Declining trend in the estimated annual rupture rate of unruptured cerebral aneurysms in Japan: a nationwide study.

The incidence of subarachnoid hemorrhages (SAHs) in Japan has recently decreased. However, trends in the annual rates of unruptured cerebral aneurysms (UCAs) are unclear because calculations based on follow-up periods are limited to patients with ruptured cerebral aneurysms. We aimed to clarify current trends in the estimated annual rupture rates of UCAs in Japan and to identify the most relevant contributing factors. We analyzed data from the Japanese Ministry of Health, Labour and Welfare and records of the Japan Neurosurgical Society. The estimated annual rupture rates of UCAs between 2003 and 2018 were calculated according to age-adjusted mortality rates of SAH and number of treated ruptured cerebral aneurysms (RCAs). We estimated trends in annual rupture rates using sensitivity analysis and assessed associations between estimated annual rupture rates and the prevalences of hypertension and current smoking. The estimated annual rupture rate of UCAs significantly decreased from 1.44 to 0.87% and from 0.92 to 0.76%, respectively, in terms of age-adjusted mortality rates of SAH and number of treated RCAs (p < 0.001). The range of changes in estimated annual rupture rates of UCAs was - 1.13%‒0.83%, representing a declining UCA trend of 88%. The estimated annual rupture rates of UCAs declined by 0.02-0.10% and 0.01-0.05% with every percent decrease in hypertension and current smoking prevalence, respectively. The estimated annual rupture rate of UCAs has recently decreased in Japan, possibly due to a decrease in the prevalence of hypertension rather than smoking.

Outcome of CAS under flow reversal and analysis for the intraprocedural flow of internal carotid artery.

OBJECTIVE: Carotid artery stenting (CAS) under flow reversal with dual protection using a proximal balloon and distal filter has been an established procedure for internal carotid artery (ICA) stenosis. This study investigates the effect of external carotid artery (ECA) occlusion on outcomes of CAS and ICA flow under flow reversal. METHODS: We reviewed 231 cases of CAS under flow reversal with ECA occlusion and 32 without. In the last 14 of 32 cases, the flow in the ICA under flow reversal was analyzed by ultrasound. The collateral index, which was defined as the total value of the maximum diameters of the ipsilateral anterior cerebral artery at the A1 segment and the anterior communicating artery, as well as those of the ipsilateral posterior cerebral artery at the P1 segment and the ipsilateral posterior communicating artery, and the maximum diameter of the ipsilateral ECA were correlated with the flow direction in the ICA. RESULTS: There was no significant difference in the outcome of CAS between the groups with or without ECA occlusion. Among the 14 cases without ECA occlusion, antegrade flow in the ICA was observed in 6 cases (42.9 %). The group with the antegrade flow in the ICA exhibited a significantly lower collateral index (5.08±0.33 vs 6.71±0.28, p=0.01) and a significantly larger ECA diameter (4.66±0.51 mm vs 3.21±1.24 mm, p=0.01) than the group with the stagnant or retrograde flow in the ICA. CONCLUSIONS: The outcomes of CAS under flow reversal were acceptable even without ECA occlusion. The ECA occlusion may not be necessary for CAS under dual protection; however, distal filter protection should be used even under flow reversal.

Super T2-FLAIR mismatch sign: a prognostic imaging biomarker for non-enhancing astrocytoma, IDH-mutant.

