Chest ImagingLung cancer staging
Patients who are likely to benefit from surgical resection are those with localized disease. Only stages I, II and IIIA can be considered as technically resectable (see
lung cancer stage grouping). Patients considered as definitely irresectable are those having distant metastases (M1), contralateral or subclavian
lymph node metastases (N3) or
tumour classified as T4 (
lung cancer TNM classification). Limited chest wall or
mediastinal fat invasion is classified T3 in technically resectable
lung cancer. However, the mortality rate associated with
en bloc resection of the
tumour and the contiguous structures is still substantial. Therefore, information about chest wall and
mediastinal invasion is still one of the most important factors in the clinical decision to
perform surgery in a particular patient.
Tumour staging (T)
CT continues to play a major role in preoperative staging of non-small cell lung cancer for selecting those patients with localized disease. Certain CT findings have been demonstrated as being diagnostic of unresectable disease such as a lysis of vertebral body adjacent to the tumour, and gross invasion of mediastinum with incasement and distorsion of the major mediastinal structures (Fig.1) (Fig.2). In many of these situations, biopsy proof of diagnosis is necessary but thoracotomy is not indicated. Although gross mediastinal invasion can be confidently diagnosed with CT, the contiguity of tumour with adjacent mediastinal structures is not equivalent to definite invasion. A contact between the tumour and a mediastinal structure superior to 180 has a very high positive predictive value of mediastinal invasion (Fig.3). MR has the same limitations as CT in distinguishing tumour contiguity from tumour extension into mediastinal structure. Some studies, however, have showed a slightly better accuracy for MR in diagnosing mediastinal invasion. The superiority of MR was due to:
longitudinal images;
high contrast between tumour, mediastinal fat and vessels; and
good visibility of the pericardium and myocardium.
Currently, these advantages have disappeared since helical CT scanning technique has permitted:
the acquisition of a large number of thin sections, during a single breathhold;
consistent opacification of vascular structures after bolus injection of contrast medium; and
multiplanar reconstructions facilitating the analysis of tumour invasion into adjacent structures.
The contiguity of tumour with parietal pleura is not equivalent to definite invasion of the chest wall even when associated with a pleural thickening contiguous to the tumour. Complementary expiratory scans may be helpful to evaluate the respiratory shift that is defined as a change in the relative location between the peripheral lung tumour and the chest wall, with deep inspiration and expiration at CT (see expiratory CT). The presence of respiratory shift is a reliable indicator of the lack of parietal invasion for tumour located in the middle and lower lobes. The only CT finding with high positive predictive value of chest wall invasion is bone destruction adjacent to the lung mass or extension of the mass beyond the line of the ribs or the intercostal stripe (Fig.4). Owing to its superior contrast resolution, MR may demonstrate subtle chest wall invasion and be superior to CT in this regard. The use of surface coils provides high resolution images and chest wall invasion in best depicted as a disruption of the normal extrapleural fat (Fig.5). These advantages are particularly appreciated for staging Pancoasts neoplasm.
One p Fig.6
). According to the location of the primary tumour and using a regional classification scheme (see lymph node classification chest), CT findings may direct preoperative lymph nodes sampling with different invasive techniques. Cervical mediastinoscopy may access to the highest (1), paratracheal (2, 4) and subcarinal mediastinal nodes. Anterior or parasternal mediastinoscopy permits to sample subaortic (5) and para-aortic (6) mediastinal nodes. Thoracoscopy and video-assisted thoracoscopic surgery (VATS) allow a panoramic view of ipsilateral hemithorax including the hilum, mediastinum, visceral pleura and chest wall. In the right hemithorax, they permit an access to the right lower paratracheal (4R) pulmonary ligament (9) and hilar nodes (10). By right-sided thoracoscopy, prevascular (3A) and retrotracheal (3P), subcarinal (7) and paraesophageal (8) may be also assessed. In the left hemithorax, the nodes that can be evaluated include subaortic (5), paraaortic (6), left pulmonary ligament (9L) and hilar (10L). VATS is particularly useful in diagnosis, staging, and eventually treatment of an indeterminate peripheral lung nodule (see solitary pulmonary nodule).
MR has no superiority over CT in the detection of mediastinal nodal metastases.
Distant Metastases (M)
Certain CT findings have been demonstrated as being diagnostic of metastatic disease to the contralateral lung or the chest wall (Fig.7). In most of the cases, however, the biopsy proof is required. Because the adrenal glands are the most common site for extrathoracic metastases, the CT examination used for staging bronchogenic carcinoma should include the upper abdomen. An adrenal mass, however, may represent an incidental adenoma. Most incidental nonhyperfunctioning adrenal masses are less than 3 cm in diameter and of uniform low attenuation (less than 10 UH) because of their fat content. Routine unenhanced CT of the adrenal glands allows prospective characterization of many adrenal masses in patients with lung carcinoma. Adrenal masses demonstrating high attenuation at unenhanced CT should probably proceed to biopsy when the adrenal gland is the only potential site of metastatic disease. MR has been reported to be helpful in the distinction of adrenal metastases from an adenoma when chemical shift imaging is used.
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