Which lung pathology is indicated by dullness on percussion?

Dullness on percussion is typically associated with pleural effusion, which occurs when excess fluid accumulates in the pleural space surrounding the lungs. This fluid causes a change in the normal resonance of the lung when tapped or percussed, resulting in a dull sound rather than the normal resonance. The presence of fluid inhibits the ability of sound waves to travel through the area, leading to this dullness.

In contrast, conditions such as pneumothorax would produce a hyper-resonant sound due to the presence of air in the pleural space, while bronchitis and asthma are conditions affecting the airways rather than leading to changes detectable through percussion of the lung fields. Thus, dullness specifically signifies the presence of fluid in the pleural space, making pleural effusion the correct indication for dullness on percussion.