PURPOSE: The T2-FLAIR mismatch sign is a highly specific diagnostic imaging biomarker for astrocytoma, IDH-mutant. However, a definitive prognostic imaging biomarker has yet to be identified. This study investigated imaging prognostic markers, specifically analyzing T2-weighted and FLAIR images of this tumor. METHODS: We retrospectively analyzed 31 cases of non-enhancing astrocytoma, IDH-mutant treated at our institution, and 30 cases from The Cancer Genome Atlas (TCGA)/The Cancer Imaging Archive (TCIA). We defined "super T2-FLAIR mismatch sign" as having a significantly strong low signal comparable to cerebrospinal fluid at non-cystic lesions rather than just a pale FLAIR low-signal tumor lesion as in conventional T2-FLAIR mismatch sign. Cysts were defined as having a round or oval shape and were excluded from the criteria for the super T2-FLAIR mismatch sign. We evaluated the presence or absence of the T2-FLAIR mismatch sign and super T2-FLAIR mismatch sign using preoperative MRI and analyzed the progression-free survival (PFS) and overall survival (OS) by log-rank test. RESULTS: The T2-FLAIR mismatch sign was present in 17 cases (55%) in our institution and 9 cases (30%) within the TCGA-LGG dataset without any correlation with PFS or OS. However, the super T2-FLAIR mismatch sign was detected in 8 cases (26%) at our institution and 13 cases (43%) in the TCGA-LGG dataset. At our institution, patients displaying the super T2-FLAIR mismatch sign showed significantly extended PFS (122.7 vs. 35.9 months, p = 0.0491) and OS (not reached vs. 116.7 months, p = 0.0232). Similarly, in the TCGA-LGG dataset, those with the super T2-FLAIR mismatch sign exhibited notably longer OS (not reached vs. 44.0 months, p = 0.0177). CONCLUSION: The super T2-FLAIR mismatch is a promising prognostic imaging biomarker for non-enhancing astrocytoma, IDH-mutant.

Lower Cervical Dural Arteriovenous Fistula with a "Skip Lesion" in the Brainstem: A Case Report.

Spinal dural arteriovenous fistulas (SDAVFs) are rare vascular malformations that can occur anywhere in the spine. Most SDAVFs lead to slow aggressive myelopathy due to venous congestion at a level adjacent to the shunt point. However, rare cases of localized brainstem edema without spinal cord lesions have been reported. In this study, we present a case of a lower cervical SDAVF that showed localized congestive edema of the medulla in the absence of an edematous change in the cervical spinal cord. The patient was a 57-year-old woman who experienced vertigo and vomiting without myelopathy that did not improve with conservative treatment. Magnetic resonance imaging (MRI) revealed high signal intensity in the left medulla on T2-weighted imaging (T2WI), while angiography revealed an SDAVF at the right C8 segmental level supplied by the right thyrocervical trunk. She underwent surgical interruption of the draining vein, which led to a rapid improvement in her symptoms. A subsequent follow-up MRI confirmed resolution of both the medullary edema and the dilated draining vein. SDAVFs may cause vertigo and vomiting, which are brainstem symptoms. Early diagnosis and surgical intervention are crucial for successful treatment outcomes.

[Training of Academic Neurosurgeons: Current Status and Challenges in Japan].

The concept of translational research, which emphasizes the importance of applying research findings to clinical practice, was first introduced in the early 21st century. Since then, Japan has actively promoted translational research through government and academic institutions, fostering collaboration between basic scientists and clinicians. Despite this, Japan's academic competitiveness has declined globally, particularly in fields such as neurosurgery, due to unique training systems and reduced time for research and education amidst physician work reforms. Herein, we discuss the significance of academic pursuits among clinicians, particularly in Japan's neurosurgery landscape, alongside future challenges.

Preventing Post-incisional Dural Shrink in Craniotomy: Introducing the "Roll-up Technique".

