Suboccipito-Retrosigmoidal Approach for Resection of Acoustic Neurinoma [Indications] (1) Auditory neuroma growing towards the pontocerebellar horn of the cerebellum. (2) Acoustic neuroma located in the ossicular canal of the internal auditory canal. Contraindications】 No special contraindications. Preoperative preparation】 (1) See “Neurosurgery” for preoperative preparation. (2) If the giant auditory neuroma has caused the increase of intracranial pressure, the ventricle should be continuously drained 2-3 days before surgery. Anesthesia and position】 Mostly general anesthesia with intubation is used. The airway must be kept open during the operation. Sitting position or lateral prone position (park-bench position) with the affected side upward. The head is fixed with a three-peg head frame. The skin, subcutaneous tissues and muscle layer are incised to reach the surface of the occipital bone and the incision is retracted with an automatic retractor. (2) Craniotomy: make a hole in the occipital bone below the superior collar line and enlarge the bone window depending on the size of the tumor: the upper border shows the lower edge of the transverse sinus, the outer border is near the posterior edge of the sigmoid sinus and down to the foramen magnum of the occipital bone. (3) Flap-shaped or radial incision of the dura mater, with a silk wire suspension to hold it open. The cerebellar hemispheres are retracted medially with a cerebral pressure plate, and the cerebellar medullary pool and the arachnoid membrane of the pontine pool are torn open to drain the cerebrospinal fluid and reduce the intracranial pressure. The cerebellar bridge is explored along the lateral aspect of the posterior cranial fossa toward the cerebellum. When approaching the inner ear foramen, the tumor can be found. Auditory neuromas are mostly grayish-purple or grayish-brown in color, with tumor regression and yellowish-brown in case of cystic change. Sometimes the tumor surface adheres to the arachnoid membrane or forms a cyst by the accumulation of cerebrospinal fluid (Figure 1B). (4) Removal of tumor: Generally, the tumor envelope is electrocoagulated first, and then the tumor is cut longitudinally, and the intracapsular tumor is removed by suction, biopsy forceps or scraping spoon (Figure 2). If there is more bleeding when resecting the tumor, the tumor can be freed from the periphery of the tumor first and enter the lower pole of the tumor. The small blood supply arteries on the inner side and upper pole are cut off after electrocoagulation one by one, and then continue to resect the tumor from the capsule. The more tumor tissues are removed from the capsule, the better the collapse of tumor envelope, which is beneficial to tumor resection. (5) Separate the lower pole of the tumor from the 9th, 10th and 11th cranial nerves, and then free the inner side of the tumor from the upper pole. When freeing the superior pole, the branch from the superior cerebellar artery to the tumor must be electrocoagulated first and cut off. Then the tumor is separated from the trigeminal nerve. If the tumor has protruded upward into the fissure of the cerebellar curtain, the tumor is carefully pulled downward for resection in pieces. The tumor envelope is pulled outward to see the facial nerve located in front and below the tumor, and the facial nerve is freed from the tumor envelope to near the internal auditory foramen (Figure 3). Then the tumor is cut off from the inner ear foramen and the tumor is removed (Figure 4). The tumor tissue remaining in the inner ear foramen can be removed by grinding the posterior wall of the inner ear canal with a high-speed microdrill to reveal the part of the tumor inside the inner ear canal without damaging the facial nerve (Figure 5). After the tumor is basically removed from the capsule, it is sometimes extremely difficult to separate the tumor because its inner side is closely adhered to the brainstem or embedded in the brainstem, so if it is forcibly peeled off, it will aggravate the brainstem injury. If the tumor has been resected from the capsule or embedded in the brainstem, it may be extremely difficult to separate the tumor. The adhesion of cystic auditory neuroma with brainstem and cranial nerve is tight and the interface is unclear, so it especially needs careful identification during surgery. (6) Carefully stop the bleeding, flush the wound, place a drainage tube in the tumor bed and perform closed drainage. If the total tumor resection goes smoothly, the dura mater can be sutured and the muscle layer, subcutaneous and skin layer can be sutured layer by layer. (7) If the tumor is huge and exceeds the midline, double incision surgery can be used. That is to make a midline incision in the posterior cranial fossa and perform extensive decompression in the posterior cranial fossa. Removing the tumor from the lateral incision is conducive to the full exposure and resection of the tumor. It is also easy to decompress after surgery, so that the postoperative period is more stable. (1) Do not tear the tumor blood supply artery when exploring and freeing the tumor, because the artery retracts after tearing, and because of the deep surgical field, the hemostasis is very passive, and it is easy to injure the important cranial nerves and brainstem by mistake. (2) Do not damage the brainstem and brainstem blood supply arteries to avoid brainstem infarction and brainstem edema after surgery, resulting in serious consequences such as brainstem failure. (3) Pay attention to protect the 5th and 7th cranial nerves from injury. The 9th, 10th and 11th cranial nerves should be protected with cotton sheets at the subxiphoid level. (4) Stop bleeding thoroughly to avoid complications of postoperative hematoma. Postoperative management] (1) See the postoperative management of “cranial surgery”. (2) Closely observe changes in consciousness and vital signs to detect postoperative complications of hematoma in a timely manner. (3) Strengthen the care. If there is simultaneous injury to the trigeminal nerve and facial nerve, protect the affected eye with an eye shield to prevent exposure keratitis and corneal ulceration. In case of linguopharyngeal and vagus nerve injury, prevent pneumonia and asphyxia caused by misaspiration. (4) Keep the ventricular drainage open if it has been performed before surgery, and prevent complications of meningitis. Main complications] (1) Meningitis: postoperative local compression bandage is insufficient, forming pseudocysts and secondary infection. (2) Facial nerve injury: with the application of microsurgical techniques, this complication has been significantly reduced. (3) Brainstem injury: direct surgical injury or injury to its supplying artery. (4) The 9th and 10th cranial nerve injury. (5) 5th and 7th cranial nerve injury causing corneal ulceration.