Translucent Appearance of Middle Cerebral Artery Bifurcation Aneurysms Is Risk Factor for Intraoperative Aneurysm Rupture During Clipping

Impact of preaneurysmal M1 length in unruptured middle cerebral artery aneurysm: mid-term outcome and single-center experience

OBJECTIVE

This study was design to investigate the surgical and functional outcome based on the preaneurysmal M1 length for unruptured MCA aneurysm.

METHODS

Among 250 consecutive patients with unruptured aneurysms operated in our institution between 2015 and 2017, 72 were MCA aneurysms. Risk factors for IR (i.e., intraoperative rupture) were investigated including age, sex, preaneurysmal M1 length, maximal MCA aneurysm diameter, neck size, aneurysm shape, sphenoid ridge proximation sign. Outcome was measured at discharge, 1 yr and last follow-up. Outcome was compared according to the preaneurysmal M1 length.

RESULTS

Among 68 patients included, five patients (7.3%) suffered IR. Mean maximal diameter of MCA aneurysm (7.9 mm ± 3.4 vs. 4.5 ± 1.8; p = 0.01) was significantly associated with IR risk. Mean M1 length seemed to be shorter in the IR group although not statistically significant (16.2 mm ± 5.1 vs. 11.5 mm ± 4.8; p = 0.053). Mid-term outcome was favorable for all patients at last follow-up but was worsen in case of short preaneurysmal M1 segment (10.7 mm ± 4.8 vs. 16.4 mm ± 5.3, p = 0.02). Complete aneurysm occlusion was achieved for sixty-nine patients (95.5%) with 6.9% of early postoperative complications.

CONCLUSIONS

The microsurgical treatment of unruptured MCA aneurysm was associated with favorable mid-term outcome in all patients and high rates of complete occlusion. Aneurysm size was significantly associated with the intraoperative rupture risk for unruptured MCA aneurysm and patients with a short preaneurysmal M1 segment seemed to have a greater risk of intraoperative rupture although not statistically significant. Short preaneurysmal M1 patients had worsen mid-term outcome.

Clinical and Hemodynamic Features of Aneurysm Rupture in Coil Embolization of Intracranial Aneurysms

Intraprocedural rupture (IPR) during coil embolization (CE) of an intracranial aneurysm is a significant clinical concern that necessitates a comprehensive understanding of its clinical and hemodynamic predictors. Between January 2012 and December 2023, 435 saccular cerebral aneurysms were treated with CE at our institution. The inclusion criterion was extravasation or coil protrusion during CE. Postoperative data were used to confirm rupture points, and computational fluid dynamics (CFD) analysis was performed to assess hemodynamic characteristics, focusing on maximum pressure (Pmax) and wall shear stress (WSS). IPR occurred in six aneurysms (1.3%; three ruptured and three unruptured), with a dome size of 4.7 ± 1.8 mm and a D/N ratio of 1.5 ± 0.5. There were four aneurysms in the internal carotid artery (ICA), one in the anterior cerebral artery, and one in the middle cerebral artery. ICA aneurysms were treated using adjunctive techniques (three balloon-assisted, one stent-assisted). Two aneurysms (M1M2 and A1) were treated simply, yet had relatively small and misaligned domes. CFD analysis identified the rupture point as a flow impingement zone with Pmax in five aneurysms (83.3%). Time-averaged WSS was locally reduced around this area (1.3 ± 0.7 [Pa]), significantly lower than the aneurysmal dome (p < 0.01). Hemodynamically unstable areas have fragile, thin walls with rupture risk. A microcatheter was inserted along the inflow zone, directed towards the caution area. These findings underscore the importance of identifying hemodynamically unstable areas during CE. Adjunctive techniques should be applied with caution, especially in small aneurysms with axial misalignment, to minimize the rupture risk.

Trends in the Age of Patients Treated for Unruptured Intracranial Aneurysms from 1990 to 2020

BACKGROUND

The decision for treatment for unruptured intracranial aneurysms (UIAs) is often difficult. Innovation in endovascular devices have improved the benefit-to-risk profile especially for elderly patients; however, the treatment guidelines from the past decade often recommend conservative management. It is unknown how these changes have affected the overall age of the patients selected for treatment. Herein, we aimed to study potential changes in the average age of the patients that are being treated over time.

METHODS

A systematic search of the literature was performed to identify all studies describing the age of the UIAs that were treated by any modality. Scatter diagrams with trend lines were used to plot the age of the patients treated over time and assess the presence of a potential significant trend via statistical correlation tests.

