To explore the microsurgical treatment techniques for large auditory neuromas. Methods Using microsurgical techniques, 38 cases of large auditory neuromas were surgically resected using a posterior transseptal approach to the inferior occipital sigmoid sinus, and the patients were closely followed up after surgery. Results: 35 cases (93%) were completely resected, 2 cases (6%) were sub-total resection, and 1 case died. The facial nerve anatomy was preserved in 33 cases (90%), and the facial nerve was reconstructed in 3 cases and failed to be preserved in 2 cases. Conclusion Microsurgical treatment of large auditory neuroma is the treatment of choice. Clinical data 1. General data There were 38 cases in this group 18 male and 20 female. The minimum age was 19 years old, the maximum age was 60 years old, the average age was 44 years old, the shortest disease duration was 6 months, the longest was 5 years, the average was 1.5 years. The tumors were located on the left side in 18 cases and on the right side in 20 cases. The diameter of tumor was 4-6 cm in 28 cases and more than 6 cm in 10 cases. 2. Preoperative symptoms and signs: hearing loss in 5 cases (13%), hearing loss in 33 cases (87%), vertigo in 4 cases (10%), facial palsy in 3 cases (8%), and limb ataxia in 9 cases (23%). Visual acuity was decreased in 20 cases (52%). Signs of cranial nerve involvement: VIII nerve (hearing impairment in 38 cases), VII nerve in 3 cases, V nerve in 5 cases, and optic papilledema in 31 cases. Cerebellar signs were found in 19 cases. 3. Diagnosis: MRI plain + enhancement was performed in all cases. The large auditory nerve reported in this paper was measured by MRI as the standard (≥4.0 cm) or more. METHODS All cases in this group were treated with suboccipital craniotomy and microsurgical resection of the tumor via the internal auditory tract approach after the sigmoid sinus. All suboccipital (postauricular) inverted hook-shaped incisions were made, and bone flap craniotomy was performed in 31 cases [1,2 ], and the bone flap was reset after surgery. The tumor was resected first by intracapsular resection, then by sequential resection of the upper and lower poles of the tumor wall in blocks, and finally by grinding open the posterior wall of the internal auditory canal to remove the tumor from the internal auditory canal. The surgery was performed with general anesthesia intubation, lateral recumbency, head frame fixation, 20° of chest forward, 30° of head down, and 10° of head down to the lateral side, with the external occipital ridge as the highest point. (The advantage of this position is that it is easy to reveal the skull, easy to mill the bone flap with a milling knife, and the cerebrospinal fluid is not easy to flow empty, and there is no intracranial air.) The incision was made as a “barb-shaped incision” behind the ear, with the upper transverse incision 1 cm above the transverse sinus and 5-6 cm down the occipital ridge along the superior collar line. (31 out of 38 cases with open flap, the flap was repositioned and fixed with titanium nail.) The transverse and ethmoid sinuses need to be exposed. If the mastoid airspace is opened, it should be closed with bone wax. The dura mater should be cut. Before cutting, a “1” incision should be made in the dura mater, and a cerebral pressure plate should be put in to gently press the cerebellum and release the cerebrospinal fluid to make the cerebellum retracted and prevent the cerebellum from being damaged by the high intracranial pressure when the dura mater is cut. Automatic pull hook gently reveals the upper pole of the tumor, electrocautery the tumor envelope and cut it open and then do intracapsular resection first, use ultrasound to fragment the suction gently and choose lower power. For larger bleeding, bipolar electrocoagulation is used. After intracapsular resection of the tumor, the cystic wall is then resected in pieces, and the tumor cystic wall must be lifted carefully and gently, and the cerebellar side or brainstem side is protected by cotton sheets and sponges. The tumor envelope should be peeled off in the process of easy first and then difficult. If there is difficulty in stripping or bleeding, gelatin sponge and cotton sheet can be used to stop bleeding. During the operation, the cyst wall should be removed while peeling. The lower pole of the tumor is often surrounded by branches of the anterior inferior cerebellar or posterior inferior cerebellar artery. Except for the branch of small artery which is determined to penetrate into the tumor and can be electrocoagulated, the other arteries must be protected. If the thicker bypass artery on the capsule wall is blindly treated, it may cause partial ischemia of the brainstem. Results The extent of tumor resection: 35 cases of total tumor resection [3] (including 28 cases of 4-6 cm tumor and 7 cases of more than 6 cm) and 3 cases of near total resection (more than 99% of tumor body resection), all of which were more than 6 cm tumor. There was one case of postoperative death. The facial nerve was preserved anatomically in 33 cases (90%) [4] (including 28 cases containing tumors of 4-6 cm and 5 cases of 6 cm or more), and the facial nerve was reconstructed in 3 cases and failed to be preserved in 2 cases, the latter 5 cases being all those larger than 6 cm. The last 5 cases were all larger than 6 cm. The follow-up period ranged from 6 months to 3 years. Hearing recovery was not seen in all 38 patients after surgery. The recovery of facial palsy was 85% at 1 year after surgery (able to close the eyes and open the mouth lightly with force), and 90% of visual acuity was restored, ranging from 0.2 to 1.0 better than before surgery. Discussion In the surgery of auditory neuroma, preservation of the facial nerve is most important. The posterior approach to the inferior sigmoid sinus is suitable for any size of tumor, and the surgical result depends on the size, texture, cystic change, growth direction, adhesion to the nerve, and the experience of the surgeon. The relationship between the nerve and the tumor has a certain pattern, which is located in the upper 20%-40% of the anterior part of the tumor, 31%-80% of the lower part of the anterior part, 20% of the anterior part and 5% of the anterolateral part. It is also important to protect the facial nerve when removing the tumor from the internal auditory canal. After the tumor capsule wall is completely separated from the brainstem, the dura mater is separated from the tumor capsule wall along the upper edge of the internal auditory canal, and the width of the posterior wall of the internal auditory canal is determined. After grinding the posterior wall of the internal auditory canal, the dura mater of the internal auditory canal is cut longitudinally, and after removing part of the tumor of the internal auditory canal, the tumor is completely separated from the surface of the facial auditory nerve after turning up the tumor capsule and identifying the position of the facial auditory nerve. The interface is not easy to recognize, especially when the tumor is soft. The anatomical preservation of the facial nerve is the basis for obtaining the ideal facial nerve function, and it is important to identify the pathological relationship between the nerve and the tumor. First, the facial nerve root (brainstem end) can be identified according to the normal anatomy. When removing the lower pole of the tumor and the medial capsule wall, attention should be paid to the choroid plexus that protrudes from the lateral foramen of the four chambers to the subarachnoid space, and the root of the facial nerve is located in the lower lateral part of the plexus. The facial nerve was confirmed to be the facial nerve and then the tumor capsule wall was turned to the lateral side to separate it. Although the initial segment of the facial nerve was fixed and never adhered to the tumor capsule wall, the facial nerve could be compressed, elongated and squeezed in different directions at the inner ear gate, which was sometimes extremely difficult to distinguish from the tumor capsule wall. In this group of cases, most of the facial nerve was located in the ventral median of the tumor, followed by the facial nerve running up the brainstem, and the adhesion site was located in the inner superior pole of the tumor. In the other case, the facial nerve traveled downward in the direction of the brainstem and adhered to the inner lower pole of the tumor. The authors used to remove the tumor in the internal auditory canal last to prevent separation of the dura mater with the tumor adhesion at the inner ear gate and the gravitational effect of the tumor and pulling the facial nerve. In conclusion, anatomical preservation of the facial nerve is the basis for preserving the function of the facial nerve. The authors summarized the method of anatomical preservation of the facial nerve as follows: firstly, identify the brainstem end, the end of the internal auditory canal and the distal and proximal ends of the facial nerve adherent to the tumor, then separate the facial nerve from the distal and proximal ends along the facial nerve course toward the adhesion of the facial nerve to the tumor wall, gradually turn over and sharply separate the tumor wall until the tumor wall adherent to the facial nerve is completely removed. However, anatomical preservation of the facial nerve is not the same as having complete facial nerve function. The reasons for facial nerve palsy of different degrees even after facial nerve anatomical preservation are: 1. direct traumatic pull on the facial nerve; 2. affected blood supply to the facial nerve; 3. degeneration of the facial nerve due to tumor compression and pull by the tumor because it is too large. The authors appreciate that the measures to avoid facial nerve injury are: 1. when separating the facial nerve from the tumor adhesion, the tumor should be pulled instead of the facial nerve; 2. insist on sharp separation; 3. do not pull the cerebellum excessively to avoid indirectly pulling the facial nerve; 4. preserve the blood supply of the facial nerve as much as possible; 5. avoid thermal injury from the electrocoagulator.