Compare the left and right upper, middle and lower lung zones
Decide which side is abnormal
Compare an area of abnormality with the rest of the lung on the same side
The whiter side is not always the abnormal side
Remember many lung diseases are bilateral and symmetrical
Lung zones
Assess the lungs by comparing the upper, middle and lower lung zones on the left and right. Asymmetry of lung density is represented as either abnormal whiteness (increased density), or abnormal blackness (decreased density). Once you have spotted asymmetry, the next step is to decide which side is abnormal. If there is an area that is different from the surrounding ipsilateral lung, then this is likely to be the abnormal area.
Consolidation
If the alveoli and small airways fill with dense material, the lung is said to be consolidated. It is important to be aware that consolidation does not always mean there is infection, and the small airways may fill with material other than pus (as in pneumonia), such as fluid (pulmonary oedema), blood (pulmonary haemorrhage), or cells (cancer). They all look similar and clinical information will often help you decide the diagnosis.
Air bronchogram
If an area of lung is consolidated it becomes dense and white. If the larger airways are spared, they are of relatively low density (blacker). This phenomenon is known as air bronchogram and it is a characteristic sign of consolidation.
This patient had a history of intravenous drug abuse and presented with a high fever
Diagnosis
Septic embolus
Differential diagnosis of lung cavities
Lung abscess - TB, Klebsiella or Staph aureus
Lung cancer
Septic embolus - infected thrombus
Fungal infection - if immunocompromised
Granulomatosis with polyangiitis
Bilateral lung abnormalities
Comparing sides does not always give the answer. The lungs may be abnormal on both sides and so awareness of the normal appearances of lung parenchyma becomes more important.
