Kenichi Kono

Hemodynamic characteristics at the rupture site of cerebral aneurysms: a case study.

BACKGROUND AND IMPORTANCE Hemodynamics play an important role in the mechanisms of aneurysm formation, growth, and rupture. However, little is known about the hemodynamics of rupture sites. CLINICAL PRESENTATION We incidentally acquired 3-dimensional images before and at the moment of rebleeding of a cerebral aneurysm in a patient. Comparison of these 2 images enabled precise identification of the rupture site. On the basis of computational fluid dynamics simulation, we propose that there are characteristic hemodynamic parameters of the rupture site in cerebral aneurysms. We evaluated flow velocity, wall shear stress (WSS), pressure, and the oscillatory shear index to determine characteristic parameters at the rupture site. Among the hemodynamic parameters in the cardiac cycle, the rupture site was most markedly distinguished by a combination of low WSS at end diastole and high pressure at peak systole. The flow patterns around the rupture site uniquely changed in the cardiac cycle. The rupture site was an impingement zone at peak systole. Flow separation at the rupture site was observed at end diastole. CONCLUSION In this case, a region with low WSS at end diastole and high pressure at peak systole was at the rupture site. A possible mechanism of rupture in this particular aneurysm is that low WSS at end diastole caused degeneration and thinning of the aneurysm wall and that high pressure at peak systole (impingement zone) resulted in rupture of the thinning wall.

Hemodynamic Effects of Stent Struts versus Straightening of Vessels in Stent-Assisted Coil Embolization for Sidewall Cerebral Aneurysms

Background Recent clinical studies have shown that recanalization rates are lower in stent-assisted coil embolization than in coiling alone in the treatment of cerebral aneurysms. Objective This study aimed to assess and compare the hemodynamic effect of stent struts and straightening of vessels by stent placement on reducing flow velocity in sidewall aneurysms, with the goal of reducing recanalization rates. Methods We evaluated 16 sidewall aneurysms treated with Enterprise stents. We performed computational fluid dynamics simulations using patient-specific geometries before and after treatment, with or without stent struts. Results Stent placement straightened vessels by a mean (±standard deviation) of 12.9°±13.1° 6 months after treatment. Placement of stent struts in the initial vessel geometries reduced flow velocity in aneurysms by 23.1%±6.3%. Straightening of vessels without stent struts reduced flow velocity by 9.6%±12.6%. Stent struts had significantly stronger effects on reducing flow velocity than straightening (P = 0.004, Wilcoxon test). Deviation of the effects was larger by straightening than by stent struts (P = 0.01, F-test). The combination of stent struts and straightening reduced flow velocity by 32.6%±12.2%. There was a trend that larger inflow angles produced a larger reduction in flow velocity by straightening of vessels (P = 0.16). Conclusion In sidewall aneurysms, stent struts have stronger effects (approximately 2 times) on reduction in flow velocity than straightening of vessels. Hemodynamic effects by straightening vary in each case and can be predicted by inflow angles of pre-operative vessel geometry. These results may be useful to design a treatment strategy for reducing recanalization rates.

Stent-assisted coil embolization and computational fluid dynamics simulations of bilateral vertebral artery dissecting aneurysms presenting with subarachnoid hemorrhage: case report.

BACKGROUND AND IMPORTANCE A vertebral artery dissecting aneurysm (VADA) is a relatively rare cause of subarachnoid hemorrhage. Bilateral VADAs are even rarer, and management strategies are controversial. We report a case of bilateral VADAs presenting with subarachnoid hemorrhage. We treated the patient by stent-assisted coil embolization of both aneurysms at a single session on the basis of results of preoperative computational fluid dynamic simulations. CLINICAL PRESENTATION A 48-year-old man presented with subarachnoid hemorrhage resulting from bilateral VADAs. We treated the patient by stent-assisted coil embolization of both aneurysms at a single session. Before the treatment, we performed computational fluid dynamics simulations to predict the ruptured side. We also estimated the increase in wall shear stress on an aneurysm in case of trapping of another aneurysm, which might cause enlargement and rupture of the aneurysm. The treatment was performed successfully. The patient remains neurologically intact at 14 months from the onset. CONCLUSION Stent-assisted coil embolization of subarachnoid hemorrhage with bilateral VADAs for both sides is a reasonable treatment because it prevents rebleeding and preserves bilateral vertebral arteries without increasing hemodynamic stress. To the best of our knowledge, this is the first report to describe this type of treatment for bilateral VADAs with subarachnoid hemorrhage. Computational fluid dynamics simulations may be useful for developing treatment strategies for aneurysms.

