Masaaki Shojima

Role of the Bloodstream Impacting Force and the Local Pressure Elevation in the Rupture of Cerebral Aneurysms

Background and Purpose— Inertial force of the bloodstream results in the local elevation of intravascular pressure secondary to flow impact. Previous studies suggest that this “impacting force” and the local pressure elevation at the aneurysm may have a large contribution to the development of cerebral aneurysms. The goal of the present study is to evaluate how the bloodstream impacting force and the local pressure elevation at the aneurysm influences the rupture of cerebral aneurysms. Methods— A total of 29 aneurysms were created in 26 patient-specific vessel models, and computer simulations were used to calculate pressure distributions around the vessel branching points and the aneurysms. Results— Direct impact of the parent artery bloodstream resulted in local elevation in pressure at branch points, and bends in arteries (231.2±198.1 Pa; 100 Pa=0.75 mm Hg). The bloodstream entered into the aneurysm with a decreased velocity after it impacted on the branching points or bends. Thus, the flow impact at the aneurysm occurred usually weakly. At the top or the rupture point of the aneurysm, the flow velocity was always delayed. The local pressure elevation at the aneurysm was 119.3±91.2 Pa. Conclusions— The pressure elevation at the area of flow impact and at the aneurysm constituted only 1% to 2% of the peak intravascular pressure. The results suggest that the bloodstream impacting force and the local pressure elevation at the aneurysm may have less contribution to the rupture of cerebral aneurysms than was expected previously.

A new strategic neurosurgical planning tool for brainstem cavernous malformations using interactive computer graphics with multimodal fusion images

OBJECT In this study, the authors used preoperative simulation employing 3D computer graphics (interactive computer graphics) to fuse all imaging data for brainstem cavernous malformations. The authors evaluated whether interactive computer graphics or 2D imaging correlated better with the actual operative field, particularly in identifying a developmental venous anomaly (DVA). METHODS The study population consisted of 10 patients scheduled for surgical treatment of brainstem cavernous malformations. Data from preoperative imaging (MRI, CT, and 3D rotational angiography) were automatically fused using a normalized mutual information method, and then reconstructed by a hybrid method combining surface rendering and volume rendering methods. With surface rendering, multimodality and multithreshold techniques for 1 tissue were applied. The completed interactive computer graphics were used for simulation of surgical approaches and assumed surgical fields. Preoperative diagnostic rates for a DVA associated with brainstem cavernous malformation were compared between conventional 2D imaging and interactive computer graphics employing receiver operating characteristic (ROC) analysis. RESULTS The time required for reconstruction of 3D images was 3-6 hours for interactive computer graphics. Observation in interactive mode required approximately 15 minutes. Detailed anatomical information for operative procedures, from the craniotomy to microsurgical operations, could be visualized and simulated three-dimensionally as 1 computer graphic using interactive computer graphics. Virtual surgical views were consistent with actual operative views. This technique was very useful for examining various surgical approaches. Mean (±SEM) area under the ROC curve for rate of DVA diagnosis was significantly better for interactive computer graphics (1.000±0.000) than for 2D imaging (0.766±0.091; p<0.001, Mann-Whitney U-test). CONCLUSIONS The authors report a new method for automatic registration of preoperative imaging data from CT, MRI, and 3D rotational angiography for reconstruction into 1 computer graphic. The diagnostic rate of DVA associated with brainstem cavernous malformation was significantly better using interactive computer graphics than with 2D images. Interactive computer graphics was also useful in helping to plan the surgical access corridor.

Role of shear stress in the blister formation of cerebral aneurysms.

BACKGROUND:The development of cerebral aneurysms is related to hemodynamic stress. OBJECTIVE:To elucidate the role of shear stress in the blister formation of cerebral aneurysms. METHODS:Among 82 aneurysms detected during catheter-based 3D rotational angiography (3DRA), 4 aneurysms enlarged with blister formation during a mean follow-up period of 10.1 month. Three of these 4 aneurysms were analyzed in this study. The regions of blister formation were characterized by comparing 3DRA before and after blister formation, and computational fluid dynamic simulations were performed based on the aneurysm geometry before blister formation. RESULTS:The spatially averaged shear magnitude was lower in the aneurysm region (0.97 ± 0.39 Pa) than in the parent artery (2.75 ± 0.92 Pa). The spatially averaged shear magnitude of the blister-forming area was extremely low (0.48 ± 0.12 Pa), and the shear magnitude dropped precipitately to subphysiological levels, resulting in a high shear gradient near the border of the blister-forming area. CONCLUSION:These data suggest that low shear magnitude may trigger the progression of cerebral aneurysms and that blister formation is associated with high shear gradient in the large region of low shear magnitude on the aneurysm wall.

