Large cystic aneurysms of the intracranial vertebral artery and its branch arteries are most commonly known as vertebral artery-posterior inferior cerebellar artery (VA-PICA) aneurysms.Large cystic aneurysms of the VA-PICA have an occupying effect. and a part of the aneurysm has a tendency to gradually increase in size, and when the symptoms of brainstem compression become progressively more severe, interventional therapy fails to relieve the occupying effect, or even the increasing trend of the aneurysm [1], and surgical treatment is needed to relieve the compression. However, there are relatively few large cystic aneurysms that have been reported in this area, and the location of vertebral artery and posterior inferior cerebellar artery is deep and the surrounding tissue structure is important, so the surgical risk is higher, which is a difficult problem in neurosurgical surgical treatment. Diagnosis of VA-PICA large cystic aneurysms Some patients with VA-PICA large cystic aneurysms were diagnosed with dysfunction of the brainstem, cranial nerves, and cerebellum due to the occupying effect, or with insufficient cerebral blood supply as the first manifestation. In the other part, subarachnoid hemorrhage was the first symptom. In the former case, the routine CT and MRI examination can often find occupying lesions, but at this time, further cerebral angiography should be carried out to avoid misdiagnosis. 1.1 Cerebral angiography Cerebral angiography is a necessary examination for analyzing and evaluating intracranial and extracranial cerebral vascular structure, blood flow supply, and aneurysm situation, and the literature reports that large cystic aneurysms of VA-PICA that were treated by surgery underwent whole cerebral angiography. 1.2 Three-dimensional CT angiography (3D-CTA) A clear understanding of the aneurysm and its surrounding structures before surgery and a careful planning of the surgical approach and method are very important for the successful completion of the surgery. 3D-CTA not only reconstructs the images of the major intracranial blood vessels, including the aneurysm, but also reconstructs the bony structure of the base of the skull at the same time, which is very important for the understanding of the aneurysm, the aneurysm-carrying artery, and their relationship with the aneurysm before surgery. Huynh-Le [2] et al. summarized the surgical treatment of five cases of VA-PICA aneurysms, and performed 3D-CTA along with preoperative total cerebral angiography to reconstruct the aneurysm, the aneurysm-carrying artery, and the surrounding cranial bone in three dimensions, and observed the relationship between the aneurysm and jugular venous node and sublingual neural canal, and understood the top of the aneurysm, the pointing of the aneurysm, the structure of the aneurysm neck, and the relationship of the aneurysm with the jugular vein node and sublingual neural canal. After observing the relationship of the aneurysm with the jugular vein node and the hypoglossal nerve canal, and understanding the direction of the aneurysm roof, the structure of the aneurysm neck, and the relationship of the aneurysm with the VA and the PICA, the operation was successfully completed by choosing the trans-occipital condylar fossa, trans-occipital condylar, and the extremely distal and lateral simultaneous concurrently with the cervical laminectomy. 2. Surgical treatment of VA-PICA large cystic aneurysm. Endovascular intervention to embolize the aneurysm has greater advantages than direct craniotomy for posterior circulation aneurysms, especially those with deep location and high risk, but for larger VA-PICA aneurysms, the intervention could not solve the occupying effect of the aneurysm on the brainstem, and at the same time, the intervention also has the risk of aneurysm recanalization, enlargement, and hemorrhage. neurosurgeons should not completely abandon surgery because endovascular intervention can embolize aneurysms, and they should continue to master and continuously improve the surgical treatment of VA-PICA aneurysms. 2.1 Surgical Approach. The optimal surgical treatment of intracranial aneurysms is to maintain the normal flow and volume of blood within the vessel and to exclude the aneurysm from the circulatory system. The surgical approach is determined on a case-by-case basis based on total cerebral angiography and 3D-CTA, as well as the patient’s clinical presentation. The key to surgery is to maintain the blood supply of the affected PICA, so only when the aneurysm is located in the proximal end of the affected PICA, and the contralateral VA is able to supply blood to the affected PICA and the symptoms of brainstem compression are not obvious, then it is feasible to perform proximal clamping of the affected tumor-carrying VA aneurysm so that the aneurysm will be embolized by itself, otherwise, it is necessary to perform neck clamping or isolation, and if the same side of the PICA’s blood supply is compromised, then it is necessary to perform PICA reconstructive surgery. 