De Novo Cerebral Aneurysm Formation Associated With Proximal Stenosis

BACKGROUND Hemodynamic insults--high wall shear stress (WSS) combined with high positive WSS gradient (WSSG)--have been proposed to link to cerebral aneurysm initiation. We report 4 cases of aneurysms with proximal stenosis, including 1 de novo aneurysm, that might be associated with hemodynamic insults caused by the proximal stenosis. CLINICAL PRESENTATION In 4 clinical cases, the diameter stenosis was 37% to 49% (mean, 42%) located 2.7 to 4.7 mm (mean, 3.7 mm) from the apex. We performed computational fluid dynamics simulations for 2 cases: a ruptured basilar terminus aneurysm with proximal stenosis (which had an angiogram taken 15 years previously that showed no aneurysm and no stenosis) and a cavernous carotid artery aneurysm with proximal stenosis. In both cases, the stenosis caused unphysiologically high WSS (> 7 Pa) at the apex, nearly doubling the WSS and WSSG values. To investigate the relationship between stenosis and distal hemodynamic elevation, we created a series of T-shaped vascular models by varying the degree and location of stenosis. We found that stenosis > 40% by diameter located within 10 mm from the apex caused unphysiologically high WSS and WSSG. All 4 clinical cases satisfied these conditions. CONCLUSION Proximal stenosis could produce high WSS and high positive WSSG at the apex, thus potentially inducing de novo aneurysm formation. ABBREVIATIONS BT, basilar terminusCFD, computational fluid dynamicsICA, internal carotid arteryWSS, wall shear stressWSS, wall shear stress gradient.

Retreatment of recanalized aneurysms after Y-stent-assisted coil embolization with double enterprise stents: case report and systematic review of the literature.

It is necessary to consider possibility of recanalization and retreatment after coil embolization for cerebral aneurysms. There is concern that retreatment for recanalized aneurysms after Y-stent-assisted coil embolization may be difficult because of double stents, especially in Y-stents with double closed-cell stents owing to narrowed structures. However, no detailed reports of retreatment after Y-stent have been reported. Between July 2010 and June 2013, we treated four aneurysms with Y-stent-assisted coil embolization using Enterprise closed-cell stents. Recanalization occurred in one case (25%), and retreatment was performed. We easily navigated a microcatheter into the target portions of the aneurysm through the Y-stent and occluded the aneurysm with coils. Additionally, by systematically searching in PubMed, we found 105 cases of Y-stent-assisted coil embolization using Enterprise stents or Neuroform stents with more than 6 months of follow-up. Among them, retreatment was performed in 10 cases (9.5%). There were no significant differences in retreatment rates among different stent combinations (P=0.91; Fishers exact test). In conclusion, navigation of a microcatheter into the aneurysm through the Y-stent with double Enterprise stents was feasible, and retreatment rates after Y-stent-assisted coiling may not depend on stent combinations.

Encephaloduroarteriosynangiosis for cerebral proliferative angiopathy with cerebral ischemia

