Collapse Radiologic signs

Direct signs

1.Displacement of interlobar fissures

2.Crowding of vessels and bronchi

Indirect signs

1.local increase in opacity

2.elevation of hemidiaphragm

3.displacement of the mediastinum

4.compensatory over inflation

5. Approximation of the ribs

6.Absence of  an air bronchogram(resorption atelectasis only)

7.Absence of visibility of interlobar artery(in lower lobe atelectasis only)

Reference -Fraser volume 1 page 529