Sinus cysts account for a significant proportion of rhinological diseases. Sinus cysts can be divided into mucus cysts and mucosal retention cysts. Sinus mucus cysts I. Pathogenesis and causes Main causes: due to inflammatory changes in the duct; obstruction of the nasofrontal canal caused by trauma to the frontal sinus near the frontal nasal canal, surgery and the growth of osteoma in the frontal sinus. Obstruction of the mucous gland ducts in the sinus and proliferation of the glands are also important causes. Sinus mucus cysts are classified as primary and secondary. The cause of primary mucous cysts is currently unknown. Secondary mucous cysts are thought to be obstruction of the sinus orifice and obstruction of sinus drainage. The frontal sinus has a high chance of being obstructed along the way because of its drainage through the long nasofrontal canal. Therefore, the chance of occurrence is particularly high. Sinus mucus cysts are most commonly found in the frontal and septal sinuses, occasionally in the maxillary sinus, and rarely in the pterygoid sinus. Maxillary sinus mucus cysts are mostly a complication of maxillary sinus surgery and facial trauma. Chronic inflammation, with narrowing and closure of the natural opening due to metaplasia, is also a cause. Sinus mucosal retention cysts II. Pathogenesis The formation is generally believed to be due to obstruction of the plasma mucus gland ducts of the mucosa, accumulation of secretions, expansion of the glands, rupture and fusion of small retention cysts, and formation of larger cysts. Mucosal retention cysts in the sinuses are mostly found in the maxillary sinus, and are not uncommon in the rest of the sinus cavities. III. Clinical symptoms Early stage is mostly asymptomatic. When the cyst swells involving the adjacent anatomical region, the corresponding symptoms appear. If the cyst is pressed into the skull, it can cause headache; if it is pressed into the orbit, it can cause eye symptoms such as proptosis, diplopia, eye pain and visual impairment; if it expands into the pterygopalatine fossa, it can cause difficulty in opening the mouth, facial numbness and swelling pain, etc. Mucosal retention cysts in the sinuses are sometimes ipsilateral head or eye sunkenness, with occasional reports of abnormal sensation or pain. More common are facial numbness or facial pain, painful smothering of the maxillary sinus itself or ipsilateral toothache. IV. Signs The signs of mucous cysts are manifested as limited facial elevation, which can have a cystic sensation or ping-pong feeling when touched. On local examination of the nasal cavity, if the cyst is confined to a single sinus cavity in the early stage and does not expand to the surrounding area, there is no abnormal change in the middle nasal tract on nasal endoscopy; in the later stage, when the cyst expands significantly and presses to the surrounding area, it can be manifested in the middle nasal tract as hooks or sieve vesicles expand and protrude or disappear in the middle turbinate fusion, and the structure of the middle nasal tract is indistinguishable. The diagnosis of sinus cysts is mainly based on sinus radiographs and CT or MRI. CT is the most valuable examination before nasal endoscopy, and MRI shows mucous cysts more clearly. The endoscopic sinus surgery is the simplest, safest and most appropriate method than the previous surgery. The surgery is performed under local anesthesia plus superficial anesthesia. It is performed under direct vision of 0 degree mirror and 30 degree and 70 degree mirror. The principles of surgical management: complete removal of the cystic wall or removal of most of the cystic wall, if possible. Under direct vision, the whole set of sinuses can be opened and the whole sinus opening and even the whole sinus cavity can be clearly observed, so it is very easy to complete the “fistula” of the cyst, while the damage to the surrounding structures is minimal, which reduces the blindness of the operation and avoids the complications such as facial scarring and facial swelling left by the traditional method; it can also deal with the nasal sinus cavity at the same time. It also allows simultaneous treatment of nasal sinus lesions, such as sinusitis, nasal polyps, deviated nasal septum, etc. The surgical procedure for each sinus mucus cyst is the same as the basic method of nasal endoscopic surgery. The main points of nasal endoscopic surgery for different sinus cysts and the principles of surgical management are as follows: 1. Sieve sinus mucus cyst: remove the hooks and open the sieve vesicles under 0 degree microscope. Open the anterior and posterior sieve while opening the bottom wall of the mucus cyst in the anterior and posterior group of septal sinuses and enlarge it as much as possible. 2.Frontal sinus mucus cyst: open the anterior sieve completely, especially after the opening of the nasal mound air space, you can fully open the opening of the frontal sinus, drain the frontal sinus cyst, and expand and bite away the bottom wall of the frontal sinus under 30 degree or 70 degree microscope, and fully “fistula” drainage; if necessary, you can remove the middle turbinate to facilitate the opening and drainage of the frontal sinus. 3.Mucous cyst of pterygoid sinus: open the anterior wall of pterygoid sinus through sieve sinus, if the bone wall is thick and hard, use bone chisel to open the anterior wall. Expose the anterior wall of the pterygoid sinus and open the pterygoid sinus directly for “fistula”. The outer wall and parietal wall of the pterygoid sinus should not be removed blindly to avoid major complications. In the case of suspected meningeal prolapse, the speed of cystic fluid discharge should not be too fast. 4, maxillary sinus mucus cyst: open the maxillary sinus through the middle nasal tract and open and enlarge the natural mouth at 70 degrees with antitension occlusal forceps and mucosal scissors (do not damage the nasolacrimal duct). The cyst wall is removed largely or completely with a suction cutter or forceps at different angles. For cysts that are difficult to remove via the middle nasal tract, the procedure can be completed by drilling a hole in the anterior wall of the maxillary sinus or the inferior nasal tract and placing an aspirator under the display of the endoscope of the middle nasal tract. If none of the above methods work, an anterior maxillary sinus wall opening is performed. Postoperative treatment As with sinus endoscopy, the operation is usually performed with little bleeding and the nasal cavity is only filled with a little soluble hemostatic material, such as hemostatic gauze, hemostatic damask, gelatin sponge, etc. The maxillary sinus cavity, if filled with gauze, should be led out of the middle nasal passage.