A physical examination of a patient on mechanical ventilation shows normal breath sounds and percussion except over the right middle lobe, where late inspiratory crackles are heard and the area is dull to percussion. A chest radiograph reveals infiltrates in the right middle lobe. Based on these findings, what is the most likely diagnosis?

• A. Left lower lobe pneumonia.
• B. Right upper lobe pneumonia.
• C. Right middle lobe pneumonia.
• D. Pleural effusion with no infiltrates.

Answer: (C)

When pneumonia is localized to a specific lung lobe, the physical exam often shows focal signs in that same region—dullness to percussion and crackles indicating consolidation. In this case, those findings are over the right middle lobe, and the chest radiograph confirms an infiltrate in the same area. Putting these together points to pneumonia localized to the right middle lobe rather than another lobe or a different process.

Left lower lobe pneumonia would produce focal findings on the left; right upper lobe pneumonia would show abnormalities higher up in the right lung; pleural effusion can cause dullness but usually presents with decreased breath sounds and a characteristic effusion on imaging rather than a lobar infiltrate.