Dural dryness makes suturing difficult during dural closure after craniotomy. In this case, dural plasty is often performed using a membrane taken from the surrounding tissue (e.g., fascia or periosteum) or an artificial replacement membrane. Herein, we introduce our novel "roll-up technique" to reduce the utilization of substitute membranes and explore its effectiveness in dural closure. We retrospectively examined the medical records of 50 patients who underwent craniotomy for the first time for supratentorial intracranial lesions between 2015 and 2022. Furthermore, we divided them into two groups: (1) the conventional technique group, which consisted of patients in whom the dura mater was flipped after incision and protected with a moistened gauze (n = 23), and (2) the roll-up technique group, which consisted of patients in whom the dura mater was incised in a U shape, rolled up, and protected with a moist gauze (n = 27). After surgery, we compared the success rates of primary closure, operating time, craniotomy area, and percentage of complications (e.g., cerebrospinal fluid [CSF] leakage or infection) between the groups. Dural closure without dural substitutes using the roll-up technique had a higher success rate than that using the conventional technique (26/27 [96.3%] cases vs. 14/23 [60.9%] cases; P = 0.003). Postoperative CSF leakage or infection did not occur, and no statistically significant difference was observed in the operating time between the groups (P = 0.247). The roll-up technique for dural closure may effectively prevent post-incisional dural shrink after craniotomy.

Characteristics of radiation-induced brain tumors: case series and systematic review.

OBJECTIVE: Radiation therapy (RT) improves the outcome of patients with cancer but introduces the risk of radiation-induced neoplasms in cancer survivors. The most common radiation-induced brain tumors (RIBTs) are gliomas (RIGs), meningiomas (RIMs), and sarcomas (RISs). To investigate the characteristics of these RIBTs, the authors conducted a comprehensive review and analysis of their case series and relevant cases from the literature. METHODS: Sixteen patients in the case series and 941 patients from the literature who previously underwent cranial irradiation were included in this study. The age at irradiation for primary disease was recorded, and the latency period from irradiation to the development of RIBT and the median overall survival (OS) of patients with RIBTs were analyzed using the Kaplan-Meier method. Patients were stratified by age at the time of irradiation (pediatric vs nonpediatric) and the irradiation dose (higher vs lower dose), and latency and OS were compared using the log-rank test. RESULTS: Among patients with RIBTs, 23.4% underwent radiation at < 5 years of age, and 46.6% underwent RT in the 1st decade of life. The median ages at cranial irradiation were 8.4 (IQR 4.1-16) years in patients with RIMs, 9 (IQR 5-23) years in patients with RIGs, and 27.7 (IQR 13.8-40) years in patients with RISs. The median latency period from irradiation to the development of RIM was significantly longer than that to the development of RIG and RIS (RIM: 20 years, RIG: 9 years, RIS: 10 years; p < 0.0001). The latency period was shorter in the nonpediatric patient group with RIMs (p = 0.047). The OS was significantly longer in patients with RIMs than in those with RIGs and RISs (RIM: not reached, RIG: 11 months, RIS: 11 months; p < 0.0001). The OS of patients with RIMs and RIGs was significantly shorter in patients who received higher radiation doses (p = 0.0095 and p = 0.0026, respectively). CONCLUSIONS: The prognosis was poor and worse for patients with RIGs and RISs than for those with RIMs, and patients with RIBTs who underwent higher-dose irradiation for primary disease had poor prognoses. Because RIBTs develop more than a decade after cranial irradiation, long-term follow-up is crucial.

Flow alteration surgery using a radial artery graft for recurrent ruptured vertebral artery dissecting aneurysm after stent-assisted coil embolization: A case report.

BACKGROUND: Ruptured vertebral artery dissecting aneurysm (VADA) is often treated surgically with coil embolization and sometimes recurs. We herein report a case of recurrent ruptured VADA after stent-assisted coil embolization (SAC) that was successfully treated with flow alteration surgery using a radial artery (RA) graft. CASE DESCRIPTION: A 67-year-old woman presented with headache and coma. Enhanced CT revealed subarachnoid hemorrhage due to right VADA. Since the left VA was hypoplastic, the aneurysm was treated with SAC. However, follow-up angiography revealed recurrence of the aneurysm. Additional embolization was not considered due to the small size of the recurrent lesion and the presence of a stent; therefore, flow alteration surgery was performed using a RA graft. There were no neurological deficits after surgery or recurrence. CONCLUSION: Flow alteration surgery using a RA graft is useful for recurrent VADA after SAC.

Surgical Risk in Elderly Patients with Meningiomas in Japan.

