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INTRODUCTION

Benign lung masses comprise a heterogeneous group of neoplastic lesions originating from pulmonary structures 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. Although benign lung tumors do not pose a significant health problem, complications can result if an obstructive lesion predisposes the patient to develop pneumonia, atelectasis, or hemoptysis.

In a classic study, Martini,1 who investigated the Memorial Sloan Kettering experience in 1982, 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 determined to be benign.2 The increasing use of CT scanning for lung cancer screening and PET/CT for staging, as well as for other cardiopulmonary diagnostic purposes, has led to an increase in the number of patients diagnosed with pulmonary nodules. Differentiating between a benign and malignant lung mass can 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 diagnosis. It is this evaluation and correct characterization of an indeterminate pulmonary nodule that is invaluable in guiding treatment planning and assessing the overall prognosis of the patient.

THE INDETERMINATE SOLITARY PULMONARY NODULE

A solitary pulmonary nodule is defined as a discrete, well-marginated, rounded lesion or opacity 3 cm or less in diameter that is completely surrounded by otherwise normal lung parenchyma. The nodule does not touch the hilar structures or mediastinum, and it is not associated with adenopathy, atelectasis, or pleural effusion. Lesions larger than 3 cm are considered masses and generally treated as malignant until proven otherwise.

Some imaging features are particularly helpful in distinguishing between benign and malignant lesions. Nodules with doubling times of fewer than 10 or more than 450 days are most likely benign. Calcifications seen on a chest radiograph or CT scan that have a central, diffuse, speckled laminar or popcorn pattern most likely reflect a benign mass, whereas eccentric calcifications are more characteristic of malignancy. The following sections describe the imaging techniques used in the diagnosis of solitary pulmonary nodules.

CT

CT is the most used imaging technique to find and diagnose nodules on the lungs, which are often found incidentally during an evaluation performed for other reasons. Radiologic characteristics of nodules with ill-defined and speculated borders favor malignant tumors as well as involvement of bronchi or vessels, and will enlarge more rapidly than benign tumors.3 CT can also 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 provided a definitive diagnosis ...

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