Central airway stenosis is a narrowing of the trachea, the right and left main bronchi and the right middle segment bronchi due to various types of pathologies. They often require urgent intervention because they may cause significant clinical symptoms due to significant impairment of pulmonary ventilation. They can be broadly classified as benign or malignant stenoses according to their etiology. Benign stenoses are more difficult to manage than malignant stenoses. This is mainly due to the long survival period of patients, who and their families often hope to obtain long-term symptomatic relief. At the same time, long-term complications of treatment are more likely to arise. In contrast, treatment of adolescent patients also requires consideration of growth and development. In addition, patients and families have higher expectations of outcome than in malignant disease, and have difficulty accepting the serious near- and long-term complications associated with surgery. Therefore, the management of benign central airway stenosis is a difficult area in the field of interventional respiratory pathology. The causes of benign central airway stenosis are numerous and can be broadly classified into infectious factors, cartilage disease, granulation tissue formation, foreign body stenosis, granulomatous disease, benign tumors, external pressure stenosis, and other causes of central airway stenosis. In China, tuberculous stenosis is more common. Types of benign central airway stenosis According to the mechanism of benign central airway stenosis, it can be roughly divided into benign proliferative stenosis, benign scar constriction stenosis, foreign body stenosis, dynamic stenosis, and external pressure stenosis. Because of the specificity of foreign body stenosis, it is not included in the discussion of this article. Benign proliferative stenosis is a narrowing of the lumen due to hyperplasia of the canal wall or mucosal tissue. Benign scar constrictive stenosis is caused by damage to the canal wall after infection, trauma, or surgery, which causes proliferation of fibrous tissue, forming a fibrous ring around the tracheal and bronchial walls, and later contraction of the fibrous tissue, resulting in luminal narrowing. Scar constrictive stenosis can be classified into mesh-like stenosis, bottleneck-like stenosis and mixed stenosis according to its microscopic manifestation. Dynamic stenosis is due to the loss of support function of the central airway cartilage, which cannot maintain the patency of the airway. Interventional respiratory treatments for benign central airway stenosis and their characteristics: The traditional treatment for benign airway stenosis is mainly cuffed tracheal and bronchial resection with airway reconstruction. However, surgical resection can be difficult to perform in the following cases. First, the stenotic segment is too long, and it is generally believed that the maximum length of tracheal resection should not exceed 6 cm, otherwise the anastomosis is too high tension and difficult to heal; second, stenosis after tracheotomy; third, stenosis after airway burn or trauma; fourth, tracheal and bronchial softening, which is extensive and involves multi-site stenosis, so resection is also very difficult; fifth, external pressure stenosis, where bronchiectomy alone does not solve the problem and the compression should be The cause should be removed. According to the current treatment of airway stenosis, we can divide it into two categories: tissue growth reduction and airway dilation. The methods of decompression include direct excisional decompression, thermal decompression, cold decompression, radiological decompression, and chemical decompression. For benign disease treatment, thermal and cold therapy are the main options. Thermal therapy has the advantage of fast onset of action, but is prone to airway perforation and fire in the airway, and there is also a risk of electrical injury if electroablation is used. More critically, thermal therapy can promote scar growth and is therefore not the best choice for fibrous scar stenosis. The disadvantage of cold therapy is that it is slow to take effect, and freezing requires a period of time before cell necrosis occurs, making it unsuitable for emergency relief of airway stenosis. However, it has the advantage of being less prone to perforation, no electrical trauma and no intra-airway fires. Another great advantage for benign lesions is the improvement of collagen synthesis and differentiation of keloidal fibroblast (scarring fibroblasts) to normal fibroblasts, thus reducing the proliferation of scar tissue. Direct dilation of the lumen is mainly used for stenosis after fibrous scar contraction and external pressure stenosis and consists of balloon dilation, direct rigid bronchoscopic dilation and placement of an airway stent. Balloon dilation is easy to perform and can be done via a bendable bronchoscope [6]. However, its dilating effect is short-lived, prone to recurrence, and requires the cartilage structure and function of the airway to be intact. However, it is more suitable for the treatment of benign lesions because of its few long-term complications. Direct dilatation of the stenosis is performed by rigid bronchoscopy, but this approach is not long-lasting, is difficult to treat tougher scar tissue, and tends to injure the airway wall. It is not generally used for airway dilation in benign stenoses. Airway stenting is a very important treatment for airway stenosis, with the advantage that it has long-term efficacy and is more suitable for cases with incomplete cartilage structure and function. However, its operation is relatively complex and, more importantly, due to the long-term placement of foreign bodies, it has many long-term complications, mainly causing granulation and thus new stenoses. The current stents are divided into three categories according to the materials used for their production, namely, metal stents, silicone stents, and silicone metal composite stents. Metal stents are mainly used in China at present. Metal stents do have many advantages, for example, they are not easily displaced after placement, they do not reduce the internal diameter of the lumen, and discharge of secretions is relatively easy. Most of them do not require the use of a rigid microscope when they are placed, and most of them do not require airway dilation first, so they are better tolerated by patients. However, metal stents are difficult to remove after placement, especially after prolonged placement, and rigid bronchoscopy is required. Because