Herein, we present the results of four prospective in-house cohort studies investigating adult patients with ischemic moyamoya disease (aMMD). From the results of this analysis, we concluded the following: Patients not treated with misery perfusion should first receive strict medical management alone, including cilostazol, and should undergo revascularization surgery when ischemic symptoms recur. The incidence of angiographic disease progression was 2.4% per year in patients with aMMD without misery perfusion who underwent medical management alone. Patients with further ischemic events generally exhibited angiographic disease progression with reduced cerebral perfusion. Further, the incidence of an interval increase in cerebral microbleeds was 3.2% per year in patients with aMMD without misery perfusion who underwent medical management alone, and this increase was associated with cognitive decline. Approximately one-third of patients with aMMD with cerebral misery perfusion who underwent direct revascularization surgery developed irreversible cognitive decline due to cerebral hyperperfusion. Cognitive decline is caused by de novo cerebral microbleeding and delayed brain atrophy. In patients with aMMD with misery perfusion, indirect revascularization surgery alone resulted in sufficient collateral circulation, improved cerebral hemodynamics, and the recovery of cognitive function. The latter two beneficial effects were greater than those in aMMD patients treated with direct revascularization surgery. Periventricular anastomosis regressed following indirect revascularization surgery alone for aMMD with misperfusion. Finally, medical management alone was associated with considerably poor outcomes in aMMD patients with misery perfusion.

We advocate early identification of the posterior belly of the digastric muscle for dissecting the distal internal carotid artery (ICA) during carotid endarterectomy (CEA). This method is characterized by early identification of the posterior belly of the digastric muscle and extensive utilization of the adjacent space. It avoids harm to the marginal mandibular branch of facial nerve and hypoglossal nerve, both of which are particularly susceptible to injury during the dissection of the distal ICA, and facilitates the creation of a substantial working space around it. In this study, we validated the outcomes of this technique in 191 consecutive patients. The incidence of damage to the marginal mandibular branch of facial nerve and hypoglossal nerve was 0.5%. This rate is lower than those reported in previous studies. The incidence of ipsilateral cerebral infarction within 30 days postoperatively did not increase even in cases of high-positioned CEA using this technique. We posit that this technique is also beneficial for mastering the procedure for dissecting the distal ICA, both safely and efficiently.

Background: Exoscopes have recently been introduced in the neurosurgical field and their usefulness has been reported. Exoscopes can improve surgical field visibility with 4K-3D monitors and alleviate the physical strain associated with surgeons’ neutral posture. Herein, we report our early experiences with exoscopic aneurysm surgery at our facility.

Methods: The study sample included 134 patients with unruptured intracranial aneurysms who underwent surgical procedures between January 2021 and August 2022. Two patients who did not undergo surgical clipping were excluded. The baseline characteristics, setup time, operative time, surgical complications, and clinical outcomes were compared between exoscopic and microscopic repair.

Results: Seventy-five patients (55.1%) underwent exoscopic clipping. The patient characteristics were similar between the two groups. There were no significant differences in the setup time (63 min vs. 62 min; P=0.120), operative time (295 min vs. 304 min, P=0.990), rate of surgical complications (5.3% vs. 3.3%, P=0.691), or favorable outcomes (97.3% vs. 95.1%, P=0.657) between the two groups. In the postoperative questionnaire evaluation, the exoscope received higher scores in terms of “image quality”(78.9%), “brightness” (84.2%), “operability” (73.7%), and “education” (57.9%). In contrast, the conventional microscope received higher scores in terms of “assistant work” (73.7%).

Conclusion: The benefits of the exoscope were high image quality, expanded view with digital zoom, a compact body, and comfortable resting position, which led to reduced fatigue among neurosurgeons. The exoscope was useful for surgical clipping, and the clinical outcomes were acceptable.

Objective: The relationship between the aneurysm wall characteristics and local hemodynamics remains unexplored. Thin, red aneurysm walls observed under microsurgical conditions indicate fragility associated with the risk of aneurysm rupture. In contrast, atherosclerotic lesions on the aneurysm wall caused by hyperplastic remodeling pose a risk of incomplete obliteration during neck clipping. In this study, we aimed to elucidate the relationship between hemodynamic parameters determined using computational fluid dynamics (CFD) and aneurysm wall characteristics. Such insights may provide valuable information for making decision in the treatment of intracranial aneurysms.

Methods: In this retrospective study, 45 unruptured saccular intracranial aneurysms were examined using intraoperative video recordings and steady-state analysis. The relationship between aneurysm wall characteristics, examined under an operative microscope, and hemodynamic properties, examined using CFD, were analyzed.

Results: Among the observed findings, 15 out of 18 regions with coexistence of low normalized wall shear stress (NWSS) and collisional wall shear stress (WSS) vectors demonstrated hyperplastic remodeling. In contrast, 26 out of 36 regions with a high NWSS exhibited thin, red aneurysm walls. In addition, 17 out of 21 regions with concurrent high NWSS and parallel WSS vectors exhibited destructive remodeling.