2.1.1 Direct clipping: After choosing the appropriate access route, direct clipping often achieves better results. matsushima et al [3] reported that 8 cases of VA-PICA aneurysms were directly clipped by transoccipital condylar fossa and transoccipital condylar approach, of which 6 cases were ruptured, 3 cases of Hunt-Hess classification 2, 1 case of 3, 2 cases of 4, 2 cases of unruptured aneurysms, and 2 cases of non-ruptured aneurysms. The aneurysms were about 10 mm in diameter, and two cases were located in the medulla oblongata next to the medulla ventralis midline slope, and there was no rupture of the aneurysm and bleeding during the operation. A cystic aneurysm was found in the medial aspect of the left VA, anterior to the medulla oblongata. Moriuchi et al. [5] reported a case of a large cystic aneurysm of the VA-PICA with facial muscle spasm as the first symptom, which directly compressed the intracranial segment of the facial nerve, and underwent aneurysm-clamping and occupational resection. Clamping and occupying resection surgery, completely relieved the facial muscle spasm, intraoperative aneurysm wall was seen to be very thin, almost rupture, he believed that the sudden appearance of facial muscle spasm is the aneurysm gradually increased in size a warning. 2.1.2 Isolation (Trapping) + vascular anastomosis (bypassoranastomosis). Some circumstances, such as the size and shape of the aneurysm, surgical access, and whether the neck of the aneurysm can be separated, may make direct surgical clamping of the aneurysm very difficult. If the proximal end of the VA or PICA is blocked by isolation, the VA-PICA pathway needs to be reconstructed to rebuild the blood supply vessels for the ipsilateral PICA and to protect the artery supplying the medulla from the PICA to the medulla, so as to prevent the medulla extensa syndrome from occurring. There are many ways of PICA reconstruction, including intracranial and extracranial anastomosis of OA (occipital artery)-PICA, lateral-lateral anastomosis of both PICAs, and anastomosis of PICA-VA, etc. The OA was first used for intracranial and extracranial vascular anastomosis, but the OA is located deep in and is surrounded by the head-clamping muscles, head-half spine muscle, head-most-longest muscle, head-inferior oblique muscle, and head-longest muscle. muscle, cephalic ramus, cephalic ramus inferior, cephalic ramus superior, etc., and has many branches and forms a complex with the veins of its counterparts, which requires penetration of the dura mater after the anastomosis.The anastomosis from PICA to VA is complex to perform and is limited by the length of the portion of the vessel that can be freed by PICA, and this portion of the vessel often sends out a feeding branch toward the medulla oblongata. Kakino et al [6] performed a surgical procedure of VA block and vascular anastomosis of PICA to PICACPICA in six VA-PICA aneurysms using a transoccipital condylar fossa (transcondylar fossa) approach, where the VA was blocked at each end of the aneurysm port, the PICA was blocked at the distal end of the aneurysm port, and a side-to-side anastomosis of PICA on both sides was performed in the posterior part of the medulla oblongata of PICA. -Lateral anastomosis was performed at the posterior segment of the medulla oblongata of the PICA. Postoperatively, the anastomosed vessels filled well and the aneurysms shrunk in 5 cases, 1 case had contralateral distal hypokinesia due to intraoperative cerebral pressure plate compression, and 1 case died due to rupture and bleeding of the intercalated aneurysm in the contralateral VA, while the other 4 cases did not present any postoperative complications. Hamada [7] et al. performed posterior inferior cerebellar artery vascular reconstruction anastomosis with the superficial temporal artery as the graft vessel in 9 cases of aneurysms involving VA-PICA. After exposing the aneurysm intraoperatively, a segment of the superficial temporal artery was isolated one by one (about 5 cm) because of the irregularity of the neck of the aneurysm or its pike-like shape and could not be directly clamped, and then a section of the superficial temporal artery (about 5 cm) was isolated by aneurysm clamping (Trapping) with the superficial temporal VA-PICA anastomosis was performed, i.e., the distal end of the superficial temporal artery was anastomosed with PICA, and the proximal end was anastomosed with VA. Postoperatively, one patient developed partial extramedullary syndrome, but postoperative angiography showed good vascular filling in all patients, and no complications such as hemorrhage or cerebral ischemia occurred. 