Role of Gamma Knife surgery in the treatment of intracranial dural arteriovenous fistulas

OBJECT The goal of this study was to assess the efficacy of Gamma Knife surgery (GKS) in the management of dural arteriovenous fistulas (dAVFs). METHODS The authors performed a retrospective analysis of a group of 22 patients who underwent GKS for dAVFs at the University of Tokyo Hospital between 1991 and 2009. The patients underwent CT or MR imaging with contrast enhancement every 6 months after GKS; when obliteration of a dAVF was indicated by these images, patients also underwent angiography. Follow-up in these patients ranged from 12 months to 100 months (median 33 months) after GKS. RESULTS Obliteration of the dAVF was confirmed by neuroimaging in 12 patients (55%). According to a Kaplan-Meier analysis, obliteration rates for the dAVFs were 51% at 3 years and 80% at 5 years. The obliteration rate for lesions without cortical venous drainage (CVD) was 86%, which was significantly higher than the rate for dAVFs with CVD (47%) (p = 0.007). Hemorrhage at presentation (p = 0.03), a target volume less than 1.5 cm(3) (p = 0.009), and Cognard Type III or IV dAVF (p = 0.005) were factors associated with a higher obliteration rate. Among 10 patients whose dAVFs were not obliterated by the initial GKS, 5 patients underwent additional treatment and complete obliteration was achieved in all. Relief of tinnitus was obtained in 5 (83%) of 6 patients with transverse-sigmoid sinus dAVFs, and ophthalmic symptoms improved in 2 (67%) of 3 patients with cavernous sinus dAVFs. No patient experienced interval hemorrhage or radiation-induced complications after treatment. CONCLUSIONS Gamma Knife surgery is a safe and effective treatment for dAVF. It can be a first line of therapy in the multidisciplinary treatment strategy for dAVFs, especially when significant morbidity is anticipated with other therapeutic options. One should be very careful about recommending GKS for patients harboring dAVFs with CVD because of the expected natural history of such a lesion and the possibility of other therapeutic options.

A high-resolution method with increased matrix size can characterize small arteries around a giant aneurysm in three dimensions.

Visualization of the small arteries around a giant intracranial aneurysm remains challenging, even with three-dimensional (3D) rotational angiography. Here we present a new method with the increased matrix size to visualize three-dimensional course of the anterior choroidal artery around a giant aneurysm to help estimate the risk of intraoperative complications.

Surgical Simulation of Cerebrovascular Disease With Multimodal Fusion 3-Dimensional Computer Graphics

Although recent advancements in medical imaging technology have allowed detailed preoperative examinations, neurosurgeons still have to interpret large amounts of medical imaging data. In various modalities such as computed tomography (CT), magnetic resonance imaging (MRI), and angiography, there are multiple sequences and 3-dimensional (3-D) images, and it is not uncommon for there to be several hundred to several thousand section images per case. Clinicians have to interpret each of these multimodalities/sequences individually and consolidate this information in their heads to form a 3-D image that can be used in preoperative planning. From the perspectives of accuracy, reproducibility, and sharing information with other people, it is hard to ensure sufficient precision. Furthermore, the spatial resolution of the 3-D images used in today’s clinical settings is inferior to that in 2-dimensional (2-D) imaging because the processing methods are limited. Consequently, ascertaining detailed findings from 3-D images alone is unsatisfactory; clinicians must additionally interpret 2-D section images of the same site. In this report, we describe the fusion of all image data required for preoperative examination and the construction of 3-D computer graphics (3-DCG) with a high spatial resolution using our own image processing technique. We then apply this to surgical strategies in cerebral vascular disease and report our experience and the usefulness of the technique.

