Differentiation between malignancy and inflammation in pulmonary ground-glass nodules: The feasibility of integrated (18)F-FDG PET/CT.
BACKGROUND
(18)F-FDG PET/CT has been used to differentiate malignant solid lung nodules from benign nodules. We assess the feasibility of integrated (18)F-FDG PET/CT for the differentiation of malignancy from inflammation manifested as ground-glass nodules (GGNs) on chest CT.


METHODS
A total of 68 GGNs in 45 patients (M:F=24:21; mean age, 61) fulfilled the following criteria: (a) nodules composed of >/=50% ground-glass opacity, (b) patients who underwent integrated PET/CT within 1 week following dedicated chest CT, (c) definitive diagnosis determined by pathological specimen or at least 9 months of follow-up, and (d) lesions >/=10mm in diameter. 36 malignant GGNs were pathologically proved as adenocarcinoma (n=20), bronchioloalveolar carcinoma (n=11), low-grade lymphoma (n=3), metastatic mucinous adenocarcinoma (n=1) and unknown low-grade malignancy (n=1). 32 inflammatory GGNs were confirmed as pneumonic infiltration as they had disappeared on follow-up CT and were associated with compatible clinical features (n=26) or as chronic inflammation with fibrosis by VATS biopsy (n=6). Using CT density histogram analysis, 14 were classified as pure GGNs and 54 as part-solid nodules. Integrated PET/CT was evaluated by measuring the maximum standardized uptake value (SUV) at the region of interest located at each lesion. The Mann-Whitney U test was performed to compare the SUV of malignancy and inflammation. The optimal cut-off value of SUV to differentiate malignancy from inflammation was determined using a receiver operating characteristic-based positive test. Sensitivity, specificity, accuracy, and positive predictive values (PPV) and negative predictive values (NPV) were calculated at the level of the optimal cut-off value. SUV showing 100% PPV for inflammatory GGNs was evaluated.


RESULTS
In part-solid nodules, the maximum SUV was significantly higher in inflammation (2.00+/-1.18; range, 0.48-5.60) than in malignancy (1.26+/-0.71; range, 0.32-2.6) (P=0.018). On the other hand, in pure GGNs, the maximum SUV of malignancy (0.64+/-0.19; range, 0.43-0.96) and inflammation (0.74+/-0.28; range, 0.32-1.00) showed no difference (P=0.37). Using the optimal cut-off value of SUV as 1.2 (P=0.01) sensitivity, specificity, accuracy, PPV and NPV in part-solid nodules were 62.1%, 80.0%, 70.4%, 78.3% and 64.5%, respectively. Six part-solid nodules, which showed a maximum SUV of higher than 2.6, were all inflammations.


CONCLUSIONS
The part-solid nodules with positive FDG-PET could be inflammatory nodules rather than malignant nodules. This is a quite paradoxical result when considering the basic knowledge that malignant pulmonary nodules have higher glucose metabolism.
Chun
Eun Ju
EJ
Department of Radiology, Seoul National University Bundang Hospital, Republic of Korea.
Lee
Hyun Ju
HJ
Kang
Won Jun
WJ
Kim
Kwang Gi
KG
Goo
Jin Mo
JM
Park
Chang Min
CM
Lee
Chang Hyun
CH
D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007249:Inflammation / Q000000981:diagnostic imaging / Q000473:pathology; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D003074:Solitary Pulmonary Nodule / Q000000981:diagnostic imaging* / Q000473:pathology; D014057:Tomography, X-Ray Computed
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18