Review of radiographic characteristics of pulmonary nodules and management algorithm for nuclear medicine physicians

Learning Objectives To provide an overview of the radiographic characteristics of pulmonary nodules and to review the management for nodules found incidentally.

Solitary pulmonary nodules (SPN) are well-defined, discrete opacities measuring 3cm or less. Differential diagnosis of a SPN usually falls into one of three broad categories: malignancy, benign tumor, and infectious/inflammatory nodule. Around 150000 SPNs are detected annually on radiographic examinations, and more are being found after the start of screening chest CT scans. In nuclear medicine, SPNs are found incidentally on the companion CT of hybrid SPECT or PET scans or were previously found on other imaging exams and referred for metabolic evaluation by FDG PET. The definitive step to confirm or rule out cancer is through tissue diagnosis, either through needle biopsy or wedge resection. Certain CT characteristics can help determine the likelihood of malignancy and need for intervention. The Fleischner Society published recommendations for managing SPNs, taking into account whether or not the patient has a significant smoking history or other risk factors for lung cancer. A general rule is that if the nodule appears benign radiographically and the patient is low-risk, it can be followed by serial CT scans. In the high-risk patient, certain morphologic features are predictive of malignancy, including size over 2cm, interval growth, spiculated margins, mixed ground glass/solid components, cystic lucencies or cavitation and degree of contrast-enhancement. Often there are no clear distinguishing features and additional imaging such as FDG PET/CT is needed. In conclusion, SPNs are frequently encountered in nuclear medicine particularly in FDG PET/CT. In addition to determining the presence or absence of abnormal FDG uptake in the nodule, it is important to recognize and report the radiographic characteristics to help differentiate between benign and malignant nodules and guide the clinician for appropriate management.