How can you distinguish bacterial from viral pneumonia in a child by imaging?

• A. Bacterial pneumonia often shows focal lobar consolidation; viral pneumonia typically shows diffuse interstitial or perihilar markings.
• B. Bacterial pneumonia shows diffuse interstitial markings; viral shows focal consolidation.
• C. Imaging cannot distinguish; they are identical.
• D. Bacterial pneumonia shows only pleural effusion.

Answer: (A)

In pediatric chest imaging, the pattern of lung opacities is the best clue. Bacterial pneumonia tends to produce focal lobar consolidation, often localized to a single lobe with air bronchograms, reflecting alveolar filling in a defined region. Viral pneumonia more commonly shows diffuse interstitial markings or perihilar/peribronchial thickening, and may be accompanied by hyperinflation, reflecting airway inflammation and involvement of the interstitium. While imaging cannot always definitively determine the exact cause, this pattern distinction is the most helpful radiographic guide. Be aware that overlaps occur—some viral infections can show focal changes and some bacterial infections can have more interstitial features—so clinical context and other tests remain important.