There are a number of things that could involve the lung, although a better description (other than saying “a spot”) would help. These include: 1. Infections: Bacterial pneumonia, fungal pneumonia (coccidiomycosis, histoplasmosis, cryptococcus, blastomycosis), nocardia, Mycobacterium tuberculosis, lung abscess 2. Cancer: Lung cancer, metastatic disease, lymphoma, carcinoid, hamartoma, fibroma 3. Inflammatory: Rheumatoid arthritis, Wegener’s granulomatosis, sarcoid 4. Congenital: AV malformation, cyst 5. Other: Pulmonary infarct (clot), rounded atelectasis For now, I wouldn’t worry too much. It could be a number of things, and often a solitary pulmonary nodule is benign. The CT scan will help with the diagnosis, and he eventually may need a CT guided biopsy. Good luck and best wishes.