RESULTS

A total of 280 studies including 83,437 UIAs treated between 1987 and 2021 met all eligibility criteria and were entered in the analysis. Mean age of the patients was 55.5 years, and 70.7% were female. There was a significant increasing trend in the age of the treated patients over time (Spearman r: 0.250; P < 0.001), with a 1-year increase in the average age of the treated patients every 5 years since 1987.

CONCLUSIONS

The present study indicates that based on the treated UIA patient data published in the literature, older UIAs are being treated over time. This trend is likely driven by safer treatments while suggesting that re-evaluation of certain UIA treatment decision scores may be of great interest.

Newly Identified Hemodynamic Parameter to Predict Thin-Walled Regions of Unruptured Cerebral Aneurysms Using Computational Fluid Dynamics Analysis

BACKGROUND

The thin-walled regions (TIWRs) of intracranial aneurysms have a high risk of rupture during surgical manipulation. They have been reported to be predicted by wall shear stress and pressure (PS) based on computational fluid dynamics analysis, although this remains controversial. In this study, we investigated whether the oscillatory shear index (OSI) can predict TIWRs.

METHODS

Twenty-five unruptured aneurysms were retrospectively analyzed; the position and orientation of the computational fluid dynamics color maps were adjusted to match the intraoperative micrographs. The red area on the aneurysm wall was defined as TIWR, and if most of the regions on the color map corresponding to TIWR were OSI low (lower quartile range), time-averaged wall shear stress (TAWSS) high, or PS high (upper quartile range), each region was defined as a matched region and divided by the total number of TIWRs to calculate the match rate. In addition, the mean values of OSI, TAWSS, and PS corresponding to TIWRs were quantitatively compared with those in adjacent thick-walled regions.

RESULTS

Among 27 TIWRs of 25 aneurysms, 23, 10, and 14 regions had low OSI, high TAWSS, and high PS regions (match rate: 85.2%, 37.0%, and 51.9%), respectively. Receiver operating characteristic curve analysis demonstrated that OSI was the most effective hemodynamic parameter (area under the curve, 0.881), followed by TAWSS (0.798). Multivariate analysis showed that OSI was a significant independent predictor of TIWRs (odds ratio, 18.30 [95% CI, 3.2800-102.00], P < 0.001).

CONCLUSIONS

OSI may be a unique predictor for TIWRs. Low OSI strongly corresponds with TIWRs of intracranial aneurysms.

Correlation of Inflow Velocity Ratio Detected by Phase Contrast Magnetic Resonance Angiography with the Bleb Color of Unruptured Intracranial Aneurysms

BACKGROUND

Intraoperative rupture is the most fatal and catastrophic complication of surgery for unruptured intracranial aneurysms (UIAs); thus, it is extremely useful to predict reddish and thin-walled regions of the UIA before surgery. Although several studies have reported a relationship between the hemodynamic characteristics and intracranial aneurysm wall thickness, a consistent opinion is lacking. We aimed to investigate the relationship between objectively and quantitatively evaluated bleb wall color and hemodynamic characteristics using phase-contrast magnetic resonance angiography (PC-MRA).

METHODS

Ten patients diagnosed with UIA who underwent surgical clipping and preoperative magnetic resonance imaging along with PC-MRA were included in this study. Bleb wall color was evaluated from an intraoperative video. Based on the Red (R), Green, and Blue values, bleb wall redness (modified R value; mR) was calculated and compared with the hemodynamic characteristics obtained from PC-MRA.

RESULTS

The wall redness distribution of 18 blebs in 11 UIAs in 10 patients was analyzed. Bleb/neck inflow velocity ratio (Vb/Va: r = 0.66, P = 0.003) strongly correlated with mR, whereas bleb/neck inflow rate ratio (r = 0.58, P = 0.012) correlated moderately. Multivariate regression analysis revealed that only Vb/Va (P = 0.017) significantly correlated with mR. There was no correlation between wall shear stress and mR.

CONCLUSIONS

The bleb redness of UIAs and Vb/Va, calculated using PC-MRA, showed a significantly greater correlation. Thus, it is possible to predict bleb thickness noninvasively before surgery. This will facilitate more detailed pre- and intraoperative strategies for clipping and coiling for safe surgery.

