Treatment of Central Deafferentation and Trigeminal Neuropathic Pain by Motor Cortex Stimulation: Report of a Series of 20 Patients.

OBJECTIVE: Motor cortex stimulation (MCS) is an alternative treatment modality for central neuropathic pain, if conservative treatment failed. Study aim was outcome assessment after MCS. MATERIAL AND METHODS: This study is a retrospective case series review of patients who had undergone MCS for central pain (n = 8), deafferentation pain (n = 3) and neuropathic trigeminal pain (n = 9) between April 2001 and May 2011. In all patients, four contact-paddle electrodes were placed in the epidural space overlying the motor cortex via burr hole trepanation under local anesthesia. The follow-up period was 6 months to 6 years. Pain control was assessed by the visual analog scale (VAS). RESULTS: A total of 22 patients (11 men, 11 women) were treated; after trial stimulation two male patients were excluded for incompliance reasons. The mean patient age was 59.8 years (range: 31-79 years). In the central pain group, three patients reported complete, and four patients satisfactory pain control. In the trigeminal neuropathic pain group, seven patients reported complete, and two patients satisfactory pain control. In the deafferentation pain group, one patient reported complete, and two patients satisfactory pain control. None of the patients showed new neurologic deficits after the MCS. CONCLUSIONS: MCS is an effective treatment modality for central neuropathic pain and trigeminal pain with low morbidity and mortality. Future studies are necessary to evaluate and optimize this treatment option in more detail.

Reversible cortical blindness and internuclear ophthalmoplegia after neurosurgical operation: case report and review of the literature.

BACKGROUND: The reversible posterior leukoencephalopathy (RPL) syndrome with typical vasogenic edema in the occipital lobe and associated cortical blindness is a rare finding; however, the brainstem variant is even more infrequent. Etiologies discussed include blood pressure dysregulations, renal failure, or immunosuppression. PATIENT: A 63-year-old man with the characteristic radiographic findings of RPL syndrome presented with reversible cortical blindness and internuclear ophthalmoplegia (INO) after resection of an infratentorial hemangiopericytoma. The patient postoperatively presented with diplopia and mental status alterations followed by visual loss; these symptoms completely recovered within a few days. Fluid-attenuated inversion recovery-, and T2-weighted magnetic resonance imaging (MRI) revealed bilateral hyperintense lesions not only in the white matter of the parieto-occipital region but also in the rostral paramedian mesencephalon and pons. CONCLUSIONS: We hypothesize that the patient had an RPL, coincidentally in classic-, and brainstem localization, caused by perioperative fluctuations of blood pressure.

Stand-alone 3D-ultrasound navigation after failure of conventional image guidance for deep-seated lesions.

Image guidance has proven to be an important tool in surgery for deep-seated or eloquently located cavernomas. However, neuronavigation depending on preoperative images can fail. Thus, the displayed anatomy might be distorted already during the approach. This report demonstrates the use of three-dimensional intraoperative ultrasound (3D-US) as a rescue tool, when conventional navigation is erroneous. Two patients with symptomatic cavernomas, the one located subcortically in the right peritrigonum, the other in the left thalamus, were operated in our clinic via an image-guided approach. An integrated ultrasound-navigation system was used for neuronavigation. In both cases, navigation based on preoperative MRI failed after the craniotomy because patient-to-image registration was lost. In both cases, a simple registration of the patient's orientation was performed. Then a 3D-US volume was acquired and navigation was performed using the 3D-US data set. This is accurate as image acquisition and navigation are done in the same system. The cavernoma was visualized without difficulties in both cases. It could be reached directly via the ultrasound-guided approach. Patients' symptoms improved postoperatively and a complete resection could be documented. Two cavernomas were successfully resected using 3D-US guidance. In our experience, stand-alone 3D-US navigation is an effective option if conventional MRI-based navigation fails.

Quality of life after brainstem cavernoma surgery in 71 patients.

