Computational fluid dynamics for predicting the growth of small unruptured cerebral aneurysms.

OBJECTIVE: Larger cerebral aneurysms are more likely to enlarge, but even small aneurysms can grow. The aim of this study was to investigate the hemodynamic characteristics regarding the growth of small aneurysms using computational fluid dynamics (CFD). METHODS: The authors analyzed 185 patients with 215 unruptured cerebral aneurysms with a maximum diameter of 3-5 mm, registered in a multicenter prospective observational study of unruptured aneurysms (Systematic Multicenter Study of Unruptured Cerebral Aneurysms Based on Rheological Technique at Mie) from January 2013 to February 2022. Based on findings on repeated images, aneurysms were divided into a stable group (182 aneurysms) and a growth group (33 aneurysms). The authors developed the high shear concentration ratio (HSCR), in which high wall shear stress (HWSS) was defined as a value of 110% of the time-averaged wall shear stress of the dome. High shear area (HSA) was defined as the area with values above HWSS, and the ratio of the HSA to the surface area of the dome was defined as the HSA ratio (HSAR). They also created the flow concentration ratio (FCR) to measure the concentration of the inflow jet. Multivariate logistic regression analysis was performed to determine morphological variables and hemodynamic parameters that independently characterized the risk of growth. RESULTS: The growth group had a significantly higher projection ratio (0.74 vs 0.67, p = 0.04) and volume-to-ostium area ratio (1.72 vs 1.44, p = 0.02). Regarding the hemodynamic parameters, the growth group had significantly higher HSCR (6.39 vs 4.98, p < 0.001), lower HSAR (0.28 vs 0.33, p < 0.001), and lower FCR (0.61 vs 0.67, p = 0.005). In multivariate analyses, higher HSCR was significantly associated with growth (OR 0.81, 95% CI 7.06 e-1 to 9.36 e-1; p = 0.004). CONCLUSIONS: HSCR may be a useful hemodynamic parameter to predict the growth of small unruptured cerebral aneurysms.

Hemodynamic differences of posterior communicating artery aneurysms between adult and fetal types of posterior cerebral artery.

BACKGROUND: The recanalization of posterior communicating artery (PCoA) aneurysms after endovascular treatment has been analyzed by various factors. However, the differences between adult and fetal types of posterior cerebral artery (PCA) have not been fully investigated. The main aim of this study was to investigate hemodynamic differences of PCoA aneurysms between adult and fetal types using computational fluid dynamics (CFD). METHODS: Fifty-five PCoA aneurysms were evaluated by 3D CT angiography and divided into unruptured aneurysms with adult-type or fetal-type PCAs (19 cases, UA group; 9 cases, UF group) and ruptured aneurysms with adult-type or fetal-type PCAs (17 cases, RA group; 10 cases, RF group). These native aneurysms were analyzed by CFD regarding morphological and hemodynamic characteristics. To evaluate simulated endovascular treatment of aneurysms, CFD was performed using porous media modeling. RESULTS: Morphologically, the RA group had significantly smaller parent artery diameter (2.91 mm vs. 3.49 mm, p=0.005) and higher size ratio (2.54 vs. 1.78, p=0.023) than the RF group. CFD revealed that the UA group had significantly lower oscillatory shear index (OSI) (0.0032 vs. 0.0078, p=0.004) than the UF group and that the RA group had lower WSS (3.09 vs. 11.10, p=0.001) and higher OSI (0.014 vs. 0.006, p=0.031) than the RF group, while the RF group presented significantly higher intra-aneurysmal flow velocity (0.19 m/s vs. 0.061 m/s, p=0.002) than the RA group. Porous media modeling of simulated treatment revealed higher residual flow volume in the fetal-type groups. CONCLUSIONS: These results suggested that PCoA aneurysms with fetal-type PCAs had different morphological features and hemodynamic characteristics compared with those with adult-type PCAs, leading to high risks of recanalization.

An alternative method to evaluate lumbar interbody fusion status focusing on position change of screw-rod constructs.