Early versus Delayed Microsurgical Clipping of Additional Unruptured Aneurysms in Patients with Aneurysmal Subarachnoid Hemorrhage

BACKGROUND

The optimal timing for the surgical treatment of additional unruptured aneurysms in patients with multiple aneurysms and aneurysmal subarachnoid hemorrhage (aSAH) is unknown. Therefore, we analyzed the results of early versus delayed microsurgical treatment of unruptured aneurysms when multiple aneurysms were present in the setting of aSAH.

METHODS

The medical records from a consecutive, single-surgeon, 19-year experience of all patients with aSAH and additional unruptured aneurysms treated with a second surgery were reviewed retrospectively. Early treatment was defined as treatment within 30 days and delayed treatment as treatment more than 30 days after the initial surgery for aSAH.

RESULTS

A total of 85 patients with aSAH and multiple aneurysms were identified. Early (n = 55; 65%) or delayed (n = 30; 35%) clipping was performed for additional unruptured aneurysms. Intraoperative rupture (P = 0.028), higher Fisher grade (P = 0.046), multiple additional unruptured aneurysms (P = 0.04), and large aneurysm size of either the ruptured aneurysm (P = 0.034) or unruptured aneurysm (P = 0.022) were significant factors favoring early treatment. Significant differences were not observed with respect to outcome (modified Rankin scale), unfavorable modified Rankin scale changes between the first surgery and last follow-up, aneurysm occlusion, and shunt-dependent hydrocephalus. No ruptures of untreated aneurysms during the follow-up course were observed.

CONCLUSIONS

Both early and delayed surgical treatment of unruptured aneurysms in the setting of aSAH are safe. Factors prompting earlier intervention might include multiple additional aneurysms, larger aneurysms, and intraoperative aneurysm rupture, which could suggest a destabilized arterial wall. Delayed treatment is advisable for patients with a poor clinical presentation, greater underlying brain injury, and a swollen brain requiring decompressive craniectomy to allow time for recovery.

Decreased wall shear stress at high-pressure areas predicts the rupture point in ruptured intracranial aneurysms

OBJECTIVE

Degenerative cerebral aneurysm walls are associated with aneurysm rupture and subarachnoid hemorrhage. Thin-walled regions (TWRs) represent fragile areas that may eventually lead to aneurysm rupture. Previous computational fluid dynamics (CFD) studies reported the correlation of maximum pressure (Pmax) areas and TWRs; however, the correlation with aneurysm rupture has not been established. This study aims to investigate this hemodynamic correlation.

METHODS

The aneurysmal wall surface at the Pmax areas was intraoperatively evaluated using a fluid flow formula under pulsatile blood flow conditions in 23 patients with 23 saccular middle cerebral artery (MCA) bifurcation aneurysms (16 unruptured and 7 ruptured). The pressure difference (Pd) at the Pmax areas was calculated by subtracting the average pressure (Pave) from the Pmax and normalized by dividing this by the dynamic pressure at the aneurysm inlet side. The wall shear stress (WSS) was also calculated at the Pmax areas, aneurysm dome, and parent artery. These hemodynamic parameters were used to validate the correlation with TWRs in unruptured MCA aneurysms. The characteristic hemodynamic parameters at the rupture points in ruptured MCA aneurysms were then determined.

RESULTS

In 13 of 16 unruptured aneurysms (81.2%), Pmax areas were identified that corresponded to TWRs. In 5 of the 7 ruptured cerebral aneurysms, the Pmax areas coincided with the rupture point. At these areas, the Pd values were not higher than those of the TWRs in unruptured cerebral aneurysms; however, minimum WSS, time-averaged WSS, and normalized WSS at the rupture point were significantly lower than those of the TWRs in unruptured aneurysms (p < 0.01).

CONCLUSIONS

At the Pmax area of TWRs, decreased WSS appears to be the crucial hemodynamic parameter that indicates the risk of aneurysm rupture.

Hemodynamic Features of Microsurgically Identified, Thin-Walled Regions of Unruptured Middle Cerebral Artery Aneurysms Characterized Using Computational Fluid Dynamics

BACKGROUND

Thin-walled regions (TWRs) of aneurysm surfaces observed in microscopic surgery are thought to be vulnerable areas for growth and rupture of unruptured intracranial aneurysms (UIAs).

OBJECTIVE

To identify hemodynamic features of TWRs of aneurysms by using computational fluid dynamics (CFD) analyses of unruptured middle cerebral artery bifurcation (MCAB) aneurysms.

