1. Pathogenesis: Most tumors originate from the vestibular portion of the auditory nerve, 3/4 originate from the superior vestibular nerve, and a few from the cochlear portion. The tumors originate from Schwann cells, and about 3/4 of the tumors occur in the lateral part of the internal auditory canal and only 1/4 in the medial part. As the tumor grows and enlarges, the tumor may cause enlargement of the internal auditory canal, protruding into the pontine angle of the cerebellum and filling the pontine angle of the cerebellum. The majority of tumors are unilateral, and a few are bilateral; the opposite is true if accompanied by neurofibromatosis. The incidence of bilateral tumors varies, but in general, the incidence of left and right side is almost equal. Pathogenesis: Auditory nerve sheath tumor causes cerebellar pontine horn syndrome, which includes the dysfunction of the vestibular part of the nerve and the cochlea. The symptoms include dizziness and vertigo. Tinnitus, deafness and adjacent cranial nerve irritation or paralysis symptoms, balance disorders, unsteady walking and symptoms of increased intracranial pressure. However, the actual symptoms manifested are not the same, and the symptoms can be mild or severe, which are mainly related to the starting site of the tumor, growth rate, direction of development, size of the tumor, blood supply, and whether there is cystic degeneration and other factors. At the beginning of the tumor, the vestibular part of the patient is the first to be damaged, thus in the early stage, there are thirty or reduced vestibular function on one side and irritation or partial paralysis of cochlear nerve (early symptoms are dizziness, vertigo, tinnitus, deafness, etc.). With the growth of the tumor, the anterior pole of the tumor can touch the sensory root of the trigeminal nerve, causing pain on the same side of the face, hypesthesia of the face, dullness or loss of corneal reflexes, hypesthesia of the tongue and the tip of the tongue, and if the motor root of the trigeminal nerve is also affected, the patient can have weakness of the chewing muscles of the same side of the face, the opening of the mouth and lower jaw is biased to the affected side, and the chewing muscles and temporal muscles atrophy. 3, Pathology: The tumor of the auditory nerve sheath has complete envelope, and the surface is mostly smooth. Sometimes, it can be slightly nodular, and its shape and size depend on the growth of the tumor. Generally, after the clinical diagnosis is established, its volume mostly exceeds the diameter of more than 2.5cm. The parenchymal part of the tumor is grayish-yellow to grayish-red in color, with a firm and brittle texture. The tumor tissue often contains cystic cavities of varying sizes, which contain yellowish transparent cystic fluid and sometimes fibrin clots. The tumor is tightly adherent to the cerebellar adventitia, but generally does not invade the cerebellar parenchyma and is clearly demarcated. The tumor often has a corner that penetrates deep into the internal auditory canal, enlarging its opening, where the meninges are often tightly adherent to the tumor. The facial nerve is closely attached to the medial side of the tumor, and because of the numerous adhesions, it is often impossible to distinguish them with the naked eye, making surgical preservation of the facial nerve a challenge. The histopathological features of auditory nerve sheath tumors can be summarized into four types: (1) small fenestrated arrangement of tumor cells; (2) intertwined bundles of fibers; (3) foci of degeneration and small areas of pigmentation; (4) a fenestrated arrangement of foamy cells and nuclei, with the protofibers of the cells parallel to each other, and the bundles of cells and protofibers intertwined with each other; the protofibrils of the tumor cells in this kind of quasi-polar arrangement are known as the Antioni A-type tissues, and the Antioni B-type tissues are sparsely packed, and the Antioni B-type tissues are sparsely packed. Antioni B-type tissue has a lax reticular nonpolar arrangement, which is also called mixed type. Regardless of the predominance of the tumor composition, the mesenchyme of the tumor is composed of fine reticulated fibrous tissue with few collagenous fibers, which is often accompanied by various degenerative changes, such as steatosis, chromophores, and hemorrhage in small areas.