BACKGROUND: Symptomatic patients with a brainstem cavernoma are treated surgically with increasing frequency. Generally, the patient's benefit from this difficult surgical intervention is quantified by the assessment of neurological symptoms. OBJECTIVE: To document the beneficial effect of surgery in a larger patient population by assessing the postoperative quality of life (QoL). METHODS: In a series of 71 surgically treated patients, a detailed neurological status was assessed by Patzold Rating and Karnofsky Performance Status Scale. Patients rated their QoL with the Short Form 36 Health Survey. To document the effect of surgery on QoL, we devised a supplementary questionnaire. The last 24 patients completed Short Form 36 Health Survey pre- and postoperatively. RESULTS: Karnofsky Performance Status Scale improved in 44 of 71 surgical patients (62%), remained unchanged in 19 (27%), and deteriorated in 8 (11%) individuals. Patzold Rating showed a more detailed picture of the neurological symptoms. It correlated significantly with Karnofsky Performance Status Scale, which underscores its usefulness for patients with brainstem lesions. In the Short Form 36 Health Survey score, the Mental Component Summary improved with surgery (paired test, P = .015). In addition, 58 individuals (82%) declared a clear subjective benefit of surgery. CONCLUSION: The results of this large series support the notion that microsurgical removal of a brainstem cavernoma represents an effective therapy in experienced hands and is generally associated with good clinical outcome, both neurologically and in terms of QoL.

Intraoperative ultrasound assistance in treatment of intradural spinal tumours.

OBJECTIVE: Currently, the standard practice to treat intradural spinal tumours involves microsurgical resection of the lesions. It is essential to be able to locate the lesion precisely to reduce the risk of neurological morbidity. The purpose of this study was to evaluate intraoperative ultrasonography (IOUS) in visualizing intradural spinal tumours, and assess its potential to improve surgical precision and minimize surgical trauma. METHODS: Between January 2006 and July 2007, 30 patients with suspected intradural spinal tumours underwent surgery with the aid of IOUS. There were 13 patients with intramedullary tumours (ependymoma=2, astrocytoma=5, hemangioblastoma=2 and metastasis=4); and 14 patients with extramedullary tumours (meningioma=6, neurinoma=6, filum terminale ependymoma=1 and lipoma=1). In 3 patients histopathology did not reveal any neoplasm despite an MRI suggesting tumour. Their sonographic features are analyzed and the advantages of IOUS are discussed. RESULTS: The shape and expansion of intradural tumours could be visualized on IOUS. The sonographic visualization allowed adapting the approach to an appropriate location and size before dura opening. Certain sonographic features can be used for a differential diagnosis of different intradural tumours. In addition, IOUS can inform neurosurgeons about the location of the neoplastic tissue, its relation to the spinal cord and the size of residual tumour following excision. CONCLUSIONS: IOUS is a sensitive intraoperative tool. When appropriately applied to assist surgical procedures, it offers additional intraoperative information that helps to improve surgical precision and therefore might reduce the procedure related morbidity.

The role of underlying structural cause for epilepsy classification: clinical features and prognosis in mesial temporal lobe epilepsy caused by hippocampal sclerosis versus cavernoma.

PURPOSE: The recent "Report of the ILAE Commission on Classification and Terminology" recommends an epilepsy classification that gives more emphasis to the underlying structural or metabolic cause rather than to the localization of the epileptogenic zone. The aim of the present study was to investigate differences in clinical features, treatment response, and prognosis in patients with mesial temporal lobe epilepsy (MTLE) caused by hippocampal sclerosis (MTLE-HS) or singular mesiotemporal cavernomas (MTLE-C) in order to evaluate the impact of underlying pathology on the course of the disease while controlling for localization. METHODS: Age at onset, age at surgery, seizure frequency and semiology, pharmacoresistance, psychiatric comorbidities, memory deficits, or initial precipitating insults (e.g., febrile seizures, traumatic brain injury, infection of the central nervous system, birth complications) as well as postoperative outcome were compared in eleven patients with MTLE-C and 33 patients with MTLE-HS using nonparametric statistical methods. KEY FINDINGS: The postoperative outcome was significantly better in patients with MTLE-C, even after controlling for preoperative epilepsy duration. Patients with MTLE-HS more frequently were drug resistant (88% vs. 36%) and more often presented with an initial precipitating insult (70% vs. 27%) and with automotor seizures (79% vs. 46%). SIGNIFICANCE: The results suggest that patients with MTLE-C show a more favorable postoperative outcome, supporting the commission's suggestion to put more emphasis on the underlying cause in future epilepsy classifications.

A 54-year-old woman with a meningeal lesion compressing the medulla oblongata.

