Solitary Pulmonary Nodule: A solitary pulmonary nodule (SPN) is a single lung abnormality. Causes of a solitary pulmonary nodule include neoplastic growths, sarcomas, infectious agents, inflammatory conditions, congenital malformations, and a miscellaneous group of causes. Most people do not know they have a solitary pulmonary nodule as it is generally discovered as an incidental finding. Treatment for solitary pulmonary nodule depends on the size and characteristics of the nodule.