The right lung is approximately 55% and left lung 45%. In
atelectasis this apportionment will change and can be a
clue to recognition of atelectasis. .

15. Signs of Loss of Lung Volume:
Hemithorax Asymmetry
In normals, the right and left hemithorax are equal in size.
The size of the hemithorax will be asymmetrical and
smaller on the side of atelectasis

16. Signs of Loss of Lung Volume:
Generalized
Shift of mediastinum: The trachea and heart gets shifted towards the atelectatic lung.
Elevation of diaphragm: The diaphragm moves up and the normal relationship between left
and right side gets altered.
Drooping of shoulder.
Crowding of ribs: The interspace between the ribs is narrower compared to the opposite side.
Movement of Fissures
You need a lateral view to appreciate the movement of oblique fissures. Forward movement of
oblique fissure in LUL atelectasis. Backward movement in lower lobe atelectasis.
Movement of transverse fissure can be recognized in the PA film.
Movement of Hilum
The right hilum is normally slightly lower than the left. This relationship will change with lobar
atelectasis.
Compensatory Hyperinflation
Compensatory hyperinflation as evidenced by increased radiolucency and splaying of vessels
can be seen with the normal lobe or opposite lung.
Alterations in Proportion of Left and Right Lung
The right lung is approximately 55% and left lung 45%. In atelectasis this apportionment will
change and can be a clue to recognition of atelectasis.
Hemithorax Asymmetry
In normals, the right and left hemithorax are equal in size. The size of the hemithorax will be
asymmetrical and smaller on the side of atelectasis

17. Atelectasis Right Lung
Homogenous density right hemithorax
Mediastinal shift to right
Right hemithorax smaller
Right heart and diaphragmatic silhouette are not identifiable

18. Atelectasis Left Lung
Homogenous density left hemithorax
Mediastinal shift to left
Left hemithorax smaller
Diaphragm and heart silhouette are not identifiable

19. Left Lower Lobe Atelectasis
•
•
•
•
Inhomogeneous cardiac density
Left hilum pulled down
Non-visualization of left diaphragm
Triangular retrocardiac atelectatic LLL

20. Atelectasis Left Lower Lobe
Double density over heart
Inhomogenous cardiac density
 Triangular retrocardiac density
Left hilum pulled down
Other findings include:
Pneumomediastinum

21. Atelectasis Left
Upper Lobe
Mediastinal shift to left
Density left upper lung field
Loss of aortic knob and left hilar
silhouettes
Herniation of right lung
Atelectatic left upper lobe
Forward movement of left
oblique fissure "Bowing sign"

22. Atelectasis Left Upper
Lobe
Hazy density over left
upper lung field
Loss of left heart
silhouette
Tracheal shift to left
Lateral
A: Forward movement of
oblique fissure
B: Herniated right lung
C: Atelectatic LUL

23. Atelectasis Right Upper Lobe
Homogenous density right upper lung
field
Mediastinal shift to right
Loss of silhouette of ascending aorta
Lateral
Movement of oblique and transverse
fissures

24. Atelectasis Right Upper Lobe
Homogenous density right upper lung field
Mediastinal shift to right
Loss of silhouette of ascending aorta
Lateral
Movement of oblique and transverse
fissures

25. RML Atelectasis
Vague density in right lower lung field, almost normal
RML atelectasis in lateral view, not evident in PA view

26. Vague density in right lower lung field (almost a normal film).
Dramatic RML atelectasis in lateral view, not evident in PA view. Movement of
transverse fissure.
Other findings include: Azygous lobe

27. Atelectasis Right Lower Lobe
Density in right lower lung field
Indistinct right diaphragm
Right heart silhouette retained
Transverse fissure moved down
Right hilum moved down

28. Adhesive Atelectasis
Alveoli are kept open by the integrity of surfactant. When there is loss
of surfactant, alveoli collapse. ARDS is an example of diffuse alveolar
atelectasis.
Plate-like atelectasis is an example of focal loss of surfactant.

29. Relaxation Atelectasis
The lung is held in apposition to the chest wall because of negative pressure
in the pleura. When the negative pressure is lost, as in pneumothorax or
pleural effusion, the lung relaxes to its atelectatic position. The atelectasis is
a secondary event. The pleural problem is primary and dictates other
radiological findings.

30. Round Atelectasis
Mass like density
Pleural based
Base of lungs
Blunting of costophrenic angle
Pleural thickening
Pulmonary vasculature curving
into the density
Esophageal surgical clips

31. Round Atelectasis
Mass like density
Pleural based
Base of lungs
Blunting of costophrenic angle, pleural thickening
Pulmonary vasculature curving into the density

32. RML Lateral Segment Atelectasis

33. Sub-segmental Atelectasis

34. Atelectasis
Segmental
Anterior sub-segment of RUL
"Bronchial wedge"

35. CT image near the hilum. The convex lateral
margin of the collapsed lobe is due to a
central mass lesion.
CT image through the lower portion of the
collapsed lobe The contour of the major fissure is
slightly convex; this is normal in the lower portion
of the lobe.
CT image through the lower portion of collapsed
lobe.The contour of the major fissure is concave.

36. CT image through the upper portion of the
left lower lobe. The superior segmental
bronchus is patent (arrow) and leads to
aerated lung.
CT image through the mid portion of the left lower
lobe. The hyperinflated superior segment is present
posterior to the collapsed basal segments .
CT image through the lower portion of the left lower
lobe. There is collapse of the basal segments .

37. CT image. The collapsed superior segment has
a typical wedge-shaped configuration with the
apex directed laterally. The superior segmental
bronchus (arrow) is seen entering the collapse
The collapsed lower lobe is surrounded by pleural
fluid. The fluid anterior to the collapsed lobe is located
within the major fissure. There is also a loculated
collection of fluid
CT image through the upper portion of the
collapsed left lower lobe. The collapsed lobe is
surrounded by pleural fluid. As a result of the
supine position of the patient, most of the fluid
collects posteriorly. The fluid located anteriorly
lies within the major fissure .

38. CT image through the base of the collapsed lower
lobe. The central lucency (arrows) is produced by
pleural fluid below the collapsed lobe rather than by
necrosis within the lobe.
CT image at the hilar level. The collapsed middle lobe has a
triangular configuration with the apex directed laterally; the
triangle is relatively small at this level. The lateral margin of
the collapsed lobe has retracted medially from the chest
wall. The hyperinflated right upper and lower lobes occupy
the area lateral to the collapsed middle lobe.
CT image 1 cm below , The triangle is larger at
this level

39. CT image near the level of the hilum. The collapsed
upper lobe lies medially against the mediastinum.
The major fissure (arrow) separates the
hyperexpanded middle and lower lobes. The middle
lobe is located lateral to the collapsed lobe; the
superior segment of the lower lobe is located
posteriorly. There is narrowing and anterior
displacement of the right main bronchus .
CT scan at the level of the aortic arch. The
collapsed right upper lobe lies adjacent to the
superior mediastinum. A large mass lesion is
visible as an area of relative lucency (arrows) within
the collapsed lobe. The mass produces a prominent
convex bulge in the contour of the major fissure.