Conclusion: CFD demonstrated the ability to predict aneurysm wall characteristics based on the hemodynamic features in a clinical setting, and it may allow for optimal decision making in the treatment of unruptured intracranial aneurysms.

Dysplasia of the terminal portion of the internal carotid artery (C1) is rare in occurrence. Herein, we reported a case of dysplasia at the C1 portion of the internal carotid artery leading to the development, rupture, and subsequent expansion of an aneurysm due to the fragility of the twig-like vascular networks.

The patient was a 66-year-old man who presented with subarachnoid and cerebral hemorrhages along with acute hydrocephalus due to third ventricular obstruction. Cerebral angiography revealed splitting of the right internal carotid artery into two anomalous collateral vessels immediately after the bifurcation of the posterior communicating artery, forming twig-like vascular networks with an abnormal branch from the posterior communicating artery, which coursed through the middle cerebral artery. The aneurysm developed within these twig-like vascular networks.

Intraoperative findings revealed hypoplasia in the right C1 portion. The proximal portions of the right A1 and M1 portions were identifiable; however, after the bifurcation of the collateral vessels, they underwent transformation into cord-like structures, resulting in occlusion.

The aneurysm was enclosed within twig-like networks and was difficult to identify; therefore, neck clipping was performed using intraoperative cerebral angiography.

We report a case of a ruptured isolated dissecting aneurysm of the posterior inferior cerebellar artery (PICA). A 74-year-old woman presented with a sudden disturbance of consciousness. Computed tomography (CT) of the head revealed a massive subarachnoid hemorrhage (SAH) in the basal cistern. Digital subtraction angiography (DSA) revealed a dissecting fusiform aneurysm of 3.0 mm in diameter in the lateral medullary segment of the left PICA. Embolization of the aneurysm using a coil is challenging because of its small size. LVIS Jr. overlap stenting was preferred over parent artery occlusion owing to the risk of brainstem infarction for the rectification effect. The patient reported temporary hoarseness postoperatively; however, a modified Rankin scale score of 0 was observed at discharge. A follow-up DSA performed after 4 weeks revealed the absence of an aneurysm, which did not recur until 3 months. Ruptured isolated dissecting aneurysms of PICA are rare, and accounting for 0.5–2.2% of all intracranial aneurysms, have a high re-bleeding rate, and are prone to complications associated with deconstructive treatments. Reconstructive surgery is associated with fewer complications. However, in this case, because of the small size of the fusiform aneurysm, reconstructive treatment was not recommended. Overlap stenting is effective in treating aneurysms in different regions owing to its rectification effect. Hence, we performed overlap stenting using LVIS Jr., which showed good short- and mid-term outcomes. To date, no study has reported overlap stenting of LVIS Jr. for ruptured isolated dissecting aneurysms of the PICA. Therefore, our study contributes to increasing knowledge of effective treatment modalities for this rare type of aneurysm.

Vertebral artery (VA) injury is a possible complication of posterior cervical fixation; however, this injury rarely develops long after surgery. Herein, we report a case of cerebellar infarction which developed one year and four months after this operation. A 67-year-old man with a history of cervical spondylosis treated with posterior fixation at another hospital in March 2020 visited our hospital upon experiencing astasia in July 2021. Neurological findings revealed consciousness disorder (JCS 3), conjugate deviation to the left, dysarthria, right facial paralysis, and right limb ataxia. The National Institute of Health Stroke Scale was 15. Head magnetic resonance imaging and computed tomography (CT) revealed massive infarction in the right cerebellar hemisphere and vermis. Contrast-enhanced CT showed aberrant progression of the right C2 screw into the transverse foramen, causing injury to the VA. On day 4 of admission, stenosis was observed on digital subtraction angiography of the VA. We performed coil embolization of the parent artery to prevent repetition of infarction. The patient recovered well and was discharged with a modified Rankin Scale score of 2. This case indicates that VA injury after posterior cervical fixation can develop in the remote period following surgery. Although no clear evidence has yet been established, we suggest that parent artery embolization is both safe and useful.

A 74-year-old man presented with a giant thrombosed aneurysm (maximum diameter: 37 mm) which was incidentally found in the left distal anterior cerebral artery. The left A3 was branching from the aneurysm dome; thus, revascularization was essential. The left callosomarginal artery was anastomosed to the radial artery graft in end-to-side fashion with the conduit passing along a gutter in the frontal bone, then the end of the radial artery was anastomosed to the superficial temporal artery in end-to-side fashion, forming the hemi-bonnet bypass. The aneurysm was trapped and thrombectomy was performed. No complications were observed. Bypass patency was confirmed 3 years after the operation. Revascularization of the anterior cerebral artery by hemi-bonnet bypass is easy to anastomose and safe.

