Lumbar Lordosis is a Risk Factor for Lumbar Catheter Fracture of Lumboperitoneal Shunt.

OBJECTIVE: This study aimed to investigate the causes of lumboperitoneal (LP) shunt failure and determine risk factors for lumbar catheter fracture. METHODS: We retrospectively investigated 149 patients who underwent LP shunting in our hospital between January 2012 and March 2023. Shunt reconstruction occurred in 22 patients (14.8%). Among these, cause of failure was lumbar catheter fracture in 5 (22.7%). Patient backgrounds, cause of LP shunt failure, surgical technique factors, and anatomical characteristics were extracted for comparative analysis and risk factors of lumbar catheter fracture were analyzed. RESULTS: Compared with the no reoperation group (n = 127), patients in the lumbar catheter fracture tended to be younger (63 ± 20 vs. 72 ± 11 years) and favorable neurologic status (modified Rankin scale score ≤2) after initial LP shunt; however, the differences were not significant. Lumbar lordosis was significantly higher in the lumbar catheter fracture group (52.7°± 14.8° vs. 37.1°± 12.3°; P = 0.0067). CONCLUSIONS: Excessive lumbar lordosis is a risk factor for lumbar catheter fracture in patients undergoing LP shunting. Younger age and higher level of postoperative activities of daily living might also be associated with lumbar catheter fracture.

A novel predictor of ischemic complications in the treatment of ruptured middle cerebral artery aneurysms: Neck-branching angle.

Objective: The risk factors of procedural cerebral ischemia (CI) in ruptured middle cerebral artery (MCA) aneurysms are unclear. This study proposed the neck-branching angle (NBA), a simple quantitative indicator of the aneurysm neck and branch vessels, and analyzed its usefulness as a predictor of procedural CI in ruptured MCA aneurysms. Methods: We retrospectively analyzed 128 patients with ruptured saccular MCA aneurysms who underwent surgical or endovascular treatment between January 2014 and June 2021. We defined the NBA as the angle formed by the MCA aneurysm neck and M2 superior or inferior branch vessel line. The superior and inferior NBA were measured on admission via three-dimensional computed tomography angiography on admission. We divided the patients into clipping (106 patients) and coiling (22 patients) groups according to the treatment. Risk factors associated with procedural CI were analyzed in each group. Results: Both groups showed that an enlarged superior NBA was a significant risk factor for procedural CI (clipping, P < 0.0005; coiling group, P = 0.007). The receiver operating characteristic curve showed the closed thresholds of the superior NBA with procedural CI in both groups (clipping group, 128.5°, sensitivity and specificity of 0.667 and 0.848, respectively; coiling group, 130.9°, sensitivity and specificity of 1 and 0.889, respectively). Conclusion: The NBA can estimate the procedural risk of ruptured MCA aneurysms. In addition, an enlarged superior NBA is a risk factor for procedural CI in both clipping and coiling techniques.

Statistical Analysis of the Factors that Affect Postoperative Length of Hospital Stay after Unruptured Intracranial Aneurysm Treatment in Japan: A 20-year Nationwide Multicenter Study.

Treatment strategies for unruptured intracranial aneurysms (UIAs) should be carefully considered with reference to rupture and complication rates. It is also important to minimize the length of hospital stay (LOS) and to ensure a high quality of medical care. In this study, we aim to clarify the factors that affect the LOS of patients treated for UIAs using the Inpatient Clinico-Occupational Database of the Rosai Hospital Group (ICOD-R). This was a nationwide-multicenter study based on ICOD-R data from 2000 to 2019. Patients diagnosed with UIAs who were treated with clipping or coiling were included in the study. Multivariate analysis was performed to identify the factors affecting LOS. LOS was also compared between groups classified by surgical procedure or treatment period. We identified 3294 patients on the database who underwent clipping or coiling of UIAs during the study period. Multivariate analysis revealed hospital admission during the early 2000s and the late 2010s, age, and treating institution to be significantly correlated with LOS (p < 0.05). There was a significant difference between the mean LOS of the clipping group (20.3 days) and the coiling group (9.65 days) (p < 0.001). Compared by treatment period, LOS significantly shortened over time. Our results suggest that the type of treatment, time of treatment, patient age, and the treating institution affect postoperative LOS for UIAs. Although coiling was found to lead to a lower average LOS than clipping, treatment selection should take the characteristics of each patient's aneurysm into consideration.

