Diagnostic Efficacy of PET-FDG Imaging in Solitary Pulmonary Nodules

Solitary pulmonary nodules are parenchymal lung lesions that are usually well defined and less than 4 cm in diameter. An estimated 130,000 new benign or malignant solitary pulmonary nodules are discovered each year in the United States. It is estimated that about 40 to 50 percent of all solitary pulmonary nodules and 90 percent of benign nodules are infectious granulomas.2 The only two definite criteria for benign solitary pulmonary nodules are the presence of central, concentric, or stippled calcification as seen on chest radiographs or computed tomographic (CT) scan and stability of the nodule for more than 2 years. canadian family pharmacy online

Other criteria that may support the diagnosis of benign nodules include (1) transthoracic fine needle aspiration biopsy specimen showing a specific benign process, and (2) patients younger than 35 years. Although fine needle aspiration biopsy specimen of the nodule may provide a diagnosis in up to half of the benign nodules, a nonspecific diagnosis of benign nodules is not universally accepted.
At present, plain chest radiographs and CT are the most common imaging modalities used to differentiate benign from malignant nodules. Despite significant advancement in the use of these techniques, a substantial proportion of solitary pulmonary nodules remain radiographically indeterminate. It is evident that current noninvasive methods that assess morphologic details are not satisfactory in separating benign from malignant nodules. A new noninvasive test that can predictably differentiate benign from malignant nodules could significantly change the evaluation and treatment of patients with solitary pulmonary nodules.
Positron emission tomography (PET), a new noninvasive imaging modality using 2-[F-18]-fluoro-2-deoxy-D-glucose (FDG), has demonstrated increased glucose metabolism in malignant cells. Recent studies with PET imaging have documented increased FDG uptake by lung tumors- as compared with normal tissue. More recently, in a prospective study of 20 patients with solitary pulmonary nodules up to 4 cm in size, we demonstrated that PET-FDG imaging was highly accurate in differentiating benign from malignant nodules. There were no false-positive or false-negative cases in this limited study.
Factors that increase the probability of malignancy include the following: (1) age greater than 35 years; (2) irregular margins of the nodule; (3) absence of calcification; (4) amount of cigarette smoking; and (5) size of the nodule. In a recent study of lung nodules larger than 3 cm, 98 percent of the nodules were malignant and only 2 percent were benign. Because size of the nodule is an important factor in determining the probability of malignancy, it was believed that it would be more useful to assess the utility of PET-FDG imaging in differentiating benign from malignant pulmonary nodules less than 3 cm in size. Therefore, we analyzed the 18 cases previously studied along with 12 additional new patients and report our results in 30 patients with solitary pulmonary nodules less than 3 cm.