Pulmonary Carcinoma Staging

Radiography

The presence of pulmonary carcinoma is often first suspected on the chest radiograph. The radiograph also provides information about the T staging by demonstrating the size of the lesion in patients in whom it is circumscribed and the degree of associated atelectasis or obstructive pneumonitis in the presence of airway obstruction in patients in whom it is not circumscribed. It may also show the presence of pleural effusion and, in some cases, evidence of chest wall or mediastinal invasion. Direct extension of a neoplasm into the chest wall may be established by radiographic evidence of destruction of ribs or vertebrae or clinical evidence of a palpable mass. Evidence of invasion into the mediastinum may be suggested by marked elevation of a hemidiaphragm (related to phrenic nerve paralysis). With these few exceptions, however, the chest radiograph is unreliable in detecting invasion of the chest wall, diaphragm, or the mediastinum.

Computed Tomography

The seventh edition of the TNM classification for lung cancer emphasized the prognostic impact of the tumor size and subclassified T descriptors according to the tumor size. This finding was also confirmed in the new IASLC database for the eighth edition of the TNM classification. Although the 3-cm cutpoint still remains a landmark to separate T1 from T2 tumors, the survival analyses showed that a progressive degradation of survival was observed for each 1-cm cutpoint. On the basis of the new IASLC database, the following rearrangement of T descriptors was provided: T1 tumors were subdivided into three subgroups at 1-cm cutpoints; T2 tumors were subdivided into two subgroups; T2 tumors greater than 5 cm and less than or equal to 7 cm were reclassified as T3; T3 tumors greater than 7 cm were reclassified as T4 (see Table 18.2 ). The survival analysis also showed that involvement of the main bronchus either less than 2 cm or more than 2 cm from the carina has a similar prognosis. Therefore the new IASLC database provided that T3 tumors classified by endobronchial location were combined as T2 tumor. Total atelectasis or pneumonitis, a T3 descriptor in the seventh edition, showed better prognosis than other T3 tumors in the new IASLC database; therefore the IASLC project provided grouping of partial and total atelectasis/pneumonitis as a T2 descriptor. It also reclassified diaphragm invasion as a T4 descriptor. Mediastinal pleural invasion without mediastinal tissue invasion is difficult to determine clinically and is rare at pathologic staging; therefore the new IASLC staging deleted mediastinal pleural invasion as a T descriptor.

Other T3 and T4 descriptors were not changed from the seventh edition of TNM staging. It is important to emphasize that if a tumor abuts a pleural surface or when pleural thickening is noted immediately adjacent to a tumor mass, the CT findings must be interpreted as indeterminate or merely as suspicious for pleural and chest wall invasion. Chest wall invasion can be diagnosed confidently only when tumor obliterates the fat planes between parietal pleura and chest wall muscle or when there is associated bone destruction ( Figs. 18.1 and 18.2 ). Lung carcinomas are likely to be extensively invasive and unresectable (T4) if they involve the tracheal carina or surround, encase, or abut more than 180 degrees of the circumference of the aorta ( Fig. 18.3 ), main or proximal portion of the right or left pulmonary arteries, or the esophagus. Primary pulmonary carcinoma may be unresectable (T4) if it invades the heart, great vessels, or the vertebral body.

Magnetic Resonance Imaging

MRI is superior to CT in the demonstration of the pericardium, cardiac chambers, and mediastinal vessels with the added advantage of not requiring IV contrast medium (see Fig. 18.3 ). Disruption of the normal 2- to 3-mm-thickness low signal intensity of the pericardium is suggestive of pericardial infiltration, although this does not preclude complete surgical resection. Coronal images are particularly helpful in the assessment of tumor extension into the subcarinal region, aortopulmonary window, and superior vena cava.

MRI may allow better delineation of mediastinal and superior sulcus invasion ( Fig. 18.4 ). MRI is especially useful in the evaluation of brachial plexus, subclavian vessel, or vertebral body invasion in Pancoast tumors. However, there is no significant difference in the overall diagnostic accuracy between CT and MRI. In one large study, the sensitivity of CT and MRI was 63% and 56%, respectively, and the specificity was 84% and 80% for distinguishing T3 and T4 tumors from less extensive pulmonary carcinomas. Similar to CT, the main limitation of MRI is the inability to distinguish tumor invasion of mediastinal fat from inflammatory changes.

Disadvantages of MRI include lower spatial resolution than CT, longer scan time, higher cost, and artifacts as a result of respiratory motion. Recently introduced MRI techniques using fast (T2W half-Fourier acquisition single-shot turbo-spin-echo (HASTE), and T1W fat-saturated three-dimensional gradient-echo sequences with nearly isotropic resolution) and high-quality (breath-hold, electrocardiogram-gated, black-blood techniques on T2W turbo-spin-echo [TSE] and short-T1 inversion recovery [STIR] sequences) scan parameters have greatly improved the image quality and the potential role of MRI in the staging of lung cancer ( Figs. 18.5 and 18.6 ). Moreover, increased spatial resolution can be obtained using parallel acquisition and reconstruction techniques: sensitivity encoding (SENSE) and simultaneous acquisition of spatial harmonics (SMASH). Recent analyses of T staging using advanced MRI protocols showed that diagnostic accuracies of MRI were 82% to 94.3%, which were comparable to those of PET-CT (86%–91.4%).

Positron Emission Tomography

Integrated PET-CT provides morphologic as well as metabolic data of lung cancer and is widely accepted to be the first-line imaging tool for staging. It has been shown to be more useful than CT alone in determining the T stage of the primary tumor and in assessing chest wall invasion. According to a report, although statistically not significant ( P =.25), integrated PET-CT accurately staged the primary tumor (T stage) in 86% (91 of 106) of patients, whereas CT accurately staged the primary tumor in only 79% (84 of 106) of patients.

The main limitation of PET-CT in the T staging is false positivity in cases of inflammatory lesions. In this context, the newly introduced PET-MRI system with superior soft tissue contrast and dedicated sequences has the potential to compensate the shortcomings of PET-CT. According to the studies with comparison of PET-MRI and PET-CT in the preoperative staging of NSCLC, the diagnostic accuracy of PET-MRI (65%–94.3%) in the T staging was comparable to that of PET-CT (70%–91.4%).