2.1.3 Intraoperative monitoring measures In order to ensure the safety of the organs and tissues involved in the operative area during the surgical procedure, intraoperative instrumental monitoring to reflect the physiological status of the patient in a timely manner is essential. Commonly used electrophysiological monitoring measures include somatosensory evoked potentials (SEP), motor evoked potentials (MEP), visual evoked potentials (VEP), auditory evoked potentials (ABR), etc. Intraoperative ultrasonic Doppler monitoring, laser ultrasonic blood flow monitoring, and direct measurement of intraoperative intravascular blood pressure can be adopted for intravascular hemodynamic monitoring. These detection means can directly respond the physiological situation of the nerve tissue and intravascular during the operation to the operator to ensure the smooth operation. 2.2 Surgical access. Successful surgery requires preoperative selection of an appropriate anatomical approach. The traditional very far lateral craniocervical approach can reach the mediospinal junction and lower slope, on the basis of which the resection of different bones, such as occipital condyles, jugular vein nodes, and cervical 1/ and 2 vertebral plates, can make different variations of this approach, such as transfacetalapproach (TFA), posterior occipital condylar approach ( Retrocondylarapproach,CRA), PartialTranscondylarapproach,PTCA), CompleteTranscondylarapproach,CTCA), Extreme-LateralTransjugularApproach( Extreme-LateralTransjugularapproach,ETJA), Transtubercularapproach (TTA), etc [8]. Matsushima [3] et al. modified the above approaches and proposed the following two approaches. Transoccipital condylar fossa (TCF) approach: also known as supracondylar transjugular jugular vein node approach (supracondylartransjugulartubercle), this is a modification of the extreme distal lateral approach, which epidurally removes the posterior portion of the jugular vein node without damaging the circum-occipital joint. During the operation, the bone window of the occipital bone ranges from the midline to the sigmoid sinus, and both sides of the foramen magnum of the occipital bone are fully opened, and whether or not the cervical 1 vertebral plate is opened depends on the specific case, and then the posterior fossa of the occipital condyle and the posterior portion of the jugular vein node to the hypoglossal nerve canal are resected using the posterior lateral canal of the occipital condyle and the penetrating vein therein as the anatomical landmarks, and the posterior part of the occipital condyle and jugular vein node to the sublingual nerve canal is resected. The cerebellar medullary pool and the vertebral artery in it, the beginning of the posterior inferior cerebellar artery, and the 9th, 10th, 11th, and 12th cranial nerves are seen. This approach is directed between the jugular vein nodes and the hypoglossal canal and is indicated for VA aneurysms located above the hypoglossal canal. Transoccipital condylar approach (transcondylar, TC): requires partial resection of the occipital condyle and the lateral mass of the cricoid vertebrae, and is suitable for VA aneurysms located below the hypoglossal neural canal. 3, Surgical complications 3.1 Bleeding in the operation area: Tamano et al [9] reported that in a case of VA-PICA aneurysm on the second day after the isolated operation, bleeding in the operation area, the second operation of the original operation area and there is no aneurysm clip dislodged or new blood vessel hemorrhage, which they think may be a manifestation of the normal perfusion pressure breakthrough after the operation. 3.2 Vascular injury: vertebral artery via PICA to the medulla oblongata blood supply artery damage, vertebral basilar artery vasospasm, etc. are possible complications of vascular injury of the operation, the former most common is the emergence of medulla oblongata syndrome, and the latter can cause the manifestation of extensive ischemia in the posterior circulation. 3.3 Nerve injury: direct injury to the brainstem, facial auditory nerve or posterior group of cranial nerves, the patient may appear such as contralateral hemianesthesia, diplopia, facial paralysis, hearing loss, dysphagia, hoarseness, hypoglossal palsy, etc. Sometimes the nerve injury is indirect and needs to be analyzed in depth. Sometimes the nerve injury is indirect and requires in-depth analysis of the clinical manifestations, for example, Ishiyama [10] reported a case of aneurysm neck clamping of VA-PICA aneurysm, the patient developed tongue enlargement after surgery, they had suspected that this might be a complication of venous obstruction after intraoperative head overcurvature but the tongue enlargement gradually worsened within four days after surgery, then began to recover naturally and was completely normal after four weeks, they finally concluded that that this was an abnormality of the vegetative nervous system, including damage to the stellate ganglion, glossopharyngeal nerve, and vagus nerve as possible causes of the pathogenesis. 3.4 Complications of posterior cranial fossa surgery: e.g. sigmoid sinus tethering, hydrocephalus, cerebrospinal fluid leakage. 3.5 Others: such as aspiration pneumonia. Under the current technical conditions, the occurrence of surgical complications still can not be completely avoided, although there are cases of complete cure reported in the literature, but still need to pay great attention in clinical treatment.