METHODS

Nine patients with 11 MCAB aneurysms were enrolled, and their TWRs were identified. CFD analysis was performed using 3 parameters: pressure, wall shear stress (WSS), and WSS divergence (WSSD). Each parameter was evaluated for its correspondence with TWR.

RESULTS

Among 11 aneurysms, 15 TWRs were identified. Corresponding matches with CFD parameters (pressure, WSS, and WSSD) were 73.33, 46.67, and 86.67%, respectively.

CONCLUSION

WSSD, a hemodynamic parameter that accounts for both magnitude and directionality of WSS, showed the highest correspondence. High WSSD might correspond with TWR of intracranial aneurysms, which are likely high-risk areas for rupture.

Hemodynamic characteristics associated with thinner regions of intracranial aneurysm wall

Aneurysm wall thickness is an important determinant of aneurysm progression and intra-procedural rupture. Several previous studies have evaluated the association between hemodynamic stress and aneurysm wall thickness, but conflicting results were obtained and no consensus has been achieved. According to the intraoperative findings, twenty-eight unruptured middle cerebral artery (MCA) aneurysms presented with thin-walled regions were enrolled in our study. Patient-specific 3D aneurysm models were constructed from preoperative computed tomography angiography (CTA) data and computational fluid dynamics (CFD) analyses were performed under pulsatile-flow conditions. Thin-walled regions of aneurysm dome were recognized by two experienced reviewers based on the intraoperative microscopy findings. Hemodynamic parameters derived from CFD analysis, including normalized wall shear stress (NWSS), normalized pressure (NP), the oscillatory shear index (OSI) and relative residence time (RRT), were compared between thin-walled regions and surrounding normal-thickness areas. Of the included aneurysms, twenty-eight pairs of thin-walled and normal surrounding regions were determined. Compared with surrounding tissues, thin-walled regions of aneurysm wall tended to present with higher pressure (1.232 vs 1.043, p < 0.05) and lower wall shear stress (0.693 vs 0.868, p < 0.05). Multivariate analysis revealed that elevated NP was significantly associated with thinning of the local aneurysm wall. Higher pressure and lower WSS were characteristic hemodynamic features associated with thinner regions of the aneurysm wall, elevated NP was an independent risk factor for local aneurysm wall thinning. CFD seems to be a useful method to estimate the location of thin-walled region, which will be helpful in reducing the risk of intraoperative rupture.

Intraoperative Aneurysm Rupture During Microsurgical Clipping: Risk Re-evaluation in the Post-International Subarachnoid Aneurysm Trial Era

OBJECTIVES

Intraoperative aneurysm rupture (IOAR) is a common complication during intracranial aneurysm (IA) surgery. In light of the paradigm shift regarding IA selected for clipping in the post-International Subarachnoid Aneurysm Trial (ISAT) era, we aimed to evaluate the risk factors and effects of IOAR in an institutional series of clipped ruptured IA (RIA) and unruptured IA (UIA).

MATERIAL AND METHODS

All IAs treated with microsurgical clipping at our institution between 2003 and 2016 were eligible for this study. Demographic, clinical, and radiographic factors were correlated with occurrence of IOAR in univariate and multivariate analyses. The effect on outcome was analyzed for RIA and UIA separately.

RESULTS

Nine hundred and three clipped IAs were included in the final analysis (538 UIA and 365 RIA). IOAR occurred in 163 cases (18.1%), mostly during clipping of RIA (37.5% vs. 4.8%) In multivariate analysis, ruptured status (adjusted odds ratio [aOR], 10.46; P < 0.001), sack size (aOR, 1.05 per mm increase; P = 0.038) and IA location in the anterior communicating artery (aOR, 2.31; P < 0.001) independently predicted IOAR. For RIA cases, IOAR was also independently predicted by rebleeding before therapy (aOR, 3.11; P = 0.033) and clinical severity of subarachnoid hemorrhage (aOR, 1.18 per WFNS grade increase; P = 0.049). IOAR independently predicted poor outcome (aOR, 1.83; P = 0.042) after RIA surgery. In turn, IOAR affected only the risk for cerebral infarct (OR, 3.75; P = 0.003) and incomplete IA occlusion (OR, 3.45; P = 0.003) for UIA cases, but not the outcome (P = 0.263).

CONCLUSIONS

IOAR was independently predicted by the ruptured status, location, and size of IA and by initial severity of aneurysmal bleeding and pretreatment rebleeding. The influence of IOAR differed between RIA and UIA cases.