Background/Objective: No guidelines indicate surgical risk factors for the elderly because of the lack of data from general neurosurgeons. To better understand the management of surgical risk in elderly patients with meningiomas based on a national database in Japan. Methods: Results of surgically treated meningiomas were explored in 8138 patients registered in the Diagnosis Procedure Combination database in Japan during 2010-2015. Age (<65, 65-74, and ≥75 years), sex, Barthel index (BI), medical history, tumor location, oral medication prescriptions on admission, and stroke complications were evaluated. Multivariate logistic regression analysis identified risk factors for stroke complications, BI deterioration between admission and discharge, and in-hospital mortality. Results: Advanced age was the prominent risk factor for BI deterioration (odds ratio: 3.26; 95% confidence interval: 2.69-3.95) but not for in-hospital mortality. Lower BI (60-80) on admission increased the risk of BI deterioration in all age groups; however, BI < 60 demonstrated a significant inverse risk (0.47; 0.32-0.69) in the elderly (≥75 years). Location (falx, parasagittal, and deep) and anticoagulants were not significant risk factors for BI deterioration in patients aged ≥ 75 years, despite being significant risk factors in patients aged <65 and/or 65-74 years. Conclusions: Although advanced age could lead to postoperative functional decline at discharge, it was not sufficiently significant enough to be associated with in-hospital mortality. Because of the possibility of recovery even in elderly patients with severe disabilities, appropriate surgical selection and optimal management may lead to favorable functional outcomes in elderly patients with meningiomas.

Magnetoencephalographic detection of synchronized epileptic activity between the hippocampus and insular cortex.

Most magnetoencephalographic signals are derived from synchronized activity in the brain surface cortex. By contrast, the contribution of synchronized activity in the deep brain to magnetoencephalography (MEG) has remained unclear. We compared stereotactic electroencephalography (sEEG) with simultaneous MEG findings in a patient with temporal lobe epilepsy to determine the conditions under which MEG could also detect sEEG findings. The synchrony and similarity of the waves were evaluated using visual inspection and wavelet coherence. A 45-year-old woman with intractable temporal lobe epilepsy underwent sEEG and MEG simultaneously to determine the laterality and precise location of the epileptic focus. When spike-and-waves were seen in the right hippocampal head alone, no distinct spike-and-waves were observed visually in the right temporal MEG. The seizure then spread to the right insula on sEEG with a rhythmic theta frequency while synchronous activity was observed in the right temporal MEG channels. When polyspikes appeared in the right hippocampus, the right temporal MEG showed electrical activity with relatively high similarity to that of the right hippocampal head and insular cortex but less similarity to that of the right lateral temporal lobe cortex. MEG might detect epileptic activity synchronized between the hippocampus and insular cortex.

Artificial intelligence for volumetric measurement of cerebral white matter hyperintensities on thick-slice fluid-attenuated inversion recovery (FLAIR) magnetic resonance images from multiple centers.

We aimed to develop a new artificial intelligence software that can automatically extract and measure the volume of white matter hyperintensities (WMHs) in head magnetic resonance imaging (MRI) using only thick-slice fluid-attenuated inversion recovery (FLAIR) sequences from multiple centers. We enrolled 1092 participants in Japan, comprising the thick-slice Private Dataset. Based on 207 randomly selected participants, neuroradiologists annotated WMHs using predefined guidelines. The annotated images of participants were divided into training (n = 138) and test (n = 69) datasets. The WMH segmentation model comprised a U-Net ensemble and was trained using the Private Dataset. Two other models were trained for validation using either both thin- and thick-slice MRI datasets or the thin-slice dataset alone. The voxel-wise Dice similarity coefficient (DSC) was used as the evaluation metric. The model trained using only thick-slice MRI showed a DSC of 0.820 for the test dataset, which is comparable to the accuracy of human readers. The model trained with the additional thin-slice dataset showed only a slightly improved DSC of 0.822. This automatic WMH segmentation model comprising a U-Net ensemble trained on a thick-slice FLAIR MRI dataset is a promising new method. Despite some limitations, this model may be applicable in clinical practice.