The Usefulness of Surgical Titanium Microclips for Mucosal Repair in the Frontal Sinus Using ORBEYE: A Technical Note.

Bifrontal craniotomy frequently involves opening the frontal sinus and mucosal injury. We report a new technique for mucosal repair in the frontal sinus using surgical titanium microclips. Six consecutive patients who underwent bifrontal craniotomy with frontal sinus exposure and mucosal injury underwent mucosal repair using surgical titanium microclips between April 2019 and August 2022. In all cases, the frontal sinus mucosa was peeled from the inner walls of the frontal sinus to ensure sufficient mucosal margin for clipping using ORBEYE. The repair was accomplished with the microclips in all cases. We also sealed the mucosal wound using fibrin glue and sufficiently filled the frontal sinus with bone debris, resulting in zero incidence of postoperative liquorrhea in all cases. Repairing the mucosa using surgical titanium microclips using ORBEYE may be a simple and quick technique when the frontal sinus mucosa is injured during craniotomy.

Cerebral Venous Sinus Thrombosis Successfully Treated with Mechanical Thrombectomy under Intracranial Pressure Monitoring: A Case Report.

A 54-year-old man with no medical history presented to our hospital with vomiting, left hemiplegia, and seizures. On arrival, he was experiencing generalized tonic-clonic seizures, which required him to be intubated and deeply sedated. Contrast-enhanced computed tomography revealed extensive venous sinus obstruction from the superior sagittal sinus to the bilateral sigmoid sinus and cerebral edema with intracranial hemorrhage. An intracranial pressure (ICP) monitor was immediately placed intracranially, and mechanical thrombectomy (MT) was performed under ICP monitoring. MT was immediately terminated when the venous sinus was partially recanalized enough to decrease the ICP; then, anticoagulation therapy was initiated. Postoperative follow-up angiography revealed that venous sinus obstruction and intracranial venous perfusion improved over time. Although he had intracranial hemorrhage-induced left hemiplegia and sensory deficits, his condition improved with rehabilitation, and the patient was eventually discharged home. The indication criteria and techniques for MT for cerebral venous sinus thrombosis are yet to be established. As in this case, in patients with impaired consciousness due to intracranial hemorrhage or epilepsy, preoperative ICP monitor placement is deemed useful to evaluate venous perfusion during MT and decide the treatment goal.

Japan Trevo Registry: Real-world Registry of Stent Retriever Alone or in Combined Therapy with Aspiration Catheter for Acute Ischemic Stroke in Japan.

Endovascular therapy (EVT) for real-world patients after extended time frames is associated with concerns about its efficacy and safety. We conducted a prospective registry at 77 centers between November 2019 and October 2020. The registry criteria included patients treated with Trevo Retriever alone or in combined therapy with an aspiration catheter. The primary outcome was effective reperfusion (thrombolysis in cerebral infarction grade ≥ 2b), the secondary outcome was a modified Rankin scale 0-2 at 90 days, and the safety outcomes were worsening of neurologic symptoms within 24 h postoperatively, intracranial hemorrhage (ICH) within 24 h after EVT and mortality. We also exlpored the difference between patients whose last known well time (LKWT) to a puncture was less than 6 h (0-6 h) and those whose LKWT was 6 h or more but less than 24 h (6-24 h). Among the 1041 patients registered, 1025 patients were analyzed. The mean age was 76.9 years, and 53.6% of the participants were males. The 6-24 h group was 206/998 (20.6%), the median National Institute of Health Stroke Scale (NIHSS) score at admission was 18, and the median Alberta Stroke Program Early CT score was 8. Combined technique as the first pass was used on 817 (79.7%) patients. The primary outcome was 934 (91.1%). The secondary outcome was 433/1021 (42.4%). Symptomatic ICH, any ICH, and mortality were 10/1019 (1.0%), 311/1019 (30.5%), and 75 (7.3%). In the subanalysis, the 6-24 h group was lower in NIHSS (median;18 vs 16), and the secondary outcome was not significantly different in the <6 h group. Even after treatment time expansion, this result was comparable to other Trevo-based trials and nationwide registries.

Long-term Patency of Retrograde Bypass Using a Distal Stump of the Parietal Superficial Temporal Artery for Moyamoya Disease.

