[Abstract] Objective To investigate the clinical efficacy and complications of applying microsurgery to resect large pontocerebellar horn tumors. Methods One hundred and twenty-two cases of large pontocerebellar horn tumors (81 cases of auditory neuroma, 37 cases of meningioma, 2 cases of trigeminal neuroma, and 1 case of cholesteatoma) were resected by microsurgical techniques, and the clinical results were analyzed. The results were: 68 cases of 81 auditory neuromas were completely resected, 13 cases were sub-total resection; 25 cases of 37 meningiomas were completely resected, 10 cases were sub-total resection, and 2 cases were partial resection; 2 cases of trigeminal neuromas were sub-total resection. There were 12 cases of postoperative facial palsy or aggravation of facial palsy, and 2 cases of improvement compared with preoperative; 16 cases of hearing loss or aggravation, 2 cases of postoperative facial numbness, and 2 cases of improvement compared with preoperative; 1 case of death after reoperation for cerebral hemorrhage. Conclusion Large pontocerebellar horn tumor surgery is challenging, and good microsurgical skills can improve the total resection rate and reduce complications. Tumors in the pontocerebellar angle (CPA) are commonly known as auditory neuroma and meningioma, and the main treatment for tumors larger than 3 cm CPA is surgical resection. In our department, 22 cases of CPA tumors were resected by microsurgery since May 2002, and the preliminary report is as follows: Data and methods 1, clinical data Among the 122 cases, there were 9 males and 13 females, aged 18-84 years, average 49.9 years, 81 cases of auditory neuroma, 37 cases of meningioma, 2 cases of trigeminal neuroma, 1 case of cholesteatoma, tumor diameter 3.5-6.5.0, average 4.18 The tumor diameter ranged from 3.5 to 6.5.0 cm, with an average of 4.18 cm. The clinical manifestations were headache in 14 cases, accompanied by trigeminal neuralgia in 2 cases; tinnitus and hearing loss in 16 cases (including deafness in 4 cases); facial numbness in 9 cases; facial palsy in 6 cases; difficulty in tongue and throat choking in 7 cases; loss or weakening of gag reflex in 14 cases; dizziness and ataxia in 15 cases; incontinence in 2 cases; unilateral limb weakness in 8 cases, inability to take care of themselves in 4 cases, and bedridden in 1.5 years in 1 case. All the cases were diagnosed by CT scan and MRI scan plus enhancement examination before surgery, and there were 5 cases with hydrocephalus. 2.Surgical method All of the cases were performed under general anesthesia in the trachea, and two of them underwent extraventricular drainage first because of heavy hydrocephalus. The dura was incised and suspended with a “ten” incision. In case of high cranial pressure, mannitol should be applied beforehand or supplemented with hyperventilation, and as long as there is considerable space for operation, the occipital pool and other brain pools should be opened first to release cerebrospinal fluid and lower cranial pressure to facilitate operation. The tumor should be revealed by gently pulling it backward with an automatic retractor. For cystic tumor, the cystic fluid should be extracted by puncture to make the tumor smaller and easier to operate. For patients with auditory neuroma, first electrocautery the blood vessels on the surface of the tumor, cut open longitudinally, and remove the tumor by “heart gouging” inside the envelope, stopping bleeding while gouging to reduce the volume of the tumor. The patient should be careful not to dig through the tumor wall, so as not to damage the brainstem and facial nerve by blind clamping. After the tumor is reduced, the posterior lower part of the tumor wall is picked up with tumor removal forceps, and the tumor wall is pulled toward the central position of the bone window to reveal the posterior group of cranial nerves, which is carefully separated from the tumor and protected with cotton sheets. When separating the tumor wall envelope, we should always pay attention to observe and understand the facial nerve. The facial nerve is often displaced by compression and becomes thin, so we should not just cut the longitudinal fiber cords or membranous tissue on the surface of the envelope, especially in the front and bottom of the tumor. If possible, intraoperative electrophysiological monitoring is preferable to preserve the facial nerve as much as possible. For meningioma, the same method is used to reveal the surface of the tumor, and “carpet” electrocautery can be used to cauterize some of the tumor vessels, which can partially reduce the size of the tumor. At the base of the tumor, the tumor is cut by electrocautery and slightly pulled by a brain press while leaning against the rock bone or the canopy to sever the tumor blood vessels and fibrous cords at the base. After reaching a certain level, the tumor will be cut, and the tumor in the exposed area will be excised in pieces, at this time, the bleeding of the tumor will not be too serious. When the tumor wall (superficial layer) is thin, the tumor wall will be pulled toward the center, and the cerebellum or brainstem will be padded with a package, and the blood vessels on the surface of the tumor will be electrocautery, at this time, the arachnoid membrane on the surface of the tumor should be pushed away before operation, so as not to damage the blood vessels and nerves across the surface of the tumor. According to the size of the tumor, when there is a certain gap we should first separate the posterior group of cranial nerves with cotton sheets to protect them, and when they reach a certain depth, protect the facial auditory nerve and trigeminal nerve by the same method. When the tumor is near the anterior inferior wall, the tumor wall should be turned over from the cerebellar direction to the rock, so that the cranial nerves can be clearly pushed away before electrocautery resection. When the tumor is near the brainstem, it should be separated by a cotton piece first, then carefully divided into small pieces to avoid damaging the brainstem and the blood vessels crossing the surface of the brainstem, and finally remove the tumor tissue at the base to achieve total resection. The tumor cavity should be flushed, and the dura should be tightly sutured to prevent cerebrospinal fluid leakage. Results 1. 