OBJECTIVES: The evaluation of lumbar interbody fusion status is generally subjective and may differ among raters. The authors examined whether the assessment of position change of screw-rod constructs could be an alternative method for the evaluation of fusion status. METHODS: Sixty-three patients undergoing lumbar interbody single-level fusion were retrospectively reviewed. Three-dimensional images of screw-rod constructs were created from baseline CT examination on the day after surgery and follow-up CT examinations (3-5 months, 6-11 months, and ≥ 12 months) and superposed, with position change of screw-rod constructs being evaluated by the distance between the 3-dimensional images at baseline and follow-up. The evaluation was repeated twice to confirm the reproducibility. Fusion status on follow-up CT examinations was assessed by three raters, where inter-rater reliability was evaluated with Fleiss' kappa. The results of the fusion status were classified into fusion and incomplete fusion groups in each timing of follow-up CT examinations, where the amount of position change was compared between the two groups. RESULTS: The evaluation of position change was completely reproducible. The Fleiss' kappa (agreements) was 0.481 (69.4%). The medians of the amount of position change in fusion and incomplete fusion groups were 0.134 mm and 0.158 mm at 3-5 months (p = 0.21), 0.160 mm and 0.190 mm at 6-11 months (p = 0.02), and 0.156 mm and 0.314 mm at ≥ 12 months (p = 0.004). CONCLUSIONS: The assessment of position change of screw-rod constructs at 6 months or more after surgery can be an alternative method for evaluating lumbar interbody fusion status. KEY POINTS: • Lumbar interbody fusion status (satisfactory, incomplete, or failed) is associated with the quantification of position change of screw-rod in this study. • Reference values for the evaluation of position change in identifying interbody fusion status are provided. • Position change of screw-rod could be a supportive method for evaluating interbody fusion status.

Glioblastoma with concomitant moyamoya vasculopathy in neurofibromatosis type 1: illustrative case.

BACKGROUND: In a case of concurrent glioblastoma and moyamoya vasculopathy, it is arduous to safely perform surgery because the brain is highly vulnerable and collaterals are sometimes well developed. In addition, radiotherapy carries a risk of aggravating moyamoya vasculopathy, and chemotherapeutic agents also have a risk of interfering with collateral development. OBSERVATIONS: A 48-year-old woman with neurofibromatosis type 1 was admitted because of left hemiparesis and hemispatial neglect. Brain imaging studies revealed a large mass with peripheral enhancement in the right frontal lobe and occlusion of the bilateral middle cerebral arteries with an abnormal vascular network at the base of the brain. Total tumor resection was performed, and the pathological diagnosis was isocitrate dehydrogenase-mutant glioblastoma. Radiotherapy with a total dose of 60 Gy was delivered with concurrent temozolomide, and thereafter six cycles of adjuvant temozolomide were given. Progression of moyamoya vasculopathy without symptoms was observed after the completion of each of radiotherapy and adjuvant temozolomide. LESSONS: The authors present the first adult case of glioblastoma with moyamoya vasculopathy. Careful consideration and attention should be given throughout treatment to avoiding moyamoya vasculopathy-related ischemic and hemorrhagic events. Although the patient did not exhibit neurological deterioration, progression of moyamoya vasculopathy occurred early after radiotherapy and continued thereafter.

Machine learning prediction of hematoma expansion in acute intracerebral hemorrhage.

To examine whether machine learning (ML) approach can be used to predict hematoma expansion in acute intracerebral hemorrhage (ICH) with accuracy and widespread applicability, we applied ML algorithms to multicenter clinical data and CT findings on admission. Patients with acute ICH from three hospitals (n = 351) and those from another hospital (n = 71) were retrospectively assigned to the development and validation cohorts, respectively. To develop ML predictive models, the k-nearest neighbors (k-NN) algorithm, logistic regression, support vector machines (SVMs), random forests, and XGBoost were applied to the patient data in the development cohort. The models were evaluated for their performance on the patient data in the validation cohort, which was compared with previous scoring methods, the BAT, BRAIN, and 9-point scores. The k-NN algorithm achieved the highest area under the receiver operating characteristic curve (AUC) of 0.790 among all ML models, and the sensitivity, specificity, and accuracy were 0.846, 0.733, and 0.775, respectively. The BRAIN score achieved the highest AUC of 0.676 among all previous scoring methods, which was lower than the k-NN algorithm (p = 0.016). We developed and validated ML predictive models of hematoma expansion in acute ICH. The models demonstrated good predictive ability, showing better performance than the previous scoring methods.