There have been a number of anastomosis methods of bypass techniques reported for moyamoya disease. However, there are yet no randomized controlled trials conducted on the anastomosis method. Retrograde blood flow of the superficial temporal artery (STA) may be used as one of the donor options. Here, we examined the tolerability of retrograde bypass using a distal stump of the parietal STA (dsPSTA). Anastomosis between the dsPSTA and middle cerebral artery (MCA) was performed for consecutive patients with moyamoya disease whose parietal STA was visualized to be longer than 10 cm using contrast-enhanced computed tomography preoperatively. Retrospectively, we have examined its patency and clinical outcome. Retrograde dsPSTA-MCA bypass was performed in 22 hemispheres of 17 patients. The patency of retrograde dsPSTA-MCA bypass in all 22 anastomoses could be confirmed during follow-up periods (mean: 5.5, range: 2-15 years). No recurrence of ischemic events was observed. The dsPSTA-MCA bypass using retrograde blood flow has been determined as one of the many promising anastomosis methods, and long-term patency was achieved in moyamoya disease.

Overlapped Double-Layer Micromesh Stents for Giant Extracranial Internal Carotid Artery Aneurysm.

Objective: Extracranial internal carotid artery aneurysms (ECAAs) are rare. We herein describe a case of overlapped stenting with two double-layer micromesh stents for a giant ECAA. Case Presentation: A 73-year-old man presented to our hospital with an enlarged right posterior cervical mass. A right internal carotid artery (ICA) angiogram revealed a giant aneurysm of 50 × 60 mm. We chose a carotid double-layer micromesh stent for stenting. With the patient under general anesthesia, the first double-layer micromesh stent (CASPER Rx, 10 × 30 mm; Terumo, Tokyo, Japan) was deployed between the ICA distal to the aneurysm and the common carotid artery (CCA). The second stent was also deployed from a site more proximal than the first one. Ten coils were then placed from a microcatheter that had been placed in the aneurysm. A right CCA angiogram after the procedure revealed a flow-diversion effect for the aneurysm. The patient was discharged with no complications. At the 6-month follow-up angiogram, blood flow into the aneurysm had completely disappeared. Conclusion: A flow-diversion effect using overlapped double-layer micromesh stents can result in thrombosis and healing of giant ECAAs.

Tension Pneumocephalus Following LP Shunt due to Congenital Bone Defects: A Case Report.

A 72-year-old man who had undergone a lumboperitoneal shunt for idiopathic normal pressure hydrocephalus was admitted to our emergency department with fever and disturbance of consciousness 8 days after placement. Computed tomography scan showed pneumocephalus and a right-sided temporal porencephalic cyst with a small bone defect in the right petrous bone. Shunt valve pressure was raised from 145 mmH2O to "virtual off" setting. After 2 weeks, follow-up computed tomography showed improvement of pneumocephalus, and the shunt valve pressure was lowered to 215 mmH2O. Since that time, the patient has a good clinical course without recurrence. Tension pneumocephalus following shunt placement for idiopathic normal pressure hydrocephalus is rare and has never been reported in the early postoperative stage after lumboperitoneal shunt, except for the present one. Temporary raising shunt valve pressure is effective in improving the pneumocephalus. Preoperative screening for congenital bone defects by thin-slice computed tomography may be useful for selecting types of shunt valve and determining postoperative pressure setting.

Neoplastic Ruptured Cerebral Aneurysm Caused by Intimal Sarcoma: A Case Report.

Intimal sarcomas (ISAs) are extremely rare malignant tumors that histologically occur in the tunica intima of large blood vessels of the systemic and pulmonary circulation. Herein, we describe a case of an ISA-based neoplastic aneurysm in the middle cerebral artery (MCA) that resulted in a subarachnoid hemorrhage (SAH). The patient presented to our hospital with severe consciousness disturbance (Glasgow Coma Scale E1V1M2) and anisocoria. On admission, computed tomography (CT) showed a diffuse SAH. At 8 months prior, he presented to a previous hospital with hoarseness. Thoracic CT revealed a threatened rupture of the aorta of the arch. After total arch replacement, he had been diagnosed with ISA from the pathological findings of the resected aorta. Thereafter, he had been treated with adjuvant chemotherapy and radiotherapy without any cerebral vascular imaging studies, before admission at our hospital. Angiogram revealed a multilobar fusiform aneurysm on the right MCA. We performed a superficial temporal artery-MCA anastomosis, trapping, and resection of the affected MCA (including the aneurysm), followed by external decompression. Microscopic hematoxylin-eosin staining showed proliferation of atypical spindle-shaped cells with enlarged nuclei in the lumen of the affected MCA. Immunostaining showed CD31 (±), ERG (+), MDM2 (+), CDK4 (+, slightly), SMA (±), MIB-1 index 13.9%, factor VIII (±), and desmin (-). These pathological findings indicated metastasis of the ISA, which formed the neoplastic aneurysm. An ISA can cause a neoplastic cerebral aneurysm. Therefore, once a patient is diagnosed with an ISA, it is necessary to check periodically the cerebral arteries.

