What is a solitary pulmonary nodule (SPN)?
An SPN is a solitary focal lesion in the lung that measures 3 cm or less. A solitary focal lesion that is greater than 3 cm is considered to be a mass, and most masses are malignant. Approximately 150,000 SPNs are detected annually in the United States, often incidentally on imaging. A goal of radiologic evaluation of SPN is to noninvasively assess the likelihood of malignancy within the nodule. SPN is the initial radiographic finding in 30% of patients with lung cancer, and the prognosis depends partly on the stage at presentation.