Pathological haemodynamics of a middle cerebral artery stenosis validated by computational fluid dynamics.

Intracranial arterial stenosis (ICAS) is one of the important causes of ischaemic stroke. However, the treatment for ICAS is not optimised, including medical therapies, because the mechanisms are diverse. The authors report a case of severe middle cerebral arterial stenosis accompanied by a floating thrombus, which caused artery-to-artery cerebral emboli. The patient was successfully treated with multiple antithrombotics including an anticoagulant, and the thrombus disappeared. Local haemodynamics around the middle cerebral arterial stenosis was analysed by computational fluid dynamics (CFD) using the patient-specific model. CFD analysis demonstrated that thrombus formation occurred at the poststenotic area with severe stagnant flow, which was judged by both wall shear stress and shear rate less than the specific thresholds. These findings suggest that CFD may be useful to diagnose the risk of stagnant flow-induced thrombosis and to predict the effectiveness of anticoagulant agents to prevent distal embolisms in ICAS.

Radiolucent Zone around Screws is Associated with Position Change of Screw-rod Constructs.

PURPOSE: A radiologic assessment method to measure position change of screw-rod constructs over time by superposing the 3­dimensional images assists in quantitative evaluation of screw loosening. We investigated the association between position change and radiolucent zone that was commonly used for diagnosing screw loosening. METHODS: In this study 101 patients who underwent lumbar fusion were reviewed. Patient characteristics included age, sex, indications for surgery, number of fused levels, surgical procedures, and timing of follow-up computed tomography (CT, 1-5 months, 6-11 months, and ≥ 12 months). The Hounsfield unit values of L1 vertebra on preoperative CT were measured, and the radiolucent zone on each follow-up CT was evaluated. Using baseline CT on the day after surgery and follow-up CT, 3­dimensional images of screw-rod constructs were generated and superposed. Position change was assessed by the median of the distances between the 3­dimensional images at baseline and follow-up using the automated measurement method. Patient characteristics, the Hounsfield unit values of L1, and the amount of position change were categorized into the radiolucent zone presence and absence groups and compared. RESULTS: The medians of position change were 0.281 mm and 0.136 mm in the radiolucent zone presence and absence groups, respectively (P < 0.001 by Mann-Whitney U-test). The area under the curve for position change in identifying radiolucent zone was 0.846; the cut-off value was 1.76 mm. In multivariable analysis, position change was independently associated with radiolucent zone (adjusted odds ratio per 0.1 mm, 2.80, 95% confidence interval 1.70-4.61). CONCLUSION: Radiolucent zone was associated with position change of screw-rod constructs.

A case presenting as fatal subarachnoid hemorrhage due to segmental arterial mediolysis associated with Crohn's disease.

BACKGROUND: Segmental arterial mediolysis (SAM) is a rare arterial pathology and can cause rupture or dissection of the intracranial arterial wall. The etiology is unveiled, but vasospastic stimuli such as migraine are considered as a possible cause of SAM. We present the first case of subarachnoid hemorrhage (SAH) due to SAM associated with Crohn's disease and migraine, and discuss the possible contribution of Crohn's disease to the development of SAM besides migraine. CASE DESCRIPTION: A 33-year-old man with Crohn's disease, which had been treated with adalimumab, repeatedly underwent 3-tesla magnetic resonance (MR) imaging and angiography for severe headache due to migraine and the subsequent development of fatigue in the left arm and both legs. At 7 months after the last MR imaging studies showing no abnormalities, he had a sudden onset of severe SAH, which was caused by rupture or dissection of the terminal portion in the right internal carotid artery. As his brain-stem reflexes were absent, the patient was conservatively treated and died 6 days after the ictus. By postmortem histopathological examination, SAM was diagnosed as the cause of SAH. Vasa vasorum was also observed around the rupture point. CONCLUSIONS: Our case suggests that: 1) the formation of vasa vasorum may be an antecedent pathology for vessel rupture of the fragile arterial wall affected by SAM, and 2) vasospastic nature of both Crohn's disease and migraine may contribute to the development of intracranial SAM.

