Evidence-based medicine does not refer to the exclusion of scientifically unproven medical practices but to the action guidelines used for optimization of individualized treatment through comprehensive evaluation of the three elements of “evidence, ” “experience and knowledge of specialists,” and “patient values.” This concept represents Aristotle's theory of phronesis. Correct application of evidence requires an accurate understanding of not only the results of clinical studies on which the evidence is based but also on the study design, patient background, evaluation methods, and historical background. The International Subarachnoid Aneurysm Trial and Barrow Ruptured Aneurysm Trial, which compared surgical outcomes of clipping and coiling for ruptured intracranial aneurysms (IAs) and the Unruptured Cerebral Aneurysm Study Japan, which describes the natural history of unruptured IAs in the Japanese population include evidence-based trials of IAs. Results of basic research using animal models, radiomics based on imaging data, and research using artificial intelligence are expected to establish new evidence in future.

  Advances in endovascular treatment have led to a paradigm shift in the role of surgical clipping for intracranial aneurysms. Even deep-seated aneurysms can be accessed and treated relatively easily via the endovascular approach, which serves as an advantage of this method. However, surgical clipping scores over endovascular treatment for middle cerebral artery aneurysms, which is attributable to the fact that the middle cerebral artery is a shallow vessel for open surgery but peripheral for endovascular treatment. A surgically shallow operative field facilitates successful obliteration of saccular aneurysms of varied shapes, and bypass reconstruction can be performed in patients in whom trapping is feasible. Therefore, the open neurosurgeon should be aware of creation of a shallow operative field even for deep-seated aneurysms.

  Development of novel endovascular devices in the future may expand the indications for the application of endovascular therapy for middle cerebral artery lesions. Open surgery is useful for treatment of aneurysms for which endovascular treatment is challenging.

  In this report, we discuss selection of the optimal surgical approach and strategies for creation of a wide operative field for anterior circulation and basilar artery apex aneurysms.

  Currently, treatment of cerebral aneurysms is not restricted to clipping or coil embolization, and a variety of useful therapeutic strategies are available in the present “era of diversity.” It is necessary for neurosurgeons to familiarize themselves with the merits and demerits of all treatment options and design individualized treatment regimens from the various therapeutic alternatives available.

  Decision-making for management of brain arteriovenous malformations (bAVM) is challenging owing to the diverse and rare clinical presentations. A Randomized Trial of Unruptured Brain Arteriovenous Malformations (ARUBA) study, which is the only randomized controlled trial to describe management of unruptured bAVM, has reported that medical management alone is superior to interventional therapy for prevention of death or stroke. However, recent studies have criticized the ARUBA trial with regard to its design, low enrollment rate, several biases, lack of subgroup analysis, and short follow-up, reviewing the ARUBA-eligible patients treated by interventional therapy to reconsider benefit of interventional therapy for unruptured bAVM. Japanese neurosurgeons should contribute to improvements in bAVM management through stratification of patients who are deemed suitable for interventional treatment and through establishment of novel interventional devices and skill enhancement.

  An 82-year-old man was transferred to the emergency department for evaluation of headache and disturbance of consciousness. Computed tomography revealed cerebral hemorrhage in the right occipital lobe and a right acute subdural hematoma. Digital subtraction angiography showed a non-sinus type dural arteriovenous fistula (AVF) in the vicinity of the transverse sinus, which formed a varix in the cortical vein and drained into the superior sagittal sinus. Blood flow was also observed from the right posterior cerebral artery (PCA) into the same cortical vein via a pial AVF. We performed direct surgery for shunt disconnection. Cortical venous drainage of the dural AVF was disconnected in the vicinity of the dura mater. A PCA branch was connected to the same cortical vein, and this shunt point was disconnected. Direct surgery is preferred in patients in whom dural and pial AVFs are observed with shunt points located both on the dura mater and on the brain (as in the present case) because the exact location of the shunt point can be confirmed under direct vision, which facilitates safe and accurate intervention.

  We report a rare case of mature teratoma in the posterior cranial fossa with clinical and imaging findings consistent with dermoid/epidermoid cyst. A 17-year-old male presented with persistent headache after head trauma and a cerebellar tumor was incidentally found. MRI showed a cystic lesion with diffusion restriction in the left cerebellar hemisphere. Hair was observed intraoperatively, which suggested a diagnosis of dermoid cyst. However, histopathological examination revealed a mesodermal component, and the final diagnosis was mature teratoma. Definitive diagnosis based on histopathological findings is important because the different characteristics of mature teratoma and dermoid/epidermoid cyst imply different prognosis for the patient and requirement for postoperative adjuvant therapy. In addition, mature teratoma requires careful follow-up because of the possibility of malignant transformation and recurrence.