Pituitary apoplexy is the sudden loss of the pituitary gland’s blood supply, leading to tissue necrosis and hemorrhage. Its clinical symptoms are characterized by sudden onset of headache, nausea, vomiting, ophthalmic symptoms, and hormonal dysfunction. A 75-year-old woman presented with headache and oculomotor palsy. Pituitary swelling with T1 high intensity on brain magnetic resonance imaging suggested pituitary apoplexy. Considering a significant decrease in pituitary anterior lobe hormone as well as central diabetes insipidus, high-dose hydrocortisone was administered. The patient underwent transsphenoidal surgery. Postoperatively, oculomotor nerve palsy improved. Early diagnosis and treatment, including surgical decompression, are crucial in patients with oculomotor nerve palsy in pituitary apoplexy.

Here we described the case of a 57-year-old woman with a incidental large internal carotid paraclinoid aneurysm which recurred soon after stent-assisted coiling. Angiography revealed constant filling of the aneurysm dome, with no space for neck clipping; however, the patient rejected further endovascular surgery. Extracranial-intracranial high-flow bypass with internal carotid artery ligation in the neck was successfully performed without any sequelae. No recurrence was detected at 12 months after bypass surgery. We propose that paraclinoid aneurysms that persist after endovascular surgery or are unclippable may be treated with high-flow bypass with parent artery occlusion.

Herein, we report a case of visual impairment following parent artery occlusion (PAO) of a ruptured collateral vessel aneurysm in a patient with Moyamoya disease. A 55-year-old woman who presented with headache and disorientation was diagnosed with a subdural hematoma and Moyamoya disease based on the results of magnetic resonance imaging, and was subsequently referred to our hospital. Digital subtraction angiography (DSA) revealed a pseudoaneurysm in the collateral vessels of the anterior ethmoidal artery; the aneurysm was identified as the source of subdural hematoma bleeding. Subsequently, parent artery occlusion (PAO) was performed under general anesthesia. DSA performed immediately after embolization confirmed disappearance of the aneurysm and allowed visualization of the central retinal artery and retinal choroidal brush. However, visual impairment was observed upon awakening from anesthesia. This case highlights that PAO of a ruptured aneurysm of the collateral vessels in Moyamoya disease should not be applied without full consideration, owing to the possibility of embolic complications.

Herein, we report a case of a 47-year-old man with a ruptured middle cerebral artery aneurysm with cervical carotid artery dissection. The patient initially experienced posterior cervical pain after returning home from work. The next day, he was found in a state of impaired consciousness, and was transported to our hospital by ambulance. The patient was diagnosed with a ruptured middle cerebral artery aneurysm, which was clipped on Day 0. Magnetic resonance imaging after treatment revealed stenosis of the left internal carotid artery (ICA) and infarction of the left insular cortex. We suspected a relationship between cerebral infarction and stenosis of the ICA. Digital subtraction angiography on Day 11 revealed a “string sign” in the cervical portion of the left ICA; thus, the patient was diagnosed with internal carotid artery dissection. Because stenosis did not improve, carotid artery stenting was performed on Day 32. The patient was discharged from our hospital with a modified Rankin Scale score of 0 on Day 44. If subarachnoid hemorrhage is accompanied by posterior cervical pain, the possibility of carotid artery dissection should be considered.

A 25-year-old woman was admitted to our hospital with the primary complaint of a sudden headache and disturbed consciousness. Computed tomography (CT) scanning indicated a left thalamic hemorrhage and hydrocephalus. Angiograms revealed a characteristic vasculature suggestive of moyamoya disease, while a microaneurysm was observed in the right thalamoperforating artery (TPA), branching off from the right posterior cerebral artery. Preservation of the parent artery is difficult when performing embolization of a microaneurysm. As such, we administered endovascular treatment following identification of the collateral vascular network on cone-beam CT. During the procedure, a microcatheter was navigated into the right TPA; however, we were unable to advance it into the dome of the microaneurysm because the proximal portion of the microaneurysm was tortuous. However, on cone-beam CT, we noted that the distal portion of the right TPA was supplied by the posterior choroidal arteries. We, therefore, occluded the proximal portion of the right TPA using a coil, and the microaneurysm almost disappeared. Post-embolization magnetic resonance imaging (MRI) showed no ischemic lesions. The patient was discharged without any more neurological deficits following placement of a ventriculo-peritoneal shunt.

While managing this case, we were able to recognize the vascular structure of the microaneurysm and the collateral vascular network between the TPA and the posterior choroidal arteries using conebeam CT. We, therefore, suggest that cone-beam CT can be used to evaluate the vascular structure of microaneurysms and vascular anastomosis, despite a complicated collateral vascular network. Conebeam CT is, thus, a useful treatment strategy.