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Notes on the X Ray appearances of Lobar Collapse


Collapse or atelectasis is a reduction in the volume of an area of lung.
The X Ray signs of lobar or segmental collapse are described under three headings.
1.  Changes in density-  (usually  a late sign)
(a) The collapsing area may appear denser due to approximation of the vessels within it.

(b) The surrounding lung may appear less dense due to compensatory emphysema (CE) usually identified by increased spaces between vessels as compared with the other side rather than an obvious increase in blackness. A comparative vessel count is often useful.
 2. Changes in position- the hilum , mediastinum and diaphragm may shift towards the site of the collapse. Fissures show characteristic movement.

3    Borders adjacent to collapsed airless lung may be lost.

The following descriptions are of isolated lobar collapse. In practice there is often some associated consolidation or pre existing  disease, particularly   fibrosis,   which  alter appearances. The appearances described below are only a guide to interpretation  in practice.

 Total collapse of a lung gives a whiteout on the affected side due to the airless lung and movement of the mediastinum and hemi- diaphragm to fill the space. Ribs on the affected side move closer. The other lung shows CE and may appear to cross the midline.

Rt. upper lobe collapse

The horizontal fissure  moves from the horizontal towards the vertical  and the upper end of the oblique fissure moves forward.


Fig 1. Fissure movement in RUL collapse

AP                              Lateral.








1.(a) RUL vessels move closer and just before total collapse a density appears alongside the superior mediastinum.

   (b) CE in the mid & lower zones
 2. The horizontal fissure pivots on the hilum. Its lateral and anterior ends moving upwards. The upper half of the oblique fissure moves anteriorly . In severe collapse the two meet up against the superior mediastinum. Trachea moves to the RT.

RT hilum  is elevated and more prominent.

Tenting may occur
 3. In severe collapse the upper mediastinal border may be lost.


Fig 2. Example of RUL collapse

(1)There is crowding of vessels in the RT. upper lobe plus some increase in density which the lateral shows to be due to associated consolidation immediately superior to the oblique fissure in the posterior segment. The anterior segment is not consolidated. The consolidation demonstrates the anterior position of the oblique fissure. The normally positioned left oblique fissure can be seen more posteriorly. (2.)
On the PA it can be seen that the hila are at the same level. Normally the Rt. hilum is  slightly below the Lft.



Tenting of the diaphragm is often a feature of upper lobe collapse or fibrosis,  particularly following TB.  If seen as a new feature it may be diagnostic of upper lobe collapse. It is due to the elevation of the hilum  pulling  on the pulmonary ligament and accessory fissures. The pulmonary ligament is a strand of fibrous tissue between the hilum  and the diaphragm.


Left Upper Lobe Collapse
Oblique fissure  moves forwards (straight  arrows) and  comes to lie  close to the anterior chest wall. In  severe collapse the anterior part of the lobe moves posteriorly  away from the anterior chest wall. The lower lobe then comes over the top of the collapsed lobe (curved arrow) and comes to lie against the anterior chest wall. On the frontal view the fissure is not seen but the collapsed lung may become evident against the upper mediastinum.


FIG 3 Fissure movement in LUL collapse

1. (a) The vessels in the LUL approximate and a density appears around the aortic knuckle (PA). The anterior part of the chest becomes increasingly denser (lat).

(b) CE in the LLL.
2. The fissure moves as shown in Fig 3. Trachea moves left. As the LLL expands the diaphragm and the L hilum may elevate, tenting may occur.
3. As the lobe collapses it rests against the aortic knuckle which lies anteriorly. As it loses air and becomes dense the aortic knuckle disappears. If the collapse advances further the knuckle may be seen again outlined against the lower lobe.



An example of advanced LUL collapse. The collapsed lobe is closing down onto the hilum, becoming denser and causing the veil -like  shadowing around the hilum. Note that there is no shift of the mediastinum, trachea, hemi diaphragm or hilum.  Nor is there any obvious compensatory emphysema. There is no pre existing lung disease and the lower lobe is sufficiently large and flexible  to fill  the available  space. It is large enough to have come round medial to and above the collapsing lobe causing the lucency around the aortic knuckle and allowing this structure to be clearly seen.

Right Middle Lobe Collapse
The horizontal fissure & lower half of the oblique fissure approximate. The horizontal fissure is the more mobile. The collapsed lobe comes to lie against the heart border.


Fig 5 fissure movement in middle lobe collapse

1 Because the lobe is small CE is rarely seen. There may be a vague density against the heart border (PA)  better seen on the Lateral as a clear wedge shaped opacity.
2 Fissure movement as described. Best seen on the lateral. On a PA film  if the horizontal fissure is not seen any other changes may not be recognised.
3 In the late stages the RT. heart border may be lost.



Fig 6 Example of middle lobe collapse




There is loss of the right heart border. The horizontal fissure cannot be seen. On the lateral the horizontal fissure and the oblique fissure have approximated to each other leaving the middle lobe as a linear density overlying the heart shadow (arrowed).




Lower Lobe Collapse
The pattern is similar on both sides. The oblique fissure moves backwards and medially. The fully collapsed lobe becomes a wedge of tissue lying up against the posterior mediastinum. The middle and upper lobes expand to fill the space lateral and anterior to the collapsing lobe.

Fig 7 fissure movement in lower lobe collapse


1.(a) As the lobe moves posteriorly  it becomes increasingly dense on the Lat. On the AP view it may be seen as a wedge shape (through the heart shadow on the left).
(b) CE in the RUL.

2. The oblique fissure moves backwards. On the Rt the horizontal fissure may move in a similar way to RML collapse but the lung underneath it becomes less rather than more dense. There is movement of the heart shadow towards the side of the collapse and the hemi-diaphragm may elevate especially if  there is pre-existing lung  disease limiting  the CE. The hilum becomes depressed.




1.There is a triangular opacity behind the heart on the left.
CE could be identified on the left by comparing the number of vessels on the two sides.
2 The heart shadow has moved slightly  to the left.
The left hilum is depressed.

On the lateral little in the way of density change can be identified.
One oblique fissure has moved backwards slightly and can be seen behind the hilum. The other can still be seen in front of the hilum (double arrow). The posterior part of the left diaphragm cannot be identified although the stomach bubble (arrow) shows you where it should be. Its anterior part can be identified in front of the little diaphragmatic "tent" near to the inferior insertion of the oblique fissure. The right hemi-diaphragm can be clearly seen. This must mean that there is a considerable increase in the density of the collapsing lung possibly with some associated consolidation.

Lingular collapse
Often involved in upper lobe collapse, but the lingula may collapse on its own. Features are identical to RML collapse except that the horizontal fissure is not there to help you. On the frontal view the only evidence may be a subtle loss of the Lft. heart border.





Plate atelectasis or linear collapse. Areas of subsegmental collapse appearing as lines of variable thickness. Often temporary and seen post operatively or may be long standing and fibrotic  when may be referred to as scarring.

Further reading

'Pulmonary  Collapse'  Seminars in Roentgenology 1980 Vol. 15

Felson 'Chest Roentgenology'   W. B. Saunders 1973