Definition of Solitary pulmonary nodule:

A solitary pulmonary nodule is a round- or oval-shaped sore (lesion) in the lungs that is seen with a chest x-ray.

Causes, incidence, and risk factors:

About 60% of all solitary pulmonary nodules are benign (not cancerous). Benign nodules have many causes, including old scars and infections.

Infectious granulomas (inflammations of granular tissue) are the cause of most benign lesions. When a nodule is malignant, lung cancer is the most common cause. Exposure to tuberculosis or an infectious fungus (histoplasmosis, coccidioidomycosis) can increase the risk of developing a solitary pulmonary nodule, but also makes it more likely that the nodule is benign.

Young age, absence of tobacco exposure, calcium in the lesion, and small lesion size are factors favoring a benign diagnosis. About 150,000 new solitary pulmonary nodules are diagnosed each year in the United States. Of these, 45,000 require no further testing besides a careful history and review of an old chest x-ray, if available.