Diagnostic efficacy of FDG-PET imaging in solitary pulmonary nodule

Abstract

Background: Over one-third of solitary pulmonary nodules are malignant, but most malignant SPNs are in the early stages at diagnosis and can be cured by surgical removal. Therefore, early diagnosis of malignant SPN is essential for the lifesaving of the patient. The incidence of pulmonary tuberculosis in Korea is somewhat higher than those of other countries and a large number of SPNs are found to be tuberculoma. Most primary physicians tend to regard newly detected solitary pulmonary nodule as tuberculoma with only noninvasive imaging such as CT and they prefer clinical observation if the findings suggest benignancy without further invasive procedures. Many kinds of noninvasive procedures for confirmatory diagnosis have been introduced to differentiate malignant SPNs from benign ones, but none of them has been satisfactory. FDG-PET is a unique tool for imaging and quantifying the status of glucose metabolism. On the basis that glucose metabolism is increased in the malignant transformed cells compared with normal cells, FDG-PET is considered to be the satisfactory noninvasive procedure which can differentiate malignant SPNs from benign SPNs. So we performed FDG-PET in patients with solitary pulmonary nodule and evaluated the diagnostic accuracy in the diagnosis of malignant SPNs. Method: 34 patients with a solitary pulmonary nodule less than 6 cm of its diameter who visited Samsung Medical Center for September, 1994 to September, 1995 were evaluated prospectively. Simple chest roentgenography, chest computer tomography, FDG-PET scan were performed for all patients. The results of FDG-PET were evaluated comparing with the results of final diagnosis confirmed by sputum study, PCNA, fiberoptic bronchoscopy, or thoracotomy. Results: (1) There was no significant difference in nodule size between malignant (3.1 1.5 cm) and benign nodule (2.81.0 cm)(P > 0.05). (2) Peak SUV (standardized uptake value) of malignant nodules (6.93.7) was significantly higher than peak SUV of benign nodules (2.71.7) and time-activity curves showed continuous increase in malignant nodules. (3) Three false negative cases were found among eighteen malignant nodule by the FDG-PET imaging study and all three cases were nonmucinous bronchiolalveolar carcinoma less than 2 cm diameter. (4) FDG-PET imaging resulted in 83% sensitivity, 100% specificity, 100% positive predictive value and 84% negative predictive value. Conclusion: FDG-PET imaging is a new noninvasive diagnostic method of solitary pulmonary nodule that has a high accuracy of differential diagnosis between malignant and benign nodule. FDG-PET imaging could be used for the differential diagnosis of SPN which is not properly diagnosed with conventional methods before thoracotomy. Considering the high accuracy of FDG-PET imaging, this procedure may play an important role in making the decision to perform thoracotomy in difficult cases.