Cholecystitis v. Other 2. Right middle lobe syndrome 2. When the airway of a lobar bronchus is occluded, the air distal to the obstruction becomes slowly absorbed by the pulmonary vascular bed. This results in the loss of volume of the lobe, which is, by definition, atelectasis. This process is the phenomenon called obstructive atelectasis.
Obstructive atelectasis produces characteristic opacities in the lung.
These can be understood if you are familiar with the normal location of the interlobar fissures. The diagrams below depict the position of the lobes and interlobar fissures. Note that all three fissures are in profile on the lateral view. The two major fissures pass obliquely from superoposterior to anteroinferior and consequently are not identified as a line on the PA view. A consequence of this is that obstructive atelectasis is often more easily identified on the lateral view.