The essential pathophysiology of an intracranial aneurysm (IA) involves the degenerative changes that lead to thinning and weakening of the vascular wall. Promoting factors of IA are classified into congenital, environmental, hemodynamic, and acquired factors. Among them, macrophage-mediated inflammation is especially important, and congenital or acquired disturbance of structural integrity of vessel walls is one of the factors promoting IA development. Owing to the development of a rat model for IA rupture, a part of the mechanism of IA rupture, which has not been clarified for a long time, is being elucidated. With respect to the natural history of unruptured IAs, scores predicting the probability of IA rupture based on size, location, and shape of IAs were established according to the results of UCAS Japan and ISUIA, and were utilized in clinical practice. As IAs growing in size during follow-up are at a high risk of rupture, patients with unruptured IA should undergo periodic imaging examinations.

  MR vessel wall imaging (VWI) is an emerging modality that offers a fundamentally different perspective by focusing on the pathology within the aneurysm wall, as opposed to the traditional imaging paradigms that prioritize the aneurysm lumen. Current evidence suggests that VWI could potentially provide new insights into the diagnosis of intracranial aneurysms. Aneurysm wall enhancement in unruptured and ruptured aneurysms may reflect an unstable state of the aneurysm and culprit lesions in cases with multiple aneurysms. The absence of enhancement in unruptured aneurysms may be a marker of a stable state. This review focuses on the utility of VWI in the diagnosis of intracranial aneurysms. First, we discuss the mechanism of aneurysm wall enhancement. Second, we review its clinical application in the diagnosis of ruptured and unruptured aneurysms, particularly the emergence of aneurysm wall enhancement as a biomarker of aneurysm evolution. The assertive implementation of VWI in routine clinical practice will be facilitated by large prospective studies to validate wall enhancement as a biomarker of aneurysm evolution.

  Open surgery for cerebral aneurysms has reached a state of maturity, owing to the accumulation of experience and efforts made by our forerunners over the years. Ordinary clipping has become quite sophisticated and widespread in terms of its approach and dissection methods. Even internal carotid artery aneurysms that interfere with the tent or oculomotor nerve are not problematic if proper procedures are followed. If the shape of the aneurysm at the tip of the basilar artery is clippable, there is no problem with the approach itself if proper fissure dissection techniques are used. Large aneurysms can also be treated with reliable low/high flow bypass techniques, and parasellar aneurysms can be treated reliably if one has mastered cranial base techniques.

  However, a large or giant aneurysm that contains a critical perforating branch is difficult to be treated by craniotomy and will have to rely on further development of the flow diverter. However, these cases are few and far between. Almost all aneurysms can be treated with open surgery.

  On the other hand, endovascular treatment is becoming increasingly applicable with the development of ever-advancing devices. Even though recurrence is possible and hemorrhagic complications tend to be serious, but the rate of endovascular treatment is likely to increase in the future. What are the responsibilities during invasive open surgery in the current situation? The answer lies in safety, certainty, and curability. In other words, any surgery that cannot guarantee these qualities will lose its value.

  Simple clipping also requires the pursuit of a closure line, which requires wide craniotomy and sufficient fissure dissection and mobilization of the vessel. The interhemispheric approach must also be able to expand widely from the corpus callosum without being overwhelmed. The bypass also needs to be a routine and reliable technique for all areas, and the skull base technique needs to be mastered with anterior clinoid process removal, petrous bone removal, and condyle removal. These methodologies have already been well developed.

  The problem that remains is how to pass on the knowledge of an open surgery to the next generation in the future, when the learning curve of craniotomy is slow and the number of cases to be treated by craniotomy is decreasing. In view of the fact that the number of difficult cases and recurrent cases will increase, this is an issue that needs to be considered seriously.

  The advantages of flow diverter (FD) treatment include no recanalization after complete occlusion. Multiple prospective clinical trials have shown the high durability of FD treatment. Treatment indications have been further expanded owing to the introduction of novel devices. Of these, Pipeline Flex with Shield technology, an innovative FD coated with an anti-thrombotic polymer, may be another potential breakthrough in the era of FD. Possible new targets of FD treatment include ruptured, dissecting, and blood blister-like aneurysms in the near future.

  However, FD treatment has important consequences, such as the risk of incomplete occlusion following FD treatment. Of the many predictive factors shown in the literature, both high age and an incorporated branch are considered while choosing a treatment in clinical practice. Periprocedural antiplatelet monitoring is important to prevent not only ischemic but also hemorrhagic complications, such as intraparenchymal hemorrhage. A standard protocol for antiplatelet monitoring should be established.

  Intracranial dissecting aneurysm (ICDA) is a relatively rare but important disease for neurosurgeons because it causes ischemic and hemorrhagic strokes. Moreover, this disease has been reported to occur more frequently in East Asians. This review aims to describe the epidemiology, clinical symptoms, treatment, and outcomes of ICDA with a focus on the most frequently occurring vertebral artery dissecting aneurysm (VADA) from reported articles (especially from Japan) and our personal experience. The prognosis of unruptured VADA is relatively good, and arterial dissection can be cured with medical treatment. In contrast, ruptured VADA has a greater chance of re-rupture during the acute phase. Therefore, emergency surgery is necessary to prevent re-rupture. The first choice of surgical procedure for ruptured VADA is believed to be endovascular internal trapping. However, this procedure involves medulla oblongata or cerebellar infarction. To avoid such complications, the use of a stent to preserve the vertebral artery or branching artery and embolizing only the dissecting part is preferred. Herein, we present our case of stent-assisted embolization for VADA in this review.

  We report a case of cervical stab injury in a 62-year-old woman with a past history of depression, who was transported to our hospital via ambulance after a suicide attempt using a kitchen knife. On physical examination, she showed mild lethargy and dysphagia, and we observed an open stab wound (8cm in the major axis) that extended to the common carotid artery on the anterior aspect of the left side of her neck ; however, we detected no active hemorrhage or massive hematoma. Magnetic resonance imaging revealed no acute ischemic lesions. Left-sided carotid angiography revealed significant vessel wall irregularity with severe stenosis extending from the distal common carotid to the origin of the internal carotid artery. Several thrombi were detected in both the common and internal carotid arteries. She was diagnosed with traumatic carotid dissection and underwent emergency carotid endarterectomy (CEA) to prevent further ischemic events. Traumatic carotid artery dissection secondary to a penetrating injury is extremely rare. CEA enables direct observation of the injured vessel and surrounding structures and is therefore recommended for repair and reconstruction of carotid artery dissection. Moreover, CEA facilitates complete removal of intraluminal thrombi, as performed in this patient. Open surgery is a useful approach to treat traumatic carotid artery dissection, particularly in patients with open wounds and intraluminal thrombi.

  We report the case of a middle-aged woman with obesity who presented with otitis media with effusion and rhinorrhea. The diagnosis was a spontaneous middle cranial fossa encephalocele. Cerebrospinal fluid leak repair was planned to prevent meningoencephalitis. We resected the encephalocele and repaired the defect of the right pyramidal bone using the fascia temporalis via a trans-middle cranial fossa approach. The symptoms disappeared postoperatively, although otitis media with effusion recurred after several months. Follow-up magnetic resonance imaging showed a pseudomeningocele at the bone defect. The pathophysiology of the patient speculated that the cerebrospinal fluid leak was caused by an occult encephalocele, which exacerbated under intracranial hypertension due to obesity. Surgical procedures should be planned, including rigid reconstruction against intracranial hypertension.