Which statement about dullness to percussion indicates pleural effusion?

• A. No abnormal findings
• B. Areas of hyperresonance due to air trapping
• C. Areas of fluid in the lung, such as in pleural effusion
• D. Increased fremitus

Answer: (C)

Dullness to percussion signals that the area underneath is denser than normal air-filled lung, which most often means there is fluid in the pleural space. In pleural effusion, fluid accumulates between the pleura and dampens sound transmission, so percussion over the affected zone sounds dull rather than resonant. This contrasts with normal lungs, which are relatively resonant; hyperresonance would suggest too much air, as in pneumothorax or certain emphysematous changes; and tactile fremitus tends to be reduced with effusion because the fluid layer dampens vibrations, whereas it can be increased with solid or consolidated tissue like pneumonia. So the dull percussion note best indicates pleural effusion.