Solitary Pulmonary Nodules (SPN)

Solitary pulmonary nodule (SPN) refers to the circular or oval nodule with a clear edge, not more than 30 mm in size, surrounded by healthy lung parenchyma, without satellite lesions, atelectasis or mediastinal lymph nodes, and other unrelated lung lesions.

With the widespread use of chest CT, SPNs detection rate have been significantly improved. It is reported that more than 150,000 new cases of SPN patients are detected annually in the United States. SPN evaluation is critical because they may be an early manifestation of lung cancer.

It was estimated that about 35% of SPNs are primary malignancies. Most malignant SPNs were in the IA stage of tumor node metastasis (TNM), with a 5-year survival rate of 61% to 75%. For small nodules, it is one of the clinical challenges to distinguish between malignant and benign nodules because of their small size and lack of specific morphological features.

It was reported that about half of lung cancer patients missed the best time for surgical treatment, resulting in 5-year survival rate decreased to 10% to 15%.[9] Therefore, accurate diagnosis of SPN patients helps to improve the accuracy of T stage and prognosis of patients with malignant nodules.


FDG PET/CT Visualizing SPN’s (Negative Example)

Attached is a screenshot showing a negative right lung nodule on FDG PET CT. Patient has extensive history of smoking and concerning for lung cancer. The nodule measures about 0.6 cm, without appreciable FDG activity on PET. Given the sub- centimeter size and a lack of metabolic activity at this time, one of good options for this patient is to continue imaging follow-up. This may avoid unnecessary invasive approaches, without adverse consequences.

NIH Comments on FDG PET/CT and SPN’s

In recent years, 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) had been regarded as a routine method for assessing lung nodule masses. Compared to conventional imaging, PET/CT can not only display the morphological features of the lesion, but also provide molecular level of nodular glucose metabolism information. The value of 18F-FDG PET/CT in the diagnosis of SPN has been widely recognized, the sensitivity and specificity of which were 82% to 96.8% and 71% to 77.8% respectively.