Relaxation or passive collapse – lung tends to
retract towards its hilum when air or increased
fluid collects in the pleural space
Cicatrisation collapse – pulmonary fibrosis
Adhesive collapse - The surface tension of the
alveoli is decreased by surfactant. If this
mechanism is disturbed, as in the respiratory
distress syndrome, collapse of alveoli occurs,
although the central airways remain patent.
Resorption collapse – CA bronchus
Displacement of interlobar fissures
Loss of aeration – if the collapsed lung is adjacent
to mediastinum or diaphragm, obscuration of
adjacent strucutres.Increased density of a
collapsed area of lung
Vascular & bronchial signs – the pulmonary
vessels & bronchi become crowded together in the
affected lobe and their orientation changes.
Compensatory hyperinflation - vessels more
Hilar displacement- The hilum may be elevated in
upper lobe collapse, and appears small in lower
Elevation of the hemidiaphragm – may be seen in
lower lobe collapse.
Mediastinal displacement – in upper lobe collapse the
trachea is often displaced toward the affected side, and in
lower lobe collapse the heart may be displaced.
Displacement of the anterior and posterior junctional line,
Opacity at apex of hemithorax.
Elevated horizontal fissure resulting in concave inferior
On lateral view, the horizontal and oblique fissure are
displaced superiorly and medially.
In severe collapse the horizontal fissure parallels the
mediastinum and appear as apical cap.
Overinflation of middle and lower lobe resulting horizontal
course of right bronchus and pul. Artery.
The hilum is elevated.
Right upper lobe collapse. (A) PA projection. Note how lesser
fissure is drawn upward, and often curved, toward the apex and
(B) Right lateral view. Lesser fissure also displaced upward. Note
some forward displacement of greater fissure above the hilum.
Right upper lobe collapse. Typical example of a collapsed right upper lobe demonstrating the
slightly concave inferior border of the opacified lung due to the horizontal fissure
An example of
right upper lobe
apical cap of
Tight right upper lobe collapse. Note how the collapsed lobe (due to a central
bronchogenic carcinoma) results in increased right paramediastinal density.
CT of right upper lobe collapse. The collapsed
lobe forms a triangular wedge of soft tissue
anteriorly in the right hemithorax.
Direction of volume lobe is anterior and medial.
Veil- like opacity in affected hemithorax, greatest at hium
and gradually fades away.
Loss of normal silhouette of structures adjacent to collapse
as the area is no longer aerated.
On lateral view the anterior outline of ascending aorta is
seen with unusual clarity due to compensatory
hyperinflation of right upper lobe.
Left main bronchus has more horizontal course.
Rarely left upper lobe collapse mimics right upper lobe
collapse when apicoposterior segment is mainly involved.
PA film shows
through which is
seen the elevated
and enlarged left
hilum, and vessels
The contour of the
aortic knuckle is
Lateral film shows the collapsed
left upper lobe between the
anteriorly displaced oblique
fissure (arrow heads) and part of
the hyperinflated lower lobe. (C)
CT demonstration of left upper
lobe collapse. Calcified lymph
nodes due to previous
tuberculosis are visible.
due to the overinflated superior segment of the ipsilateral lower lobe
occupying the space between the mediastinum and the medial aspect of
the collapsed upper lobe, resulting in a paramediastinal translucency
An useful ancillary sign of
upper lobe collapse (or a
combination of right upper and
middle lobe collapse) is a
juxtaphrenic peak of the
The sign refers to a small
triangular density at the highest
point of the dome of the
hemidiaphragm, due to the
anterior volume loss of the
affected upper lobe resulting in
traction and reorientation of an
inferior accessory fissure
The sign refers to the S shape (or more accurately, reverse S on the
right) of the fissure due to the combination of collapse and mass
centrally resulting in a focal convexity with a concave outline
A right upper lobe collapse
concavity and central convexity
(arrows) due to an underlying
resulting in a reverse S shape.
Horizontal fissure and lower half of the oblique fissure move
toward one another
Best seen in lateral projection
Loss of the silhouette with right heart border.