Computational Fluid Dynamics for Cerebral Aneurysms in Clinical Settings.

Hemodynamics is thought to play an important role in the pathogenesis of cerebral aneurysms and recent development of computer technology makes it possible to simulate blood flow using high-resolution 3D images within several hours. A lot of studies of computational fluid dynamics (CFD) for cerebral aneurysms were reported; therefore, application of CFD for cerebral aneurysms in clinical settings is reviewed in this article.CFD for cerebral aneurysms using a patient-specific geometry model was first reported in 2003 and it has been revealing that hemodynamics brings a certain contribution to understanding aneurysm pathology, including initiation, growth and rupture. Based on the knowledge of the state-of-the-art techniques, this review treats the decision-making process for using CFD in several clinical settings. We introduce our CFD procedure using digital imaging and communication in medicine (DICOM) datasets of 3D CT angiography or 3D rotational angiography. In addition, we review rupture status, hyperplastic remodeling of aneurysm wall, and recurrence of coiled aneurysms using the hemodynamic parameters such as wall shear stress (WSS), oscillatory shear index (OSI), aneurysmal inflow rate coefficient (AIRC), and residual flow volume (RFV).

A Ruptured Anterior Communicating Artery Aneurysm with Infra-optic Course of the Anterior Cerebral Artery: A Case Report and a Short Review.

Infra-optic course of the anterior cerebral artery (IOA) is rare and approximately 55 cases of this anomaly have been described. We present a case of a ruptured anterior communicating artery (ACoA) aneurysm arising at the junction between the left IOA and the bilateral A2 segments, at which the right A1 segment was absent. One of the recurrent arteries of Heubner branched off directly from the aneurysmal dome, and was obstructed at aneurysmal neck clipping via an anterior interhemispheric (AIH) approach. In this report, accompanied anatomical variations and surgical approaches for ACoA aneurysms with IOA are reviewed. An IOA is frequently associated with other vascular anomalies, and the origin of functionally important recurrent arteries of Heubner is also variable. Preoperative accurate evaluation of vessel structures and the maximal exposure at surgery are very important. Pterional approach from the ipsilesional side is reportedly to be safe, but interhemispheric approach is also suggested to be effective as to full exposure to recognize the perianeurysmal anatomical structures including potential vessel anomalies.

A screw position change at an early postoperative stage preceding the subsequent occurrence of screw loosening.

PURPOSE: The authors recently proposed the novel radiologic assessment method to measure chronological screw position changes precisely. The aim of this study was to predict the late occurrence of screw loosening, which was diagnosed by the radiographic lucent zone, by evaluating screw position changes at an early postoperative stage using the novel method. METHODS: Forty-three patients who underwent thoracolumbar screw fixation and follow-up computed tomography (CT) scans on the day, between 1 and 5 weeks, and at more than 6 months after surgery were retrospectively evaluated. Screw images were generated from CT data. Screw position changes were evaluated by superposing screw images on the day and between 1 and 5 weeks after surgery. Screw loosening was diagnosed by the radiographic lucent zone on CT images at 6 months or later post-surgery, and patients were classified into screw loosening and non-loosening groups. The early screw position changes were compared between the two groups. RESULTS: Significant differences in early screw position changes were found between the screw loosening and non-loosening groups in Mann-Whitney U test (p = 0.001). On the receiver operating characteristic (ROC) curve analysis, the area under the ROC curve was 0.791, and the best cutoff value of early screw position change for the prediction of screw loosening was 0.83 mm with a sensitivity of 64.0% and a specificity of 88.9%. CONCLUSION: We calculated a cutoff value of the screw position changes at an early postoperative stage for the prediction of subsequent development of screw loosening with the radiographic lucent zone.

Measurement of human blood viscosity a using Falling Needle Rheometer and the correlation to the Modified Herschel-Bulkley model equation.

