A 72-year-old man presents with the chief complaint of shortness of breath. His symptoms have been progressive over the past year. He is able to climb two flights of stairs before having to stop and rest. His past medical history includes hypertension and hypercholesterolemia. In a review of systems, he denies chest pain, coronary artery disease, fever, cough, hemoptysis, or weight loss. He has an 80-pack-per-year history of smoking but quit 10 years ago.

The physical examination reveals a slender, pleasant gentleman in no respiratory distress. His vital signs are within normal range. The cardiac tones are normal, and his breath sounds are diminished throughout his lung fields. There is no cervical adenopathy. The rest of the examination is unremarkable. Basic laboratory studies revealed neither electrolyte abnormalities nor anemia.

Some of the differential diagnoses for shortness of breath include obstructive airway disease, parenchymal lung disease, and cardiogenic causes. Given the patient’s clinical symptoms, the following chest x-rays and computed tomography (CT) scans are obtained.