Air Fluid Level
You can encounter air fluid level in an upright chest film in:
Cavities
Pleural space: Hydropneumothorax
Bowel: Hiatal hernia
Esophagus: Obstruction
Mediastinum: Abscess
Chest wall
Normal stomach
Dilated biliary tract
Sub diaphragmatic abscess
The x-ray on left is an example of lung abscess and tuberculosis.
LUL lung abscess
Fluid level
Necrotic mass along walls
RUL infiltrate: Tuberculosis
This appearance can also come from branchiogenous spread of abscess contents to the right lung. AFB was positive in this case.