Feasibility of Metal Artifact Reduction on CT Angiography for Planning Direct Surgery of Tentorial dAVF after Onyx Embolization.

Although Onyx is approved as an embolic material for arteriovenous malformation (AVM) and dural arteriovenous fistula (dAVF), metal artifacts due to Onyx on CT remain problematic. We report the feasibility of a metal artifact reduction (MAR) algorithm on CT angiography (CTA) in the planning of direct surgery of dAVF after transarterial Onyx embolization. A 45-year-old male patient presented with right pulsatile tinnitus, and cerebral angiography demonstrated right tentorial dAVF. As the dAVF had not completely disappeared even after Onyx transarterial embolization, we planned direct surgery. Evaluation of the lesion was difficult on normal preoperative CTA because of Onyx artifacts, but CTA using MAR enabled a detailed planning of direct surgery. Direct surgery was performed through right retrosigmoid craniotomy. Referencing CTA using MAR, we identified the draining veins originating from the main drainer, which were coagulated and cut, achieving complete occlusion of the dAVF. His symptoms disappeared with no postoperative complications. CT angiography using MAR was useful for planning direct surgery after Onyx embolization. As the incidence of direct surgery after transarterial Onyx embolization for AVM or dAVF is increasing, MAR on CTA will become more important.

Crossbow Bolt Penetrating the Neck Removed with the Assistance of an Endovascular Approach: A Case Report and Literature Review.

Penetrating neck injury by a crossbow bolt is extremely rare and can be life-threatening. When removing a crossbow bolt from the neck, it is necessary to protect against fatal bleeding from the carotid vessels. We report removing a crossbow bolt penetrating the neck, with an endovascular approach. A 49-year-old woman was shot in the neck by a crossbow and was transferred to our hospital. On presentation, the crossbow bolt totally penetrated the neck from right to left. Her level of consciousness was clear, with no significant neurological deficits except for right peripheral facial palsy. Neck contrast-enhanced computed tomography revealed the crossbow bolt in contact with bilateral external and internal carotid arteries and that the bolt caused dissection of the left main trunk of the external carotid artery. Under general anesthesia, the crossbow bolt was removed under fluoroscopy with the assistance of an endovascular approach. First, we performed coil embolization for the dissected external carotid artery. Second, we prepared for fatal bleeding from the carotid arteries during crossbow bolt removal under protection using guiding catheters placed in bilateral common carotid arteries. The bolt was removed successfully without significant bleeding, and no complications occurred during the procedure. We report the successful removal of a crossbow bolt penetrating the neck. When removing a crossbow bolt penetrating the neck, endovascular assistance may be feasible to protect against fatal bleeding from the carotid arteries.

Midline suboccipital approach to a vertebral artery-posterior inferior cerebellar artery aneurysm from the rostral end of the patient using ORBEYE.

Background: The midline suboccipital approach with the patient in the prone position is safe and effective for clipping vertebral artery-posterior inferior cerebellar artery (VA-PICA) aneurysms. Using a conventional surgical microscope from the rostral end of the patient for this approach without an extreme head-down position requires the surgeon to overhang the visual axis of the microscope and perform surgical manipulations in an uncomfortable posture. We report performing the midline suboccipital approach from the rostral end with slight head-down position using ORBEYE, a new high-definition (4K) three-dimensional exoscope. Case Description: A 65-year-old woman was admitted for clipping of a right unruptured VA-PICA aneurysm (maximum diameter, 5mm) located medially and ventral to the hypoglossal canal. After induction of general anesthesia, the patient was placed in the prone position with the head titled slightly downward. A midline suboccipital approach was performed from the rostral end of the patient using ORBEYE. Clipping was safely accomplished in a comfortable posture. No operative complications occurred. Postoperative computed tomography angiography showed complete aneurysmal obstruction. Conclusion: Exoscopic surgery using ORBEYE is feasible for a midline suboccipital approach to VA-PICA aneurysms from the rostral end of the patient with the patient in the prone with slight head-down position.

