A benign lung mass is defined as one that neither metastasizes nor invades surrounding tissue planes. The overall incidence of benign lung lesions is low. The classic study of Martini, which investigated the Memorial Sloan-Kettering experience, showed that less than 1% of resected lung lesions are benign.1 Indeed, sometimes the distinction between benign and malignant lesions is blurred. Therefore, the evaluation and correct characterization of an indeterminate pulmonary nodule is invaluable because it will determine further treatment plans and prognosis of the patient.
The solitary pulmonary nodule is a rounded lesion with well-demarcated margins. Its size may vary from a few millimeters to a few centimeters. Two features are particularly helpful in making the distinction between benign and malignant lesions: (1) Nodules with doubling times of less than 10 days or more than 450 days are most likely benign, and (2) calcifications seen on a chest radiograph or CT scan with fine cuts through the tumor that exhibit a central, diffuse, speckled, laminar, or popcorn pattern most likely reflect a benign mass, whereas eccentric calcifications are more characteristic of malignancy. Various diagnostic modalities have been used in attempts to differentiate between benign and malignant lung masses.
CT has been used to identify differences between primary lung cancers and benign nodules. Cancers were found to have an ill-defined tumor margin and spiculation, to involve bronchi or vessels, and to enlarge more rapidly than benign tumors.2 CT also can be used for guided percutaneous core needle biopsy of accessible pulmonary nodules. In a recent study of 60 patients with benign pulmonary lesions, percutaneous core needle biopsy was able to provide definitive diagnosis in 81.7% of cases as opposed to fine-needle aspiration, in which a specific benign diagnosis was made in only 16.7% of cases.3 Recent reports also have shown that 1-mm-thick slices on high-resolution CT can be used to differentiate between benign and malignant solitary pulmonary nodules with a sensitivity of 91.4%.4
Dynamic MRI is a modality that demonstrates significant kinetic and morphologic differences in vascularity and perfusion between benign and malignant solitary lung nodules. Malignant lesions show stronger enhancement and higher maximum peak signals than benign lesions.5
In addition, the use of fluorodeoxyglucose PET scanning has facilitated the determination of malignancy in nodules as small as 6 mm.6 If the nodule is glucose-avid and has a standardized uptake value of 2.5 or greater, it has a greater than 90% probability of being malignant. PET scanning can distinguish malignant from benign nodules with a sensitivity of 90%.6 Unfortunately, the sensitivity seems to decrease for nodules smaller than 10 mm in size. Similarly, the use of technetium-99m single-photon-emission CT and, more recently, methionine-based PET scanning has improved our ability to distinguish benign from malignant lung nodules. PET scanning is developing into an excellent tool for the diagnosis and staging of patients with thoracic malignancies, and it has been shown to be ...