A solitary pulmonary nodule is a round or oval spot (lesion) in the lungs that is seen with a chest x-ray or CAT scan (CT) scan. More than half of all solitary pulmonary nodules are noncancerous (benign) and may have many causes, including old scars and infections. Infectious granulomas (reactions to a past infection) cause most benign lesions. Common infections that increase the risk for developing a solitary pulmonary nodule include: tuberculosis (TB), exposure to TB, lung diseases caused by a fungus (such as: aspergillosis, coccidioidomycosis, cryptococcosis, histoplasmosis).
Lung cancer is the most common cause of cancerous (malignant) pulmonary nodules and rarely causes symptoms. A malignant solitary pulmonary nodule is most often found on a chest x-ray or a chest CT scan that has been prescribed for other symptoms or reasons.