Cerebral proliferative angiopathy (CPA) is a rare clinical entity. This disorder is characterized by diffuse vascular abnormalities with intermingled normal brain parenchyma, and is differentiated from classic arteriovenous malformations. The management of CPA in patients presenting with nonhemorrhagic neurological deficits due to cerebral ischemia is challenging and controversial. The authors report a case of adult CPA with cerebral ischemia in which neurological deficits were improved after encephaloduroarteriosynangiosis (EDAS). A 28-year-old man presented with epilepsy. Magnetic resonance imaging and angiography showed a diffuse vascular network (CPA) in the right hemisphere. Antiepileptic medications were administered. Four years after the initial onset of epilepsy, the patients left-hand grip strength gradually decreased over the course of 1 year. The MRI studies showed no infarcts, but technetium-99m-labeled ethyl cysteinate dimer ((99m)Tc-ECD) SPECT studies obtained with acetazolamide challenge demonstrated hypoperfusion and severely impaired cerebrovascular reactivity over the affected hemisphere. This suggested that the patients neurological deficits were associated with cerebral ischemia. The authors performed EDAS for cerebral ischemia, and the patients hand grip strength gradually improved after the operation. Follow-up angiography studies obtained 7 months after the operation showed profound neovascularization through the superficial temporal artery and the middle meningeal artery. A SPECT study showed slight improvement of hypoperfusion at the focal region around the right motor area, indicating clinical improvement from the operation. The authors conclude that EDAS may be a treatment option for CPA-related hypoperfusion.

Proximal stenosis may induce initiation of cerebral aneurysms by increasing wall shear stress and wall shear stress gradient

Hemodynamic parameters, such as wall shear stress (WSS), WSS gradient (WSSG), aneurysm formation indicator (AFI), or gradient oscillatory number (GON), have been proposed to be linked to initiation of cerebral aneurysms. However, how such conditions occur in humans is unclear. We encountered a rare and interesting case to address this issue. A patient had a newly formed aneurysm with proximal stenosis, which was confirmed by serial imagings. We made two pre-aneurysm models: one with stenosis and the other without stenosis. We performed computational fluid dynamics simulations for these models. Owing to jet flow caused by the stenosis, the maximum WSS and WSSG on the aneurysm initiation site were approximately doubled and tripled, respectively. However, the oscillatory shear index (OSI), AFI, and GON did not change substantially by the stenosis. Computer simulations using artificial vascular models with different degrees of proximal stenosis at different distances demonstrated that oscillatory shear index, AFI, and GON did not change substantially by the stenosis. These results showed that proximal stenosis caused high WSS and high WSSG at the aneurysm initiation site, possibly leading to aneurysm initiation. Proximal stenosis may be a potential factor to induce initiation of one class of cerebral aneurysms by increasing WSS and WSSG.

Resolution of trigeminal neuralgia following minimal coil embolization of a primitive trigeminal artery associated with a cerebellar arteriovenous malformation

Dear Editor, Trigeminal neuralgia (TN) is most often caused by the superior cerebellar artery (SCA), and microvascular decompression (MVD) is the first treatment option for uncontrollable TN by medication [2]. We report a case of TN caused by a primitive trigeminal artery (PTA) as a cerebellar arteriovenous malformation (AVM) feeder. Because the middle portion of the PTA involved perforating arteries, we occluded only the distal portion of the PTA with coils, and succeeded in relieving the pain. This minimal embolization of an offending artery with coils may be a treatment option for selected cases of TN. A 53-year-old man suffered from left-sided TN. Imagings showed a 6.3-cm AVM in the left hemispheric cerebellum associated with the left PTA (Fig. 1a, b). The Spetzler– Martin grade was V. We first treated the patient with antiTN medication. The pain became worse, and the patient had difficulty in eating. A diagnostic angiogram was performed. The PTAwas a feeder of the AVM (Fig. 1d). Detailed threedimensional analysis showed that the middle portion of the PTA (attached to the trigeminal nerve) was likely to be responsible for TN (Fig. 1c). We planned to perform endovascular treatment because MVD was technically difficult owing to the large AVM. We occluded only the distal portion of the PTA with coils expecting a collapse of the middle portion of the PTA and relief of the pain (Fig. 1e). Although we could not achieve occlusion or flow stagnation of the middle potion of the PTA, we finished the procedure because small branches at the middle portion appeared after occlusion of the distal portion of the PTA and they might have supplied normal brain parenchyma. There were no periprocedural complications. The pain was completely resolved in 1 month. Angiographic follow-up 10 months after the operation showed that the middle portion of the PTAwas narrowed and string-like, and that the distal portion of the PTAwas occluded (Fig. 1F). This narrowing suggested that contact of the PTA and the trigeminal nerve had been released. The patient remained pain-free for 12 months after the operation. Our patient had two rare conditions, which involved TN associated with both a PTA and a cerebellar AVM. To the best of our knowledge, this is the first report of these rare conditions. There are 21 cases previously reported to have TN associated with a PTA [3, 4, 7–9]. In 18 out of the 21 cases, MVD was performed, and the pain was relieved. In the remaining three cases, medication was sufficient. Considering these results, MVD would be the first option for TN associated with a PTAwhen medical treatment fails. However, in our patient, MVD was technically difficult because of the large cerebellar AVM. Lesley reviewed the literature and summarized 59 cases of TN associated with AVM [5]. Most of them were surgically treated. Only four cases of TN have been treated with endovascular surgery, and they were all associated with AVM, but not with a PTA [1, 5, 6, 10]. One of these patients [1] was treated with coils, and the other three [5, 6, 10] were treated with ethylene-vinyl alcohol copolymer (Onyx; eV3, Neurovascular, Irvine, CA, USA). In all of these four patients, the pain was relieved. Our treatment strategy was K. Kono (*) : T. Terada Department of Neurosurgery, Wakayama Rosai Hospital, 93-1 Kinomoto, Wakayama 640-8505, Japan e-mail: vyr01450@gmail.com