A 54-year-old woman had nausea, vomiting and personality changes since a few weeks. Paresis of the abducens and hypoglossal nerves on the left side, a right sided reduction of the visual field, discrete dysarthri×a and ataxia were diagnosed. Cranial magnetic resonance imaging demonstrated a contrast enhancing circular meningeal lesion of the foramen magnum. Histological examination revealed a granulomatous lesion of the meninges with focal necrosis, vasculitis and neutrophils indicating immune complex reactions. A diagnosis of primary meningeal Wegener's disease was made. Medication with low dose prednisolone led to complete remission of the lesion 1.5 years later.

Transsulcal approach supported by navigation-guided neurophysiological monitoring for resection of paracentral cavernomas.

OBJECTIVES: The aim of the study is to evaluate tools that can improve surgical precision and minimize surgical trauma for removal of cavernomas in the paracentral area. Moreover, the surgical strategies for the treatment of symptomatic epilepsy in cavernoma patients are discussed. PATIENTS AND METHODS: Between June 2000 and July 2007, 17 patients suffering from paracentral cavernoma underwent surgery via a transsulcal approach with the aid of neuronavigation, functional mapping and neurophysiological intraoperative monitoring. To optimize outcome for procedures in the paracentral area, the hemosiderin-stained tissue was removed entirely except for a small proportion on the side of precentral gyrus. RESULTS: All cavernomas and their adjacent sulci could be precisely located with the aid of ultrasonography-assisted neuronavigation. By combining preoperative fMRI and intraoperative neurophysiological monitoring, including SEP, MEP and cortical mapping, the motor cortex could be defined in all cases. Thus damage to the primary motor area could be avoided during resection of cavernomas. All the lesions located in the paracentral area were removed completely via transsulcal microsurgical approach without neurological deficits. No significant seizures were induced during surgery. CONCLUSIONS: The successful excision of these lesions was effected by the following four key factors: (1) the precise location of the lesion supported by intraoperative neuronavigation; (2) the preservation of the eloquent area with the aid of functional mapping; (3) a minimally invasive transsulcal microsurgical approach; and (4) the entire removal of cavernoma and hemosiderin-stained tissue.

Candidate genes for the progression of malignant gliomas identified by microarray analysis.

Malignant astrocytomas of World Health Organization (WHO) grade III or IV have a reduced median survival time, and possible pathways have been described for the progression of anaplastic astrocytomas and glioblastomas, but the molecular basis of malignant astrocytoma progression is still poorly understood. Microarray analysis provides the chance to accelerate studies by comparison of the expression of thousands of genes in these tumours and consequently identify targeting genes. We compared the transcriptional profile of 4,608 genes in tumours of 15 patients including 6 anaplastic astrocytomas (WHO grade III) and 9 glioblastomas (WHO grade IV) using microarray analysis. The microarray data were corroborated by real-time reverse transcription-polymerase chain reaction analysis of two selected genes. We identified 166 gene alterations with a fold change of 2 and higher whose mRNA levels differed (absolute value of the t statistic of 1.96) between the two malignant glioma groups. Further analyses confirmed same transcription directions for Olig2 and IL-13Ralpha2 in anaplastic astrocytomas as compared to glioblastomas. Microarray analyses with a close binary question reveal numerous interesting candidate genes, which need further histochemical testing after selection for confirmation. IL-13Ralpha2 and Olig2 have been identified and confirmed to be interesting candidate genes whose differential expression likely plays a role in malignant progression of astrocytomas.

Surgery of intracranial aneurysms previously treated endovascularly.

OBJECTIVE: To perform a retrospective study on the patients who underwent aneurysmal surgery following endovascular treatment. PATIENTS AND METHODS: We performed a retrospective study on eight patients who underwent aneurysmal surgery following endovascular treatment (-attempts) with gugliemi detachable coils (GDCs). The indications for surgery, surgical techniques and clinical outcomes were analyzed. RESULTS: The indications for surgical treatment after GDC coiling of aneurysm were classified into three groups. First group: surgery of incompletely coiled aneurysms (n=4). Second group: surgery of mass effect on the neural structures due to coil compaction or rebleeding (n=2). Third group: surgery of vascular complications after endovascular procedure due to parent artery occlusion or thrombus propagation from aneurysm (n=2). Aneurysm obliterations could be performed in all cases confirmed by postoperative angiography. Six patients had an excellent outcome and returned to their profession. Patient's visual acuity was improved. One individual experienced right hemiparesis (grade IV/V) and hemihypesthesia. CONCLUSIONS: Microsurgical clipping is rarely necessary for previously coiled aneurysms. Surgical treatment is uncommonly required when an acute complication arises during endovascular treatment, or when there is a dynamic change of a residual aneurysm configuration over time that is considered to be insecure.

