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

4 Approximation of the ribs

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

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

Reference -Fraser volume 1 page 529