We measured the blood viscosity of 25 male and 25 female healthy people (total 50) using a compact-sized falling needle viscometer (Falling Needle Rheometer) capable of highly accurate measurements. Based on the analysis of the flow characteristics, most of the blood specific non-Newtonian fluid (Casson fluid) behavior was confirmed. Additionally, the blood from males has a higher apparent viscosity and Casson yield value than that from women. Furthermore, a new Herschel-Bulkley type model equation representing the relationship between the shear rate and apparent viscosity of human blood was proposed based on the measured blood flow characteristics. The proposed model improved the exponential term on the shear rate and added the constant term on the yield stress so that the measured value can be correlated with a high accuracy. Using the proposed model equation, the correlation accuracy of all of the measured human blood viscosities was better than in the Herschel-Bulkley model equation and Casson model in a wide range of shear rate regions. By incorporating numerical flow analysis (computational fluid dynamics), this model equation may contribute to analyses considering the non-Newtonian fluidity of human blood.

Decision-making for endovascular treatment of a fusiform basilar trunk artery aneurysm with visualization of chronological blood mass distribution using computational fluid dynamics.

Fusiform basilar trunk artery aneurysms are rare lesions, to which stent-assisted coil embolization or flow diversion have been generally applied. When a stent is placed from the distal basilar artery or the posterior cerebral artery to the vertebral artery (VA) through a fusiform basilar artery aneurysm, the side of the VA may be determined according to its size, shape, accessibility and aneurysm projection. In the present report, we constructed stent-placement models from the distal basilar artery to either VA across the aneurysm, and investigated blood mass distribution using computational fluid dynamics. The results revealed more stagnated blood flow in the aneurysm after stenting to the left VA. According to the simulation, stent-assisted coil embolization of the aneurysm was performed, resulting in sufficient obliteration. This visualization technique could be useful for decision-making for the treatment of complicated aneurysms and has a wide range of potential applications.

Machine Learning Classification of Cerebral Aneurysm Rupture Status with Morphologic Variables and Hemodynamic Parameters.

PURPOSE: To construct a classification model of rupture status and to clarify the importance of morphologic variables and hemodynamic parameters on rupture status by applying a machine learning (ML) algorithm to morphologic and hemodynamic data of cerebral aneurysms. MATERIALS AND METHODS: Between 2011 and 2019, 226 (112 ruptured and 114 unruptured) cerebral aneurysms in 188 consecutive patients were retrospectively analyzed with computational fluid dynamics (CFD). A random forest ML algorithm was applied to the results to create three classification models consisting of only morphologic variables (model 1), only hemodynamic parameters (model 2), and both morphologic variables and hemodynamic parameters (model 3). The accuracy of rupture status classification and the importance of each variable or parameter in the models were computed. RESULTS: The accuracy was 77.0% in model 1, 71.2% in model 2, and 78.3% in model 3. The three most important features were projection ratio, size ratio, and aspect ratio in model 1; low shear area ratio, oscillatory shear index, and oscillatory velocity index in model 2; and projection ratio, irregular shape, and size ratio in model 3. CONCLUSION: Classification models of rupture status of cerebral aneurysms were constructed by applying an ML algorithm to morphologic variables and hemodynamic parameters. The model worked with relatively high accuracy, in which projection ratio, irregular shape, and size ratio were important for the discrimination of ruptured aneurysms.Supplemental material is available for this article.© RSNA, 2020.

Dysphagia following C1 laminectomy and posterior atlantoaxial fixation for retro-odontoid pseudotumor: a case report.

Purpose: Although dysphagia is known potential complication of cervical spine surgery, it rarely occurs after a posterior approach. We describe an unusual case of a retro-odontoid pseudotumor that suffered dysphagia following a C1 laminectomy and posterior atlantoaxial fixation.Materials and methods: A 79-year-old man presented with progressive tetraparesis and bladder and bowel dysfunction due to severe compression to cervical cord at C1 from a retro-odontoid pseudotumor. After C1 laminectomy and atlantoaxial fixation, the symptoms improved, but dysphagia and aspiration developed, associated with pharyngeal and esophageal stases on videofluoroscopy.Results and conclusions: Possible explanations for postoperative dysphagia include limitation of cervical spine motion, and cervical cord reperfusion injury in addition to the baseline anterior osteophyte and aging. This is the first case of dysphagia developing after laminectomy and posterior atlantoaxial fixation not involving the occipital bone.