The lordotic projection brings the displaced fissure into the line of
the Xray beam, and may elegantly demonstrate right middle
Right middle lobe collapse. In both projections the
lesser fissure fissure is drawn downward. In the PA
view (A) the fissure finally merges with the
mediastinum and disappears. Note in the lateral view
(B) that the lower part of the greater fissure may be
Right middle lobe collapse. (A) PA film shows loss of definition of the right
heart border indicating loss of aeration of the middle lobe.
(B) A lateral film shows partial collapse of the middle lobe evident as a wedge-
shaped opacity (arrows).
The oblique fissure is displaced posteriorly and medially,
and the collapsed lobe lies in the posteromedial portion of
On the frontal radiograph, the collapsed lower lobes
usually form a triangular density behind the heart
The medial portion of the hemidiaphragm may be
obscured as it is no longer outlined by aerated lung
On the lateral radiograph, a posterior portion of the
hemidiaphragm may not be seen
The vertebral column appears progressively denser
inferiorly in lower lobe collapse
Right lower lobe collapse.
(A) Frontal view of an
example of right lower lobe
collapse demonstrating a
triangular density which does
not obscure the right
(B) The lateral radiograph
shows the typical features of
increased density of the
posterior costophrenic angle
and loss of the silhouette of
the right diaphragm
Left lower lobe collapse. A typical appearance of left lower
lobe collapse resulting in a triangular density behind the
heart (arrowheads). The contour of the medial left
hemidiaphragm is lost.
On the frontal radiograph the lower lobe pulmonary
artery is usually not seen in lower lobe collapse as it is no
longer outlined by aerated lung
There are several features involving the upper
mediastinum which are sometimes helpful in diagnosing
lower lobe collapse
Superior triangle sign - triangular density to the
right of the mediastinum seen in right lower lobe collapse
due to displacement of anterior junctional structures
Superior triangle sign. (A) An
initial image shows the normal
appearances (note the lower lobe
artery is clearly visible). (B) The
subsequent image shows a right
lower lobe collapse
demonstrating the superior
triangle sign (arrow) (which
should not be confused with a
right upper lobe collapse). The
lower lobe artery can no longer
‘flat waist sign’ is seen in extensive collapse of the
left lower lobe and describes flattening of the
contours of the aortic knuckle and main
pulmonary artery due to cardiac rotation and
displacement to the left
Third, the outline of the superior aortic knuckle
may be lost in severe left lower lobe collapse
Complete opacification or ‘white-out’ of the affected
In adults, the cause is often an obstructing neoplasm
in the right or left main bronchi
There is marked volume loss with compensatory
hyperinflation of the contralateral lung across the
The cardinal feature of volume loss can help
discriminate between collapsed lung and a large
By comparison, the opacity of the hemithorax is
more uniform on the lateral view in large pleural
effusion and may be a useful discriminating feature
in equivocal cases.
Collapse of the right middle and right lower lobes is often
due to an obstructing lesion in the bronchus intermedius
The features are similar to right lower lobe collapse with
the exception that the opacity extends laterally to the
costophrenic angle on the frontal view and from the front to
the back of the hemithorax on the lateral view
Collapse of the right upper and right middle lobes is more
unusual as these lobes do not have a common bronchial
origin which spares the lower lobe
Both bilateral lower lobe and upper lobe collapse are
exceedingly rare and may occur as a result of metachronous
bronchial neoplasms or mucous plugging
This is an unusual form of pulmonary collapse which may
be misdiagnosed as a pulmonary mass.
Appears on plain film as a homogeneous mass, upto 5 cm in
diameter, with ill-defined edges
Always pleural based & associated with pleural thickening
Vascular shadows may be seen to radiate from part of the
opacity, resembling a comet's tail.
The appearance is caused by peripheral lung tissue folding
in on itself
Often related to asbestos exposure, but may occur secondary
to any exudative pleural effusion
It is not of any pathological significance.
CT appearance is usually diagnostic, & enables
differentiation from other pulmonary masses
Rounded atelectasis in a patient with a history of asbestos exposure. (A) Chest
radiograph shows en face pleural plaque on the right with calcified pleural plaques
over the dome of the right diaphragm (arrowheads). There is the suggestion of a right
infrahilar mass. (B) Highresolution CT demonstrates indrawing of the
bronchovascular structures into a pleurally based mass. The appearances are typical
of rounded atelectasis.there is widespread calcified pleural plaques