Relevance of the Foramen of Vesalius for Preoperative Tumor Embolization in Skull Base Meningioma.

OBJECTIVE: The objective of this study was to investigate the role of the foramen of Vesalius (FV) in the pathogenesis of skull base meningioma by analyzing data from various multi-image modalities. METHODS: For this single-center retrospective study, 39 consecutive patients with skull base meningioma who underwent tumor resection between January 2020 and March 2023 were enrolled. The anatomical and pathological characteristics of the FV were evaluated using computed tomography and 3-dimensional digital subtraction angiography. The clinical significance of the FV in tumor hemodynamics and treatment, such as preoperative tumor embolization, was investigated using the 3-dimensional digital subtraction angiography/computed tomography fusion images. RESULTS: We identified FV in 52% (17/27) of the finally included patients. In 10 (30%) patients, the FV was found bilaterally with no significant variation in appearance between the healthy and tumor-affected sides (P = 0.786). The mean FV diameter was significantly larger on the tumor-affected side (P = 0.010). No significant anatomical differences, like duplication and partial assimilation with the foramen ovale, were observed between the 2 sides. The FV was involved in venous skull base perfusion around the tumor in 9 cases. In 4 cases where it was the pathway for tumor feeders, preoperative tumor embolization via the FV resulted in disappearance of the tumor stain. No complications associated with endovascular treatment were observed. CONCLUSIONS: This study elucidated the anatomical asymmetry of the FV and its role in the hemodynamics of skull base meningioma. Our findings highlight the significance of performing anatomical and pathological evaluations of the FV in determining treatment strategies, including preoperative embolization, for skull base lesions.

Compatibility of the semijailing technique with extremely soft i-ED coils for ruptured blood blister-like and dissecting aneurysms: patient series.

BACKGROUND: Optimal treatment options for ruptured blood blister-like aneurysms (BBAs) and dissecting aneurysms (DAs) have not yet been established. Endovascular treatment may achieve vessel reconstruction with the preservation of antegrade blood flow; however, securing curative hemostasis at the fragile rupture point remains a major concern. OBSERVATIONS: Two ruptured BBAs and two ruptured DAs treated by stent-assisted coiling with the semijailing technique in the last 2 years are described herein. The devices used were braided stents and i-ED coils, which are new low-memory shape and extremely soft coils. Neither rebleeding nor ischemic complications were observed. All patients had a favorable outcome and showed no recurrence after treatment. LESSONS: All aneurysms were treated without ischemic complications or rebleeding. The good compatibility of braided stents and the new concept coils in stent-assisted coiling by the semijailing technique provides insight into these intractable hemorrhagic vascular pathologies.

[Thrombectomy].

Endovascular procedures have become the standard treatment for acute stroke caused by large vessel occlusion. Various strategies are available, including stent retrieval, aspiration catheter placement, and combined techniques. However, the first-pass effect can be maximized using the technique most familiar to each surgeon and institution. Therefore, it is necessary to understand the characteristics of each device and develop case-specific treatment strategies.

[Preoperative Simulation in Epilepsy Surgery].

In patients with intractable epilepsy, seizure focus resection can yield favorable seizure outcomes. First, the localization of the seizure focus is estimated by noninvasive methods such as magnetic resonance imaging(MRI), video-electroencephalography(EEG)monitoring, nuclear medicine examinations, magnetoencephalography, and neuropsychological tests. A subgroup of patients may require additional information obtained from the intracranial EEG. There are two major methods for intracranial EEG: intracranial EEG with subdural grid electrodes(SDG)and stereotactic electroencephalography. If the estimated seizure focus overlaps with the eloquent area in noninvasive studies, the margin and extent of the resection are determined by the results of intracranial EEG and functional mapping by electrical cortical stimulation. Herein, we present a case of lobe epilepsy with subtle MRI lesions in the superior temporal sulcus of the language-dominant hemisphere. The results of the SDG and functional mapping showed that the seizure onset zone overlapped with the language area. Resection of the middle and inferior temporal gyri and multiple transections of the language area resulted in Engel IIB seizure outcomes. In such cases, a thorough preoperative simulation is required to determine the best resection margin for seizure control and functional preservation.

