Since the direction of maxillary sinus mucus transmission and removal is always toward the natural opening of the maxillary sinus, the direction of maxillary sinus mucus cilia removal remains unchanged even with inferior nasal opening, therefore, nasal endoscopic maxillary sinus opening through the middle nasal passage is the basic procedure of maxillary sinus surgery. The surgical treatment of maxillary sinus lesions should first be considered via the middle nasal passage approach, which has the least impact on the physiological function of the maxillary sinus. This procedure can resolve most maxillary sinus problems, but because of anatomic features and limitations of available instrumentation, a transmedian nasal opening is not possible to treat any area of the maxillary sinus. Anatomically, the maxillary sinus resembles a cone with a base above it, creating areas that are difficult to visualize and treat via the middle nasal passage, such as the medial and anterior walls of the maxillary sinus, the odontoid crypt, and the anterior lacrimal crypt. Therefore, some patients require a combined open window or lateral nasal wall dissection surgical approach. For maxillary sinus cysts and maxillary sinus hemorrhagic necrotic polyps, the maxillary sinus opening window through the middle nasal tract can handle most of the lesions, and most of the lesions within the anterior maxillary sinus can be successfully removed by enlarging the maxillary sinus opening window forward appropriately. The normal mucosa should be preserved and minimized during surgery, so that even if there is bone exposed at the lesion, the surrounding mucosa can cover it as soon as possible. Smaller cysts in the anterior and inferior part of the maxillary sinus that cannot be treated via the middle nasal passage can be combined with an inferior nasal opening. To prevent mucosal avulsion of the lateral wall of the inferior nasal tract during window opening, the mucosa can be incised or excised first, and after bony window opening, the mucosa can be treated with a cutting suction device. For single small cysts of maxillary sinus with clinical symptoms, such as located in the anterior and inferior part of maxillary sinus, when the natural opening of maxillary sinus is well drained and there is no obstruction in the sinus orifice nasal tract complex, the cyst can be removed by simply performing an opening of the inferior nasal tract or an opening of the canine fossa. This has less impact on maxillary sinus function. Posterior maxillary sinus polyps often have an enlarged natural opening in the middle nasal passage, and the polyp portion in the maxillary sinus is actually mostly composed of cysts; if the cysts in the sinus cannot be completely removed, recurrence often cannot be avoided. In case of adult patients, the lesion can be removed in combination with an opening of the inferior nasal canal or canine fossa. In the case of children under 16 years of age, the inferior nasal tract or canine fossa approach may interfere with maxillofacial development and should be avoided. In pediatric patients, forward enlargement of the natural opening of the maxillary sinus is contraindicated by the fear of damaging the nasolacrimal duct, and the combined approach may interfere with maxillofacial development; therefore, the management of posterior maxillary sinus polyps in children is tricky, and better and easy-to-use specialized instruments such as bendable endoscopes and instruments are expected. Fungal maxillary sinusitis can be operated through the middle nasal passage in most cases, with a few cases requiring a combined inferior nasal opening. If some of the fungal masses are tightly adhered to the maxillary sinus wall, an elbow suction device can be used for strong irrigation, and if it still cannot be eliminated, the front end of the finer suction device can be folded into a larger angle and placed through the open window to separate the fungal masses from the mucosa and then removed by strong irrigation. The absolute spaciousness of the maxillary sinus opening needs to be maintained after fungal maxillary sinusitis in order to change the low-oxygen moist environment in the maxillary sinus and eliminate the favorable conditions for fungal growth. This opens the maxillary sinus opening backward to the posterior wall of the maxillary sinus, upward to the orbital floor wall, and downward to the superior border of the inferior turbinate. In cases of excessive anterior enlargement of the middle turbinate, it needs to be partially removed to ensure good aeration and drainage of the maxillary sinus. Endorectal papilloma that originates in the maxillary sinus or has extensive tumor involvement in the maxillary sinus requires either a medial wall resection of the maxillary sinus or a combined canine fossa approach or a combined Denker procedure. After medial wall resection of the maxillary sinus, complete resection can be accomplished for most involuted papillomas, or combined with a canine fossa approach if the maxillary sinus is well developed in the alveolar crypt. In this way, there is basically no dead space in the maxillary sinus to be treated. Since the endoscopic excision of the medial wall of the maxillary sinus is slightly complicated, especially for tumors originating in the anterior wall of the maxillary sinus, it is still inconvenient to treat them. Recently, some scholars have adopted the endoscopic Denker procedure, in which a longitudinal incision is made through the lateral nasal vestibule and the bone of the anterior medial maxillary sinus is removed in the nose, completing the same osteotomy range as the Denker procedure, but avoiding the labiogingival incision, which is worth promoting.