Computational Fluid Dynamic Simulation of a Giant Basilar Tip Aneurysm with Eventual Rupture After Hunterian Ligation

BACKGROUND Hunterian ligation is performed to reduce and to change the flow of an aneurysm; it is a surgical option for a complex aneurysm that cannot be managed by either clipping or coiling. However, it may be associated with adverse effects. This study was carried out to analyze how Hunterian ligation changed the flow dynamics of a particular cerebral aneurysm. METHODS A case of giant basilar tip aneurysm, in which Hunterian ligation resulted in rupture 6 months later, was subjected to computational fluid dynamic simulation. Among the simulations with various boundary conditions, the flow dynamic parameters of streamlines, velocities, and wall shear stresses were compared and analyzed qualitatively and quantitatively. RESULTS Hunterian ligation switched the parent artery from the basilar artery to the left posterior communicating artery. The changes in the direction and the diameter of the parent arteries resulted in the focal elevation of the shear magnitude and the high shear gradient on the posterior wall of the aneurysm after the ligation. These hemodynamic changes might have been associated with the eventual rupture of the aneurysm. CONCLUSIONS Hunterian ligation is a useful flow diversion surgery, but it might worsen the flow dynamics in specific cases.

Stent-assisted Coiling for Ruptured Basilar Artery Dissecting Aneurysms: An Initial Experience of Four Cases

No treatment strategy has been established for subarachnoid hemorrhages due to basilar artery (BA) trunk dissecting aneurysms. Our aim was to report our initial experience performing stent-assisted coiling (SAC) for ruptured BA dissecting aneurysms to validate the effectiveness of this treatment. We experienced four consecutive cases of ruptured dissecting BA trunk aneurysm treated with SAC between 2008 and 2014 at three institutions. Aneurysm rebleeding was prevented without causing severe brainstem ischemia in all cases. In our opinion, both the blockage of the inflow to aneurysms and the preservation of the antegrade flow of the BA can be achieved by SAC, although controversies regarding long-term stability and appropriate antiplatelet therapy remain.

Numerical simulation of the intra-aneurysmal flow dynamics.

Intra-aneurysmal flow dynamics is analyzed qualitatively and quantitatively with numerical simulation technique, and presented for the future clinical application in embolizing cerebral aneurysms. From the volumetric data obtained by three-dimensional computed tomographic angiography, patient-specific vessel models were created for 16 middle cerebral artery aneurysms. Intra-aneurysmal flow dynamics was visualized and analyzed qualitatively, and the geometrical parameters of vessels and aneurysms that affect the intra-aneurysmal flow dynamics were determined quantitatively by correlation analysis. The flow velocity was delayed in the aneurysm cavity, especially at its tip where the rupture usually occurs. The intra-aneurysmal flow dynamics was considerably influenced by the geometrical parameters that are related to the width of the neck and the branching angle of larger branch artery. The intra-aneurysmal flow dynamics is complex, and the numerical flow simulations with patient-specific vascular models seems effective in understanding the flow dynamics and planning the endovascular treatment of cerebral aneurysms.

Microsurgical and endovascular treatments of spinal extradural arteriovenous fistulas with or without intradural venous drainage

OBJECTIVE To present treatment strategies for spinal extradural arteriovenous fistulas (AVFs) in relation to angioarchitecture. METHODS A retrospective analysis comprising 14 patients treated at 2 hospitals was performed. RESULTS The 14 AVFs included 4 cervical, 1 thoracic, and 9 lumbosacral lesions. Three key angiographic features were observed: the feeding artery, an enlarged extradural venous plexus, and intradural retrograde venous drainage. In 3 patients (3 cervical AVFs) with compressive myelopathy owing to an enlarged venous plexus, the treatment goal was mass reduction of the venous plexus. Combined endovascular and microsurgical treatments may be curative for a large venous lake with multiple feeders. No intradural procedure was required because of the absence of intradural venous drainage. In contrast, in the other 11 patients (1 cervical, 1 thoracic, and 9 lumbosacral AVFs) with congestive myelopathy owing to intradural retrograde venous drainage, the goal of treatment was occlusion of the intradural proximal vein. Microsurgery or endovascular treatment may be curative by itself for a small venous pouch with a single intradural draining vein. Extradural procedures were not required in most patients treated by microsurgery because the extradural venous plexus was small. In all 14 patients, neurologic deficits improved or stabilized, and no recurrence was noted in the follow-up period (29 months). CONCLUSIONS Spinal extradural AVFs consist of 2 subtypes-type A with intradural drainage and type B without intradural drainage-characterized by regional differences at each spinal level in angioarchitecture, causes of myelopathy, and treatment goals.