Is the image guidance of ultrasonography beneficial for neurosurgical routine?

BACKGROUND: Intraoperative US has been widely used in neurosurgical procedures. However, images are often difficult to read. In the present study, we evaluate whether the image guidance of ultrasonography is helpful for the interpretation of US scans. METHODS: Twenty-nine patients with tumor were operated on with the aid of intraoperative US from January to June 2005. Image-guided sonography was used in 13 cases and nonnavigated US technology in the remaining cases. We compared the 2 technologies retrospectively. RESULTS: Although image quality was good in most cases, orientation remained difficult in 8 of the 16 patients where conventional sonography was used. With the aid of image fusion for navigated sonography, the orientation was judged superior to nonnavigated US. CONCLUSION: In our experience, integration of the US into the navigation system facilitates anatomical understanding. Thus, we feel that this technology is beneficial for neurosurgical routine.

Image-guided transsylvian, transinsular approach for insular cavernous angiomas.

OBJECTIVE: Surgical treatment of cavernomas arising in the insula is especially challenging because of the proximity to the internal capsule and lenticulostriate arteries. We present our technique of image guidance for operations on insular cavernomas and assess its clinical usefulness. METHODS: Between 1997 and 2003, with the guidance of a frameless stereotactic system (BrainLab AG, Munich, Germany), we operated on eight patients who harbored an insular cavernoma. Neuronavigation was used for 1) accurate planning of the craniotomy, 2) identification of the distal sylvian fissure, and, finally, 3) finding the exact site for insular corticotomy. Postoperative clinical and neuroradiological evaluations were performed in each patient. RESULTS: The navigation system worked properly in all eight neurosurgical patients. Exact planning of the approach and determination of the ideal trajectory of dissection toward the cavernoma was possible in every patient. All cavernomas were readily identified and completely removed by use of microsurgical techniques. No surgical complications occurred, and the postoperative course was uneventful in all patients. CONCLUSION: Image guidance during surgery for insular cavernomas provides high accuracy for lesion targeting and permits excellent anatomic orientation. Accordingly, safe exposure can be obtained because of a tailored dissection of the sylvian fissure and minimal insular corticotomy.

Clinical impact of CCM mutation detection in familial cavernous angioma.

INTRODUCTION AND BACKGROUND: A 3-year-old Bosnian girl with a large symptomatic brainstem and multiple supratentorial cavernous angiomas, who underwent neurosurgical treatment, is presented. As multiple cavernomas are more common in familial cases, genetic analyses and neuroradiological imaging were performed in the patient and her parents to see whether there was any evidence for inheritance. This information is important for genetic counseling and provision of medical care for at-risk relatives. Currently, no recommendation is available on how to manage these cases. RESULTS: Genetic analyses demonstrated a novel CCM1 frameshift mutation (c.1683_1684insA; p.V562SfsX6) in the child and the asymptomatic 27-year-old mother. Sensitive gradient-echo magnetic resonance imaging of the mother revealed multiple supratentorial lesions, whereas analogous imaging of the father showed no pathological findings. CONCLUSION: This case exemplifies that seemingly sporadic cases with multiple lesions might well be hereditary and that presymptomatic genetic testing of family members may identify relatives for whom clinical and neuroradiological monitoring is indicated.

Treatment of a partially thrombosed giant aneurysm of the vertebral artery by aneurysm trapping and direct vertebral artery-posterior inferior cerebellar artery end-to-end anastomosis: technical case report.

