A patient two days after surgery presents with bibasilar infiltrates and dull percussion in both lower lobes. The most likely diagnosis is which of the following?

• A. Pulmonary edema
• B. Pneumonia
• C. Atelectasis
• D. Pleural effusion

Answer: (B)

In the immediate postoperative period, shallow breathing and limited chest expansion commonly lead to collapse of the dependent lung tissue, especially at the bases. This results in atelectasis, which presents on imaging as bibasilar opacities and on exam with dullness to percussion from loss of air in the affected segments. Two days after surgery is a typical window for this to occur, as pain and immobility reduce deep breaths and coughing. Pneumonia would usually bring signs of infection such as fever and leukocytosis, and often a more focal consolidation with productive cough, whereas the described pattern of basilar involvement after surgery most strongly points to atelectasis. Pulmonary edema would involve a different pattern of fluid overload and diffuse/interstitial markings, and pleural effusion would more commonly show fluid accumulation with corresponding signs rather than straightforward bibasilar atelectasis.