Recent multicenter-prospective studies on unruptured intracranial aneurysms have demonstrated their annual and cumulative rupture rates in detail. These data have been mainly presented according to the location, size, and shape of the aneurysms. It is especially notable that the rupture rates in the Japanese population are significantly higher than those in the West.
  In the clinical field especially, the therapeutic decision for unruptured aneurysms should be based on these up-to-date data to prevent their rupture. In addition, every neurosurgeon should consider the specific problems of each patient including their life expectancy, possible systemic diseases and health-related quality of life.
  On the macroscopic point of view, a radical reduction in the number of domestic subarachnoid hemorrhage seems to be quite difficult to achieve when it is solely based on the conventional “Find and Treat” strategy. A simple simulation can show that this strategy requires an extremely large population to be screened to find medium- to large sized aneurysms which are prone to rupture. Only a novel paradigm of the therapeutic management of intracranial aneurysms will solve this problem in the future.

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  For complexed aneurysm such as a giant, thrombosed, and dissecting aneurysms, some kind of bypasses compound surgery is performed. Aneurysmal conditions and the strategies for treatment are really rather varied, and the best way to assemble a surgery strategy is to gradually establish it under a common understanding.
  A bypass typically includes a high flow bypass using a radial artery or a saphenous vein and a low flow bypass using either a superficial temporal artery or an occipital artery. And the role of the bypass is classified roughly into (1) ischemic protection during temporary parent artery occlusion, (2) branch alteration which is sacrificed, or (3) flow reversal with trapping or parent artery occlusion. It is necessary to plan a surgical strategy minutely so that normal brain perfusion is secured steadily throughout.
  And intra-operative monitoring to determine whether the planned surgery yield the desired effect precisely is extremely important in the surgery. Electrophysiological monitoring such as motor evoked potentials or somatosensory evoked potentials will be required. However, the judgment of whether the flow of the bypass which was selected is appropriate may be sometimes be difficult. But using a hybrid operating room with an operating table and an angiography device or indocyanine green fluorescence angiography or transit-time flowmetry can greatly contribute to a precise perioperative judgment.

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  Endovascular treatment is a less invasive therapy for treating cerebral aneurysms. Various new devices manufactured by medical companies have greatly helped to further improve and develop this treatment. Also, simple and similar procedures enable a short learning curve for physicians. Endo-saccular coiling is indicated for most aneurysms except for fusiform, giant or partially thrombosed aneurysms. Stents are used for wide-neck aneurysms, and achieve less recanalization with more ischemic complications. Parent artery occlusion is still the standard treatment for fusiform, giant, partially thrombosed aneurysms if it is feasible. The balloon occlusion test is useful to determine the indication for bypass surgery prior to parent artery occlusion. The flow diverter stent is a newly developed device to facilitate the gradual thrombosis of the aneurysm and neointimal remodeling of the aneurysmal neck, and enable us to cure large/giant lateral type aneurysms of the proximal internal carotid artery. It will be indicated for unruptured cavernous and paraclinoid large/giant aneurysms in Japan.

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  Management strategies for cerebral arteriovenous malformations (AVM) have undergone considerable evolution with the advent of advance in surgical, endovascular, and radiosurgical technologies. However, controversy still remains regarding the indications for invasive treatment, especially for unruptured lesions as demonstrated by the results of a randomized trial of unruptured brain arteriovenous malformation (ARUBA) study. Similarly, the role of acute craniotomy remains to be elucidated. This article describes our current strategy for those complex lesions and illustrates recent futuristic technologies and techniques aiming to improve outcomes in AVM surgeries. Particularly, the significance of patient selection, and the choice of preoperative and intraoperative endovascular treatment (hybrid surgery) are discussed.

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  When treating dural arteriovenous fistulas (DAVF), it is recognized that the disease course depends on the disturbance of the cerebral blood flow such as cortical venous drainage and venous congestion. Recent reports suggested that symptomatology is also an important factor affecting the natural history of this pathology. Decision tree analysis used in data mining identified factors associated at different levels of significance (symptomatology>cortical venous drainage>lesion location) with an aggressive presentation in patients with DAVF. These factors can help to predict the future development of intracranial hemorrhage/infarction in DAVF patients. Therefore treatment indication should be carefully determined based upon various factors to best affect the natural course.
  Most of DAVFs can be treated by endovascular technique except for some specific lesion locations including the craniocervical junction and anterior cranial fossa. Trans-venous embolization which is results in the outlet occlusion of DAVF is an established therapy with high curability and low morbidity. Transarterial and trans-fistulous embolization with NBCA or Onyx can also be expected with higher curability, although all of the possible procedure-related complications are not yet fully elucidated.

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  The prognosis for intracranial hemorrhage associated with moyamoya disease is extremely poor. The objective of the Japan Adult Moyamoya (JAM) Trial, a multicentered prospective randomized controlled trial conducted by 22 institutions in Japan, was to test the hypothesis that extracranial-intracranial direct bypasses reduce the rebleeding risk in adult patients with moyamoya disease. Eighty adult patients with hemorrhagic moyamoya disease were allocated either to conservative care or to bilateral extracranial-intracranial direct bypass and observed for five years thereafter. The results of the JAM Trial strongly support the beneficial effect of direct bypass surgery for hemorrhagic moyamoya disease. Clinicians should, however, keep in mind that the results were achieved under very low complication rate and cannot be applied to indirect bypasses.

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  Microcystic meningioma is a rare meningioma subtype that is sometimes confused with glioma or metastatic brain tumor. We report a case of a microcystic meningioma, which was undiagnosable preoperatively. A 65-year-old woman was admitted to our hospital because of gait and memory disturbances. A CT scan disclosed a low density lesion in her right frontotemporal lobe with a massive perifocal edema. The lesion demostrated as a hypointense mass on T1-weighted MRI and as a hyperintense mass on T2-weighted MRI. Contrast-enhanced MRI showed slight and heterogeneous enhancement of this tumor without dural tail sign. The external and internal carotid angiograms failed to reveal either tumor feeding arteries or tumor stain. At the time of surgery, the tumor was not adhered to the dura mater. A part of this tumor mass involved the frontal lobe arachnoid membrane, which suggested that the tumor derived from the arachnoid membrane. The pathological findings confirmed the diagnosis of microcystic meningioma. Microcystic meningioma often lacks the typical radiological findings of meningioma. It is only the characteristic MR findings, the so-called ‘faint reticular enhancement’ that may help us to make a correct preoperative diagnosis.

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