OBJECTIVE: The purpose of this article is to focus for the first time on the operative management of a direct vertebral artery (VA)-posterior inferior cerebellar artery (PICA) end-to-end anastomosis in a partially thrombosed giant VA-PICA-complex aneurysm and to underline its usefulness as an additional treatment option. METHODS: The operative technique of a direct VA-PICA end-to-end anatomosis is described in detail. The VA was entering the large aneurysm sack. Distally, the PICA originated from the aneurysm sack-VA-complex. The donor and recipient vessel were cut close to the aneurysm. Whereas the VA was cut in a straight manner, the PICA was cut at an oblique 45-degree angle to enlarge the vascular end diameter. Vessel ends were flushed with heparinized saline and sutured. The thrombotic material inside the aneurysm sack was removed and the distal VA clipped, leaving the anterior spinal artery and brainstem perforators free. RESULTS: The patient regained consciousness without additional morbidity. Magnetic resonance imaging scans revealed a completely decompressed brainstem without infarction. The postoperative angiograms demonstrated a good filling of the anastomosed PICA. CONCLUSION: Despite the caliber mistmatch of these two vessels the direct VA-PICA end-to-end anastomosis provides an accurate alternative in addition to other anastomoses and bypass techniques, when donor and recipient vessels are suitable and medullary perforators do not have to be disrupted.

A novel platform for image-guided ultrasound.

OBJECTIVE: The combination of classic neuronavigation and intraoperative ultrasound is a recent innovation in image guidance technology. However, this technique requires two hardware components (neuronavigation and an ultrasound system). It was the aim of the study to describe a new simplified technology of a so-called one-platform navigation system developed by our institution in collaboration with the industry and to demonstrate its range of various applications. METHODS: An ultrasound device (IGSonic; BrainLAB, Munich, Germany) is integrated into the VectorVision2 navigation system (BrainLAB, Munich, Germany). The IGSonic Probe 10V5 is connected to the VectorVision Navigation station via an IGSonic Device Box. Once the ultrasound probe is calibrated, the navigated ultrasound displays the sonographic image of the intracranial anatomy on the navigation screen in a composed overlay fashion. It might depict vascular structures within the ultrasound plane by a duplex mode. Ultrasound can also be operated independently from navigation. RESULTS: The VectorVision2 system combines intraoperative ultrasound data sets with preoperatively acquired neuronavigation data sets in plug and play fashion. The system provides a cost-effective intraoperative imaging modality that offers a good anatomic orientation by various composite images, including the display of the amount of brain shift. In our institution, the comprehensible interface led to a routine use of the technology by several neurosurgeons who had not been familiar with the ultrasound technology before. CONCLUSION: The integration of an ultrasound device into an existing navigation system has been successfully developed. The system offers a friendly user interface and cost-effective intraoperative imaging feedback. Although brain shift can be visualized by an image overlay technology as demonstrated by the present system, future developments should aim at fusion techniques of both intra- and preoperative image data sets.

Immune surveillance of the human central nervous system (CNS): different migration pathways of immune cells through the blood-brain barrier and blood-cerebrospinal fluid barrier in healthy persons.

BACKGROUND: Since for immune surveillance, only lymphocytes in the activated state are able to enter normal human central nervous system (CNS), available data are briefly reviewed to reveal lymphocyte transfer through blood-brain barrier (bbb) and blood-cerebrospinal fluid barrier (bCSFb). METHODS: With immuno-histochemical and -cytochemical methods, bbb was studied on brain microvessels and bCSFb on choroid plexus epithelium and microvessels. Lymphocyte transfer capacity on the barriers was determined with blood/CSF cell ratios revealed by quantified multicolour flow-cytometry of CSF and blood sample pairs. RESULTS: Four paths attenuated the restricted transfer of lymphocyte and NK cell subsets (none for B cells) through bbb and bCSFb, preferring memory cells in normal human brain, using different cell adhesion molecules (CAM). CAM pattern changed in choroid plexus where indication of lymphocyte recirculating from CSF into blood may exist in animal brains. CONCLUSIONS: Since efficiency of migration of blood-borne lymphocytes into CSF across bbb or bCSFb of normal human brain is not fully revealed, further data are needed to understand the transfer of immune cells across the barriers in health and disease.

Biological activity of adult cavernous malformations: a study of 56 patients.

