Diagnosis of previous case

Clues - left and right hemidiaphragm

Normal lateral chest X ray

Right hemidiaphragm can be traced back to the posterior wall, but left hemidiaphragm will get silhouetted by the heart ( which lies on the left )

In the previous CXR, the right hemidiaphragm cannot be traced back to the posterior wall, suggesting silhouette sign of posterior part of right hemidiaphragm. This is a right lower lobe pneumonia. Also the lateral CXR should get more radiolucent as it approaches the inferior part, but in the previous picture, it gets more radio-opaque

Add caption

Lateral Chest X ray is always a challenge for me, but there are few simple take home points

#1 - The lateral CXR always gets more radiolucent inferiorly; if it gets more radio-opaque, suspect pneumonia in lower lobe ( left/right )

#2 - The retrosternal space is also radiolucent; if it gets radio-opaque, can be retrosternal fat pad, anterior mediastinal masses and RV enlargement

#3 - Remember RALS - right pulmonary artery anterior to right main bronchus and left pulmonary artery 

superior to left main bronchus

#4 - Below and posterior to distal trachea ( or origin of bronchus ) is always radiolucent; if it is radio-opaque, suspect pulmonary hypertension ( distension of right/left pulmonary artery ) or lymphadenopathy ( Doughnut sign of Sarcoidosis )

#5 - Right hemidiaphragm can be traced back from anterior to posterior, but left hemidiaphragm can only be traced back from posterior up to the heart; suspect pneumonia in right lower lobe if tracing of right hemidiaphragm is incomplete; suspect pneumomediastinum if the left hemidiaphragm can be traced from front to back ( continuous diaphragm sign )

Reference

Radiology Assistant

Chest X-Ray - Basic Interpretation

http://www.radiologyassistant.nl/en/p497b2a265d96d/chest-x-ray-basic-interpretation.html