Multiple pulmonary nodules detected by computed tomography: diagnostic implications

Prior to the advent of CT, the radiographic demonstration of multiple nonmiliary lung nodules usually indicated the presence of metastases or, less likely, granulomas. The increased sensitivity of CT at detecting small parenchymal pulmonary densities is accompanied by loss of specificity, creating uncertainty as to the significance of nodules detected at CT in any individual patient. During a 1 year period we reviewed all CT scans in our institution demonstrating three or more focal lung densities, noting these parameters: number of densities, maximum lesion size, presence of calcification as determined visually, and lesion morphology (linear or nodular). Of 137 patients with three or more focal lung densities at CT, nodule diagnosis was established on pathologic or clinical grounds in 114. Metastases accounted for 73%, with primary colon and lung malignancies and lymphoma the most common causes. Malignant nodules were statistically significantly larger, more numerous, and more rounded, whereas calcification was significantly associated with benign disease. However, no single criterion or combination of criteria was foolproof. Based on our results, we offer recommendations for further evaluation of nodules in several common clinical settings.