[Carotid Artery Stenting].

Currently, stricter indications for carotid artery stenosis are required owing to improvements in multifaceted medical treatment, including the intensive management of risk factors for atherosclerosis and lifestyle changes. High-risk factors for carotid artery stenting, such as vulnerable plaques, severe calcification, pseudo-occlusion, and difficult access, should be evaluated before endovascular intervention. Therefore, we need to understand the characteristics of each device to achieve maximum risk reduction for carotid artery stenting.

Usefulness of combined bypass surgery for moyamoya disease in infants under 1 year of age: A technical case report.

Background: Among pediatric cases of moyamoya disease (MMD), cerebral ischemic symptoms often progress and worsen rapidly in infants under one year of age; therefore, it is important to treat them as early as possible. However, direct bypass surgery is often technically difficult for infants due to their small blood vessels. Here, we describe our technique to resolve the technical challenges encountered during superficial temporal artery-to-middle cerebral artery (STA-MCA) bypass surgery in infants aged <1 year with MMD, focusing on specific procedures. Case Description: We performed bilateral STA-MCA and indirect bypass in a 1-year-old girl with MMD and cerebral infarction. Before treatment, a peripherally inserted central venous catheter (PICC) was placed to avoid ischemic attacks associated with crying, dehydration, and malnutrition. All examinations and procedures that would be stressful to the patient, such as blood examinations, were performed using PICC or under sedation. The STA-MCA diameters were 0.8 and 1.2 mm, respectively. After suturing the planned anastomosis with one stitch using an 11-0 monofilament nylon thread, the thread was lifted upward, and the arterial wall was incised. Anastomosis was performed using an 11-0 monofilament nylon thread with 2-4 stitches on each side. The operation was completed without patency problems. Postoperative blood flow improved, and the patient had a good treatment course. Conclusion: Direct bypass for MMD patients aged <1 year is technically challenging; however, the vessels can be connected if the procedure is carefully performed with consideration of the characteristics of the infant's vessels.

Retained Intracerebral Depth Electrode after Stereotactic Electroencephalography Monitoring: A Case Report.

Stereotactic electroencephalography (SEEG) is an increasingly popular surgical modality for localizing the epileptogenic zone. Robot-guided stereotactic electrode placement has been covered in Japan by National Health Insurance since 2020. However, several surgical devices, such as the anchor bolt (a thin, hollow, metal shaft that serves as a guide screw or fixing for each electrode), have not been approved. A 14-year-old female who underwent SEEG for intractable epilepsy and required additional surgery to remove a retained depth electrode from the skull after the SEEG monitoring was finished. She had uncontrolled focal seizures consisting of nausea and laryngeal constriction at the onset. After a comprehensive presurgical evaluation, robot-guided stereotactic electrode implantation was performed to evaluate her seizures by SEEG. Nine depth electrodes were implanted through the twist drill hole. The electrodes were sutured to her skin for fixation without anchor bolts. When we attempted to remove the electrodes after 8 days of SEEG monitoring, one of the electrodes was retained. The retained electrode was removed through an additional skin incision and a small craniectomy under general anesthesia. We confirmed narrowing of the twist drill hole pathway in the internal table of the skull due to osteogenesis, which locked the electrode. This complication might be avoided if an anchor bolt had been used. This case report prompts the approval of the anchor bolts to avoid difficulty in electrode removal. Moreover, approval of a depth electrode with a thinner diameter and more consistent hardness is needed.

Characteristics of MicroRNA Expression Depending on the Presence or Absence of Meningioma in Patients with Neurofibromatosis Type 2: A Secondary Analysis.