of the poor histocompatibility of metal, most patients will develop new granulation tissue after prolonged placement, which will lead to luminal narrowing again, and such narrowing is often more difficult to deal with than the original disease, especially when the granulation tissue grows inside the stent. The advantage of silicone stents compared to metal stents is that they are easy to remove, but of course they also need to be removed by rigid bronchoscopy. It is more histocompatible, so there is less risk of granulation tissue proliferation. However, the disadvantage of silicone stents is that they have thicker walls and can therefore reduce the lumen inner diameter, thereby increasing airway resistance. It can also lead to difficulties in discharge of secretions and can be prone to displacement. It is also relatively difficult to place using a rigid scope. Even so, if stenting is an option for benign lesions, silicone stents should be preferred. Metal stents should only be considered when other treatments have been exhausted and the airway stenosis cannot be resolved. It is very unfortunate that silicone stents are not yet available in the domestic market, which creates great difficulties in the treatment of many patients and is one of the reasons why benign diseases are commonly treated with metal stents in China. There is a lack of clinical control studies on whether composite stents made of metal materials and silicone materials are suitable for the treatment of benign lesions. In the future, we expect that as technology advances, materials with better histocompatibility will be developed or drug-eluting stents suitable for placement in the airway will be developed, thus avoiding the shortcomings of current stents, especially metal stents, and reducing or avoiding long-term complications, thus providing a better treatment for benign central airway stenosis. Principles for the selection of treatment for benign central airway stenosis: Benign stenosis is more difficult to deal with than malignant stenosis. In addition to relieving the clinical symptoms of airway stenosis, more attention should be paid to its long-term prognosis, and long-term complications from treatment should be avoided as much as possible. Different treatment options are available for different types of stenosis: 1. Proliferative stenosis: laser, ablation, APC, freezing and direct scleroscopic ablation can be used. If it is a sparing benign tumor, all these methods can be used. However, if the lesion is located in the trachea, thermal therapy or direct scleroscopic reduction is more appropriate for relatively rapid relief of airway stenosis. For granulation tissue hyperplastic stenosis, especially if the granulation tissue has been growing for a long time and the tissue is relatively tough, scleroscopic resection may be difficult and therefore thermal ablation or cryotherapy should be used. In order to avoid possible damage to the canal wall or even perforation caused by thermal treatment, we often use thermal treatment to remove most of the granulation tissue first, and use cryotherapy for the base of the lesion to avoid perforation on the one hand, and avoid thermal treatment to damage the mucosa and submucosa tissue on the other hand to prevent further stimulation of granulation tissue proliferation, which is beneficial to reduce recurrence. In addition, since cartilage is not sensitive to cold injury, the use of cryotherapy can also prevent damage to cartilage and prevent secondary power stenosis. 2. Scar contracture stenosis: Scar contracture stenosis is due to the presence of a fibrous ring around the lumen, and the contracture of the fibrous ring leads to narrowing of the airway. If the stenosis is to be resolved, the fibrous ring can be disrupted by applying a radial external force in the lumen. Direct airway dilation is generally used, which mainly includes balloon dilation, placement of stents and direct dilation using a scleroscope. For mesh-like stenosis, balloon dilation is preferred, and most patients achieve long-term relief with a single dilation, with few recurrences. Some investigators have treated dilatation with balloons filled with liquid rhenium 188 and found to improve the prognosis of refractory benign airway stenosis. For bottleneck-like stenosis, balloon dilation is much less effective than for mesh-like stenosis, but it should still be tried first. With some lesions dilated over time and several times, the scar of the stenotic segment is stabilized and does not continue to contract. Although time-consuming and laborious, it is worth trying compared to the long-term complications associated with the placement of stents, especially metal ones. If other methods do not work, stents should be used. A silicone stent is preferred and can be removed when the scar is stable and the contracture has stopped. Although metal stents can also be removed, they should be avoided if possible due to their poor histocompatibility. In the case of mixed stenosis, the above treatment options are required depending on the situation. Thermal treatment should be avoided as much as possible for scar contracture stenosis, which may cause perforation on the one hand and further stimulate granulation tissue proliferation and aggravate the stenosis on the other. 3. External pressure stenosis: Removal of the cause of external pressure stenosis is the best treatment, but if the external pressure cause cannot be removed or if the airway stenosis is too severe to be removed by other methods, interventional respiratory pathology can be used for treatment. The treatment of external pressure stenosis also requires the application of radial external forces in the airway lumen, but the principles used are completely different from those of scar contracture stenosis. The main treatment for this type of stenosis is the placement of a stent. 4. Dynamic stenosis: In dynamic stenosis, stenting is the only treatment because of the loss of cartilage support in the airway. Because of the need for lifelong placement, silicone stents should be preferred and metal stents should be avoided whenever possible. In conclusion, benign central airway stenosis is a difficult area of treatment in the field of interventional respiratory pathology. The choice of treatment should be more focused on its long-term efficacy and long-term complications. The appropriate treatment should be selected correctly for the type and characteristics of different stenoses. Long-term adverse consequences due to improper choice of treatment should be avoided as much as possible.