PET–CT Evaluation of Solitary Pulmonary Nodules: Correlation with Maximum Standardized Uptake Value and Pathology

Abstract

18-fluorine fluorodeoxyglucose ((18)F-FDG) positron emission tomography-computed tomography (PET-CT) has an established role for the characterization of solitary pulmonary nodules (SPN). Visual assessment of nodule morphology, together with maximum standardized uptake value (SUVmax), is used to estimate likelihood of malignancy. We correlated SUVmax value with pathology of SPN and assessed diagnostic accuracy in differentiating malignant from benign nodule, using 2.5 as threshold SUVmax. Retrospective review of PET-CT scans for SPN characterization between April 2008 and June 2011 was performed. Only cases with pathological verification were included. A total of 641 PET-CTs were performed for SPN characterization and staging; 186 patients (77 males, 109 females) with pathological confirmation were included, and 158 (85%) nodules were malignant: adenocarcinomas (n=66), squamous cell carcinomas (n=40), and metastases (n=20) were the commonest. 28 lesions (15%) were benign, including granuloma/chronic inflammation (n=8), infection (n=7), and hamartomas (n=5). Using cutoff SUVmax of 2.5, the accuracy of PET-CT in diagnosing malignant SPN is 81.2%, with sensitivity 86.7%, specificity 50%, PPV 90.7%, and NPV 40%. The likelihood of malignancy increases with SUVmax. Nevertheless, even with SUVmax <2.5, there is a 62% chance that a nodule is malignant. Although PET-CT is useful in diagnostic workup of SPN, it cannot replace "gold standard" tissue diagnosis.