Solitary pulmonary nodules: Part I. Morphologic evaluation for differentiation of benign and malignant lesions

The solitary pulmonary nodule is a common radiologic abnormality that is of ten detected incidentally. Although most solitary pulmonary nodules have be nign causes, many represent stage I lung cancers and must be distinguished from benign nodules in an expeditious and cost-effective manner. Evaluation of specific morphologic features of a solitary pulmonary nodule with conve ntional imaging techniques can help differentiate benign from malignant nod ules and obviate further costly assessment. Small size and smooth, well-def ined margins are suggestive of but not diagnostic for benignity. Lobulated contour as well as an irregular or spiculated margin with distortion of adj acent vessels are typically associated with malignancy. There is considerab le overlap in the internal characteristics (eg, attenuation, cavitation, wa ll thickness) of benign and malignant nodules. The presence of intranodular fat is a reliable indicator of a hamartoma. The presence and pattern of ca lcification can also help differentiate benign from malignant nodules. Comp uted tomography (CT) (particularly thin-section CT) is 10-20 times more sen sitive than standard radiography and allows objective, quantitative assessm ent of calcification. Initial evaluation often results in nonspecific findi ngs, in which case nodules are classified as indeterminate and require furt her evaluation to exclude malignancy. Growth rate assessment, Bayesian anal ysis, contrast material-enhanced CT, positron emission tomography, and tran sthoracic needle aspiration biopsy can be useful in this regard.