Carotid-carotid crossover bypass after mechanical thrombectomy for internal carotid artery occlusion due to plaque from stenosed innominate artery.

BACKGROUND: The treatment for internal carotid artery occlusion (ICAO) due to innominate artery stenosis is not well established. We herein describe a case of carotid-carotid crossover bypass and common carotid artery (CCA) ligation after mechanical thrombectomy for ICAO due to a plaque from the stenosed innominate artery. CASE DESCRIPTION: A 70-year-old man was transferred to our hospital because of left-sided hemiparalysis. Head magnetic resonance imaging/angiography showed a cerebral infarction in the right middle cerebral artery area and the right ICAO due to a plaque from the stenosed innominate artery. Immediately, we performed mechanical thrombectomy and successfully attained partial revascularization (Thrombolysis in Cerebral Infarction Grade 2B). After a conference with cardiovascular group, we performed carotid-carotid crossover bypass and the right CCA ligation. The treatment was successful, and no complications occurred. CONCLUSION: Carotid-carotid crossover bypass and CCA ligation may be a better option for innominate artery stenosis in selected patients.

Exoscopic carotid endarterectomy using movable 4K 3D monitor: Technical note.

BACKGROUND: Carotid endarterectomy (CEA) using conventional surgical microscope has been already established as golden standard. Recently, exoscope was introduced into the field of neurosurgery, and various merits of it have been reported. We report the experiences of exoscopic CEA using a movable 4K 3D monitor and discuss the feasibility of it. METHODS: We report a consecutive series of 15 cases of exoscopic CEA for internal carotid artery (ICA) stenosis using a movable 4K 3D monitor between January 2020 and April 2021. We utilized ORBEYE as an exoscope system and a 31-inch movable 4K 3D monitor, which was installed in the Maquet Moduevo ceiling supply unit. RESULTS: In all 15 cases, the procedures were accomplished only using the ORBEYE. There were no operative complications due to the use of the exoscope. In response to the operative site, the 4K 3D monitor was moved to face the operator. Even when the angle of the visual axis of the exoscope against the horizontal plane was small during the surgical manipulation in the distal portion of ICA, the operator was able to maintain a comfortable posture. CONCLUSION: Using the movable 4K 3D monitor, exoscopic CEA can be performed ergonomically. The operator can manipulate the distal portion of the ICA or proximal portion of the common carotid artery in a comfortable posture and face the monitor by adjusting its position.

Four Hands Surgery for Intracerebral Hemorrhage using Orbeye: Educational Values and Ergonomic Advantages - A Technical Note.

We have developed a new educational approach to microsurgery in which a trainee and supervisor can cooperate with "4 hands" using the exoscope. We evaluated 4-hands surgery for intracranial hemorrhage (ICH) using the exoscope to validate the educational value and ergonomic advantages of this method. Thirty consecutive patients who underwent surgery for ICH using the exoscope between December 2018 and May 2020 were studied retrospectively. All operations were performed by a team comprising a supervisor (assistant) and a trainee (main operator). The assistant set the visual axis of the exoscope, and adjusted focus and magnification as a scopist. After setting the ORBEYE, the supervisor helped retract the brain and withdraw and irrigate the hematoma using suction tubes or brain retractors. Moreover, the trainee evacuated the hematoma with a suction tube and coagulated using bipolar forceps. Patient background and results of treatment were evaluated. Intraoperative postures of the operators were observed, and schemas compared with the use of a conventional microscope were developed. All microsurgical procedures were accomplished by a trainee with a supervisor using only the exoscope. During the surgery, the surgeons could work in a comfortable posture, and the supervisor and trainee could cooperate in microsurgical procedures using their four hands. The results of the present case series concerning evacuation of ICH were not inferior to those described in previous reports. To increase opportunities for education in microsurgery, 4-hands surgery for ICH using the exoscope appears feasible and safe and offered excellent educational value and ergonomic advantages.

Balloon anchoring to traverse the sigmoid sinus for delivery of large-caliber venous stents: A technical note.