Prediction of the extent of thrombus formation in the parent artery after endovascular occlusion of a distal anterior cerebral artery aneurysm using computational fluid dynamics.

Endovascular coiling of a cerebral aneurysm and coil occlusion of the parent artery have been occasionally performed to treat cerebral aneurysms; however, it is difficult to predict the accurate extent of thrombus formation in the parent artery proximal to the coiled aneurysm and the coil-occluded parent artery preoperatively, and unexpected occlusion of the arterial branches can occur by thrombus extension into or in the parent artery. The authors describe a case of a distal anterior cerebral artery (ACA) aneurysm treated by endovascular parent artery occlusion (PAO) with preoperative computational fluid dynamics (CFD) prediction of the extent of thrombus formation. A 73-year-old woman presented with subarachnoid hemorrhage and an aneurysm that was located on the right pericallosal artery distal to the paracentral artery bifurcation. Endovascular coiling of the aneurysm and the pericallosal artery was planned. In advance of the treatment, CFD was performed to predict the extent of thrombus formation with specific wall shear stress and shear rate thresholds. The hemodynamic results indicated that coiling of the aneurysm resulted in thrombus formation in the pericallosal artery up to just distal to the paracentral artery ostium; therefore, the treatment was implemented according to the CFD prediction. Postoperative digital subtraction angiography revealed that the extent of thrombus formation was consistent with the preoperative CFD prediction. This technique may prevent unexpected occlusion of arterial branches.

Role of Computational Fluid Dynamics for Predicting Delayed Cerebral Ischemia After Aneurysmal Subarachnoid Hemorrhage: Study Protocol for a Multicenter Prospective Study.

BACKGROUND: Delayed cerebral ischemia (DCI) is a significant cause of morbidity and mortality after aneurysmal subarachnoid hemorrhage (SAH). Recently, we reported the possibility that computational fluid dynamics (CFD) could predict DCI in terms of the cross-sectional area and flow velocity of the ipsilateral extracranial internal carotid and distal parent arteries in a single-center retrospective study. METHODS: This is a multicenter, prospective, cohort study. Patients with aneurysmal SAH will undergo CFD analyses using preoperative three-dimensional computed tomography angiography, and we will investigate hemodynamic features of cerebral arteries in an acute stage of SAH. Primary outcome measures will be CFD features in patients with subsequent occurrence of DCI. Secondary outcome measures will be CFD features in patients with subsequent occurrence of cerebral vasospasm and cerebral infarction and the relationships with eventual modified Rankin scale score at 3 months. CONCLUSIONS: The present protocol for a multicenter prospective study is expected to provide a novel diagnostic method to predict DCI before aneurysmal obliteration in an acute stage of SAH.

A Ruptured Blood Blister-Like Aneurysm Associated with Intraperitoneal Hemorrhage due to Segmental Arterial Mediolysis: A Case Report and Literature Review.

BACKGROUND: Segmental arterial mediolysis (SAM) is a rare non-atherosclerotic, noninflammatory vascular disease, characterized by mediolysis. We report an extremely rare case of subarachnoid hemorrhage (SAH) due to a ruptured blood blister-like aneurysm (BBA) of the internal carotid artery associated with SAM-related arteriopathy. CASE DESCRIPTION: We experienced a case of SAH followed by intraperitoneal hemorrhage that occurred 12 days after the SAH onset. SAH was caused by a ruptured BBA of the internal carotid artery, which was treated by trapping with high-flow bypass. Intraperitoneal hemorrhage was caused by a rupture of a posterior inferior pancreaticoduodenal artery (PIPDA) aneurysm, which induced hypovolemic shock resulting in death in spite of endovascular internal trapping. Postmortem pathologic examination revealed that the PIPDA pseudoaneurysm was due to SAM. CONCLUSIONS: We should pay attention to the association of SAM, which is a potentially life-threatening pathology when treating cerebral BBAs.