After blunt chest trauma, a patient has dullness to percussion and elevation of the right hemidiaphragm with diminished breath sounds. Which is the most likely diagnosis?

• A. Bronchiectasis
• B. Pleural Effusion
• C. Atelectasis
• D. Pneumothorax

Answer: (C)

Lung volume loss from atelectasis is the pattern this scenario points to. After blunt chest trauma, pain and shallow breathing can cause the affected lung regions to collapse, especially basally. When a lung or a portion of it collapses, there is less air in that lung area, so the tissue becomes denser. That increased density gives dullness to percussion, and the reduced air entry lowers breath sounds over the affected side. Because the volume on that side has decreased, the diaphragm on that side is pulled upward, which is why you see elevation of the hemidiaphragm on exam.

Pneumothorax would more typically produce a hyperresonant percussion note with decreased breath sounds and possible tracheal shift if it’s large or tension. Pleural effusion can also cause dullness and diminished breath sounds with an elevated diaphragm, but in the acute post-traumatic setting, atelectasis from shallow breathing due to pain and injury is the more likely explanation for these findings. Bronchiectasis is a chronic condition and wouldn’t present acutely after trauma.