Meningioma is the second most frequent tumor in patients with neurofibromatosis type 2 (NF2). The presence of meningioma is believed to be a negative prognostic marker in these patients. However, the molecular mechanisms involved in the tumorigenesis of NF2-associated meningioma are not well characterized. Epigenetic regulation, including microRNAs (miRNAs), may be involved in the development of different tumor types in patients with NF2. The objective of this study is to explore the different characteristics of serum miRNA expression depending on the presence or absence of meningioma in patients with NF2. Nine patients with NF2 who were treated at the Department of Neurosurgery, Hiroshima University Hospital, were included. Total RNA (including small RNAs) was extracted from serum samples for the preparation of a small RNA library for next-generation sequencing analysis. Differentially expressed miRNAs (DEMs) were analyzed using the DESeq2 package to compare the characteristic miRNA expression profiles of patients with and without meningioma. In small RNA sequencing analysis, out of a total of 1,879 miRNAs registered in the database, the expressions of 657 miRNAs were observed. In DEM analysis, the expressions of four miRNAs, namely, hsa-miR-664b, hsa-miR-7706, hsa-miR-590, and hsa-miR-6513, were downregulated in patients with NF2 with meningioma compared with patients with NF2 without meningioma. Hsa-miR-193a was identified as the only upregulated miRNA in patients with NF2 with meningioma. In conclusion, we identified different circulating miRNA expression characteristics depending on the presence or absence of meningioma in patients with NF2.

High signal intensity of the intraaneurysmal sac on T1 CUBE imaging as a predictor of aneurysm stability after coil embolization.

OBJECTIVE: Histopathological studies of aneurysms after coil embolization showed that thrombus formation during the first month after endovascular treatment (EVT) played an important role in the healing process. The authors hypothesized that dedicated T1-weighted imaging may be used to predict stable aneurysms by visualizing the thrombus status within coil-treated aneurysms. Therefore, this study investigated the relationship between the signal intensity (SI) of the intraaneurysmal sac after coil embolization and aneurysm stability. METHODS: The study population included 82 patients with 86 aneurysms who underwent T1-weighted 3D black-blood fast spin-echo (T1 CUBE) imaging within 1 month after coil embolization between 2019 and 2022. The relative SI of a coil-treated aneurysm (RSIcoiled) was calculated as follows: the mean SI of the intraaneurysmal sac/the mean SI of the genu of the corpus callosum. Aneurysms with enlarged remnants on MR angiography (MRA) within 6 months after EVT were defined as recurrence, while a decrease of intraaneurysmal flow on MRA was defined as improved embolization status. Stable aneurysms were defined as improvement or no change in embolization status 6 months after coil embolization. The volume embolization ratio (VER) was calculated as the ratio of the packed coil volume to the aneurysm volume. Differences between stable and recurrent aneurysms were examined. All aneurysms were divided into high and low RSIcoiled groups based on the cutoff value of RSIcoiled, and differences between the two groups were also evaluated. RESULTS: Recurrence was confirmed for 26 of 86 aneurysms. A univariable analysis showed that small aneurysms, high VER, and high RSIcoiled were associated with aneurysm stability. In the receiver operating characteristic curve analysis, the optimal cutoff value for RSIcoiled to differentiate stable from recurrent aneurysms was 0.54. The cutoff value for RSIcoiled was selected as 0.50 (sensitivity 0.77, specificity 0.70) because it was half the value of the SI of the corpus callosum and close to the optimal cutoff value. In a multivariable analysis, RSIcoiled > 0.50 (OR 8.1, 95% CI 2.5-27) remained a significant factor for aneurysm stability. The high RSIcoiled group showed a higher rate of an improved embolization status (26% vs 6.1%, p = 0.022) and stable aneurysms (85% vs 15%, p = 0.0002). CONCLUSIONS: RSIcoiled was associated with postcoiling aneurysm stability. High RSIcoiled might imply intraaneurysmal thrombus formation associated with the healing process of coil-treated aneurysms.