68 cases of 81 auditory neuromas were completely resected, 13 cases of sub-total resection; 25 cases of 37 meningiomas were completely resected, 10 cases of sub-total resection, and 2 cases of partial resection; 2 cases of trigeminal neuromas were sub-total resection; 1 case of cholesteatoma was completely resected. 2. 20 cases were cured or discharged well after surgery, 1 case of myelopathy and 1 case of mild paralysis of the lower body occurred after surgery due to infection, and 1 case of death after re-operation for hematoma occurred. 3. Complications or complications occurred after surgery The patients were discharged from the hospital after surgery due to infection, and one case died after surgery. One case died after discharge. 4. Improvement of preoperative symptoms at discharge: headache disappeared, facial palsy improved in 2 cases, facial numbness improved in 3 cases, hearing improved in 2 cases, dysphagia and choking improved in 4 cases, obstructive hydrocephalus was discharged in 5 cases, and ataxia improved in 3 cases. The tumors in the pontocerebellar angle (CPA) are mostly benign tumors such as auditory neuroma (80%) and meningioma (6-13%), which grow slowly and insidiously, and the tumors are mostly large in size by the time the clinical manifestations are obvious. Thorough preoperative evaluation and surgical planning, rigorous and precise surgical operation skills are the keys to successful surgery. First of all, the systemic condition should be assessed, such as preoperative choking, cranial hypertension, bedridden for a longer period of time, the patient is often malnourished, weak, anemic, etc. should be corrected with supportive therapy. In patients with hydrocephalus and prolonged vomiting, attention should be paid to the water-electrolyte balance. A patient with CPA meningioma, female, 56 years old, with a tumor diameter of 6.3 cm and severe hydrocephalus, had been unable to take care of herself for nearly 2 years and bedridden for more than 1 year, accompanied by urinary and fecal incontinence, choking and coughing after eating. After admission, the patient was treated with supportive therapy to correct anemia and electrolyte disturbance. The tumor was completely excised without any postoperative complications, and his cranial nerve function gradually recovered and he was discharged from the hospital four weeks after surgery. In addition to the evaluation of the general condition, the preoperative evaluation of the CPA tumor is more important. Due to the special nature of the anatomical location of CPA tumor, the tumor was huge, and there were other special features in the treatment of brain tumor and its outcome. Firstly, the degree of tumor resection should be evaluated, secondly, the preservation and functional recovery of facial nerve should be evaluated, and thirdly, the recovery of other neurological functions before and after surgery should be estimated. The patient’s symptoms and signs appear in sequence and severity, and the operator’s surgical skills are used as the basis for assessment. Also the patient’s family’s ability to tolerate possible complications or adverse consequences should be fully considered before making the surgical decision. The requirements for the operator are: (1) a rich foundation in microscopic anatomy; and (2) microsurgical skills in total resection of tumor facial nerve anatomy and function preservation (2). The surgical plan is made on the basis of the above assessment based on the imaging data, the nature, size and location of the tumor in relation to the brain, nerves and blood vessels in the CPA area. For those who have obvious hydrocephalus or huge tumor, it is estimated that there is difficulty in revealing the tumor, extraventricular drainage should be performed in stages or at the same time, which can remove the further damage of hydrocephalus to brain function and facilitate the CPA tumor resection operation. With regard to the choice of surgical approach, many scholars have similar views, and the commonly used ones are (1) posterior suboccipital sigmoid sinus approach; (2) vagus-cerebellar curtain approach; (3) vagus-suboccipital approach; (4) inferior temporal-cerebellar curtain approach; and (5) combined temporo-occipital superior-inferior curtain approach. They also introduced in detail the indications and advantages of the various approaches and the operation points. Some scholars have also suggested that the posterior suboccipital sigmoid sinus approach can fully reveal the nerves and blood vessels in the CPA area and can remove tumors of any size, which is the commonly used approach for CPA surgery [4, 5]. However, it is still necessary to choose the approach according to: (1) the sequence of clinical symptoms and signs to estimate the direction of tumor growth; (2) CT, MRI and even MRA or DSA data to understand the size, growth direction and vascular displacement of tumor; and (3) the familiarity of the operator with various approaches. With thorough and accurate preoperative evaluation and surgical planning, coupled with rigorous and precise surgical skills, high-risk and difficult CPA tumors also achieve satisfactory results. In this case, a 84-year-old female patient with trigeminal nerve sheath tumor, a retired teacher, was treated with gamma-knife one year ago. The tumor gradually increased in size and became cystic until the patient developed significant facial palsy, facial sensory disorder, hearing loss, ataxia, difficulty in tongue and throat, weakness of the deviated muscles, inability to stand and walk alone, and loss of life ability. After a thorough preoperative evaluation and surgical preparation, a posterior suboccipital sigmoid sinus approach with a 3-cm bone window was adopted, and the tumor was basically completely resected. Two weeks after surgery, most of the facial palsy was recovered and the patient was able to walk spontaneously. 1 month later, the facial palsy was cured and the patient was walking smoothly and taking care of himself. In conclusion, large CPA tumors are challenging in terms of difficulty and risk, and total tumor resection and neurological function protection are the goals pursued by neurosurgeons.