BACKGROUND: In the reconstruction of the superior sagittal sinus or transverse sinus, it is desirable to place a large-diameter guiding catheter into the transverse sinus to introduce the stent delivery system smoothly. The utility of an anchoring technique with a percutaneous transluminal angioplasty (PTA) balloon for navigating an 8 F guiding catheter into the transverse sinus is demonstrated.Case Descriptions: Two dural arteriovenous fistula (dAVF) cases (Cognard type II a +b, Borden type II) that underwent sinus stenting are presented. In both cases, when the 8 F guiding catheter was placed in the jugular vein, the stent delivery system could not enter the transverse sinus because it could not pass through the transverse-sigmoid sinus junction. Introduction of an 8 F guiding catheter into the transverse sinus was attempted but failed. An 8-mm or 9-mm PTA balloon was used as a distal anchor, and this technique allowed easier guiding of catheter advancement into the transverse sinus. In both cases, Carotid WALLSTENTS were placed in the sinus easily, with no complications. CONCLUSION: Balloon anchoring in the venous system is useful for achieving large-caliber catheter access across difficult anatomy and is technically feasible.

Retrosigmoid Approach in the Supine Position Using ORBEYE: A Consecutive Series of 14 Cases.

One of the merits of recently introduced exoscopes, including ORBEYE, is that they are superior to a conventional microscope in terms of ergonomic features. Taking advantage of it, the retrosigmoid approach can be performed in the supine position using ORBEYE. We report a consecutive series of 14 operations through the retrosigmoid approach in the supine position using ORBEYE. Fourteen consecutive patients who underwent surgery through the retrosigmoid approach for cerebellopontine (CP) angle lesions in the supine position using ORBEYE were targeted, and surgical outcomes and complications were examined. We evaluated the posture of the operator and the surgical field during this approach compared with those using a conventional microscope. In all 14 cases, all operative procedures were accomplished only using the ORBEYE. There were no operative complications due to this approach. Using ORBEYE, even when the angle of the operative visual axis was horizontal, the operators could manipulate in a comfortable posture. They were not forced to be in an uncomfortable posture that extended their arms, as is often the case with a conventional microscope. Therefore, they could use shorter surgical instruments. As the cerebellum shifted downward with gravity even using slight retraction during this approach, the working space of the surgical field was easily secured. Through this approach, the operators can perform stable microsurgery of CP angle lesions in a comfortable posture. This approach can reduce the burden on the operator and the patient, leading to a refined surgical procedure.

Reduction of radiation exposure using low pulse rate fluoroscopy during neuroendovascular surgery.

INTRODUCTION: Endovascular surgery is minimally invasive, but the radiation exposure can be problematic. There is no report assessing whether radiation exposure can be reduced by using a low pulse rate during carotid artery stenting (CAS). The aim of this study was to evaluate whether reducing the pulse rate from 7.5 to 4 frames per second (f/s) can reduce the radiation exposure while maintaining safety during CAS procedure. METHODS: We retrospectively reviewed the radiation data and clinical features of all 100 patients who underwent CAS between 2014 and 2019. We changed the pulse rate from 7.5 to 4 f/s in 2017. The fluoroscopic time (FT), dose area product (DAP), and total air kerma (AK) were collected. Statistical analyses were performed between the pulse rate and clinical outcomes, including radiation exposure.

Sphenoid Ridge Keyhole Approach Using the Lone Star Retractor System in Clipping of Unruptured Middle Cerebral Artery Aneurysms: Technical Note.

BACKGROUND: We report a technique for the sphenoid ridge keyhole approach using the Lone Star (LS) retractor system as an extracranial tissue retractor in microsurgical clipping of unruptured middle cerebral artery aneurysms. METHODS: The LS retractor system is used as the extracranial tissue retractor. A skin incision (50-60 mm) without shaving is made. The temporal fascia is cut, and skin and fascia flap are reflected anteriorly. On the temporal muscle, keyhole craniotomy is registered using the navigation system such that the lateral edge of the sphenoid ridge is the center of the craniotomy. After the temporal muscle is split in the direction of the muscle fiber, keyhole craniotomy of approximately 30 mm in diameter is created. After dural incision, the Sylvian fissure is dissected by a standard microsurgical technique using brain retractors, and the target aneurysm is clipped. RESULTS: By precise registration of the sphenoid ridge keyhole craniotomy, the Sylvian fissure emerged in the center of the keyhole. Using the LS retractor system, a flat and shallow operative field was obtained. There were no complications using this method. CONCLUSIONS: We optimized the craniotomy, manipulating the target aneurysm in the center of the keyhole. It did not interfere with conventional microsurgical techniques.