Methods: A total of 158 patients (83 males, 75 females; mean age 64 years; range 32 to 91 years) underwent FDG-PET to reveal the metabolic activity of an SPN, <3 cm in size, incidentally detected on a chest X-ray or computed tomography. The findings were correlated with those of (i) histology after lobectomy in 43 patients (27.2%) and transthoracic or open biopsy in 97 patients (61.4%), (ii) bronchial washing in two patients (1.3%), or (iii) clinical follow-up for a period of time not less than six months in 16 patients (10.1%).

Results: Malignancy was documented in 119 nodules (75.3%), being primary lung cancer in 115, and metastatic lesions in four patients. FDG-PET revealed malignant disease successfully in 115 patients. PET scanning was false positive in four patients whose definitive diagnoses were histoplasmosis, granuloma, tuberculosis, and histiocytosis with organizing pneumonia, respectively. FDG-PET was also concluded to be false positive in two patients because no malignancy was noted histologically after performing transthoracic needleaspiration biopsy. FDG-PET yielded a true negative result in 33 patients. It was false negative in four patients with bronchoalveolar carcinoma (n=2) and adenocarcinoma (n=2). The sensitivity, specificity, negative-positive predictive value, and accuracy of FDG-PET were 96.6%, 84.6%, 89.2%-95.0% and 93.7%, respectively.

Conclusion: In the evaluation of an indeterminate SPN, FDG-PET can be used as a noninvasive diagnostic alternative with no risk or complications, that may otherwise necessitate more invasive surgical interventions.