OBJECT: Cerebral cavernous malformations (CCMs) have previously been considered as congenital and biologically static malformations. On the other hand, the potential for growth and de novo generation of CCMs have also been reported. It is therefore important to study the proliferative and neoangiogenetic capacity of these lesions. METHODS: The authors studied the surgical specimens of 56 CCMs (23 deep and 33 superficial) obtained from adult patients. The proliferative activity of the endothelium and the neoangiogenetic capacity of these lesions were considered through immunohistochemical anaylsis of proliferating cell nuclear antigen (PCNA), MIB-1, Flk-1, vascular endothelial growth factor (VEGF), hypoxia-inducible factor (HIF)-1alpha, and endoglin antibodies. Positive immunostaining of endothelial cells occurred in 86% of patients for PCNA and in 38% of the cases for MIB 1. The expression of Flk-1 was observed in the endothelium of 71% of the cases, for VEGF in 41%, for HIF-1 alpha in 48.1%, and for endoglin in 63.6% of the cases. The correlation of immunohistochemical and clinical data indicated that VEGF was expressed in significantly less deep-seated lesions when compared with superficial CCMs. Neither the expression of the proliferative markers nor the expression of the angiogenetic antibodies correlated with patient age at surgery, sex, or the number of recent prior hemorrhagic episodes in the patients. CONCLUSIONS: The CCMs from adult patients are active lesions exhibiting endothelial proliferation and neoangiogenesis. According to the data in this study, neoangiogenesis is more prominent in superficial CCMs than in deep-seated CCMs and is not associated with recent prior hemorrhages.

Intraoperative landmarking of vascular anatomy by integration of duplex and Doppler ultrasonography in image-guided surgery. Technical note.

BACKGROUND: The integration of ultrasound technology into neuronavigation systems has recently been the subject of reports by several groups. This article describes our preliminary findings with regard to the integration of data derived from intraoperative duplex (color mode) and Doppler ultrasonography into a neuronavigational data set. It was the aim of the study to investigate (1) whether the intraoperative landmarking of vessels that are outlined with ultrasound technology is possible and (2) whether such a technique might be of clinical interest for neurosurgical interventions. METHODS: The video image of an ultrasound plane (Toshiba, Powervision 6000 SSA-370A, Tokyo, Japan) was integrated into our neuronavigation system (VectorVision2, BrainLab, Heimstetten, Germany). For calibration of the ultrasound plane, an instrument adapter was fixed to the ultrasound probe and then calibrated using a special, predefined calibration phantom. RESULTS: Accordingly, the system supported a combination of the ultrasound plane functionality with the preoperatively acquired neuronavigational data. The duplex and Doppler mode of the ultrasound system displayed the intraoperative vascular anatomy. Once a vessel was outlined during surgery, it could be landmarked by touching the navigation screen. These landmarks were integrated automatically into the neuronavigational data set and could be used to provide intraoperative image updates of the vascular anatomy. This technique was successful in 45 of 47 (95.7%) surgical interventions. CONCLUSIONS: Both image-guided ultrasound and duplex-guided integration of vascular anatomy into the neuronavigational data set are technically possible. In the future, this technology may provide useful intraoperative information during surgery of complex cerebral pathologies.

Is preoperative high-resolution magnetic resonance imaging accurate in predicting neurovascular compression in patients with trigeminal neuralgia? A single-blind study.

High-resolution magnetic resonance imaging (HR-MRI) using three-dimensional fast imaging employing steady-state acquisition (3D-FIESTA) and double-dose contrast-enhanced three-dimensional fast spoiled gradient echo (3D-FSPGR) sequences is considered to be a useful tool in detecting neurovascular compression in patients with trigeminal neuralgia. The purpose of this study was to analyze the accuracy and preoperative diagnostic value of these high-resolution imaging techniques in patients with trigeminal neuralgia, in a single-blind study. The preoperative MRI images of 21 consecutive patients were matched to one neuroradiologist, who was blind as to which side exhibited the symptoms. The images and post-processing multiplanar reconstructions were compared with the video-documented operative observations. HR-MRI using only 3D-FSPGR sequences demonstrated neurovascular compression in accordance with the intraoperative finding in 11 patients (52.4%). In the subgroup where, additionally, 3D-FIESTA sequences were available, neurovascular compression was in accordance with the intraoperative finding in 71.4% (n = 7). High-resolution magnetic resonance imaging using double-dose contrast-enhanced 3D-FSPGR and 3D-FIESTA sequences is currently not sufficient enough to make an accurate prediction of neurovascular compression in a single-blind setting. These 3D imaging techniques currently provide only limited information, and one should consider their use carefully when identifying patients with trigeminal neuralgia from operation until image quality is improved by superior image resolution that can accurately discriminate vessels surrounding the trigeminal root entry zone.