Malignant primary central airway lesions refer to lesions originating in the trachea, main bronchus and right middle segment bronchus. Unlike malignant tumors originating in the lung, the type, nature and clinical stage of the lesions are different. At present, there is no uniform classification and staging method, and the treatment is not standardized. In recent years, after several thousand cases of tracheoscopic interventions, the authors have accumulated a lot of experience and put forward some new concepts with reference to foreign methods [1], hoping to reach a consensus with colleagues. I. Central airway zoning Based on the authors’ experience, the central airway was divided into eight zones (Table 1) for the purpose of comparison and summary, and the nature of the lesion and the means of treatment were different for different zones. In addition, according to the extent of lesion invasion, they were divided into limited and diffuse types. The limited type refers to lesions invading one zone, while the diffuse type refers to lesions invading more than two zones. The limited type can be surgically removed, while the diffuse type is not indicated for surgery. If the lesion is limited to one zone, there is a strong indication for surgery, and if the lesion is more than two zones, surgery should be done with caution. For lesions in segments I and VIII, it is difficult to place stents of any shape, and for lesions in segments III, IV, V, and VII, it is difficult to place straight stents, and bifurcated stents should be placed. Table 1: Sites of airway lesions Subdivisions Lesion sites Ⅰ upper 1/3 of main trachea Ⅱ middle 1/3 of main trachea Ⅲ lower 1/3 of main trachea Ⅳ bulge Ⅴ right main bronchus Ⅵ right middle bronchus Ⅶ near 1/2 of left main bronchus Ⅷ far 1/2 of left main bronchus II. Primary tracheal tumors in adults are more than 90% of malignant tumors [2, 3, 4]. Malignant tumors originating in the lower 1/3 of the trachea and the bulge account for 40% to 50%, those located in the upper 1/3 of the trachea account for 30% to 35%, and those located in the middle 1/3 of the trachea account for 5% to 10%. Primary central airway malignancies mainly originate from mucosal epithelial cells and salivary glands, with squamous carcinoma, adenoid cystic carcinoma (the first two accounting for more than 75%) [3], adenocarcinoma, carcinoid tumor and small cell carcinoma. Squamous carcinoma is the most common in elderly people aged 60-70 years and accounts for the most common malignant tumor of the trachea (48%) [5], often occurring in the posterior wall of the middle and lower trachea, with infiltrative growth in the wall, brittle and bleeding easily when touched. [6]. Adenoid cystic carcinoma (ACC) occurs most frequently in people aged 40-50 years, accounting for the second most common tracheal malignancy (33%) [7], and is a locally invasive, low-grade malignancy accounting for 20-35% of tracheal carcinomas. About 2/3 of adenoid cystic carcinomas occur in the lower part of the trachea, near the level of the bulge and the beginning of the left and right bronchi. 1/3 occur at the beginning of the large bronchi. The tumor is polypoid, hard, grayish white, pink or light brown in color, with a maximum diameter of several centimeters, and extends through the cartilaginous wall to the surrounding tissues, the surface mucosa is usually undamaged, sometimes ulcers can be seen, it can metastasize to the paratracheal lymph nodes or distant organs, such as liver and bone, and biopsy can make a definite diagnosis.FDG-PET shows enhanced radioaggregation and increased SUV values [6]. Mucinous epidermoid carcinoma (MEC): it occurs in about 50% of young people under 30 years of age, is less common, and accounts for only 0.1% to 0.2% of pulmonary malignancies, and originates from tiny salivary glands in the airways. Most of them occur in lobes or segments of bronchi, and the carcinomas grow aggressively, but most of them grow slowly and have a long course. Depending on the degree of differentiation of MEC, FDG-PET shows low to high radiolucency enhancement with mildly increased SUV values [6]. FDG-PET shows a low degree of radiolucent enhancement and a mild increase in SUV value [6]. III. Lesion sites Referring to the literature [3], the authors classified the CT findings of airway tumors occurring in the central type into four types: intraductal, mural, extraductal and mixed types. (1) Intraductal type: the tumor appears as a polyp or nodule protruding into the lumen, with a tip attached to the duct wall and narrowing the lumen. The tumor originates from the mucosal epithelium and glandular tissue of the trachea and grows infiltratively along the wall of the trachea, thickening the whole wall, the whole circumference or the near whole circumference and narrowing the lumen of the trachea. The tumor grows outside the duct wall and has an irregular or lobulated outline. It can compress the lumen and cause narrowing of the lumen, and the extra-luminal growth often involves the mediastinum and cervical structures. ④Mixed type: It can be a combination of any two or more lesions of the first three forms. IV. Stenosis degree of central airway lesions Referring to the foreign grading method of airway stenosis [1], the authors proposed a combination of descriptive grading and numerical grading to classify the degree of stenosis at the narrowest part of the airway as mild (grade I), moderate (grades II and III), severe (grade IV), and very severe (grade V), as shown in Table 2, which coincides with the shortness of breath scale (1, 2, 3, and 4 points) [9]. Patients with mild stenosis may have no obvious clinical symptoms, while moderate stenosis may present with cough, chest tightness and shortness of breath, while severe stenosis may present with significant dyspnea, and very severe may be at risk of asphyxia at any time. The degree of these stenoses is related to the shortness of breath score, Table 2 Criteria for determining the degree of airway stenosis [2] Grading Degree of stenosis of the diameter of the tube (%) Ⅰ ≤25 Ⅱ 26-50 Ⅲ 51-75 Ⅳ 76-90 Ⅴ 91-100