Benign lung masses comprise a heterogeneous group of tumors that are defined by their lack of malignant features histologically and their nonaggressive clinical behavior. This is evidenced by the absence of invasion into surrounding tissue planes or metastatic spread to other structures. In a classic study, Martini1, who investigated the Memorial Sloan Kettering experience, demonstrated that less than 1% of resected lung lesions are benign. More recent reports have shown that despite advances in preoperative imaging and assessment, up to 9% of nodules suspected of being malignant prior to resection are found to be benign.2 Increasing utilization of CT scanning for lung cancer screening as well as for other cardiopulmonary diagnostic purposes has led to an increase in the number of patients being identified with pulmonary nodules. Given the overall low incidence of these tumors, differentiating a benign from a malignant lung mass can sometimes be difficult. Using a combination of clinical tools including a detailed history and physical examination, laboratory workup, radiographic imaging, and tissue sampling techniques, it is often possible to achieve an accurate assessment of a benign lung mass. It is this evaluation and correct characterization of an indeterminate pulmonary nodule that is invaluable in guiding treatment planning as well as assessing the overall prognosis of the patient.
The Indeterminate Solitary Pulmonary Nodule
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 are available and used to differentiate between benign and malignant lung lesions presenting as a solitary pulmonary nodule.
Often performed early in the evaluation of a pulmonary nodule, the radiographic appearance of a mass on CT can help identify differences between primary lung cancers and benign nodules. Cancers will often have ill-defined tumor margins and spiculation, will involve bronchi or vessels, and will enlarge more rapidly than benign tumors.3 CT also can be used for guided percutaneous core needle biopsy of accessible pulmonary nodules. In a study of 60 patients with benign pulmonary lesions, percutaneous core needle biopsy was able to provide a 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.4 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%.5 Continued ...