If the tumor is confined to the mucosa and does not constitute bronchial stenosis or obstruction, there may be no positive X-ray findings. If the tumor causes bronchial stenosis, emphysema of one side or lobe may appear. It is easy to be shown in deep whistle position photograph. (iii) If the bronchial stenosis caused by carcinoma results in poor drainage of secretion, obstructive pneumonia or obstructive pulmonary atelectasis may occur. (iv) Obstructive atelectasis occurs when the cancer tumor causes bronchial obstruction. In addition, the cancer tumor spreads out of the bronchus and forms a mass in the hilar region. A typical transverse “S” sign may appear in right upper lobe lung cancer. ⑤ The tumor mainly spreads to the extra-bronchial area, forming masses and nodules in the hilar region, with lobulated or irregular margins. The right side of the tumor may show the disappearance of hilar angle. (6) Bronchogram shows irregular thickening of bronchial wall, limited irregular narrowing or even truncation of lumen. (7) Bronchography shows symmetric or irregular narrowing of the lumen, bronchial obstruction and cupping-like filling defects. CT manifestations ①Tumor growth along the bronchial wall, showing irregular thickening of the bronchial wall and narrowing of the lumen, even causing bronchial occlusion. ② The tumor causes bronchial stenosis and occurs obstructive emphysema, obstructive pneumonia, and even lung abscess. (iii) The tumor forms a large hilar mass, which is often combined with lung atelectasis, and the mass is connected with atelectasis, forming “S”-shaped or anti-“S”-shaped edge. ④Central lung cancer can directly invade mediastinum, which is manifested as mediastinal mass connected with hilar tumor. Enhanced examination not only helps to distinguish hilar mass from blood vessels, but also shows that hilar and mediastinal mass connected with it show the same degree of enhancement. MRI ① The affected bronchial tubes are rat-tailed or tubular narrowing, or even completely occluded. ② Normal hilar bronchus and pulmonary vessels are signalless structures and lung tissue is also signalless, so it is easy to find hilar masses. (3) The mass is often lobulated, and its signal is slightly higher than that of the muscle in T1-weighted image, while in T2-weighted image, the mass is often non-homogeneous and high signal. When necrosis occurs in the mass, the T1 and T2 values of the tissue in the necrotic area are prolonged. ⑤ Obstruction of the bronchus by the tumor may result in obstructive pneumonia or atelectasis, which can be revealed against the surrounding signal-free lung tissue. The mass can be differentiated from obstructive pneumonia and pulmonary atelectasis with different signal intensities. (6) When the tumor directly invades the mediastinum, MRI is often better than CT for mediastinal involvement because of the obvious signal difference between the tumor and the mediastinal vessels and fat, and because it can be displayed in transverse, coronal, and sagittal directions. (7) MRI is easy to detect mediastinal lymph node metastasis, especially when coronal imaging clearly shows enlarged lymph nodes under the bulge and the main pulmonary arteries, and so on. Same as CT, MRI can not identify metastatic or inflammatory lymph node enlargement, as the criteria for lymph node enlargement is greater than 15 cm.