Stent-Assisted Coil Embolization for Cavernous Carotid Artery Aneurysms

Internal carotid artery (ICA) occlusion with or without a bypass surgery is the traditional treatment for cavernous sinus (CS) aneurysms with cranial nerve (CN) dysfunction. Coil embolization without stents frequently requires retreatment because of the large size of CS aneurysms. We report the mid-term results of six unruptured CS aneurysms treated with stent-assisted coil embolization (SACE). The mean age of the patients was 72 years. The mean size of the aneurysms was 19.8 mm (range: 13–26 mm). Before treatment, four patients presented with CN dysfunction and two patients had no symptoms. SACE was performed under local or general anesthesia in three patients each. Mean packing density was 29.1% and tight packing was achieved. There were no neurological complications. CN dysfunction was cured in three patients (75%) and partly resolved in one patient (25%). Transient new CN dysfunction was observed in two patients (33%). Clinical and imaging follow-up ranged from 6 to 26 months (median: 16 months). Recanalization was observed in three patients (50%; neck remnant in two patients and dome filling in one patient), but no retreatment has yet been required. No recurrence of CN dysfunction has occurred yet. In summary, SACE increases packing density and may reduce requirement of retreatment with an acceptable cure rate of CN dysfunction. SACE may be a superior treatment for coiling without stents and be an alternative treatment of ICA occlusion for selected patients, such as older patients and those who require a high-flow bypass surgeryor cannot receive general anesthesia.

Simultaneous bilateral hypertensive putaminal or thalamic hemorrhage: case report and systematic review of the literature.

Simultaneous multiple hypertensive intracranial hemorrhage is rare, and its mechanism is unclear. We report a case of simultaneous hypertensive bilateral thalamic hemorrhage. A 58-year-old man presented with sudden mild right hemiparesis. Computed tomography 1 hour after the onset showed bilateral thalamic hemorrhage. Gradient-echo T2-weighted magnetic resonance imaging showed 17 microbleeds. The patient was treated with medication, discharged home, and achieved a modified Rankin scale of 1 at 3 months from the onset. Additionally, by systematically searching in PubMed, we found 41 cases of simultaneous bilateral hypertensive putaminal or thalamic hemorrhage, including our case: 18 bilateral putaminal, 12 bilateral thalamic, and 11 unilateral putaminal and contralateral thalamic hemorrhage. Symmetric hemorrhage occurred more frequently than expected ratios of hemorrhage occurring randomly in terms of location (p=0.013; Fishers exact test). These new findings raise the hypothesis that patients may have symmetrically vulnerable vessels. Such conditions would result in coincidence or subsequent rupture of perforating arteries or micro-aneurysms by increased blood pressure and cause symmetric hemorrhages. Studies on the distribution of microbleeds may address these issues.