The conventional radiologic assessment of an SPN is complemented by the use of PET and the radiopharmaceutical ¹⁸F-2-deoxy-D-glucose (FDG), a D-glucose analog labeled with fluorine-18. The reported sensitivity and specificity of PET for malignant pulmonary lesions are 97% and 78%, respectively. The spatial resolution of PET scanners is in the range of 6 mm; therefore, smaller lesions should not be evaluated with PET. When FDG uptake by a solid nodule ≽ 1 cm in diameter is low, the likelihood of malignancy is generally considered to be low. However, in a study of 360 patients with lung nodules evaluated by FDG-PET, 43 patients had solid nodules with a standardized uptake value (SUV) <2.5, 16 of which were malignant [17]. False-negative results for malignancy include slow-growing cancers, especially adenocarcinomas with subsolid morphology and carcinoid tumors (Fig. 4). Nomori et al. reported that nine of ten well-differentiated adenocarcinomas manifesting as ground glass nodular opacities were falsely negative on FDG-PET [18]. The sensitivity (10%) and specificity (20%) for ground glass opacities in that study were significantly lower than for solid nodules (90% and 71%, respectively). False-positive results are most commonly caused by infections and inflammatory processes, including Wegener’s granulomatosis, sarcoidosis, organizing pneumonia, amyloid and rheumatoid nodules.

The Fleischner Society guidelines for the evaluation of an incidentally discovered solid nodule in an adult patient integrate lesion morphology, growth rate, patient age, and smoking history (see below). In addition, to complement the recommendations for incidentally detected solid nodules, the Society recently published recommendations specifically aimed at the management of ground glass and partly solid nodules (see below) [19, 20]. Importantly, for both, risk factors such as smoking history, family history of lung cancer, or exposure to carcinogenic agents are not considered in the current guidelines due to a lack of sufficient data. Other issues to be aware of are that a slight temporary decrease in size can be seen with adenocarcinomas manifesting as ground glass or partly solid nodules, due to fibrosis or atelectasis, and enlargement and/or increasing attenuation with or without the new appearance of a solid component during follow up should be managed with a high degree of suspicion [20].

The Fleischner Society guidelines [19] are summarized in the following.

The Fleischner Society guidelines [20] are summarized in the following.

Staging, a standardized anatomic description of disease extent, is determined both clinically and pathologically and guides appropriate treatment. In general, the clinical stage underestimates the extent of disease compared with the pathologic stage. Radiologic imaging is an essential component of clinical staging and allows the assessment of disease manifestations that are important for surgical, oncological, and radiation therapy planning, including size of the primary tumor, its location and relationship to normal anatomic structures in the thorax, and the presence of nodal and or metastatic disease. The 7th edition of the tumor node metastasis (TNM) staging system allows a standardized definition of stage and consequently, indicates the most appropriate treatment. While useful in ascertaining advanced disease, chest radiography is limited in accurately determining TNM descriptors in patients with potentially resectable disease, which typically requires imaging with CT and/or magnetic resonance imaging (MRI) and/or PET/CT. A contrast-enhanced CT of the chest is recommended for the evaluation of all patients with known or suspected primary lung cancer [21]. CT accurately assesses most characteristics of the primary tumor (T descriptor), including size and location, but loco-egional invasion can be difficult to determine. CT is also useful in detecting nodal metastasis and determining the absence or presence of intra- and extrathoracic metastatic disease, including contralateral lung nodule(s), pleural and pericardial nodule(s) and effusions, bone metastases, and adrenal nodules/masses. CT of the chest alone is sufficient for the staging of patients with pure ground glass nodules and an otherwise normal study, and for patients with peripheral stage IA disease [21]. Otherwise, further imaging with FDG-PET is recommended for patients eligible for curative treatment. FDG-PET/CT has an increasing role in staging, particularly for detecting nodal (N descriptor) and distant (M descriptor) metastasis. When PET is unavailable or cannot be performed a contrast-enhanced CT of the abdomen is recommended [21].

The T descriptor defines the size, location, and extent of the primary tumor and is based on differences in survival (Fig. 5). However, although a T4 descriptor generally precludes resection, tumors with cardiac, tracheal, and vertebral-body invasion are designated in the 7th edition staging system as being potentially resectable in the absence of N2 and or N3 disease.

The following parameters must be analyzed regarding T descriptor determination: (1) size, (2) location, (3) extension.

CT and MRI are useful in determining gross chest wall or mediastinal invasion (Fig. 7). However, limited loco-regional invasion is difficult to differentiate from abutment. MRI can be used to assess myocardial invasion and to evaluate superior sulcus tumors for involvement of the brachial plexus, regional vasculature, and adjacent spine and vertebra (Fig. 8). This is important since involvement of the brachial plexus roots or trunks superior to the T1 nerve root, invasion of the trachea or esophagus, and >50% invasion of a vertebral body are absolute contraindications to surgical resection [22, 23].

The N descriptor, which specifies the presence and location of nodal metastatic disease, has a significant effect on management (Fig. 5). N descriptors are designated according to lymph node maps in which the nodal stations are numbered based on relationships to anatomic structures [24, 25]. For the 7th TNM edition, a standardized nodal map with seven node zones, created by unifying the Mountain/Dressler-ATS (MD-ATS) node map and the Japanese Naruke map, is used. The International Association for the Study of Lung Cancer (IASLC) nodal map designates the oncologic midline of the superior mediastinum to correspond with the left lateral border of the trachea, such that all nodes anterior to the trachea are grouped with right paratracheal nodes (Fig. 9). Surgical resection and the potential use of adjuvant therapy depend on the N descriptor, such that its accurate determination is important. Ipsilateral peribronchial, or hilar (N1) nodes are usually resectable while mediastinal nodes have a major influence on resectability. Specifically, ipsilateral mediastinal (including subcarinal) nodal metastasis (N2) can be resectable (usually after induction chemotherapy), while contralateral mediastinal and scalene or supraclavicular disease (N3) is not. To potentially improve patient management, data are currently being collected based on grouping nodal stations together in six zones within the current N1 and N2 patient subsets for further evaluation [26].